Calculating Distance Below Deck

[CBODY67]

Engines with LO, W rod ratios are "torque"-oriented, generally, and can have poor flowing heads and intake as the pistons spend less dwell time at TDC and YANK harder on the mixture stream than engines with higher rod ratios (302 Chevy small blocks, Chrysler 383) at right at 1.9. Some of OEM engines have approached 2.0, but I don't remember off hand which Oldsmobile V-8s they were.

What Chrysler did (according to an article in the old MoPerformance magazine) was to limit the swing of the connecting rod to 15 degrees, to keep side loading of the skirts in an area that didn't increase piston friction against the cylinder walls. Another approach to "rod ratio", which was first mentioned in a "Hot Rod" magazine article on the Chevy 430 Can-AM motor (NOT a version of the 427!).

In more modern engine designs, it seems that rod ratio is not a real consideration.

I have a NOS '72 440 Motor Home short block. The piston is .125" in the hole, for a rated 8.2CR. I measured it.

I first saw the quench dome piston at Mopar Nats a good while back. Hughes Engines had them for sale there. Basically makes a 906 head into a closed-chamber head, by changing pistons. Pretty neat.

David Vizzard has quite an extensive explanation of quench dimensions in one of his books on cylinder heads. His spec is .020" distance from the piston to the quench part of the combustion chamber. When that particular book came out, it proposed that more power could really be made with a closed chamber head, with less detonation tendencies, at higher CR, than with the traditional open chamber head. Gets back to chamber turbulence and keeping the air flow "active", by design.

As noted, using a longer rod to get a higher piston position will do nothing for CID.

Almost ALL current OEM pistons are much shorter than they used to be, by observation. Skirt length is less pronounced, by observation. The lack of the longer skirt dimensions can certainly increase their tendency to "rock" in the bore, BUT apparently if they are coated and fitted tight enough, that's not an issue. Hypereutectics have the strength of forged, but can be fitted as "cast" pistons. I have a set in my '77 Camaro 350 +.030. Over 200K miles and no piston noise . . . the Cloyes Plus Roller timing chain can still be heard.

Now, there are several stroker 440 builds in here. I believe they all use a 3.23 gear ratio and run in the 13 second 1/4 mile realm? HATE to be those u-joints!

Consider that the Imperials had a 2.94 rear axle ratio. Combined with the taller tires they had, it works out to the same mph/1000rpm as a 2.76 and H78x14 tire size used on NY in the later '60s. With that consideration . . .

You could build a "torque" 440 (using the stock cam and such), with normal-type parts, 9.0 CR, a 2.5" dual exhaust with good mufflers, and it should idle really nice in gear with the a/c on. THEN, change the 3-speed TF for one of the 4spd-OD units and change the rear axle ratio to 4.10 (which would still give you a lower cruise rpm in OD than what you now have with the 2.94 and tall tires. Would need a new driveshaft built, so you could opt for either carbon-fiber or aluminum.

Inside the motor? Use the lightest pistons you can find and it be reliable. Chrysler B/RB pistons usually hit 1000gms in weight! That's a LOT of metal swing around in there, not even considering the rod weight! Of course, a balance job would be necessary. The more power that can get to the flywheel, the better. And this is ONE way to do it.

Nothing exotic in the cylinder heads other than just a normal NHRA-legal port job and normal valve sizes. Maybe some aftermarket alloy heads, but not too big on the port flow specs as you want port velocity rather than pure volume. You want lots of "low lift" flow rather than huge flow at .600" lift. Choose a cam with assymetrical lobe shapes, to put more area under the lift curve. The old Comp Cams "HiEnergy" cams did this and newer Lunatis also claim to have this feature. A roller cam (if you can afford one) and roller rocker arms are another way to get friction out of the engine, but too many roller cams are "race cams", by observation, so "flat tappet hydraulic" might be the best way to go.

A torque motor that has no issues with hitting 5000rpm easily would be the ultimate goal. Having the "gear" can help that, too.

Does your Imperial have the factory "torque strap" on the rh side of the rear axle tube?

Just some thoughts,
CBODY67

 

[bajajoaquin]

A lot to process here, thank you. Perhaps I should get Joey to change the title of the thread.

I'm interested in what can be done with off-the-shelf parts. There's no budget for custom parts, and the custom work has to be limited to some clearancing for a stroker crank and a balance job. The 440-source (and others, of course) stroker kits use Chevy rods for many of the combinations because the journals require less clearancing. I understand that it was also a trick to get an increased stroke, by offset-grinding the crank to Chevy dimensions to get some extra cubes.

Anyway, the idea was to look at commercially-available Chevy rods and commercially-available Mopar pistons to see if there was a combination that resulted in a taller, more stable piston. With an arbitrary limit of a 1.53 rod ratio (stock 454), there really isn't.

