[4mula73]

I'm building a mild 400 for my 73 formula to be my daily driver. 212, 218 duration 110LSA 106ICL, 1.52 roller tip rockers, 96 heads, performer intake with Q-jet, DUI distributor. TH400, 3.23s. I don't want to run log manifolds. I'm looking for this to be solely a street car with about 350hp and at least 430 lb/ft. I have a set of Hedman 28140 3-tube headers, but I'm debating whether to use them or get a set of the HO manifolds from Ram Air Restorations. What do you guys think? If not the headers, should I use the stock size or the oversized manifolds?

[Lee]

Get rid of the 3-tube headers. Either the RARE manifolds, or a set of GOOD headers.

I have a chassis dyno, and have dyno'ed several Pontiacs and have a pretty good idea of what power they should make. I had a Trans Am with 3-tube headers on it awhile back, and it was at least 20hp short of what it should have been (possibly as much as 40hp).

[4mula73]

Is it because the two center cylinders (3,5; 4,6) interfering with each others exhaust pulses or is it that they just don't flow? I'm going to use the RARE manifolds. Thanks for the advice

[Lee]

I do believe it has something to do with pulse interference in the center two cylinders.

[Sirrotica]

Unless the heat crossover in the center exhaust ports is filled, they are interconnected in the cylinder head anyway. Three tube headers aren't going to make that big of a difference compared to RA manifolds on a muffled street engine. To me, I doubt the butt dyno could tell any difference and even on a rear wheel dyno your talking about 25-30 flywheel HP.

Sorry, I've run both and either are an improvement over log manifolds, but one is not that far above the other. I'd venture to say they are quite close not giving an advantage to either one.

[4mula73]

I would imagine they are a lot easier fit though, right?

[Sirrotica]

Originally Posted by 4mula73

I would imagine they are a lot easier fit though, right?

Either way there's work to be done. The head pipes will need changed or at least modified with cast iron RA manifolds. If you have existing dual exhaust already you'll have to cut the pipes to use reducers for headers. Three tube headers fit almost every chassis because the elimination of the fourth tube, they're the easiest header I've ever installed on a Pontiac. Ease of installation, or fit wouldn't be a huge difference in either case.

Probably the biggest advantage to RA manifolds would be the longevity over non coated headers of not rusting. Buying coated headers would probably even the score again.

Cost is probably in the advantage of three tube headers unless you happened across a used set of RA manifolds.

A test performed by SD Performance concluded that the more cam overlap the engine had the RA manifolds became less efficient over a four tube long tube header. It depends on how the engine was built initially as to how efficient the RA manifolds are. They recorded a 75 HP difference between 4 tube headers and RA manifolds with a modified engine with more cam overlap.

There is not an exhaust system made that fits every need of every engine, not a one size fits all choice. That being said a RA manifold and a three tube header are geared more towards a stock type engine running with mufflers, rather than a combination that is being wrung out for every last ounce of power.

Below is a quote from a test performed by the Dallas Area Pontiac Assoc.

"We have performed a similar test with the Pontiac GTO cast headers (Ram Air series) on the 12.5 second car, and they performed identically to the three tube units. The cast units are easier to install and maintain in comparison to the tube type headers, and are an excellent choice for street and street/strip applications."

[Willshire]

i have a set of coated long branch RARE's on my 64 GP. I bought them strictly on ease of install. They sound great, don't ting like bare tubes, and the coating is over a year and a half old and still looks pretty fair especially compared to the exhaust port on the head. And with steel gaskets they rarely leak. so far no leaks at all! Of course i needed a mini starter for clearance

[4mula73]

My car didn't have an exhaust system on it when I bought it. So that makes things easier since I don't have to splice to an existing pipe. I'll just get a local shop to do everything from the manifolds back

[Sirrotica]

The new system should be a minimum of 2 1/2 inch pipe along with efficient mufflers, It should be made out of mandrel bent pipe something most local exhaust shops can't accommodate. FYI, loud does not mean a muffler is efficient. A quiet exhaust system can be more efficient than a loud one.

There is power to be gained with either an exhaust crossover (X system) or an H pipe, R.A.R.E. has these parts available if you want a more efficient system than something the local exhaust shop can whip up. After spending $400 on oversize manifolds there's no sense in putting a cork in them by having a restrictive system after the manifolds.
Good luck with the install..................

[4mula73]

Will do! Thanks