sprice
Active Member
Planning to do a refresh on my 73’ Imperial. Manual says 8.2 compression on the 440. Would a 906 head be an upgrade to bring the compression up to say 9.5 or is there another option/recommendations? Thanks.
Will a head upgrade bring compression up on 73’ Imperial?
- Thread starter sprice
- Start date
See: Cylinder Heads Part I - Tech Articles - Mopar Muscle Magazine
The short answer is you will not gain much with the 906 head, the flow rates with both heads is about the same.
Dave
The short answer is you will not gain much with the 906 head, the flow rates with both heads is about the same.
Dave
906 and 452 heads are both open combustion chamber heads with same size valves-- if I remember correctly.
The 906 do not have hardened valve seats if not already rebuilt.
So not gaining anything by doing this head swap.
You can do some research on either Eddy or Trick Flow aluminum heads maybe?
The low compression is from the pistons sitting lower down the deck height.
In a perfect world, swapping in zero deck height flat top pistons would be a way to bump compression.
But with today's corn fed gas pump....ping city. Not worth the expense as it will snowball into balancing the reciprocating assembly. Not cheap.
The cheap way out is shave the heads a little and deck the block a wee bit.
Only enough so you can still bolt on the intake without any trouble.
To get more Oomph I would recommend a nice RV cam, dual exhaust, recurve the distributor,fine tune the carburetor, port match everything and massage your existing heads for more flow.
Hope this helps.
why aiming for 9.5 ? what are you hoping to accomplish - do you have a hp # you are trying to reach ?
your car would have been rated at 208 california / 215 elsewhere net hp which is equal to about 305 to 330 gross hp before they changed the rating standard in 1971/72.
@cbarge 's advice is the way to go
your car would have been rated at 208 california / 215 elsewhere net hp which is equal to about 305 to 330 gross hp before they changed the rating standard in 1971/72.
@cbarge 's advice is the way to go
Last edited:
thethee
Senior Member
Do you have a ballpark number for how much to shave the head, without shaving the intake side?
Also the replacement head gaskets are going to be thicker. Have the thickness difference removed as well as what other shaving you can do.
Stealth heads are closed chamber, lighter and pretty much ready to go out of the box.
Those heads can be shaved the gasket thickness plus some.
But if your engine is a good running engine now, I would start with a super tune.
Stealth heads are closed chamber, lighter and pretty much ready to go out of the box.
Those heads can be shaved the gasket thickness plus some.
But if your engine is a good running engine now, I would start with a super tune.
sprice
Active Member
This option sounds most reasonable and easiest on the pocketbook. Thank you.
What kind of "oomph" are you looking for? Off-line response or passing gear performance?
You can quicken the distributor advance curve to get the centrifugal advance to start a bit sooner and similar with the vac advance too. Accel pump changes, from my experiences, will not help much at all, provided it in spec to start with. Also ensuring that the centrifugal + initial advance get to about 36 degrees BTDC total. Then some fine-wire electrode NGK Iridiums for a better pow when they fire. While these things will ensure that throttle response is a good as it can be, it will NOT make the car a "fire breather", but the better throttle response can make the car more fun to drive.
Also tweak the kickdown rod adjustment so that the min-throttle 2-3 upshift occurs at about 28 mph, which will raise the normal upshift points a few mph, which can make the car feel better, too, my experiences. The easiest way to try this is to get a thin black plastic wire-tie and loop over the bottom section of the slot in the kickdown rod where it contacts the throttle stud, at the back of the slot. Then snip off the excess. Just one is what I did on my '80 Newport 360 2bbl and it was just right.
Also, make sure you have the tires inflated to 32/30 psi, f/r, for a bit sharper steering response and better tire wear. From my experiences, too.
Check the exhaust system for pipe sizes on the inlet and outlet sides of the muffler, IF they measure 2.5", going to a full dual exhaust will not make enough difference in power to justify the expense on a stock motor.