I appreciate the comments about modern pistons being shorter without harm to reliability. CBODY67, do you mind sharing compression height on your pistons if you know it? I was hoping to get hypereutectic pistons rather than forged, but that may not be (reasonably) possible.

So I think I'm back to one of the combinations listed as 500 or 512 in the 440-source catalog. They're 493 or 505 at 0.030" over. Those have rod ratios in the 1.6 range and compression heights of 1.485" to 1.8". It was a hope to find something interesting and viable, but it didn't work out.

 

[70bigblockdodge]

interested in what can be done with off-the-shelf parts. There's no budget for custom parts, and the custom work has to be limited to some clearancing for a stroker crank and a balance job

This is the issue.
KB has some hyperutectic pistons for common stroker kits. Not what you are looking at.
You can get Chevy rods in just about any length you want, offset grinding will run you about as much as buying a stroker crank, unless you know someone at a crankshaft service.
I see you are set on this idea but nonfoolish money would be better spent on heads and machine work to your block to get everything just right and the power will follow.
If you follow MEV member here basic formula you end up at the same place but with a 440 instead of a 500". Power is in the heads and attention to detail on assembly. Then pick a cam, hydraulic roller for rpm range you are looking at

 

[bajajoaquin]

With regard to the rest of the combo, I don't know if I have the torque strap on the axle tube. The car is still in TJ.

I plan to keep the 2.94 ratio, although tires are now a bit shorter since the 9.0-15s aren't available and not easily replicable in metric sizes. I've really looked at the 518 swap (I figured 3.73s would be the gears I'd go with), but I think that's too much custom work for me. I'm technically capable of it, but I just have too many competing priorities to do the work myself. I don't want to outsource something like that, as I think it has too much chance of going pear shaped.

The other requirement is that revs have to stay below 5000 rpm, since realistically I'm never going to shift the car manually to get max performance. It's got to work with normal upshifts on a reasonably-stock transmission (beefed up but not radically modified). So that means I'm looking at the stock power profile as my target to beat. 480 lb ft at 2800 RPM and 350 hp at 4400 RPM. If whatever I do can't beat that, particularly the 480 at 2800, I'm only going backwards.

In order to keep the revs low, I think it needs to have duration of 220* (0.050" lift) or less. A 500" motor may work fine at 225*, but I'm not sure.

Lunati has a hydraulic flat-tappet cam 213/220, .454/.473 (I/E) which should provide greater lift at lower durations and boost torque without increasing revs. Crane, Hugues, and Comp have similar cams available. I'm a little worried about the Huges grinds since there's rumors that the really aggressive lift profiles eat valvetrains. I'm looking for longevity here.

Things get interesting, however, if you look at roller grinds. The advantage of a roller cam isn't just friction. It allows for faster ramps on the cam, making more lift available at shorter durations, and earlier in the profile. Lunati has a factory grind of 211/219, 0.507/0.509 (I/E) which should produce prodigious torque in the rev range I'm targeting. Comp has catalog lobes that would make 212/281, 0.525/0.521 (I/E) which seems to be similar.

I've bought Engine Analyzer software to run these. I started with the stock 440 as best I could find (since they never put out specs for cams at 0.500" lift). The numbers are more pessimistic than the factory specs, but I'm not using the software to predict actual HP, but to tell me the directional and magnitude effects of changes. Anyway, it looks like either of those combinations would provide better numbers than stock, and not need to rev past 5000 RPM to make the power.

So, the ideal combination at this point is 493 or 505 with a short-duration roller cam, 440-Source Stealth heads, CH4B aluminum intake, Eddy carb, HP manifolds, 2.5" exhaust. A guesstimate would be 550-560 lb ft of torque at 2800-3000 rpm, and 425-435 hp at 4800 or so.

One big question is around cost. The marginal cost of upgrading to a roller cam is about the same as running a stroker crank. I'm not sure I can afford both. I am trying to figure out which is the better option if I can only have one. I'm guessing it will be stroker crank with a good, modern hydraulic flat tappet.

But this is already long enough.

 

[bajajoaquin]

This is the issue.
KB has some hyperutectic pistons for common stroker kits. Not what you are looking at.
You can get Chevy rods in just about any length you want, offset grinding will run you about as much as buying a stroker crank, unless you know someone at a crankshaft service.
I see you are set on this idea but nonfoolish money would be better spent on heads and machine work to your block to get everything just right and the power will follow.
If you follow MEV member here basic formula you end up at the same place but with a 440 instead of a 500". Power is in the heads and attention to detail on assembly. Then pick a cam, hydraulic roller for rpm range you are looking at

Yep. I posted while you did. I love MEV's car, it's my favorite on here. He's prioritized differently, since he's willing to shift manually for the strip, and has 3.23. So I'm looking at a shorter duration cam. But yes, that's the template I'm looking for.

