You're comparing apples to oranges here. I think the comparison he made was comparing a single pipe exhaust to one that splits or converges into from one pipe to two. Example - our stock "y-pipe" cat-back exhaust.

For instance, a single 3" exhaust all the way back from the turbo outlet to the tip would flow more efficiently than a 3" exhaust that split into two 2" or 2.5" pipes. (even though the sum diameter of both pipes added up to more)

On a twin turbo setup for our car with a dual exhaust, you're in effect running two seperate "single exhausts". I say this because the exhaust streams are entirely divorced from the time they leave the heads to the time they exit at the back of the car.

Next, you're going to have to add in the actual volume of air each head/cyl bank is moving. For instance, you can have a single turbo and 3" exhaust back moving the full 3.5l of displacement/boost, or two turbos and 2.5" pipes. Each turbo/exhaust bank will only be moving half of the volume of air, so the smaller pipes will still be more capable of flowing efficiently on the car.

Also, on a turbo setup, you've got to consider the same concept of mass air flow and its relation to turbo sizing and spool characteristics. You're pushing one large turbo with the full displacement of the motor, or on a v setup, taking two small turbos each being spooled by half of the motor's volume of exhaust gasses. Once you start going for big power and going with larger turbines, the twin turbo setup will lag just as much, if not worse, than the single setup. This is why I believe a big single would be great for high hp apps even on the Z. The MAIN limiting factor is room to actually route the piping and parts involved (see above).


Just my thoughts on this, feel free to correct/debate them if needed.

 

Ok, so an "apples to apples" question. For a big SINGLE turbo Z, what would be the best exhaust setup? 4" single exhaust? Or the more common 3"? I'm assuming that most would say the bigger the better from reading this thread, but I'll throw it out there:

HAL - what did you guys run in terms of exhaust in order to break into the 1000whp+ zone? Big f'king turbo aside, how did you get it to flow it's exhaust gasses? Single exhaust or dual via reverse y-pipe?

 

Of course bigger is always better. No exhaust and just an open dump off the back of the turbine would be ideal if you didn't care about where the heat went or how loud it was.

I'd assume that they're running at least a 3.5"-4" pipe at those power levels. The problem running a turbo in front of the motor is that without major modification or a custom setup, you're going to run into space constraints when routing the exhaust. It sucks because on most of our single setups, EVERYTHING is mounted on the drivers side. This includes the steering rack/arm/knuckle, AC compressor, and AC lines that just get in the way when trying to route the exhaust.

If performance is the only thing you're after on a single turbo setup, a single exhaust that is as wide, short, and straight as possible is the best bet.

 

+1. That's pretty much what I was thinking too, but was looking for a shop's thoughts on it...

Off topic - looking forward to Sunday's results. What exhaust did you go with??? LOL.

 

So lets cut the VQ in half...we have an inline 3 (work with me here on my ideas...lol) which is half of what the Supra is. So if a supra is running 700 wheel on 5 in exhaust, cut that in half, that leaves 1.5 liter motor with 3 cylinders which equates to 2.5" exhaust for that cylinder bank. Per say.

So if we are thinking in terms of two Single exhaust set ups, anything over 2.5 is over kill? Now I know the exhaust side of the turbo is a factor, but in general my point of this thread is that there is no reason whatsoever in a VQ regardless of the setup to run a 3" dual exhaust, especially for trying to maximize effeciency.

Now the looks are great...and the sound is tremendous..but its not producing more power vs a single exhaust...thats what I am hearing.

 

Not sure if this has already been stated but you also have to consider the overall designs of the engine. In addition, I believe the Supra's engine is closed deck which supports boost better and makes power easier than an open deck engine such as the VQ.

Overall, exhausts are INCREDIBLY simple so if there are variances in the hp, it is because of other factors, not just some tubes and whether there are two of them or not.

 

rightright...I said usually. There's always exceptions. Typically, engine design and space limitation is going to dictate how the majority of setups will run. For the Z, a dual setup just makes sense.

That dyno sheet pretty much looks like a supra. Still building power all the way to redline. Don't get me wrong, it's a cool car....but I prefer a smaller twin setup that nails full boost within about 1000rpm of hammering it. If I wanted a power ramp like that, I would have just bought a supra =)...Still a nice car though.

 

it is still dependant on the intake manifold,heads, cams, valves, exhaust manifolds, turbine housings......there are just 2 many variables to ever make an even comparison.

 

actually, it would take 4 3" pipes to equal the same area as a single 6" pipe.

Pi*R^2.

(2) 3" pipes have the same effective area as a single 4.25" pipe.

 

I understand. It is our drag car and you aren't going to make 1300+hp with small turbos. So any way you look at it with the HP we are shooting for it is going to have lag. There is always nitrous

This was the second day of tuning and we haven't strapped it on the dyno since then. There are still limitations to the power. Currently it is the intake manifold (I believe). This will spool the 47-88 much nicer than the Supra since it is a 4.2L compared to 2JZ 3.0L and stroked 2JZ 3.4L.

 

No. Again, from earlier.... "Dual 3" exhaust flows only slightly more than the supra-standard 4" single. For bigger-turbo supras 4.5 and 5" exhaust are more common now, both of which outflow dual 3"."

A single 4.5" flows more than dual 3" exhaust. As quadcam said, area=Pi*R^2


Tengai: The turbo outlet on our green 350Z is 5", which we neck down to a 4" pipe due to space constraints.

 

Cool, I see where things lie now. So I dont need to stress over big 3" (heavy) exhaust when I am only looking for 350-400RWHP. I just see guys/gals slap 3" dual on so fast,...then thinking ..."I need this for when I go FI." I just thought/think differently because of the simple fact of many single exhaust cars running similar HP levels. I put down 286RWHP with pretty much the stock exhaust on my G. HF CATS and Stillen Y pipe. I feel the backpressure, or the limit of extreme flow aided in producing such number corrected on a dyno dynamics.

The formula by quadcam was the ticket I was looking for. volume = r2 h

 

the formula for area of a circle is: Area = Pi x (radius)^2, where Pi is approx. 3.14159

 

its pretty cool seeing a straight 5" single exhaust on a BIG hp supra, kinda freakish looking.

 

the most important thing is that turbines make the most power when there is a large pressure differential across the turbine. High pressure on the compressor side, low pressure on the exhaust side. To minimize pressure, you want maximum velocity. That doesn't mean you want maximum volumetric flow- but usually maximum velocity and maximum volumetric flow are pretty close to each other in terms of piping radii especially in a low density gas..

 

inline vs V. If you have one bank like the supra, you run one big pipe....but we have two banks on the Z (V6), so dual is the only way to go when going FI. If you really have a hard on for single, just make your Y pipe and the remaining pipe bigger. I'll stick with my dual exhaust.

 

+1

 

Ok gentlemen..I think we have the VQ vs Inline turbo down. 3" dual maybe Overkill but if its boosted with twins it will provide the decent (more than decent) effeciency levels.

Now for N/A applications does the same apply? Is there a such thing as too much air flow out of the exhaust or lack of back pressure for a better word? Is there a relationship between intake pressure and exhaust pressure on the engine just as it relates to the two sides of a turbo? Alot of old muscle or track Z's and G's may run straight off the header. I can see a big V8 doing this because of the many valves/cylinders requiring massive amounts of air flow...but when you get into the 3.5 liter and below, does this still help or hurt the VQ?

Again thanks for putting up with my not so nube yet nube questions.