Originally Posted by roplusbee (Post 2422661)

I like the fact that you are actually doing your own research and not just blindly listening to what a manufacturer/builder is telling you. Since GTM is doing the work, you could have then test it with one of there 2.5" or 3" systems. That would give you a good indication of what you want without having to take a hit.

Originally Posted by Nut_N_Much (Post 2422733)

Had to make the tips fit the Zele Kit. Its non-resonated 3 inch. That car now has a Zele Exhaust on it.. I'm supposed to pick it up this weekend but I had to go out of town. I intended to put FI tips on it and sell it. Would be a lot easier and cheaper to just sell as is. I wanted to install it on mine but I don't make enough boost to justify a 3 inch, I would loose HP with it.

Holy crap thats a huge oil cooler..

Originally Posted by SharpByCoop (Post 2422739)

My exhaust: ARK Grip 2.5" pipes.

Theory: Smaller exhaust diameters are usually beneficial to midrange performance, at the expense of top end.

Real world: I have INCREDIBLE midrange power and it's helping my performance at the track (drag strip), or simply not hurting it.

I'm proof positive you do NOT have to go for a 3" diameter exhaust to get results. In fact, there may be something in my recipe that bears understanding.

You may theorize all day long, but I have a completely full weight heavy G37 and it has proven itself with smaller 2.5" pipes. Anomaly or formula?

Coop

Originally Posted by Alkatraz (Post 2422759)

^^^^^^^^^^^^^^^^

Worlds, fastest recorded 1/4 mile G37......this man he knows.
I will take Coop's experience over someone else's 'theory' any day of the week!

Originally Posted by Sh0velMan (Post 2195743)

Oh and your figure for 2.5" dual is a little off.


2.5" Dual = 9.817 sq inches
2.75" single = 5.939 sq inches
3" Single = 7.068 sq inches
3" Dual = 14.136 sq inches
3.5" Single = 9.621 sq inches
4" Single = 12.566 sq inches
4.5" Single = 15.904 sq inches

Edit: re-read your post, I see where our numbers are different, you're subtracting wall thickness. Pipe diameters should be ID rather than OD. So subtracting thicknesses should be unnecessary.

Edit 2: And the reason they over-estimate pipe size is because most of the flow is happening at the outside perimeter of the pipe, so a general rule of thumb is to add 10-15% (with the percentage being smaller the larger the pipe diameter) to the pipe size to allow for turbulence losses at the center of the pipe. Sounds silly, but it's been worked out many years ago by folks a lot smarter than us hahaha.

Originally Posted by SS_Firehawk (Post 2422783)

I'm not trying to go larger than dual 2.5". The issue is, my exhaust drops to a 2.75" single pipe.

Originally Posted by Alstann (Post 2422830)

Erm, not to dispute, but according to my fluid mechanics knowledge, the main flow of a fluid through a closed pipe is in the center. The velocity on the edges of the pipe is actually approaching zero. It's actually a large reason why polishing an intake manifold adds little to no gain, even a loss, depending on the application.

A straight increase in pipe diameter does not net a linear change in exhaust velocity, if I'm correct.