 

[CBODY67]

Thanks for the reply and kind words. Here's one consideration. As there's about a 15% power consumption in "the flywheel to the ground" Chrysler power trains back then, seeking that last bit of torque/horsepower might be a consideration. IF you're going to run heads-up drag racing, THEN it might be, but in a street driving car, where most of the time is spent in the 2500-3000rpm range on the highway, mid-range torque and throttle response are much more important. Even the stock motors were good din this respect, without needing greater displacement sizes! IF you were towing a 30' travel trailer with a huge wind load, THEN the added inches would be needed. That's the reality I see, fwiw, and the reason the "gear it differently" orientation can make more sense.

Now, in the later '50s and earlier '60s, the "big engine, loafing along at increasing highway speeds" was proven to be a better fuel economy orientation as numerically-lower rear axle ratios could be used to harness the greater low-mid-range torque of the larger engines which were coming online back then, plus 3-speed automatic transmissions. That's where the 2.6-2.8 range rear axle ratios were first used, rather than the 3.3-3.7 ratios that were more common with smaller engines and manual transmissions. I later discovered, from friends who ran them, that the beloved '55-'57 Chevies that ran well usually had 4.56 rear axle ratios for drag racing purposes!

When Chrysler finally did add the part-throttle kickdown in the '71 model year, it made a huge difference in such situations. By that time, I'd learned to do it manually with our '66 Newport. While "launch" is important, it's limited by rear tire traction, I like that feeling or torque in passing maneuvers where you get just deep enough into the throttle to get a kickdown and get past what you're passing, then return to economical cruising.

KEY thing it so make sure your rear suspension is up to the task! One reason, probably, that mid-60s Imperials had a torque strap on the rh end of the rear axle tube, like a factory traction bar to reduce rear axle wind-up. And that was with the normal 413 and 440 V-8s.

IF having "big inches" under the hood is important, that's fine. Just that having them might not be really necessary to push the car down the road at 100mph, or less, NOR having to feed them in even occasional use. But that's just me. I like the highway cruise performance rather than stop light Grand Prix or drag strip performance. I can enjoy the highway performance dynamics of the suspension, steering, engine, interior comforts, and body structure of Chrysler products for extended periods of time on the road, which make me glad I have a Chrysler product under me, which make a trip a better trip. Plus not needing a big credit card just to buy gas for those enjoyable activities. But again, that's just me, fwiw.

You might want a stock look, which can still happen with a torque engine that rpms, with a 6-speed automatic conversion. Might need to finagle the gates on the column shifter, for good measure. A minor deal. So they match what's in the transmission. Maybe a gate from a newer vehicle will fit?

Just some thoughts. Your car, your $$$$, your smiles.
CBODY67

 

[CBODY67]

I was posting while y'all were posting, too.

On the factory shift points, they are usually a little low, even the min-throttle shift points. You can modify the existing governor for higher WOT shift points. Closer to 5000rpm than the factory 4400rpm shift points. Seems like B&M used to have a kit for that? Or it used to be in Mopar Perf? Springs and weights, all that's involved, but some trans disassembly might be needed.

The .050" lift spec is a more recent development in cam issues. It was developed to get past the advertised duration listings, as the shape and length of the initial lobe ramp can vary. By .050" lift, all of that is past happening, so the .050" spec was adopted by the aftermarket cam people for comparing eggs to eggs, so to speak.

In one set of specs from 1965, it appeared that Chevy rated their cams from 0.00" lift to max lift, for duration. The numbers were well past 300 degrees of duration! Using the ramps as a part of the total duration number. Prior listings, for the same cams, were more like 270 degrees, with later .050" specs more like 190 degrees.

Steep lobe lifts CAN affect valve spring durability. My machine shop operative noted that he ahd a customer that bought a new cam with steeper lobes and more lift. He was finding fatigued valve springs after his third weekend or 1/8 mile racing. He backed-off the duration and lift a bit, ran pretty much the same times, and no more spring fatigue issues before the end of the season.

MIddle '60s Ponrtiac heads had poorer .400"+ lift port flow than other GM brands, which meant they needed more duration at lower lift to make power, but if they got too much duration, the cams became more radical and wouldn't idle as smooth as was desired.

Similar things with the earlier Buick 401 Nailheads. Longer duration for more power, but customers complained about the rough idle, so other things had to be done in later years of that engine family. The longer duration with smaller valves of that engine family tended to increase low-mid-range torque, but the ports and valve sized limited top end power. Living with a cylinder head design that was necessary with the narrower engine compartments of the 1950s car body architecture, which didn't exist past the '60 model year.

Chrysler operatives have stated that using the stock timing events, which are done to SAE specs, you can take 80% of them to approximate the .050" duration specs. Perhaps that might help in your calculations?

