[70f400]

I currently have RARE over size 2-1/2" manifolds with mandrel bent down pipes. Pypes 2-1/2" X pipe going in to flow master 40 series mufflers and a muffler shop bent 2-1/2" tail pipes exiting out the rear threw my 2-1/2" chrome tips. This was a pypes cross flow system but when I installed my Tanks Inc tank with 1/2" supply and return lines I did not have enough room to make that work.

I am considering changing this out to something that will help the flow of my 468 combo that is pushing 550 H.P. I can use this current exhaust on my 1980 TA that will be in the 425 h.p. range.

I really dont want to go back to headers on this car, and the cam I had custom ground on a 114 lsa is designed around RA manifolds.

My question is with the 2-1/2 down pipes is a 3" crossmember back exhaust going to help flow over a good mandrel bent 2-1/2" with better mufflers?

right now I believe the chambered flow master 40 and the poorly bent tail pipes are choking my combo to much at this power level. Any advise would be great. Thanks David.

[78w72]

with that much HP i would say a 3" would be an improvement over 2.5". but have also read many guys use 2.5" at that power level. IMO your biggest restriction is the flowcrapper mufflers. get some good straight through ultra flows or pypes race pro mufflers. your 2.5" tail pipes are probably ok since the ex gas is drastically cooled down at that point & your space limitations migh not allow for 3" mandrel bent.

as for the RA manifolds, i will let the experts comment on that, but IMO at 550hp a good header will flow better/make more power than manifolds. if this is a street car & your ok with keeping the manifolds then increasing the pipe size might not be much of a benefit since the manifolds are a restriction right at the start of the ex flow.

i have a ~520hp 467 in my 72 firebird & manifolds were not going to cut it for me & any future power increases i might do. yes they may work for that power level but wont flow anywhere near as good as quality headers. maybe just get a better flowing mufflers & keep the rest of the exhaust system how it is? would save some money & effort to install a new exhaust that might not be a benefit with the manifolds.

[70f400]

Thanks, I was going to just do the mufflers, but seeing how I needed exhaust for the 80 I thought maybe try the 3", but if no improvement due to the RA manifolds I wont fore go the extra expense and hassle of the 3". I had headers on this car last summer and only had 2" of ground clearance to the collectors wont go threw that again.

[78w72]

that is of course just my opinion... im sure others will chime in with actual tests or experience on the subject of 3" vs 2.5 or using RA manifolds at that power level. good idea though to use the 2.5" on your other car & upgrade this one to 3" & better mufflers.

im using 2" round port super comp headers with the 3.5" collectors on my 72 that is lowered about 2" so i know all too well about ground clearance issues on lowered cars, but with a 27.5-28" tall tire it does ok on terrible streets around here, no bottoming yet... but maybe a different header with 1 7/8 tubes & 3" collector would get more ground clearance for you? if its not a max hp race car then im sure youre ok with teh RA's & some better muff's.

[ta man]

Another vote for replacing flowmasters with ultraflows.For a street only car..this will be fine.For a car that may see the dragstrip once in a while you will not be utilizing your full engine capability.I'd expect the current exhaust even with Ultraflows to lose 3 to 4 mph and 3 to 4 tenths.
A fellow board member a few years ago swapped his ram air manifolds for 1 3/4 headers,installed 3 inch exhaust,I forget the tailpipes but I'm sure 2.5's but could be 3 inch and using good flowing mufflers.He picked up 4mph..he did a Cpl other little changes but the biggest change was the exhaust.