Lokey put in my Engine and tranny. Great dealership.

 

You're wrong in that back pressure is required for torque. Having back pressure will take away torque, always. I think you will say: so why is it that having a huge 4" exhaust takes away low end torque? It's not about back pressure at all. 4" exhaust does not promote good gas velocity which hurts exhaust gas scavenging when your engine is spinning in lower RPMs because the exhaust pulses cannot create the effect due to low gas velocity. If you put a smaller diameter tube on, the gas inside it will flow better and build up good velocity when it exists the chamber. As the gas travels down the exhaust, and I can't stress enough how important the speed at which it travels is, it momentarily creates a vacuum behind the pulse. On the subsequent exhaust cycle, that vacuum helps to evacuate the gas from the chamber on the next cycle, and on and on.
Now, introduce back pressure. Where in this cycle can it help? It cannot. If you add back pressure, you will slow the pulses down, thus reducing the effect of scavenging which is very important on NA cars. This is why test pipes are so effective on the Z. They improve the gas flow, thus improving the scavenging effect which helps improve VE during intake phase since the exhaust and intake valves do overlap for a small amount of time. If you make the tubing smaller, on other hand, that is different. You do not add back pressure, you change the diameter thus altering flow characteristics. The trade off is that as the volume of gas increases, so will the restriction which will start to slow it down. Enter compromise. It's all about compromise. Go with something that flows well enough in low end but is not a huge restriction in high RPMs.

Again, I want to be very clear about this process. Necessity of back pressure is a myth. I think people somehow connected having smaller tubing to having back pressure and it being good. It's not. I don't know how long you've been in the exhaust business. Probably longer than me. But physics don't lie and every true expert will say the same thing I just said. I don't think you're a liar. I think you have some things mixed up which can happen to the best of us. Nothing that can't be fixed

 

Don't believe anything that you read on the internet.

 

Minor correction to my last post. The exhaust pulse helps the subsequent intake cycle, not exhaust cycle. It was a typo on my part.

 

ziggy, you are 100% correct. that is exactly what i have been trying to say in all of the posts ive made regarding exhaust. i looked up the true definition of backpressure, and as it turns out, i had the wrong definition in my little brain

but i think alot of people construe backpressure to be exactly what you are talking about. the vaccum created by the gas can be thought of as pressure. but take out the word BP, and we both said basically the same thing. but i am a firm believer that a smaller diameter exhaust system on these and most street vehicles, unless your running high hp, can be waaaay more beneficial than a 3" dual system.

and just to clear up the word "backpressure"... it is tight bends and large baffles and such that RESTRICT the airflow through the exhaust, and is used to quiet the sound of the exhaust, in essence by slowing it down.

the last thing you wanna do with exhaust is slow down the airflow.. but like ziggy said, you wanna find that happy medium so that it doesnt flow aimlessly through the pipes.

thanks for settin it straight zig

 

No problemo Yes, dual 3" on an NA Z would be a huge overkill unless you just want top end. I see a lot of 2.5" duals floating around for the Z and even that seems a little big for non-FI Z. I think something like 2.25" would be a good compromise for decent top end and good low end torque. Are there any test pipes out there that are not 2.5"?

 

im not sure. i could make test pipes very easily in 2.25" and sell them. that would be alot easier than doing the whole system. do you think there would be a market for that? i just feel like nobody would feel the need to buy them, because they thing 2.5 and 3" are better. if so, how much would you pay?

 

Hm, good question. I think a dyno graph would go a long way to show that some test pipes with 2.25" would yield good results. a goos showing of nice area under ethe curve would go a long way. I think a price in range of $140 would be reasonable. Not sure what that would mean to your bottom line. I am a very frugal spender but I think I'd pay that for a properly matched set of pipes. They wouldn't even have to be stainless. Stainless is actually not the best material for exhaust since it doesn't retain heat well. Iron pipes might be better. Yes, they would corrode but they would still last for years.

BTW: I just saw your custom fabrication thread. The exhaust looks great. Good work on that. Please update with your results if you have anything as far as numbers or even your butt dyno feedback.

 

thats not too bad of an idea ziggy. i might talk to my old boss about bein partners with me on somethin like that. id probly have to get into the full exhaust market as well, but its all good.

thanks for the compliment. im really happy with how it turned out. just listening to exhaust clips on here, it kind of reminds me of the hks system. sounds really good. as for power, i think its there. not ungodly, probly like 5-6hp. thats the usual gain i see from just a muffler. driving it around you can definately tell it breathes better. i mean anyone knows that your not gonna feel a big difference unless your throwing a good amount of hp at it, but it does climb the r's better and spins the ol' rubbers a little easier.

all in all, its a very good mod. i would venture to say that the gains were equivelent or better (+ - a few hp) than a $1500 exhaust. and since i really was looking for a good sound and not so much a gigantimo gain, all is good. but im for sure gonna get some numbers since im bein hit so hard by people on the other thread lol