When I dummied-up cams in my NOS '72 MHC 440 short block, to measure them with a dial indicator, the Comp Cams HE268 cam, with its assymetrical lobes (fast opening, slow closing), it held the valve at max lift for a full 10 degrees of crank rotation. The old Direct Connection 284 Purple Stripe Street HEMI RB cam held the valve at max lift for ONE degree of crank rotation. I took measurements are intervals so I could check the .050" specs, too, but I have those items archived in my car shop.

The tire size that would be more appropriate for your car would be the P235/75R-15 size, usually. Shorter tires will effectively lower the rear axle ratio, in comparison, resulting in lower mph/1000rpm numbers. Making your existing 2.94 into something a bit more than 3.00, using the stock gear/tire size as the reference point.

As I understand it, because of the different clutch pack/bands which are applied differently in Manual Low and Automatic Low (selector in "D" rather than "1" at start), the trans shifts a bit quicker in Automatic than Manual modes. So aiming for automatic upshifts in the 4800rpm range might work best, I suspect. By the time the shift is initiated, the engine could well be at 5000-5100rpm when it actually shifts.

While the WOT shifts are determined by the internal governor, I've successfully altered the part-throttle shift points a bit with a bit more pre-load in the kickdown linkage. Not much, just like on my '80 Newport, adding a thin black wire tie to the rear of the slot in the kickdown linkage, at the carb, raised the normal shift points such that the car became peppier and more throttle responsive, as a result. On my '66 Newport, with the threaded adjustment near the carb, the factory adjustment was increased from 2 turns pre-load to 4 turns pre-load. NO durability issues at all, after many miles or use. Small adjustments are fine, just not large changes. Aim for a min throttle 2-3 automatic upshift so the engine rpm is about 1000rpm after that final upshift. Chrysler's factory settings, by observation, lug the engine after the 2-3 upshift so any acceleration is more "on the converter" than with a more "firm" converter situation. Just feels better the way I set them, which puts less strain on the pieces working to move the car.

These things were all with 383 or 400 2bbls in Chrysler Newports with 2.76 rear axle ratios and stock tire sizes. Plus my '70 Monaco with 3.23/P225/75R-15 tires. On the Chryslers, 2-3 upshift right at 28-30mph. With the Monaco, right at 25-26mph, due to the shorter rear axle ratio. The '80 Newport is a 360 2bbl/2.45 axle/P215/75R-15 tires, with the linkage adjustment moved "under-car" rather than being near the carb, hence the wire tie trick.

Chrysler just seemed to calibrate the normal shift points too low for best min-throttle inputs. Especially in the '80s, on everything! Manually shift the vehicles, even pickups, and then they seemed to "run" better. Possibly after the "grams/mile" emissions standards were in effect? By observation, better to have any torque multiplication in the gears rather than "on the converter", at lower speeds. Less throttle input, faster acceleration is the result, by observation.

The torque strap was there in the '66 model year, but might have not been there in the later models. With a big torque stroker, got to be something back there, I suspect!

Enjoy!
CBODY67

 

[bajajoaquin]

Even more good info, thanks! Sorry if I don't respond to each great bit of info individually. I am reading and considering it all.

Some quick notes: To be clear, I'm trying to avoid any custom machining. The rod stuff was to see what Chevy rods were available, since stroker Chrysler cranks use Chevy journals. I'm using 235/75-15s, as yes, they are the best available match. I can get closer to the 9.00-15 size if I go to 16" wheels, but that would mean more complexity swapping hubcaps over, and I'd lose the whitewalls. So 235/75-15 it is.

I also agree that I like the overall dynamics of the Imperial, and I want to keep them basically intact, but with more power.

One of the things about new cars is that they have more cam, and more gear to help move them. So smaller engines can produce more torque and power, but it's at higher RPM. They use 6- and 8-speed transmissions to keep them on the boil, get off the line and still have good-mileage cruising RPM. That's replicable to some extent by using a 518, but I think that's not a viable option for me, as much as I want it to. I'm going to have to pay to have the work done, as I'm facing up to my own behavior and accepting that if I don't have it done, I'll never actually complete it. Because of this, I'm targeting a good, reputable mechanic to do a stock-type rebuild, but I'm going to select the parts. So I'm confident that a 518 swap is viable, but I really don't want to try to direct that by remote. That seems to be a recipe for failure. This means I'm trying to optimize around a 727.

Most of my driving is around town, but I do some freeway trips. I want it to stay relaxed and "Imperial-like" on the freeway, and have better roll-on performance as well as just feel faster. This article on the Imperial Club website made quite an impression:

SUPREME SEDANS - Seventies Matchup - 1975 Imperial vs. Cadillac

The 500" Cadillac engine seemed to make quite a difference over the 440 in the Imperial. So I'd like to have better off-the line, better roll-on, but still feel effortless. I understand that I'm not making a drag car, and it won't keep up with a Hellcat. Can I build a 50,000- or 100,000-mile engine using more modern cams and heads, significantly improve performance, but not by changing the fundamental character of the car and engine? With cubes and cams, I think so.

