2.75" vs 3" pipe on supercharged vehicles.

SharpByCoop · 07-28-2013, 07:44 PM

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

Alkatraz · 07-28-2013, 08:01 PM

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

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!

SS_Firehawk · 07-28-2013, 08:07 PM

Quote:

Originally Posted by roplusbee

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.

I appreciate the advice. I'm not sure if they keep their exhaust systems on the shelf. But I did ask them to do a comparison between the HFC and resonator on my Y pipe. If there is no change, the Tanabe is my restriction point. If there is a change, is the exhaust still holding back top end performance? It's all theory and speculation now until I see roller results which hopefully is in the next week or two.

Quote:

Originally Posted by Nut_N_Much

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..

Ah, yeah I remember seeing that post. It was a good buy. But yes, you will lose some bottom end with that exhaust. Can't go wrong with 3" and turbo, not so much with SC's. Maybe on a built motor and using C30-94's lol.

Lol, yes, that oil cooler is pretty beefy. I hate to get rid of it

The real trick is finding it a new home that will put it to good use.

SS_Firehawk · 07-28-2013, 08:27 PM

Quote:

Originally Posted by SharpByCoop

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

Quote:

Originally Posted by Alkatraz

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

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!

I'm not trying to go larger than dual 2.5". The issue is, my exhaust drops to a 2.75" single pipe. That's about 40% larger than what I have now.

Alstann · 07-28-2013, 09:17 PM

Quote:

Originally Posted by Sh0velMan

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.

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.

SharpByCoop · 07-29-2013, 07:09 AM

Quote:

Originally Posted by SS_Firehawk

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

Ahah! I need to read more and post less. LOL!

I completely misread this was a single. Yes, 2 x 2.5" is larger than even 1 x 3".

I'm sensitive to the constant touting of the 3" duals as what is required.

Thanks for the props. I'm going to go back to the track soon, to see if I can better even this time. Carry on.

Coop

Sh0velMan · 07-29-2013, 09:22 AM

Quote:

Originally Posted by Alstann

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.

You're right, I got my facts confused.

The boundary layer @ the perimeter of the pipe has little flow but is (obviously) where the pressure is, whereas the center flow is high speed and lower pressure (naturally).

The same 10-15% loss applies, I just had my facts twisted.

And yeah, spot on the polishing bit. Actually get better flow if you texture it so the boundary layer can latch on easier.

esfourteen · 07-29-2013, 10:24 AM

just for reference: I run a stage 2 with internal gates, 2.5" test pipes, 2.5" catback. I made 575hp/540tq (dynojet) @ 15psi. top end falls off just a bit at around 7k, but so does boost, so I would not say a dual 3" is necessary at all.

SS_Firehawk · 07-29-2013, 03:44 PM

Sorry, the title is a bit misleading. It was labeled as such because I was trying to determine how much of an impact it would be on my current exhaust going from a 3" Y pipe to a 2.75" mid pipe. I'm not looking for opinions on 2.75" or 3" dual exhausts as I know they are too large for my application. I do know a true dual 2.5" exhaust setup is the best configuration at these power levels. Until GTM finishes up on the tuning and gives me some graphs to look at, this is theoretical. Turbos and superchargers have different needs when talking about exhausts. Superchargers like "some" backpressure to get into peak efficiency range. Running long tubes have been hit or miss for this reason. Sorry for any confusion

1slow370 · 07-31-2013, 01:53 AM

this is some 'murican experience here but i have seen supercharged v8's go to around 800 on dual two and half over that you need bigger pipes so since you are on a stock motor and realistically shouldn't be shooting for more than the 5-600 range you may be surprised. supercharged cars can do funny things in the exhaust compared to turbo's. other than that one point your exhaust looks pretty open so you never know you could make more power with that restriction in there than if you slapped up a dual 2.5" Being that the rotrex chargers are centrifugal and there map seems to be geared more for smaller flow this may actually be pretty likely, then again you have two of them.

