The stock exhaust system had 2.25 coming off the manifold, then it goes into the single pipe, what size is this? Someone told me it's 3".

I have older SB manifolds on my LT1 swap, they're 2". Anyone run 2" full dual exhaust (like in a swap)? I don't know if this is too much of a restriction, an exhaust place told me that the way I have it now (changing to 2.5" after the engine) doesn't do anything for the engine (velocity), it only makes it like a megaphone, and I'm trying to find the quietest mufflers. Would it have any effect if I have 2" true duals, then change to 2.25" duals after the engine?

 

Why don't you switch those manifolds to headers and run true dual 2.5 throughout the entire exhaust system?

 

I have to clear steering, I tried all kinds of headers but I only have about 2.5" of space before it gets to the steering, and headers come straight out and then make a bend which interfered with it. Even the original LT1 manifolds wouldn't work, so I'm using older SBC manifolds.

 

Ok, I talked with Flowmaster and here is what they say. 2" Pipe will handle about 250 HP w/ dual exhaust on street driven vehicles. Changing to a larger diameter further back in the system only makes it louder, slows down the exhaust but doesn't help the engine performance. They say I'll have monster low end torque though in the lower RPM range, so I'll leave it all 2" since I won't be racing, just want good street performance.

Just some info about pipe diameters...

 

That single pipe is 2.75", not 3".

 

Are you saying true duals w/ 2'' pipe can only handle 250 hp, or are you saying just a single 2 inch pipe can only handle that much. Why would flowmaster say that changing to a larger diameter further back on the system only makes it louder? That kinda shoots its Advertised HP gains with cat back systems to hell doenst it? Or maybe i am just still confused lol

 

Flowmaster said 250hp for two 2" dual (no Y) pipes for street driven (This is probably if you don't spend most your time near redline, on their website it says 2" is good for 100hp per pipe, 2.25 160/pipe, 2.5" 200/pipe) but he seemed to think for a daily driver it would be ok. Maybe the more torque at lower rpm will make it more fun on the street even w/ the loss of higher rpm power I don't know, I'll see how it turns out.

With the Y pipe on fbody's it's different though with them going into one. I would think the one pipe would need to be the size of both the front pipes in order to keep it the same, but maybe a smaller single pipe helps as the exhaust speeds up?

 

have you looked into either Block Hugger headers or header kits that you weld up yourself? The stock LT1 is already pushing more than those manifolds can handle...

 

Yeah I tried block huggers, do you mean the stock LT1 manifolds? Mine are really short so maybe that'll help some.

 

Thanks for clarifying. The largest Y Pipe i have seen is a 3incher, i got the SLP one , i thought it was a 3 incher but i found out the SLP one is 2 1/2 inch i think....how big is the stocker y pipe? I am pissed lol, i think i wasted my money on the Y Pipe lol.

 

Hmmmm

 

Yep.

2.75".

 

CamaroGuy22, your's is 2.5? They must be going with my idea and sizing down heh

 

Yeah i know lol, when i bought it i could have swore it was a 3 inch y pipe. But now the SLP site says 2.5 inches.

 

well, the stock LT1 manifolds are pretty crappy, but I don't think the SBC manifolds you have on there now are doing you much service. IMO if you can swing it, take it to a good exhaust shop and have them custom make some headers for you. Theres also several companies out there that offer weld up header kits that you put together yourself, but you really need a shop to do it (mandrel bender, welder, etc)

It won't be cheap, but probably not much more than some of these header kits out there for the f-body (can we say FLP's at $1300 a set )