Also really good info on shift points. Before buying, I'll look at different kits, but it seems that the base Trans-go kit gets good results, and seems like it would raise shift points a bit, and firm them up without being objectionably hard.

I've talked here and in other places about the "marginal $1000." There are three main things that cost about a thousand bucks over a "stock" rebuild which I could do to improve torque and power. TTI headers (yes, they improve torque, see my comments elsewhere), roller cam, and cubic inches. Headers provide the least gain, but the main concern for me is noise. Cubes seem to be the most straight-forward, but cost a bit more (like $1400 rather than $1000). Roller cam is under $1000, but may have some valvetrain durability issues, and may not give the same grunt off idle.

So headers seem to be out, and I'm trying to figure out if I can afford a roller cam and cubes. I don't think so. I think I'll end up with basically an RV-type flat-tappet cam and 500". Which gets us back to the original question which was measuring deck height to see if there was an off-the-shelf solution to getting hypereutectic pistons and a stroker kit. There doesn't seem to be.

This is a bit all over the place (intermittently wrangling two small children), but to re-re-summarize: To keep relaxed cruising, without changing the transmission, I think 2.94 gears are as deep as I want. To get the better accelleration, I'm looking at more power. Because I want to shift automatically, power needs to stay below 5,000 RPM. This seems to lead to more cubes. Because there's no other off-the-shelf stroke/rod/piston combo, I'm probably looking at 493 or 505 stroker options. Because more cubes/same cam would give underwhelming performance, I'm probably looking at more cam. No matter what, I think I need to keep duration under 220", but I might find that a little more exhaust duration is just fine. Because of hood clearance, I can't get much more manifold in there, meaning I've bought a CH4B. For quiet and under-hood temps, I'll have HP manifolds. Written out as a list:

505" Stroker
Stealth Heads
Low-duration, high-lift cam
CH4B Intake
HP Manifolds
2.5" exhaust

If anyone is still interested, I can share the cams I'm looking at.

 

[CBODY67]

Thanks for the information and explanations!

As for header sounds, they can be minimized with thicker-gauge tubes, the black header gaskets rather than the normal ones, and ThermoTec wraps for the tubes. Headers, like the HP manifolds, have become more pricey of late. Might substitute the '74+ normal manifolds with the larger pipe diameter outlets?

In order to not let the heads' port flow not be a hindrance, might need to limit total valve lift to a more stock-like .484" lift? Piston clearance would need to be checked, I suspect, for good measure anyway.

Larger displacement engines can use "more cam" and still remain stock characteristics, as long as everything remains in proportion. Within a given engine family.

An observed benefit of the newer 6+ speed automatics is that their deeper 4.5-range low gears gets the vehicle moving with less throttle input, which means less "power mixture" in that mix. Once moving, the trans quickly upshifts to more appropriate ratios that are less than 1.45, typically, with the upper ones usually being OD ratios. Kind of like a geared CVT situation, to me. On the CVT front, the Nissan Altimas I have rented over the past year have their software programmed to mimic a geared transmission feel. There are a few detents in the throttle linkage that support that function, too.

The neatest thing about the Chrysler 8-speeds is their shift quickness and feel. Allegedly in the nanoseconds' duration? But with the ratios tightly-spaced, no real shift-shock when it happens so quickly and firmly. Tach needle tells that tale.

No reason that a quality rebuild, with good machine work and (at least) OEM level parts, that an engine can't go at least 100K miles with no issues, considering modern oils and use of a quality roller timing chain set (as the Cloyes Plus Roller, Mopar Perf, or similar).

There are now some speed equipment for the Cadillac 472-500 engines. Even some YouTube videos of the dyno runs. One segment of the "Saturday morning" cable shows, a few years ago, showcased that particular dyno run. The guy that owned the Cadillac performance parts company was surprised at the numbers. Might check those out, for good measure.

Chrysler V-8 usually have had a pretty decent balance between torque, horsepower, and performance. Whereas GM and Ford engines aren't quite so well-balanced, in comparison, fwiw.

Enjoy!
CBODY67

 

[bajajoaquin]

That's a great description of way the new transmissions work, thank you. I had that vaguely in mind, but didn't have it quite so detailed. There's a guy on the Imperial Yahoo Group with a modified car he calls his '72 Imperial GT. He's considering a 6.1 swap, but wants to skip the 8-speed. I suspect that he'll have less drivability than he's hoping if he doesn't have the tight ratios.

I've also thought about the Cadillac performance stuff, but that would require moving to Cadillacs. I really, really like 1964 Cadillacs, and had a '65. But those (and the '66s) are 429s, which is a different architecture than the 472/500, and I just don't care for the '67 and later body styles. And I'm not really a Mopar guy, like most here, but I do like my Imperial. Also, my Imperial is pretty nice. Not one of the nicer ones on this board, but pretty nice. The cost difference between my car and a same-condition Cadillac is much more than the differences in cost for a stroker engine and a roller cam. I like Elwood Engle styling on this era Chrysler, too. Unless I'm going to go with a nice Superior 4-door hearse converted to a huge station wagon, I'll stick with my Imperial.

