Carburetor Upgrade and X Pipe v H Pipe

[74Newport400]

Hello! I have a 1974 Newport Custom, with the 400, 2 barrel carb, single exhaust. The original carb needs to be rebuilt, thinking its a good time to upgrade to a new intake, 4 barrel, and true dual exhaust.

I am looking at an Edelbrock intake. Looking for recommendations on what type of carb and what cfm to install. This is my weekend cruiser and long range road trip car, not a race car, but looking to get some more power out of it without completely sacrificing fuel economy.

I am sending out the exhaust manifolds to Jet Hot to get coated, then having true dual exhaust installed. I've had both X Pipe and H Pipe suggested to me - thoughts and opinions?

 

[413]

I like an Edelbrock performer intake and a stock 383 or 440 non HP AVS carb. You can buy a NAPA choke thermostat that bolts to the manifold to work with this combo. You don’t need large diameter exhaust to cruise around.

Another good bang for the buck is the rear end gears, what do you have. now? What size rear tires? What hiway speed MPH do you usually travel on your trips? Do you have a tach in the car?

I like to be around 2500-2700 RPM at my desired cruising speed on the freeway.

2.76 gears and 27-28” tall tires kill the torque. It’s Like starting out on your 10 speed in 10th gear, as an example.

Sorry to say if you like that combo.

 

[jct]

Stay with H-pipe, X-pipe is meant for high rpm flow

 

[CBODY67]

Basic Edlelbrock aluminum intake. Performer series. In modern times, an AVS2 650cfm, Street Demon 650cfm, or an Edelbrock AFB 600crm.

With a Newport and 400 2bbl as factory equipment. That usually means a 2.76/2.71 rear axle and P225/75R-15 tire size. Unless somebody special-ordered a 3.23 instead. With the 2.76, that means about 28.5mph/1000 engine rpm. That makes for good cruising on any Interstate highway, in the speed range Chrysler C-bodies usually like to be in (our '66 liked 75-90mph).

The dual exhaust will not generally help mpg, just WOT and higher-mid-range rpm power. 2.5" diameter max, is all that's needed. "H" pipe is a "sound fix", if anything at all. Similar with an "X" pipe, on a stock (or reasonably stock) engine. Chrysler didn't use either one.

The theory behind the "H" pipe is to allow "excess capacity" of one side to be used by the other side, for better flow maximaxation, and related power. This is much more of a WOT thing than for normal crusing or occasional "passing gear" use. It can also mean the pipes will need to be lower, in order to clear the drive shaft, depending upon where in the system it is placed (usually near the end of the transmission).

At normal cruise speeds, exhaust back pressure usually doesn't happen significantly, BUT at WOT and higher rpms, THEN it happens. The stock system has plenty of capacity for cruising situations, by observation. Different situation for GM vehicles or that era, typically, but not generally Chrysler products.

I believe TTI has a kit for the exhaust?

I know that we all generally want something "better than factory", but in so many cases back then, Chrysler did some pretty good work in their cars. Many were better than out-of-the-box GM cars, as-is. Whereas on a Chevy, by comparison, in order to get good performance, you needed headers, dual exhaust, and other mods to keep up with a STOCK Chrysler product, especially those with stock 4bbls.

End result, you can spend a good bit of money and end up with something not much better than you started out with, especially if cruise mpg is a consideration, by observation.

Just some thoughts,
CBODY67

 

[CBODY67]

As I recall, those particular C-bodies had "sizable" single exhaust systems under them, anyway. Measure the muffler pipe inlet and see if it's not already 2.5"?? Just as the stock exhaust manifolds are higher-flow than previous "log" manifolds were. Which, compared to some other brands' single exhaust systems, makes the Chrysler unit a "sewer pipe single" by comparison.

For something lower back pressure, there's a '72 era Chrysler Imperial muffler that is 2.5" in and out, with the normal C-body case size. Fit just right under my '67 Newport 383 4bbl, with appropriate OEM factory (Walker Exhaust supplied) pipes, front and back. Same back pressure as the OEM Street Hemi muffler, but quieter.

Unless you're going for originality, a "resonator eliminator" pipe at the very back can be used rather than the rear resonator unit (beside the gas tank).

In preparation for your suspected "future 4bbl project", scrounge the salvage yard for similar Chryslers with stock 4bbls (which will usually be TQuads) for throttle cable and kickdown linkage items.

For "right now", get the car tuned and running as good as it can. That will also include a good front end alignment, too. Enjoy it and learn how it feels and reacts to certain things/inputs. THEN start "messing with it", IF something might need attention.

Chrysler didn't just "assemble parts", they put together "combinations of parts" that usually worked pretty well. Emissions control issues got into the way a bit, sometimes, but everything was pretty well dialed-in as they were. Maybe a little tweaking of the base timing, for example? But from my experiences, pretty dang good as they were produced.

Enjoy!
CBODY67

 

[Davea Lux]

You probably do not need an H or X pipe conversion for this engine. As Willis suggested, go with the Imperial or Hemi low restriction muffler. This is an 8.2 compression ratio smog motor. You do not really have the combustion dynamics to advantage of a high performance exhaust. The Edelbrock Performer is a good aftermarket manifold that will accept a variety of carbs. My personal preference is for an AVS style carb for reasons of reliability. About 650-700 CFM is all you will need for this engine. Toss any delay valves in the distributor vacuum advance and get rid of the EGR valve and block off the port. You can then tune the carb for best overall performance.

Dave

 

[Gerald Morris]

As I recall, those particular C-bodies had "sizable" single exhaust systems under them, anyway. Measure the muffler pipe inlet and see if it's not already 2.5"??

....

