Exhaust Y Pipe Question...Power Loss?

HiLL99SS · 09-19-2005, 09:17 PM

I just went and had a custom off-road 2.5" Y-Pipe made here at a local exhaust shop. Well I previously had a 3" Y with Carsounds Cats, but had some major clearance issues since my car was lowered before I did the aftermarket header Y-Pipe combo. Would this smaller piping make me lose power or is it just in my head it just feels like my car doesnt have the POP it did before I made the change. I got the clearance I wanted but I didnt want to sacrifice and ponies for it. Anyone have any input on this issue.

Tx_Rice_Hunter · 09-19-2005, 09:48 PM

That "pop" is just your engine backfiring because of the extra free flowing exhaust due to the 3" you had. If you went from 3" to 2.5" believe it or not that does make a difference. Although you dont really need a 3" exhaust for a near stock car, it still makes a small difference.

**SeVeReDiStOrTiOn** · 09-19-2005, 10:13 PM

i think by POP he means power...spunk...ballz...ehhh...whatever else that means power

BlackHawk T/A · 09-20-2005, 10:35 PM

Originally Posted by Tx_Rice_Hunter

That "pop" is just your engine backfiring because of the extra free flowing exhaust due to the 3" you had. If you went from 3" to 2.5" believe it or not that does make a difference. Although you dont really need a 3" exhaust for a near stock car, it still makes a small difference.

It is not a backfire, that is when the engine "fires back", meaning out the intake.

**SteveC** · 09-21-2005, 06:55 PM

I would think you would gain H.P. with the 2 1/2" vice 3" on a stock motor due to some back pressure is good for the system.

SteveC

**02z28ls1** · 09-24-2005, 12:49 PM

I think I read somewhere that you don't need 3" exhaust until you have 500-600 h.p. level.Below that it's not needed-depends on what rpm range -the smaller pipe will give low rpm torque and h.p.Of course that's the theory-to check it you need a comparison with performance before and after.A G-Tech or a quarter mile run before and after-or gas mileage compare.When they custom made it how did they merge the two pipes?You could be losing flow there if there is a restriction-it would be hard to merge those pipes as nice as the aftermarket pipes do.

BlackHawk T/A · 09-25-2005, 01:10 AM

It's true, but it depends on your type of system.

If you have duals, whether it be true, X or H, 2.5" will perform the same or better than a 3" system until you are making a lot of power (500+ to the wheels). You can't have velocity without volume. Meaning exhaust gas will travel faster through the pipe - too large of pipe will kill velocity until your engine is pushing more volume of exhaust.

Hope I explained this well.

**Deviant Hawk** · 09-25-2005, 09:35 AM

I dunno where you guys get that from, but stock my car only made 318rwhp and came from SLP w/ a 3" exhaust (only 2.5" y). Now granted there is no need for a 3" y-pipe, but from the y back you should have at least 3" to let the engine exhale. Think, your moving the same volume of air through both sides of the 2.5" y and then try to cram that into a sigle 2.5" pipe,that doesn't seem logical. When I dumped my 3" SLP exhaust for the better flowing Corsa w/ 3" outlets from the muffler, I picked up 11rwhp so I guess that says something.
But w/ a true dual setup, to go 3" I think you have to be moving some serious exhaust for that to be beneficial.

BlackHawk T/A · 09-25-2005, 11:51 AM

Then the Corsa system must have had less restriction...after looking at powerbands I can tell you that 3" duals are not needed until around 500 HP.

However with a Y-Pipe you want one with a larger diameter since both sides of your exhaust have to pass through it.

If you plan to be making more power in the future though you may as well build the system accordingly so you don't have to change it later, it won't hurt anything.

**02z28ls1** · 09-25-2005, 12:03 PM

A larger diameter where they merge would make sense-I thought we were talkin about before the merge. Mainly what I was gettin at was the custom made y-pipe-it would be hard to get a clean merge and did they do mandrel bends or regular bends? Thanks for the tip on the Corsa-I'd been leaning that way cause of the sound but always wondered how it stacked up power wise.

edit-Think about this for a minute-a pipe has a boundary layer that restricts actual flow within the pipe.With dual exhaust you don't add the two pipe diameters to compare with the flow of a single pipe.I'm sure I'll start some controversy here but for street and street usable type drag cars -the Y-pipe will give gains (in the usable rpm ranges) torque and that's what everyone except the all out race car needs.The merge tunes the exhaust-if done right the motor is pulsing the exhaust out the pipe-the cylinders are not trying to push exhaust out at the same time-they're takin turns so to speak.Chew on that for a while.

**Deviant Hawk** · 09-26-2005, 08:36 AM

I love my Corsa, wouldn't have anything else. It flows just as good or better than Borla w/o the nasty, rasping, backfire rattle. It has true, deep musclecar rumble.

HiLL99SS · 09-28-2005, 06:53 PM

Yea the Custom Y was merged really well. I know the guy who was doing the job and he showed me how he cut it out and merged it together it was done well. The Y is going back into a 3" I-Pipe just to confirm that, and as far as the bends they were just the regular bends, but he didnt have to make any real intense bends so hopefully i didnt lose alot of flow through that. I wish i could have gotten mandrel but i dont know anyone around here that even has the machine to do that.

Going back to what 02Z28ls1 said, about getting better torque/HP in the low RPM's because of the velocity through the smaller pipe, I did seem to get a little more getty up out of my first gear from the low to mid's in the RPM range.