SS_Firehawk · 08-01-2013, 02:28 AM

Ran across this today... I have hope yet again!
Vortech tuned with Motordyne XYZ pipe and ART Pipes...interesting results - MY350Z.COM Forums

A very similar exhaust setup as mine with the one exception that his Amuse is a 3" pipe after the cat.

Dynojet results are on page 5 as well

07-28-2013, 07:44 PM	#16 (permalink)
SharpByCoop Enthusiast Member Join Date: Sep 2010 Location: Connecticut Posts: 286 Drives: '08 G37S - Graphite Rep Power: 14	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 show2nite, ANMVQ, Nut_N_Much and 1 others like this. __________________ Jim Cooper - (Retired: '08 Infiniti G37 Sport • TheShopCT built • 11.13 @ 123 mph (click for vid) • GTM Stage II Twin Turbo • 5-speed A/T Level Ten built • 591whp @17 lbs boost)

07-28-2013, 08:01 PM	#17 (permalink)
Alkatraz Base Member Join Date: May 2013 Location: Perth Posts: 215 Drives: 2008 Skyline 370GT Rep Power: 12	^^^^^^^^^^^^^^^^ 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! show2nite likes this.

07-29-2013, 10:24 AM	#23 (permalink)
esfourteen A True Z Fanatic Join Date: Mar 2010 Location: LI, NY Posts: 1,375 Drives: 40th TT Rep Power: 18	just for reference: I run a stage 2 with internal gates, 2.5" test pipes, 2.5" catback. I made 575hp/540tq (dynojet) @ 15psi. top end falls off just a bit at around 7k, but so does boost, so I would not say a dual 3" is necessary at all. Nut_N_Much likes this. __________________ Build Thread \| GTM TT Install Thread \| Engine Build Thread

07-29-2013, 03:44 PM	#24 (permalink)
SS_Firehawk Premium Member Join Date: Oct 2011 Location: Tampa Posts: 4,142 Drives: 13' Magma Red Nismo Rep Power: 7334	Sorry, the title is a bit misleading. It was labeled as such because I was trying to determine how much of an impact it would be on my current exhaust going from a 3" Y pipe to a 2.75" mid pipe. I'm not looking for opinions on 2.75" or 3" dual exhausts as I know they are too large for my application. I do know a true dual 2.5" exhaust setup is the best configuration at these power levels. Until GTM finishes up on the tuning and gives me some graphs to look at, this is theoretical. Turbos and superchargers have different needs when talking about exhausts. Superchargers like "some" backpressure to get into peak efficiency range. Running long tubes have been hit or miss for this reason. Sorry for any confusion __________________ Old Car:GTM TSC'd 550whp / 410lbft tq @ 11.88PSI New Car: Under Construction

07-31-2013, 01:53 AM	#25 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,732 Drives: v8 74 260z ;) Rep Power: 7250	this is some 'murican experience here but i have seen supercharged v8's go to around 800 on dual two and half over that you need bigger pipes so since you are on a stock motor and realistically shouldn't be shooting for more than the 5-600 range you may be surprised. supercharged cars can do funny things in the exhaust compared to turbo's. other than that one point your exhaust looks pretty open so you never know you could make more power with that restriction in there than if you slapped up a dual 2.5" Being that the rotrex chargers are centrifugal and there map seems to be geared more for smaller flow this may actually be pretty likely, then again you have two of them. __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50 Last edited by 1slow370; 07-31-2013 at 01:57 AM.

08-01-2013, 02:28 AM	#26 (permalink)
SS_Firehawk Premium Member Join Date: Oct 2011 Location: Tampa Posts: 4,142 Drives: 13' Magma Red Nismo Rep Power: 7334	Ran across this today... I have hope yet again! Vortech tuned with Motordyne XYZ pipe and ART Pipes...interesting results - MY350Z.COM Forums A very similar exhaust setup as mine with the one exception that his Amuse is a 3" pipe after the cat. Dynojet results are on page 5 as well __________________ Old Car:GTM TSC'd 550whp / 410lbft tq @ 11.88PSI New Car: Under Construction

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