Single Exhaust

[The Green Monster]

I was thinking of running a single exhaust system with an HKS muffler. My question is, if I'm running a single exhaust, what size piping do you think I should run?

And my car is a stock VVTI 1uz

 

[andrewzuku]

Hey, the system I'm going to do is 2.25" each side through 2 high-flow magnaflow cats, then to a Y-pipe into a 2.5" single system out a muffler.

Mine's the non-vvti engine though.

The reason I've chosen this system is...
- being n/a I don't want to loose torque by going too large
- I'd rather not attract too much attention from mr. police man
- larger diameter pipes wil have a droney sound

There's a video on you-tube with a very similar setup that sounds great:

http://www.youtube.com/watch?v=Fdde5BcKYq8

Andrew

 

[The Green Monster]

ok thanks for the input, yeah i was thinking of 3" all the way through but i'm not sure if i'll still generate enough back pressure since it is n/a. Guess i'll try to do some more research

 

[JBrady]

What car is the engine in?

For most NA applications I HIGHLY recommend the stock Y pipe into a single 2.5" system.

Worrying about too little backpressure is the WRONG way of looking at a system. You want great flow with the SMALLEST pipe sizes that will support peak power. This is not to maintain backpressure (which you never want) but instead to reduce reversion at low and mid RPM by creating velocity. Too small will eventually hurt power but on these engines the stock Y does very nicely. It can of course be improved upon but honestly you are more likely to build a poorer performing part. 2.25" duals are also too large for a single 2.5" pipe. Going with a single 3" is too large.

If you are building a system from scratch go with 2" mandrel bent pipe into a single 2.5" system. You can split the 2.5 back into twin mufflers if you wish.

This will give the best torque curve without sacrificing peak power.

 

[The Green Monster]

Thanks a lot...so basically just change the exhaust to a 2.5 from the stock y pipe and back is what you're suggesting?

i have the stock 1uz VVTI

 

[hrforever]

I'm also at that stage of getting an exhaust and getting it right in order to get the best out of the motor, keeping Mr Plod happy and getting the nod from the engineer.

I'm interested in the position of the cats. Space in my swap doesn't allow me to bolt them directly to the standard manifold as they were originally, so how far back can they go before their efficiency/heating up time becomes an issue? Is one brand/size better than any other?

Andrewzuku, the system you describe is similar to what I was looking at but with JBrady's comments above, obviously .25" can have an effect.

Anyway, I liked the exhaust note in the youtube clip. It's what I'm after as well.

 

[JBrady]

Thanks a lot...so basically just change the exhaust to a 2.5 from the stock y pipe and back is what you're suggesting?

i have the stock 1uz VVTI

Correct. Testing on a 300hp/310tq 2000 GS400 dual 2.25" into a racing style merge collector showed no gain in power but a loss of low end response and that all important feel. That is not to say that 2.25" duals is a bad choice as it is better than larger pipe. It is saying that improving the stock system is not as easy as changing to bigger pipe.

Many things go into an exhaust system and they all effect sound quality and many effect performance both good and bad.

The factory Y pipe is actually a very well engineered part.

 

[JBrady]

I'm also at that stage of getting an exhaust and getting it right in order to get the best out of the motor, keeping Mr Plod happy and getting the nod from the engineer.

I'm interested in the position of the cats. Space in my swap doesn't allow me to bolt them directly to the standard manifold as they were originally, so how far back can they go before their efficiency/heating up time becomes an issue? Is one brand/size better than any other?

Andrewzuku, the system you describe is similar to what I was looking at but with JBrady's comments above, obviously .25" can have an effect.

Anyway, I liked the exhaust note in the youtube clip. It's what I'm after as well.

The closer the better for light off. The best type are the metal substrate core units.

The pipe cross section increase from the stock 50mm pipe to a 2.25" pipe is 33% :33: that little 1/4 inch is much more than it looks. Knowing that the stock pipes support 300hp+ of exhaust flow would suggest that dual 2.25 pipes would support much more PEAK exhaust flow. If your engine is only making 300hp why bolt on a system that can more? You want the SMALLEST pipe that will support your PEAK power. This gives the best low and mid RPM performance without hurting peak power. Bigger pipe lowers velocit and hurts low to mid RPM power and does not increase peak power in most applications.

 

[brawls43]

What about the catalysts? Do you gain anything (on a stock 1UZ) by removing the catalysts? Its for a racing application, but we can't really up power output any. Not having researched this last year when I built our racecar, I went the route of cutting the stock exhaust after the first Y, welding on a 2.5 to 3" expansion, and running a single 3" out the rest of the way. I knew 3" was a greater cross sectional area then two 2", and was worried that since 2.5" was smaller, it wouldn't flow enough. Sounds like I should go back to 2.5", but I'm also interested in removing the cats. All our racing is mid to redline rpm. Everything is a rolling start, so pure low end off idle power use is limited.