I did do quite a few searches and didn't come up with anything. If I missed the wrong key words or anything, someone please let me know and mods can shut this thread down.

Now.... I am curious as to why I've not heard of anyone running a 3.5"-4" exhaust on their ST and/or TT cars. I've always heard that the least amount of backpressure possible is best for a turbo car (figuring it's tuned to be safe), and I would think it would help a little with heat issues. I've heard of quite a few Supras using large diameter exhausts. I am aware of the fact that there are not any huge exhausts on the market right now, so that could be a large factor. The only thing I can think of is that a 3" would be sufficient on the VQ for the power ranges I see alof of F/I Zs at.

Would some of you more technically educated people care to edumakate me?

Thanks in advance, and sorry if it's a dumb question, but I'm just trying to learn.

 

With the relatively small turbos that can be fit in the Z engine bay, 3" would flow more than enough. Going bigger is unlikely to add any horsepower but will certainly add much more wieght.

 

Hopefully they would include ear plugs if they did sell that... if you think about it, dual 3" exhaust is basically equivalent of a single 6" exhaust. More than enough flow.

 

dual 3" is plenty for the power levels the vq35 is at right now. unless you were setting up a full drag race car and shooting for ultimate top end hp with no noise restrictions.
now you need to keep in mind that a motor is not keeping a constant velocity or pressure through the exhaust.(at high rpm it just averages) it comes only in pulses, from the piston forcing the spent gases out the exhaust valve. my point being, the exhaust only has to be as effiecient as each cylinder firing at maximum power, or the max amount of spent gases. there are ways to take advantage of the firing order to get better scavenging, thus helping the next clyinder that fires have a cleaner intake charge.
on the currently available kits, i would look more towards header/exhaust manifold design than something like 4" duals. alot more would be had to gain from a properly designed manifold than HUGE 4" duals on a street car.
hopefully i made some sence here as i'm tired, lol.

 

Plus 4 inch dual will probably not fit under the car very well, it was a little tight when we did the 3".

 

Thats true, especially over that cross sway bar. I had to drop mine or the pipe wouldn't clear it.

 

Thanks for the replys everyone... it makes sence now.

 

Actually, IMO, stage 2 TN would benefit from a 4" single.
no need for large dual, really, and he didn't make any mention of large duals anyways.

with a ST running the GT35R or the TN 60-1 3.5" single would be fine, if not more than enough. However, it's decently easy to find good resonators when you get that size....because Semi's use that size exhaust regularly

 

Well he did mentione TT, why would you do a single 4" for a TT?

 

uh....why NOT? a TT at 500-600whp would definitely benefit from a single 4" exhaust. probably lighter weight than dual 3".

 

I would thinbk the reduction in back preasure would have to measured against the potential weight gains, clearance issues due to larger piping..... if you can achieve either 0 back preasure or close to 0 with a 3 inch pipe, you might rule out a 4 inch pipe because of its negative weight or clearance problems....just a thought.....actual calculations would differ with each turbo size.

"Exhaust Back Pressure

Since a turbocharger is effectively an exhaust gas driven compressor, it relies heavily upon the available exhaust gas energy to deliver charge air to the engine. Specifically, it relies upon the differential of exhaust gas energy across (between the turbine entry and exit) the turbocharger.

All of the above boost control discussions were based upon having sufficient energy differential to achieve the desired boost pressures. If however, a restrictive exhaust system is utilized, a great deal of backpressure is built up after the turbocharger (and to a lesser degree before the turbocharger) and there may not be sufficient differential across the turbine. In this case, regardless of the boost control mechanism employed, the turbocharger may not be able to achieve the target boost pressure. This is often seen with NA vehicles that are later turbocharged whilst using the stock exhaust system.

For the sake of simplicity, let us consider exhaust backpressure alone and ignore total exhaust gas energy as a measure of a turbocharger's ability to deliver charge air to the engine.......

As an example, let us consider a turbocharger system that experiences 30 psi backpressure before the turbocharger's turbine and 5 psi backpressure after the turbocharger's turbine. This effectively provides the turbocharger with 30 psi - 5 psi = 25 psi pressure differential across the turbine.

If a zero back pressure exhaust system is utilized, then the backpressure after the turbocharger is 0 psi. This results in 30 psi - 0 psi = 30 psi pressure differential - hence greater potential for the turbocharger to deliver higher boost pressure.

Conversely, if a very restrictive exhaust is utilized, the backpressure after the turbocharger may be as high as 10 psi. This results in 30 psi - 10 psi = 20 psi pressure differential across the turbocharger’s turbine - resulting in much lower potential for the turbocharger to deliver boost pressure to the engine....."

 

3" exhuast is enough i couldn't imagine 3.5" - 4". i Have AAM 3" Exhuast with 2.5 test pipes and thats way to loud for me. =/

 

If you figure the cross-sectional area of a dual 3" exhaust it is the same as the cross-sectional area of a single 4.24" exhaust. So in other words a 4" single will benefit less than a dual 3" setup on a TT car. As for the ST guys, I think a 4" single would work great as 3" starts to become too restrictive.

 

And lastly, keep in mind we're spinning a relatively small turbocharger, through only 3 cylinders worth of exhuast gases. A 3 inch pipe on each bank is plenty.

The Supras run 4inch exhausts, but are expelling 6 cylinders worth of exhuast gases. Hope that clarifies things.

 

I have learned alot... hopefully this might help someone in the future that searches and has the same question as me.

Thanks again.

 

2 x 3" flows about 10% more than 1 x 4" so pretty close
2 x 4" flows almost twice as much as 2 x 3"

1 x 6" flows exactly twice a 2 x 3"

 

We have a 5" exhuast on our shop Supra Its real loud

 

I've seen pics of that one before. It's damn funny lookin.

 

I dont know if you seen this one before.It actually doesnt look to big on the widebody Supra.When you pop the hood and see the 5" pipie on the back of the 88mm turbo then it looks pretty big.

 

Ah. I know I have seen pics of a full 5in exhaust on a supra. I don't think it was a widebody though.