I also think I can get 50-100k out of a good rebuild. I'm planning on having removal, rebuild, machine work, reinstallation all done by a reputable, quality mechanic. I don't anticipate that this person will be a talented "engine builder," per se, which is why I'm trying to figure out my combination before bringing it to a shop. At the same time, I'll rebuild the trans and rear end. Time frame is 2019 into 2020. With the paint and mechanical work re-done (not going for restoration), I should have a comfortable, fast, reliable car that will last me as long as I'm interested in owning it for a lot less than I'd spend on a new car (or a nice used one).

The only real hurdle after that is rear shoulder belts. My wife is cool with kids in child seats because '67 has factory safety glass and lap belts, but she's pretty adamant about rear shoulder belts for older kids. I'm still working on that.

 

[bajajoaquin]

Incidentally, here’s that ‘72 Imperial. He’s planning on upgrading it and then doing a 3000-mile shakedown trip to Alaska before a 3-month European tour.

Kenyon Wills' 1972 Imperial LeBaron

 

[PontiacJim]

Here is a quick reference for rod ratio's for many different engines. Common Connecting Rod Ratios ~ Roadkill Customs

Don't overthink this. The shorter rod ratios put more leverage on the crank, thus more torque. Build for torque, not HP, and be reasonable on your rev range. Look at the Chevy 454, Pontiac 455, Olds 455 - these are pulling engines with the lower rod ratios. The longer stroke can also build better port velocity at lower RPM's - which can mean snappier response if all things are matched.

With regards to side loading, the longer stroke pistons can have the piston pin offset to compensate and minimize side loading. Pontiac did this on their 455. This also means pistons have to be inserted correctly as lefts and rights. However, when you order many of the aftermarket pistons, they are not offset, they are centered and typically have valve reliefs so you can use them in either bank of cylinders - at least many of the aftermarket Pontiac pistons are done this way. Some kits come with longer rods to provide a better rod ratio and the piston pin is moved up into the piston to compensate for the longer rod. Pontiac factory rods are 6.625" long and with a stroker kit the rods are typically a Chevy rod at 6.7" (or 6.8") to give a better rod ratio.

Short skirted forged pistons, although lighter, can rock in the bore from what I have read, BUT may be needed on a stroker crank so there are no rotating clearance issues. Most likely this is more of an issue when cold and because they need additional clearances for expansion when they heat up. I prefer a "standard" length skirt like factory as long as there are no interference issues.

So if stroking an engine, it is often cheaper in the long run to buy a complete kit, pistons/rods/crank, so everything is matched and fitted. If you buy individual parts, you want to know what you are doing and know they will work together.

You will also want to be aware of what compression ratio you plan on shooting for. Myself, I like 9.0 - 9.3 for an iron headed Pontiac engine just so I won't have any issues with running pump gas. Here is a site that shows you the various numbers, bore/stroke, deck height, piston head valve cc's, combustion chamber cc's, etc to figure on what your compression will be. They also have a good "Frequently Asked Question" page that may help. Stroker Kits from 440 Source!!

Torque is what you should be after and in my opinion, bigger cubes is the way to go. Then you want to match your cam choice to pull the most out of the engine. You could have BIG cubes and select a crappy cam spec and have a turd on your hands and be disappointed. So you don't want to guess on this one.

Keep in mind that more TQ & HP will ply itself on the rest of your driveline - trans, driveshaft, rear end, springs, and mounts. This is often forgotten about and next thing you know you are breaking/replacing things. So upgrades might need to be considered and this will up the costs of your $$bigger engine budget when it comes down to it.

Things to consider.

 

[CBODY67]

On the rear shoulder belts, I believe the '66 FSM shows how that worked. Quite bulky with all of those belts laying back there. Might be better to mimic the LATCH tie-down points for the child safety seats, if the kids are that young. Otherwise, you'll need some reinforcements in the rear package tray area and additional buckles, as the first-gen front shoulder belts used. The '72 factory shoulder belts had a less bulky situation, using a different, single buckle set-up.

When I mentioned the Cadillac hot rod motors, it was more in the orientation to look at their combinations of parts RATHER than suggesting a change to that brand of vehicle. That's all. Just to see what it took to make the power they did, on the dyno, with the aftermarket parts installed. Seeing how others get their results, whether in business or building engines, might yield some useful information in how to do things better, by observation.

