[michaelroy]

I WILL, shortly be getting a pair of RA lll exaust manifolds. I am think of putting them on my 1966 389 YD engine.
#1 will they fit and #2 will they add any performance to my 30 overbore tripower 4 sp. engine 092 heads?
One is from 1969 and the other supposedly fr. 67? 9791637 LH / 9797072 RH.
Is this inexpensive horsepower?

[tom s]

I dont think you will be able to feel it in the "butt" dyno.Tom

[b-man]

Expensive horsepower.

After investing around $400 for the manifold and headpipe swap you might see 8hp, and probably won't feel it.

[michaelroy]

OK. Thanks for the input! 8 hp ain't enough, although a friend is giving them to me.
If I've learned one thing over the last 10 years fooling with old cars is: If it ain't broke don't fix it. Send us some of that California sunshine.

[Dick Boneske]

For as long as I can remember, the RA manifolds were worth 20 hp over the factory log manifolds. I have them on both our '64 GTO's and am very happy with the fit, appearance, and performance. I've never run a 1/4 mile time with log manifolds and switched to RA manifolds, but by seat-of-the-pants feel, they are worth at least 20 HP. JMHO.

One word of caution--the RAIII manifolds fit '68 and later A bodies. The original RA manifolds introduced in '67 fit the '64-'67 A bodies.

[Tom Vaught]

Originally Posted by Dick Boneske

One word of caution--the RAIII manifolds fit '68 and later A bodies. The original RA manifolds introduced in '67 fit the '64-'67 A bodies.

This is true, You might need to do engine crossmember mods to fit the 68-72 RAIII manifolds on your early body. Not really worth it.
You NEED 67 only manifolds that fit 64-67 behicles as Dick B posted. I ran a set for several years on a 64 GTO too.

Tom V.

[Dick Boneske]

Remember in the early '60's when the standard Tripower 389 was rated at 318 HP and the same 389 with the AFB Carter at 303 HP? That tells me they got an extra 15 HP with Tripower. With a different cam and the long branch manifolds, the s rating climbed to 333 HP with the AFB and 348HP with Tripower. That's a 30 HP increase,

I don't believe Pontiac would have spent the extra $ for only 8 HP, although I hesitate to second-guess b-man!!

[John V.]

Originally Posted by michaelroy

I WILL, shortly be getting a pair of RA lll exaust manifolds. I am think of putting them on my 1966 389 YD engine.
#1 will they fit and #2 will they add any performance to my 30 overbore tripower 4 sp. engine 092 heads?
One is from 1969 and the other supposedly fr. 67? 9791637 LH / 9797072 RH.
Is this inexpensive horsepower?

The fitment used to get discussed a lot years ago. I can't recall what fit and what didn't and have never had a set so no help that way.

What I can tell you is that the 9791637 was first used in '68.

Early in '68, Pontiac eliminated the troublesome Heat Riser Valve incorporated in the RH manifolds. Up til then, the '68 D port RA used the same RH manifold as the '67. The change affected the log manifolds. I believe the new p/n for the RH RA manifold without HRV was 9791607.

AFAIK, the 9797072 was first used in '69.

The first A body RA manifolds were used in '67, p/n 9777646 for the LH, the RH was p/n 9777642.

For the RH manifold, this is the p/n on the cast manifold itself. Pontiac did not service this manifold without the Heat Riser Valve so the p/n you will see in the MPC for the service part manifold assembly with the HRV is 9777641.

The RH 9797072 might fit. I think the bigger issue is the LH manifold, I think the 9791637 will likely hit the frame in a '64-'67.

Sometimes free can get expensive but perhaps you can find somebody willing to make a suitable trade. Or check ebay, maybe you can sell the free set for what it would take to buy a correct set.

[John V.]

Remember also that the SAE Gross HP advertised nos. in those days were representative of engine dyno results.

In '71, we started to see SAE Net HP getting advertised and the nos. dropped precipitously. SAE Gross was the engine before install in the car without fan, air cleaner, or exhaust system. SAE Net was the estimate after install with exhaust hooked up, etc. PMD typically estimated a pretty substantial reduction from gross to net. This was very obvious in '71 when they advertised both. The SAE Net HP nos. advertised on new cars today is all the more impressive when you realize the SAE Gross HP nos. of our '60s era musclecars would have been reduced by 50 HP or so had they been advertised as SAE Net HP.

I suspect Dick and b-man are both somewhat correct. The RA style exhaust manifolds provide a substantial SAE Gross HP improvement. But flowing thru the same basic restrictive exhaust system, the gain was insignificant and seat of the pants feel may be more psychological than real.

And you can't argue b-man's logic based on the cost especially considering the free manifolds won't be a direct bolt in.

[michaelroy]

AW SHUCKS.
Free ain't necessarily good or cheap. All you guys amaze me with your knowledge. Thanks for sharing. It's too bad they sure look cool.
Maybe, when I get them, someone may want to swap for ones that fit my 66 389.

[aceaceca]

We put a RAIII engine in a 64 GTO back in about 1968 or so. Cut a small section out of the frame and filled it in with 1/4 plate to provide clearance for driver side manifold. Brought the engine home from the wreckers ,aka junk yard ,in the trunk of my 62 Cat.