When launching the car, use about 1/2 throttle rather than WOT immediately off-idle. This keeps the vac advance amount greater for quicker off-line acceleration. Once moving and before the WOT 1-2 shift, THEN use WOT.
Seeking more "ommph" can be a big money pit with a heavier car. Simple and inexpensive things, as mentioned above, seem to have the best results . . . on many levels, from my experiences. LOTS of rabbit holes to go down which can not be very financially viable.
Just some thoughts,
CBODY67
You can quicken the distributor advance curve to get the centrifugal advance to start a bit sooner and similar with the vac advance too. Accel pump changes, from my experiences, will not help much at all, provided it in spec to start with. Also ensuring that the centrifugal + initial advance get to about 36 degrees BTDC total. Then some fine-wire electrode NGK Iridiums for a better pow when they fire. While these things will ensure that throttle response is a good as it can be, it will NOT make the car a "fire breather", but the better throttle response can make the car more fun to drive.
Also tweak the kickdown rod adjustment so that the min-throttle 2-3 upshift occurs at about 28 mph, which will raise the normal upshift points a few mph, which can make the car feel better, too, my experiences. The easiest way to try this is to get a thin black plastic wire-tie and loop over the bottom section of the slot in the kickdown rod where it contacts the throttle stud, at the back of the slot. Then snip off the excess. Just one is what I did on my '80 Newport 360 2bbl and it was just right.
Also, make sure you have the tires inflated to 32/30 psi, f/r, for a bit sharper steering response and better tire wear. From my experiences, too.
Check the exhaust system for pipe sizes on the inlet and outlet sides of the muffler, IF they measure 2.5", going to a full dual exhaust will not make enough difference in power to justify the expense on a stock motor.
When launching the car, use about 1/2 throttle rather than WOT immediately off-idle. This keeps the vac advance amount greater for quicker off-line acceleration. Once moving and before the WOT 1-2 shift, THEN use WOT.
Seeking more "ommph" can be a big money pit with a heavier car. Simple and inexpensive things, as mentioned above, seem to have the best results . . . on many levels, from my experiences. LOTS of rabbit holes to go down which can not be very financially viable.
Just some thoughts,
CBODY67
The_Eagles’_Nest
Well-Known Member
The hardened valve seats are a benefit for sure. It sounds like anything 72 and up benefits most from taller pistons and a more performance oriented camshaft than anything.
At the risk of being pragmatic, you really sure you want to raise the compression?
Yes, raising compression is great for performance etc. ... The issue as I see it is obtaining high octane gas. The ethanol free gas (that has been easy to get in this area) has already dropped a couple octane points and I doubt if it will ever go back up. I'd do some serious thinking about that first... Do you want to have to buy "race" gas and mix it? Or would you rather just pull up to the pump and then go have some fun driving the car.
Not trying to rain on any parades, just pointing out the obvious that needs to be considered.
stubs300
Senior Member
I think he's just throwing darts blindfolded!
57fury440
Well-Known Member
Weren't the 67 heads closed chambers? They would boost his compression some, but I think they came with smaller exhaust valves except for the high-performance versions. I would think the best way to raise compression is a piston change. He will need more octane then, which means more $$$.
Blusmbl
Member
Correct, the 915's are closed chamber. Most were open chamber heads and usually are larger than the specification too. Adding quench to a motor that doesn't have any helps with detonation resistance, but a stock 440 in most cases has pistons so far down in the hole you won't get the quench height to where you'll see any benefit.
I've milled 906 heads ~50 thou before to bump up compression, but it also required milling the intake. From what I remember, whatever is milled off the head has to be multiplied by 1.23 for the intake face, for a big block.
I'll only jump in here to say two things... one, you can avoid the head gasket issue with a thin Cometec branded head gasket....and two, I'm seeing some good suggestions such as the `915 heads and a piston change, but the reality is that this will all dig into your pocketbook, like mopars just do.
Hughes (and a few others) used to sell "quench dome pistons", which effectively made an open chamber head into a closed chamber head, with the addition of a particularly-designed and placed dome on the piston.
