GM A Body exhaust 3" or 3.5 inch maybe oval? Help

[real57vetteguy]

As some of you know by a previous thread I am making some changes to my 65 olds 442 project! The Aluminum headed 468 is getting a makeover consisting of:
CNC head and intake port job 240 cfm @ .600 Stock 321 cfm @ .600 after CNC port work
replacing 1-3/4 poor fitting hooker headers with 2" runner 3.5 collector ARH headers
Cam change from HYD to Roller 242/246 598/605
7 QT pan
better brackets for ALT and air cond
Bump the compression a little
removed 2-1/2" Magnaflow cat back system

Okay I mentioned previously that i seriously HATED the magnaflow sound on my car, maybe it was partially the X pipe but it honestly had a street bike/diesel truck/import sound to it, idle sounded nice but 2k and up it was horrible.
I am leaning towards spintech long case mufflers (the quietest ones made) I should realistically be making 520-540 hp after the changes. Its my understanding that I need to be running 3" and the car sits a bit low. I ran across Ram Air Restorations and gave them a call. He has a 3" oval kit for my car that would go to the long case spintechs but I dont like his tail pipes, I might get the kit without tailpipes and order a set of tail pipes from Flowmaster or have them done locally. My question is this.. The fellow at Ram Air restorations suggested I run a 3.5" oval x pipe to a spintech with a 3.5" oval inlet and a 3" round outlet to 3" tailpipes. I couldnt understand the reason why? The 500 HP range doesnt need 3.5" exhaust. Any ideas????? ALso I am worried about running another X pipe, if this one sounds like crap I am going to be pretty upset at spending all that money.

[protour_chevelle]

Depending on the x pipe design in 3" it could be a restriction. 3.5" could also balance out the banks easier..

[raustinss]

Some guys with 68-72 a bodies run the mufflers in the area beside the gas tank and the trunk drop offs, having said that I don't know if it's possible on a 65 but, moving the mufflers further back which changes the drone effect you might be getting, other then that a 3.5 oval would definitely flow similar numbers as a 3" round, I do think that 3 " is a Lil overkill on around 500hp I think you could definitely get by with 3"oval or 2.5" round, just my opinion
Good luck

[real57vetteguy]

Some guys with 68-72 a bodies run the mufflers in the area beside the gas tank and the trunk drop offs, having said that I don't know if it's possible on a 65 but, moving the mufflers further back which changes the drone effect you might be getting, other then that a 3.5 oval would definitely flow similar numbers as a 3" round, I do think that 3 " is a Lil overkill on around 500hp I think you could definitely get by with 3"oval or 2.5" round, just my opinion
Good luck

I appreciate the reply but I am not having drone, none at all, I am having a sound like a import car with the current or previous magnaflow set up. I was worried if the x pipe caused that and if 3.5 oval exhaust was way too big?

[raustinss]

A x pipe usually helps with making the car quieter and more importantly power, the engine is a odd fire which means 1 cylinder fires from 1 bank then the other. As the exhaust moves thru the system it tumbles at the intersection of the x pipe they cross paths and help "pull" the next exhaust pulse from the other cylinder bank. Obviously this continues and helps clear the cylinders of exhaust and pull in fresh air and fuel during valve overlap. Creating more power. A h pipe does the same thing just not as effectively or making the exhaust quieter. I believe your problem might be the pipes are too big and you might not like the mufflers...but I'd start with the pipes

[real57vetteguy]

A x pipe usually helps with making the car quieter and more importantly power, the engine is a odd fire which means 1 cylinder fires from 1 bank then the other. As the exhaust moves thru the system it tumbles at the intersection of the x pipe they cross paths and help "pull" the next exhaust pulse from the other cylinder bank. Obviously this continues and helps clear the cylinders of exhaust and pull in fresh air and fuel during valve overlap. Creating more power. A h pipe does the same thing just not as effectively or making the exhaust quieter. I believe your problem might be the pipes are too big and you might not like the mufflers...but I'd start with the pipes

The exhaust that was run on the car was a magnaflow 2-1/2 cat back system, that's the pipe and mufflers that I really disliked the sound. So I hope that for a honest 500-540 hp Big Block the 2-1/2 wasn't too big. If you read my first statement again I was leaning towards going oval, my builder, and head porter suggested running 3", The guy at Ram air restorations (where I am going to buy my oval exhaust) suggests going 3.5 oval into the mufflers (spintech) and 3" round tail pipes out

[raustinss]

Yeah I think the oval is a good idea, I'm probably going to use the same under my car because I had 2.5"true duals and after I lowered the car there wasn't a whole lot of room between them and the ground. My plan is is use oval to the rear axle kick up the convert to round into the mufflers. Again if I were you I'd start with the pipes and go from there you my decide that you like the mufflers?

[protour_chevelle]

On an LS1, true duals with no balance connector will sound like a V-8. Now put an X pipe in and it does sound way more race-car high reving that I think you are explaining.

[raustinss]

Matt read the first post...he's got a built 454-468 it should sound fantastic...my lil 396 did but it had true duels

I forgot to mention are anybody the mufflers baffles loose. Also my car had a issue with the passenger side pipe it was hitting the first cross member under the floor...until I "fixed" it
The 3.5 won't be too big because you have to keep in mind the flow rate is slightly different then a perfect circular shape