Pisont pin offsets are normal in many engines. Chrysler typically uses a .030" offset to help quiet the pistons. Turning the pistons around, so the offset is toward the centerline of the camshaft, is reputed to add another 30 horserpower in many cases. That offset if more of a way to keep the pistons quiet, even in the stock motors. Which means with their longer skirts and such. Skirt clearance is important in stroker motors, just as crank counterweight/connecting rod and engine block clearance is important, too! One good reason to use one of the kits, but clearances that would still need to be checked and adjusted as necessary.

Enjoy!
CBODY67

 

[moper]

There's so much here that either this will be a record setter post, or I'll break it up as I go and add more later. There's a lot you bring up here. I am limiting my answers to a 100% street-type build. Race engines are very different and specialized in ways a street engine typically can't be.

"Anyway, when you stroke an engine, you change rod length and piston size so that you keep the "distance below deck" roughly the same. You have limits on rod length due to rod ratio and available piston compression heights. You want shorter pistons because they're lighter and rev faster and make more power."
The "stroke" of an engine has nothing to do with the piston or rod, or pin placement. The stroke is the distance the crank forces the piston to travel to do it's work. Stroke is the single most important factor in a street (read that as low rpm) engine. The rod length is next, and IMO the higher the rod to stroke ratio the better, to a point. Last is the piston design and pin location. Smokey Yunick used to say get the stroke you want and piston you need and use whatever rod fits. So R/S ratio is a factor in some choices during paper design but honestly, not much. Not to me anyway.

"However, you make those tradeoffs in the pursuit of a certain goal. That goal is maximizing performance. What if your goal is to have a quiet, smooth engine that makes butt-loads of power but feels like a refined stock engine other than being faster? In that case, short pistons aren't an advantage. They're usually forged, which expands more than cast or hypereutectic pistons. So they make more noise when cold, and have more bore wear. They also rock more in the bore than "stock"-ish pistons, causing more wear, making more noise, etc."
Life is about compromises. Engines are no different. But you have to keep all the goals in mind. "Performance" is individualistic. Quiet and smooth should be a part of any well executed build. I've built engines with a piston height of 1.45". GM LS engines are very short and are not noisy or suffer from lower service life. Again - to me those ideas are much about nothing. A well built engine will last and be quiet. Period. Piston rock and wear are more of a consideration. I won't use ring spacers where the ring passes over the pins. Those to me are too short and I want the oil control as effective as possible.

"Rods have similar tradeoffs. Longer rods are better for some applications because you want a high stroke to bore ratio. A stock 440 has a great one at 1.8:1. A stock 454 has a crappy one at like 1.4 or 1.5:1. But lots of 454s work just fine in low-revving engines for hundreds of thousands of miles (ok, 100,000+). There's something about "dwell" at TDC and BDC that affects performance, but I really don't know how it works. I know that it is a thing, I don't know what that thing is."
Again - in your application - rods will connect the piston to the crank. So they need to have the right length, the right pin end size, and the right bottom end size. That's about enough thought about rods for this build. Dwell is a big deal when you worry about more specialized engine packages. You can ignore it, or start another post on it if you want to toss ideas around.

 

[moper]

A lot to process here, thank you. Perhaps I should get Joey to change the title of the thread.

I'm interested in what can be done with off-the-shelf parts. There's no budget for custom parts, and the custom work has to be limited to some clearancing for a stroker crank and a balance job. The 440-source (and others, of course) stroker kits use Chevy rods for many of the combinations because the journals require less clearancing. I understand that it was also a trick to get an increased stroke, by offset-grinding the crank to Chevy dimensions to get some extra cubes.

Anyway, the idea was to look at commercially-available Chevy rods and commercially-available Mopar pistons to see if there was a combination that resulted in a taller, more stable piston. With an arbitrary limit of a 1.53 rod ratio (stock 454), there really isn't.

I appreciate the comments about modern pistons being shorter without harm to reliability. CBODY67, do you mind sharing compression height on your pistons if you know it? I was hoping to get hypereutectic pistons rather than forged, but that may not be (reasonably) possible.

So I think I'm back to one of the combinations listed as 500 or 512 in the 440-source catalog. They're 493 or 505 at 0.030" over. Those have rod ratios in the 1.6 range and compression heights of 1.485" to 1.8". It was a hope to find something interesting and viable, but it didn't work out.