At the time, we were led to believe than an open chamber would breathe better than a closed chamber, but I don't know that that was really proven to be accurate. Plus, the open chamber head was supposed to help with emissions. THEN it was discovered that the quench of the closed chamber head served to put a lot more turbulence into the combustion chamber for better combustion, not just being there to "quench" the fire of combustion. LOTS about combustion dynamics was learned in those earlier times!
The '67 440/375 used the 1.74" exhaust valves. Adding that valve size to replace a 1.60 exhaust valve would also be a very good time to also install hardened seats (by a competent machine shop!), too.
Once money is starting to be spent on engine upgrades, there can be FEW stopping points. Doing the tuning issues and tweaks will be the most cost-effective things one can do, by observation. As long as the engine has decent throttle response, that's really all that's needed to get to speed and enjoy the great chassis dynamics of the Chrysler suspension. To me, that's what it's all about in driving enjoyment of the Chrysler products with TorsionAire ride.
Enjoy!
CBODY67
At the time, we were led to believe than an open chamber would breathe better than a closed chamber, but I don't know that that was really proven to be accurate. Plus, the open chamber head was supposed to help with emissions. THEN it was discovered that the quench of the closed chamber head served to put a lot more turbulence into the combustion chamber for better combustion, not just being there to "quench" the fire of combustion. LOTS about combustion dynamics was learned in those earlier times!
The '67 440/375 used the 1.74" exhaust valves. Adding that valve size to replace a 1.60 exhaust valve would also be a very good time to also install hardened seats (by a competent machine shop!), too.
Once money is starting to be spent on engine upgrades, there can be FEW stopping points. Doing the tuning issues and tweaks will be the most cost-effective things one can do, by observation. As long as the engine has decent throttle response, that's really all that's needed to get to speed and enjoy the great chassis dynamics of the Chrysler suspension. To me, that's what it's all about in driving enjoyment of the Chrysler products with TorsionAire ride.
Enjoy!
CBODY67
915 heads as cores if found are not cheap.
Then you can easily blow 800 to 1k rebuilding them.
Not far off the price of new heads ready to run out of the box.
On my 68 Newport, I used .17 thou head gaskets and the heads were planed .10 thou and the deck was skimmed just to be perfectly striaght/flat.
My intake bolted on with no issues.
My CR is about 9.2 so I can run any gas necessary just to get home on long trips.
Big blocks like to breathe.
Anything you can do to make it breathe better will gain some torque and a few horses along the way.
It is amazing what a dremel tool and a few hours on your factory heads can do to improve flow.
Then you can easily blow 800 to 1k rebuilding them.
Not far off the price of new heads ready to run out of the box.
On my 68 Newport, I used .17 thou head gaskets and the heads were planed .10 thou and the deck was skimmed just to be perfectly striaght/flat.
My intake bolted on with no issues.
My CR is about 9.2 so I can run any gas necessary just to get home on long trips.
Big blocks like to breathe.
Anything you can do to make it breathe better will gain some torque and a few horses along the way.
It is amazing what a dremel tool and a few hours on your factory heads can do to improve flow.
sprice
Active Member
Hi cbarge, this plan is perfect for what I would like to achieve. Opened a can of whoop-*** with this question, and my fault. Am assembling the bottom end of a 67" 440 and for some reason, had the 73' rebuild in my head. After sending the question I realized the lower piston position will be the problem in the 73' and like you and others have mentioned, will be an endless tail chasing to get what I thought was reasonable/possible (9-ish, yes CBODY67, 9.5 is probably too much). All good information however and thanks to everyone. Going to be doing some port and polishing on what ever I end up with however would like to get something different than the 345's that, according to my research, are in the 73'. What heads did you end up with in your 68'?
My preference is 452 castings 9n older blocks with original pistons.
Did that on both my old 68 NYer 440 and the 66 300 383.
Still plenty of cores around and they already have hardened valve seats.
67 440 will have flat top pistons with almost zero deck height.
