I'm talking a well built, good flowing Ypipe. Mandrel bent peices cut and welded to fit into a flowmaster collector. At first I assumed I was just going to have a 3" built. But the 2.5" will allow me to tuck the Pipe .5" closer to the floor board = .5" better ground clearance.

I was thinking a set up where I had a bullet cat on the end of each collector, then a 3-2.5" reducer coming off the cat all the way to the flowmaster collector into a 3" catback.

 

personally I'd say a 2.5" Y setup would be restricting power compared to a 3" system.

But the question you really need answering is by how much?

And sadly the only true way to do this is to fit both setups on you car and dyno them at the same place under identical conditions. Well lets face it, this probably isn't going to happen.

If you didn't have the cam in there, I don't think there would be any noticable difference.

 

Yea ... w/o the cam I probly wouldnt give a ****. But i'm going to be throwing in an F13 after I go to the new setup. So I don't want the cam being choked too much. A 3" Y would be ideal, I'm just wanting some input from guys running 2.5" Y's w/ similar setups to see what kind of power they're making.
The only thing thats leading me to the 2.5" Y is the better ground clearance it'd offer. But as I've already thought about ... the ground clearance difference b/w the 2.5" and the 3" could be made up by a set of coilovers.

 

2.5" on each side into a 3" True merge collector may not be bad. Ground clearance would kick ***.

 

I don't think you'll get anything more than pure conjecture with a topic like this...as stated, people just aren't gonna spend the time or money to do a dyno comparisson with that being the only change. I personally don't think you will be limiting yourself much...there are sacrifices to be made with any car. This is no different. I'd rather reduce the size of my piping and save ripping the exhaust off driving around town.

I run a pair of 3" pipes into my x-pipe, but then again, I'm not sitting on a Pro-kit. That's why I got my coil-over setup...if I start dragging, I just raise it back up. Doesn't look nearly as slick as a fully lowered car though.

 

3" Y will def be your best bet IMO.

With more bhp a 4" may really be required. But as I said it's not just what it flows but the degregation. This I don't have data for.

But suppose and engine was producing 550bhp and needed x diameter pipe. But running the size down only cost you 10-12rwhp. Could you live with it?

I probably could.

 

True ...

 

If ground clearance is a major issue then go with the 2.5. When i put on my SLP LT's with 3" X-Pipe i knew i was going to have problems, but now i deal with it everytime i go into a shopping center. If you don't mind ground clearance that much then throw on a 3" Y-Pipe, because soon as the power goes up its going to get to a point where the 2.5" is going to restrict you more.
-Joel

 

I made 432.8hp and 405torque thru a 2.5" y-pipe into a 3.5" merge and 3.5" catback.

If I'm losing 10-12hp, I can live with that as I'm lowered on Eibach Pro's.

Fodd for thought, the car is a beast, even at the low end.

 

You won't be losing anything. 2, 2.5 inch pipes have more area than a single 3 inch pipe anyways.

 

I'm not talking about after the Y ... after the Y is going to be 3" no matter what. But before the Y will be 2.5" (two pipes) or 3" (two pipes). The 3" will have more area obviously ... but the 2.5" even if giving up a few ponies seems like a better all around choice.
Up until now my car has been a dyno queen. Always made real good numbers on the rollers and have always had the 3" setups (both on my old Ypipe and my duals). If viper is making that kind of power thru a 2.5" ... I think i'll give up the bragging rights on the dyno for better all around driveability (in terms of ground clearance around town).


Thanks for all the replies guys ... I think I'm leaning towards 3" random tech cats off the collectors and then 2.5" piping from the cats back to the flowmaster merge.

 

I know. I think you missed my point. You already stated that you will run a single 3" catback no matter what correct? Now if you have dual 2.5" pipes, which have more area than a single 3" pipe, for your y pipe, how can that possibly be a restriction? I'll say it again, 2, 2.5" pipes have MORE area than a single 3" pipe. Doesn't make much sense to me to run dual 3" into single 3" anyways.

 

Oh ok, I see what your saying now. Just didn't catch it the first time.

 

Is your car lowered? If not, I dont see why it would be a problem. I have never scraped my 3" Y-pipe on anything.

 

Yes ... w/ a pro kit. I've managed the 3" duals w/ scraping very rarely and I had a 3" ypipe before my duals ... so i know that scraping is a rare thing. BUT that is also determined by how careful you drive. W/ my duals and my old 3" ypipe there were places I could not go in my car b/c of the angles of the dips, height of speed bumps, etc.

 

Stainless Works claim the 2.5" Y works better on cars up to 450 rwhp.

 

A 2.5 Y-pipe into a 3 or 3.5 will provide 0 horsepower loss up to 500 hp. If you are gonna run cats then it's a mute point. You don't want too large of a pipe. You want to keep the exaust hot inside the pipe until it exits. Being to large would allow it to cool and cold gas doesn't move as fast as hot gas. Also, each pulse from the cylinders gets pumped into the exaust and will create a low pressure pocket behind the pulse. You want to keep these pulses in some kind of happy rythm. You know what? I just realized I don't think I can explain this in writing. I will find someone who wrote this theory out.

 

http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

This is a great write up on exaust. I will try and find another one that was written by master engine builders. Enjoy

 

I have a 3" qtp y. I would go with a 2.5" anyday. You will gain lots of ground clearance. There is no way a 3" y is needed on these cars until you get to huge HP.

 

Yea thanks guys. I've definitly decided to do a 2.5" Y. This is exactly what I plan to do:

Put 3" Random Technology 7000 Race Metal Cats right on the collectors. I'll have the dr. side collector cut back if the Cat won't fit in at the length its at right now. Then from the cats, the piping will be reduced to 2.5" piping which will run into a 2.5inlet/3outlet Flowmaster Merge collector. All mandrel bent bends cut to fit the design of the pipe.

I'll post pics when its finally made and on the car in acouple months. Thanks for all the discussion and thanks to My 1st Love for the helpful links.