[jeff chmura]

Hi guys,
I have a '65 GTO with a 461, Kauffman D ports, ported 290 CFM , HFT RA4 clone cam,with a p65 2x4 edelbrock intake.
I am using 2 1/4 D port exhaust manifolds I plan on using 3" exhaust with X pipe to the tail.
Would it be worth the effort of changing out the RA manifolds to 2 1/2". How much HP am I losing keeping the 2 1/4" VS. the 2 1/2"
I'm only going to be driving this on the street with the occasional stop light blasts.

Also, down the road, I plan on changing the cam out for a roller setup.

Thanks, Jeff































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[dmac]

You won't lose anything on the street. Maybe at the top end you might lose something, but if you are hitting top end on the streets, I hope you don't live near me.

[chiphead]

Regular D-port passenger car manifolds or iron headers? Going from regular manifolds to the RA style iron headers would be worth the change. Just changing outlet sizes within the same type of manifold isn't worth much. Maybe 10 HP peak? Mice nuts.

3" exhaust is a waste of space without 4-tube headers. 2.5" and let it eat.

[jeff chmura]

Thanks for the info guys.
Yes I have 2 1/4 RA manifolds now.
Interesting chiphead about 3" exhaust....agree it would much easier and waste of space if not worth it.
Thanks, Jeff

[Sprocket]

In my experience, swapping the manifolds themselves in and out has been easy enough. The catch is that you have to pay attention to the number of outlet flange bolts/studs on each manifold. On the 2-1/4" set that I have, the LH has 2 and the RH has 3. On the 2-1/2" set that I also have, both LH and RH have 3. In other words, you may also need cut and refit a head pipe in order to install the requisite mating flange and complete the swap. Either way you go, I recommend a mandrel bent 2.5" exhaust system with an x-crossover. It has worked pretty well for me.

[Tom Vaught]

I had a set of the earlier 67 Ram Air Manifolds done by Tom Jeffers RIP and and sold by PY. Very nice pieces.
Ran the things on the car and was very happy with them vs all of the headers I had run (except for the 2" tube
round port to D-Port Head headers). Those headers were easier to put on vs the 67 Ram Air Manifolds. Flowed better too.

I looked at the other manifolds out there that had the slightly larger exit opening and saw no real benefit to "upgrading"
to them. If anything the sealing surface to the head pipe was not as good. So I passed on those parts.

A guy was trying to do the HO Racing type Tri-Y headers and I thought I might look at those some point as
the workmanship on the HO Racing stuff was quite good.

So except for above, I would leave the manifold parts the way you currently have it.

Tom V.