The 452 will drop the compression down by half a point---much needed to run on todays corn swill and NO PING.
I always did a 3 angle valve cut and opened up the bowls and as mention port and polish.
Again the cost of rebuilding any set of heads will be the same and almost as much as buying a new set already done.
For reference, the 452's came after your 345's and were used on cars and trucks right to the end.
Stay away from RV heads that have angled spark plugs. Nothing wrong with them just not for your application.
Hope this helps
PurpleBeeper
Member
Just my 2-cents....
a. You can increase compression by taller pistons or smaller combustion chambers (aka "closed chamber" heads)
b. When you rebuild the engine, you only really have to change one or the other to raise compression.
c. Milling heads/blocks will work, but as mentioned, that affects the intake/head mating surface and that can be a pain in the butt (not worth it in my opinion...I've been there)
So....why not rebuild the motor, you'll likely need pistons, so change those and leave the heads alone. If by some chance you can just re-ring the motor, change the heads. Personally, I'd just plan to swap the pistons
On the issue of new heads, I always was a little questioning of my late machine shop operative who would always pull a new, assembled cyl head apart for inspection, even if it came from the OEM. He'd pull them apart, inspect, clean, then touch the seats, and put it all back together. I didn't question that, just thought it was a bit odd . . . at the time. UNTIL I happened across a recent "Mopar Jim" YouTube video where they pulled apart two cylinder heads from different sources. One was from a more mainstream "hot rod" brand and the other one was from a higher-end brand.
You might expect anything new to be ready to go out of the box, but for the mainstream hot rod brand, that was NOT the case. Machining debris was there, even under the valve seals (B/RB heads). Not really bad, just not good. No telling how long they would have lasted before something happened. Kind of disappointing, to me.
The other brand, costing close to $1000.00 more/pair, was a much nicer situation. Very clean with very little extra "assy lube", other than what was needed. Nicer in all other aspects, too. Much more ready-to-run out of the box. It was agreed that the more expensive set was a better total deal. Still, good to pull them apart for inspection to verify what was there.
So, I concur that rebuilding a good core set, even installing hard seats in the process, CAN be better than trusting a set of new aluminum heads "out of the box" for long-term use. I know, the aluminum heads can have more recent combustion chamber designs ("trick of the week", sometimes, fwiw), that aluminum will make the heater get hot faster in cold weather, but might not be as great as compared to what we might be used to, by observation. Especially for an engine where the OEM automatic choke depends on exhaust heat to work (as many aftermarket aluminum heads do not have the exhaust crossover passages). Of course, this ALL depends upon a competent machine shop installing the hard seats correctly! Much less doing a good valve job, too.
In any event, I concur that aiming for a target 9.5CR can be good, if possible.
Just some thoughts,
CBODY67
You might expect anything new to be ready to go out of the box, but for the mainstream hot rod brand, that was NOT the case. Machining debris was there, even under the valve seals (B/RB heads). Not really bad, just not good. No telling how long they would have lasted before something happened. Kind of disappointing, to me.
The other brand, costing close to $1000.00 more/pair, was a much nicer situation. Very clean with very little extra "assy lube", other than what was needed. Nicer in all other aspects, too. Much more ready-to-run out of the box. It was agreed that the more expensive set was a better total deal. Still, good to pull them apart for inspection to verify what was there.
So, I concur that rebuilding a good core set, even installing hard seats in the process, CAN be better than trusting a set of new aluminum heads "out of the box" for long-term use. I know, the aluminum heads can have more recent combustion chamber designs ("trick of the week", sometimes, fwiw), that aluminum will make the heater get hot faster in cold weather, but might not be as great as compared to what we might be used to, by observation. Especially for an engine where the OEM automatic choke depends on exhaust heat to work (as many aftermarket aluminum heads do not have the exhaust crossover passages). Of course, this ALL depends upon a competent machine shop installing the hard seats correctly! Much less doing a good valve job, too.
In any event, I concur that aiming for a target 9.5CR can be good, if possible.
Just some thoughts,
CBODY67
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