As you note - the "off the shelf" stock type parts would need customizing you can't do yourself. There are many shelf performance options now. I've built probably 10 big block stroker engines. Maybe a few more if I really think about it. Using parts from 440Source, Eagle, Scat, MP, Diamond, SRP, KB-Silvolite, and factory Chrysler. In B and RB blocks. Never built a Hemi but I'll remedy that some day...lol. Anyway the newer forgings are not like the Speed Pro/TRW "battleship" pistons from yesteryear. They are alloys with less growth, and tighter piston to wall clearances. Machining has improved too. If you had a block bored with a boring bar by the shop down the street, then ordered your pistons and assembled it - that's not how it's done anymore (unless you have no modern option - in which case it's probably worth it to find a place further away that does - it-s that important).
Now it's been noted in other posts about quench. You cannot address quench with an open chambered factory as-cast head without a LOT of additional blueprinting and machining steps. I've built one. One. Won't bother again because there's so little value in doing it that way that it makes no sense to. If you have to use factory as cast open chamber heads, ignore the concept of quench and build it with a milder static ratio for pump fuel and a smaller camshaft. While we're on the subject - a "smaller camshaft" for a 500" engine is not a "smaller camshaft" as listed in the catalogs for a 400, or 440 for that matter. I've told people for years when camming a stroked engine combo - go bigger by the percentage increase in displacement. A 505" is 21% larger. You need to go 21% larger just to maintain the same horsepower output. That means to get the same roughly .63hp/cubic inch a 21% larger cam will give you about 320hp. Engines need air to work. Big engines need more air. Cam needs to be bigger. If you are looking at anything less than 245* @ .050" the cam will make an RV engine out of it. That might work for some definitions of performance, but it doesn't for me.

 

[70bigblockdodge]

I agree with all of what Moper said, 100%
Some things from my thoughts about this whole thing.
1. Your 67 engine is a closed chamber headed engine with factory iron heads. It should have 915 castings on it, which are considered to be the best closed chamber/port design. More on this in a moment.
2. A engine makes power by moving air, with the right amount of fuel in it, move more air and more fuel is available to burn. Yes a 500" engine will move more air but you are castrating it so low with the 5000 rpm ceiling. Which I somewhat get seeing as your intake and exhaust systems are really restrictive.
I am not seeing the need for a stroker engine with it's additional work as being able to satisfy your needs.
I really think that if you carefully and properly rebuilt your 440, with your detail oriented persona, to proper blueprint specs and adding a roller cam, paying attention to quench since either a stock head with mild port work or aftermarket head with clean up, would get you the "Holy s#/&" feeling in the seat of the car I think you want. It will also allow for many miles with no BS. It should allow you to have enough money left over to better explore transmission options, the worst of is a 518 behind a big block.

 

[bajajoaquin]

I don’t get why you guys insist on an engine that makes power above 5000 rpm. It’s an Imperial. I want it to be faster, but I am never going to do more than mash the gas pedal and expect it to move out with increased authority. Anything it makes over 5000 rpm will literally never be used.

 

[PontiacJim]

I don’t get why you guys insist on an engine that makes power above 5000 rpm. It’s an Imperial. I want it to be faster, but I am never going to do more than mash the gas pedal and expect it to move out with increased authority. Anything it makes over 5000 rpm will literally never be used.

It is because people do not read a posting from its beginning. I got what you were looking for. You want bigger cubes that will produce more torque and are not looking for a high revving high horsepower tire shredder. The Cadillac 500CI engine, is a perfect example of this. Low RPM's - 400HP @ 4400 RPM's and 550 Ft Lbs of Torque @ 3,000 RPM's. That gentlemen is a stump puller. You are not seeing an engine that needs trick heads, forged pistons, or a roller cam. Worrying about the best rod angle, fast revving short light pistons, ported heads, aluminum intakes, and headers doesn't come into play.

As a comparison, The dual quad Hemi in street trim and 10.25 compression is rated at 425 HP @ 5000 RPM's & 490 ft lbs of Torque @ 4000 RPM's. The Chevy 427 with 11.0 compression was rated at 425 HP @ 5,600 RPM's & 460 ft lbs of Torque @ 3,600 RPM's. The Ford dual quad 427 with 11.1 compression was rated at 425HP @ 6,000 RPM's and 480 ft lbs of Torque @ 3,700 RPM's.

This is the beauty of a stroker engine - more torque with HP at lower revs and not having to go all exotic on the parts to get there. Pair this up with a matching 2.76-3.07 rear axle gear and you will have a fast & hard pulling car IF you can get traction.

A cam like Comp Cams XE274, 230/236 @ .050" with 9.5 compression is all you would need - nothing all that aggressive. You might want to look into the Hughes Engine"Whiplash Cams." They could also suggest a cam for your application as well. Hughes Engines

 

[moper]

I don’t get why you guys insist on an engine that makes power above 5000 rpm. It’s an Imperial. I want it to be faster, but I am never going to do more than mash the gas pedal and expect it to move out with increased authority. Anything it makes over 5000 rpm will literally never be used.

I don't believe I "insisted" on anything. Gave you solid advice based on a fairly deep well of experience. Good luck with you project.

 

[bajajoaquin]

You might notice that the comment below yours explicitly says 5000 rpm, and your post says that if I don’t run a lot of duration, I’m going to make an RV motor. Given that RV motors aren’t known to be high-revving engines, I think it’s a fair summary of your position.

But let me ask you this: where do you think the torque and power peaks would be on a 500” engine set up as you describe with 245 degrees of duration?