Chrysler didn't just "assemble parts", they put together "combinations of parts" that usually worked pretty well. Emissions control issues got into the way a bit, sometimes, but everything was pretty well dialed-in as they were. Maybe a little tweaking of the base timing, for example? But from my experiences, pretty dang good as they were produced.

Enjoy!
CBODY67

I too have been doing a little arithmetic w.r.t. cross sectional area of exhaust pipes. I LIKE the idea of using one large pipe actually. I've been looking over Waldron's setups. W my 2.76 742 open rear end, I needn't design for burning rubber.

 

[70bigblockdodge]

Any resrtiction in the exhaust will cost fuel mileage, period. Of course open headers with a short "tuned" 3 or 3 1/2" pipe on them is a little miserable to live with, everything working back from this point is a comprise to fuel mileage. Also not get sucked into the lazy exhaust shop wives tale of small diameter exhaust builds torque, if that were true then fitting a Prius sized exhaust would be easier than a gear swap and would provide more torque than you could keep control of at 1500 rpm. I prefer a x pipe but a H is simpler to build and fit in the chassis, both will help fuel mileage the x will probably win out at WOT. The 2 bbl that is on your car should be a Holley, it is a piece of crap, not a good one at all. Any 4 bbl manifold is a improvement, the 73 up stock iron 4 bbl is a good piece, cheap. Aluminum is a good choice if you don't mind spending the $$, the weight savings is useless on a formal front end but you have to start somewhere. A Eddy carb or a new street demon in the 600 range is good, something with a air valve secondary.

 

[Gerald Morris]

Any resrtiction in the exhaust will cost fuel mileage, period. O ... .

Yes, back pressure is to be minimized. Mind you, my 516 closed quench heads and 2 barrel Stromberg are hardly high performance hardware. I wonder at what poinnt of cost/benefit getting dual pipes becomes less expensive than a single one. Cross sectional area of the pipe being proportional to the square of the radius helps one with flow calculations, but how much trouble is it to bend say, a single 3.5 inch tube which has almost the same area as two 2.5 inch diameter pipes?

 

[413]

“Any restriction in the exhaust will cost fuel mileage” that statement is pure BS. So that means if you remover the exhaust from a stock car it will get better mileage? That’s BS also. It really depends on your cruising RPM. 2500 compared 5000 RPM will like a different exhaust system.

Dual exhaust is twice the work/time/labor, think about it.

Fitting a 3.5” pipe under the car will be tricky and unnecessary.

2 small pipes are better than one big one.

You don’t need a large pipe cross section for good gas mileage on a long range cruiser.

I’ve always liked how the 62-67 383 mopar engines run and drive. Closed chamber heads, small AFB, small exhaust pipe(s) small camshaft. They have better throttle response, low end torque, and gas mileage than a 68-70 same 383 cubic inch engine with lower compression ratio, open chamber heads and AVS.

 

[70bigblockdodge]

Yes, back pressure is to be minimized. Mind you, my 516 closed quench heads and 2 barrel Stromberg are hardly high performance hardware. I wonder at what poinnt of cost/benefit getting dual pipes becomes less expensive than a single one. Cross sectional area of the pipe being proportional to the square of the radius helps one with flow calculations, but how much trouble is it to bend say, a single 3.5 inch tube which has almost the same area as two 2.5 inch diameter pipes?

The single will be cheaper. 3.5" is probably overkill for your situation, but I like the way your thinking. A c body actually has a pretty good single exhaust, the Y pipe is more of a Y not a T as with later cars and smaller bodies to fit it in. My main point to OP is not to let a exhaust shop try to talk you into using 2" all the way back.

 

[Gerald Morris]

The single will be cheaper. 3.5" is probably overkill for your situation, but I like the way your thinking. A c body actually has a pretty good single exhaust, the Y pipe is more of a Y not a T as with later cars and smaller bodies to fit it in. My main point to OP is not to let a exhaust shop try to talk you into using 2" all the way back.

Yes, we're on the same page and paragraph here. My current exhaust is woefully inadequate, consisting of the Y pipe then routed into a SINGLE 2" PIPE! I suspect even 3" pipe is more expensive than dual 2" would be, due to the extra bend radius required for larger diameter pipes. A single 2.5" probably would be the most cost effective setup for a low-flow engine, with a radius of 1.25" still giving a decent cross sectional area. A single 3" w a 1.5" radius beats dual 2" (2.25"^2 vs 2"^2) here though, so IFF one can bend 3" properly for the contours of a 66 C-body undercarriage, with a reasonable cost, one may get a very good exhaust system with a single pipe.

516 heads, while providing the closed chamber for performance, are afflicted with undersized ports, and will require induction hardening for the seats regardless. Mine seem to be serving admirably enough for the present, with the 350 cfm WWC carb good up to 4000 rpm. Given the 2.76 rear end, on the interstate highways, this all makes for a nice cruiser; which is doubtless what the Moparian Masters of Yore intended.

I venture that the maximum practical diameter of a single tube constrains the cost effectiveness of such a system. Bend radius counts for a LOT in design considerations here. I've bent some fancy EMT as an electrician yrs ago, and while that stuff isn't precisely the same as exhaust tubing, there are similar limits on it.

I have 906 and 452 heads available also, with a late 60s "Commando" short block and a 400 respectively. My long term plan is to use the steel crank from the 383 short block (if practical) in the 400 block to build a most DURABLE B block engine with optimum low end torque and a bit of passing power, nothing fancy. I like the internal balancing of the steel crank and overall structural superiority over nodular cast iron, even if I don't plan on a 7000 rpm monster. NO STROKING! I may well use the 516 heads with the built motor, given the closed combustion chamber advantage for bottom end torque.

Much research, consultation and budgeting comes before any new plant gets dropped into Mathilda's engine compartment. But a new exhaust system is in the offing, God-willing, within the next 12 months....