[footjoy]

I was just curious if anybody would have an idea if rams air exhaust manifolds would give me any extra horse power?

I have a stock 400 with 4X4h heads 230 hp, i am looking for a bolt on 25-50 horsepower without getting into the cam.

Thanks

Greg

[b-man]

At the most you're going to gain 10 HP from a manifold swap, probably closer to 8.

You'll never achieve your goal without a cam swap.

The Crower 60240 would be the perfect cam for your low-compression 400:https://www.summitracing.com/parts/c...MobileSwitchNo

[goatless]

Originally Posted by b-man

At the most you're going to gain 10 HP from a manifold swap, probably closer to 8.

You'll never achieve your goal without a cam swap.

I'm betting that on a stock 230HP motor you'll gain even less than that. The stock logs aren't really that bad and at that HP level the engine isn't moving enough air for them to be a restriction.

I agree with Bart that the only way to achieve your goals is to swap the cam.
The good news is that a cam swap is less expensive, and arguably less work, than swapping on RA manifolds.

[footjoy]

Originally Posted by b-man

At the most you're going to gain 10 HP from a manifold swap, probably closer to 8.

You'll never achieve your goal without a cam swap.

The Crower 60240 would be the perfect cam for your low-compression 400:https://www.summitracing.com/parts/c...MobileSwitchNo

would I have to change valve springs?

[b-man]

That's really something that you'll need to do, not all that difficult.

Even if you were keeping the stock cam a fresh set of springs would net you a noticeable performance improvement.

[unruhjonny]

I would be curious what an original 1973 400/230hp engine really made in 100% stock form - then what kinds of gains can be made through disabling the factory EGR setup, and doing a super tune ~ and then adding the RA exhaust manifolds.

I'd wager there's more in that engine than some think.

[Goatracer1]

Removing the EGR valve will gain you nothing. It doesn't work at wide open throttle. If it is not working correctly you might have a smoother drivability at small throttle openings. You wouldn't gain enough to warrant the cost of the manifolds and the required exhaust pipes.

[unruhjonny]

I didn't mean to suggest going through the effort to physically remove the factory EGR setup - but to disable it as it was setup from the factory;
IIRC I believe I read that the early 1973 EGR system disabled itself after the set test period, and the engines made more power than the eventually EPA approved engines with the EGR revision.
Wasn't the early hp rating on the SD455 20hp higher than the eventual EPA approved configuration?
(I don't know if that had the same '068' specs or not.)

I believe that a great deal of the guys here who run a stock appearing 1973-1979 engine, do in fact, have the factory EGR setup disabled.

Afterall a 1972 400 with the same compression and same 067 camshaft as a 73 400 had a rating of 250hp - twenty more than the 1973 engine;
Same exhaust system, same cam, same compression... but twenty more hp!?

[Goatracer1]

The SD engine has nothing in common with your engine.

[unruhjonny]

please re-read my post;
it was about diabling the EGR system...

[FrankieT/A]

In my opinion, you'd be better off changing the heads and get your compression closer to 9.5:1. Something like a 12 or 13 head, with chamfered pistons that would keep you around 9.5. That should get you 20-30 HP. Then a cam change and some RAIII manifolds down the road and ultimately you would pick up 100+HP. You would have a better launch point and still be pump friendly. Its easy(and relatively cheap) to go from 230 HP to 350 HP. The next 100 HP not so much...Lol.

[Doug]

As I understand it, your basic situation is that you are changing over a 6-cyl car to a V8. Accordingly, you are going to put an entirely different exhaust system on the car. At a minimum, that is a certain amount of fixed cost, no matter what system of manifolds, pipes, etc. First off, you will be making a decision of whether or not to make it a dual exhaust car. Next you will need to decide if you want a set of “standard” log manifolds , RA manifolds or tube headers. Then you will look at the size of the exhaust pipes, types of pipes (aluminized steel, stainless steel, etc). Each variation of the exhaust system provides for, at best, minimal increase in horsepower but the increases in costs become quite substantial.

Reading back through some of your recent posts you indicated you were “getting” a 71 400 engine. (1971 engines did not come with 4x heads.) Yet, you are saying that you have a stock 230 hp 400 with 4x heads, which indicates it is a 73 engine. It is unclear as to what year engine you are dealing with.

It is probably of no consequence as to what year engine it is other than the fact that if it is a 71 engine with 4x heads, the engine has been modified and you wouldn’t know what other changes may have been made inside of it (cam change? etc?).

In any case, there is a likelihood that the (230hp rated) engine came out of a car that had single exhaust. Installing that engine with dual exhausts is an improvement for that engine of a few horsepower by itself.

I gather that you don’t want to unbutton an otherwise drop-it-in running 400 engine itself. While it is not as extensive as taking off cylinder heads, a cam change does involve quite a bit of “dismantling” of the engine. Since the engine is outside the car, this partial dismantling of the engine would likely lead to further dismantling (removing the heads, etc, etc. )

Piecemeal improvements to the engine by bolt-on efforts (camshaft changes, expensive exhaust manifolds/headers, etc.) do not enhance the car. Basic dual exhaust systems enhance the car itself.

Since you are searching for some extra horsepower, I suspect that you are, in essence, searching for the FEEL of extra horsepower. The 6-cyl car probably has a very high (numerically low) rear ratio, maybe as low as 2.56 gears. The quickest way to get that feel of extra horsepower is to increase the rear gear ratio. A gear change would be the time to install a posi-traction rear. These modifications are an enhancement to the car itself and you certainly would feel the gain in performance. It would work well with your 200-4R transmission.

The difference in price between a set of regular log manifolds and a set of RA manifolds would go a long way towards modifications to the car’s rear end setup.

[PONTIAC LARRY]

your 1973 230 net HP 8:1 400 is not far off the power of a 1971 300 bhp 400 if both have the air cleaner removed ad exhaust opened up. So if you rlooking for a a 50 hp gain simply put some 67-70 #16,62,13 or 48/12, 670 big valve heads on. Evenwith a stock cam you r wil have your gain with better bang for the buck than the HO exhaust. Add a Summit 2801 214/224 cam and those earlier heads and you will be up around 375 bhp easily with log manifolds and duals while still on 93 octane as long as heads are not milled a lot.

[unruhjonny]

@ Doug;

Thanks for posting your findings on this poster;
I took his post at face value, and assumed his car came stock with a 1973/1974-400.

[Blued and Painted]

Biggest bang for the buck without opening up the engine.
Have the distributor professionally re-curved.
Bi-pass the five road blocks to the vacuum advance and hook the source directly to the vacuum cann. Make sure the advance diaphragm is not blown.

Preform the external Q-jet linkage adjustments out lined in Mr Cliff Book. Including getting the front and rear throttle blades to open to 90 degrees. Defeat the secondary lock-outs. And adjust the secondary top flap timing and opening angle.

Check fuel pump pressure and volume.
Check rear gear ratio and adjust if needed.

[Goatracer1]

You never said what you had for a car. If you are looking for the biggest bang for the buck swap to a lower rear end ratio. If you have a 2.69 to 1 swapping to a 3.23 or 3.42 will make all the difference in the world. Because of your engine's low HP you won't have a lot of top end but who drives 90MPH around town anyway.

[Squidward]

I vote for cam change as biggest bang for buck!

[PONTIAC LARRY]

Just the head swap on a stock engine is huge upping the compression. years ago we had done a stock rebuild on a 74 400 trans am (4X) heads 8:1 , used a new 067 cam over a new 066 , stock th400 and 3.08 gear , log manifolds and duals.. It ran some low 15 1/4 mile in that setup and with only a swap from the big 2.11 valve 4X heads to a set of just small valve 68 #15 heads (340 hp Bonneville) it dropped full second off the 1/4 mile to a low 14 with no other changes still a stock cam and all. Just saying.

[David Jones]

Originally Posted by footjoy

I was just curious if anybody would have an idea if rams air exhaust manifolds would give me any extra horse power?

I have a stock 400 with 4X4h heads 230 hp, i am looking for a bolt on 25-50 horsepower without getting into the cam.

Thanks

Greg

Greg, you say you have a stock 400/230. How stock? How tired is it? Is the carb in good shape? Stock distributor tune? Basic tune up parts are fresh...wires, cap etc? Describe the exhaust system you have now?

You may have a pretty decent supply of untapped hp by simply working with what you have 1st.

[footjoy]

OK it is a 71 400 WX block which means it was a two barrel then they put the 73 4x4h heads on it. We don't now what cam it has in it. it has a quadrajet on it now. it probably has 20-30 thousand miles on it. The heads have hardened seats.

That is all I know about it.

It is going in this 65 tempest.