There's a night and day difference in low-end when you go from stock to aftermarket exhaust, but what you sacrifice there is made up for in top end power.
Can you have TOO much exhaust flow?
My Car currently has a custom made 4 inch down pipe on the stock twins and it had upgraded exhaust pretty much identicle to factory just larger piping. I believe it was an old school greddy exhaust system.
I Figured id let her breath a lil more so i took it to a friends shop to make it a single 4 inches pipe from the cat back Temporarily untill i have enough money saved to buy Hks Ti.
before the car felt like it pulled really strong but now it feels like there is a lack in power? as if it took the turbos longer to spool maybe i need to reset my Ecu?
my 6spd has a rmm dp and hks super dragger 2 exhaust and runs like a champ.
is there a such thing as TOO much flow on the stock Twins?
Also Sometimes and only when pushing the car the check engine light comes on and then goes into a safe mode. The check engine light comes on for a few sec then turns off. i dont get it? I have a Vfac and before i modded the exhaust it wouldnt do this. Would i have to lean it out or richen it up to get rid of this problem? common problem?
Thank you so much for your time
Julio
I Figured id let her breath a lil more so i took it to a friends shop to make it a single 4 inches pipe from the cat back Temporarily untill i have enough money saved to buy Hks Ti.
before the car felt like it pulled really strong but now it feels like there is a lack in power? as if it took the turbos longer to spool maybe i need to reset my Ecu?
my 6spd has a rmm dp and hks super dragger 2 exhaust and runs like a champ.
is there a such thing as TOO much flow on the stock Twins?
Also Sometimes and only when pushing the car the check engine light comes on and then goes into a safe mode. The check engine light comes on for a few sec then turns off. i dont get it? I have a Vfac and before i modded the exhaust it wouldnt do this. Would i have to lean it out or richen it up to get rid of this problem? common problem?
Thank you so much for your time
Julio
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ive ran a few setups... dp to 3"x4" oval... ---> 4" turbo back... ---> foot long 4" dump tube... each was quicker then the one before, everywhere... i think it was mainly because of the better spool (more/quicker boost after "x" amount of time meant more power)... if you were NA you could have too much flow, but not with your turbo...
now i have a 4.5" dp into a 3"x6" oval exhaust (volume of 4.5" round) FTW...
brian
now i have a 4.5" dp into a 3"x6" oval exhaust (volume of 4.5" round) FTW...
brian
The check engine light and safe mode report makes me think something might be wrong with the O2 sensor. Did you ever pull the codes from the cel?
Too much exhaust flow no, too large an exhaust pipe, yes. Contrary to conventional thought, a large exhaust pipe will hinder flow in that the turbos can't push the air through smoothly, resulting in more turbulence. The turbulence being small whirlpools and eddies, don't evacuate the pipe, they clog up the system. An exhaust pipe should always be matched to the turbos being used. Fwiw, I made 891rwhp on a 3"OD exhaust, 2.75" ID. The stock twins aren't outflowing a 3" exhaust anytime soon.
Eric
Eric
thank you sooo much for the replies especially cowboy bebop. Thats why i figured but the car came with the 4 inch down pipe so im most likely going to order the rmm dp.
and as far as Nick i have a 93 i believe its an obd1. Idk what the deal is with that. honestly i would get rid of the Safc if i could but its my daily so i cant take the chance of not wireing it up right and my car not run at all.
and as far as Nick i have a 93 i believe its an obd1. Idk what the deal is with that. honestly i would get rid of the Safc if i could but its my daily so i cant take the chance of not wireing it up right and my car not run at all.
cowboy... i know you know more about this stuff then me and i dont doubt you made 900 on 3"...
BUT...
have you ever seen a supra make less hp on a 4" then a 3"?.. i mean apples to apples... smooth mandrel to smooth mandrel... i could see a possible problem with 4" if you were using it on a 400cc turbo motor, but, on ours?..
maybe overkill, but, a hindrance?.. again, just wondering...
brian
BUT...
have you ever seen a supra make less hp on a 4" then a 3"?.. i mean apples to apples... smooth mandrel to smooth mandrel... i could see a possible problem with 4" if you were using it on a 400cc turbo motor, but, on ours?..
maybe overkill, but, a hindrance?.. again, just wondering...
brian
You may also lose boost control precision with stock twins and a 4" exhaust. Too much flow can mean that the wastegate(s) won't work properly.
I'm with you on this. Wasn't it HPF or BL that did a back to back between a bunch of 4" exhausts on a car making ~450hp? I believe they were able to notice a difference between different 4" exhausts. They didn't even test a 3" unit.cowboy... i know you know more about this stuff then me and i dont doubt you made 900 on 3"...
BUT...
have you ever seen a supra make less hp on a 4" then a 3"?.. i mean apples to apples... smooth mandrel to smooth mandrel... i could see a possible problem with 4" if you were using it on a 400cc turbo motor, but, on ours?..
maybe overkill, but, a hindrance?.. again, just wondering...
brian
Daniel
That should say somthing right there. The difference in peak HP between a 3" and a 4" at those HP level is miniscule at best.They didn't even test a 3" unit.
Eric
steve... i think youd have a slight problem running the factory 12psi but if you can live with the 16psi or so you get from the free'er flowing 4" you can accurately regulate from 16 up...
cowboy... i knew there wasnt really any hp to be gained up top from a 4" at bpu... however, anything worth doing is worth doing right (the first time)... no need to buy a 3" just to turn around and want a 4" when you go single... at around 700whp people have seen nice gains in hp from the bump to 4"... why not just go there from the start (if you can afford it)... then you wont see gains going bigger til youre pushin 1200whp... and i still think my car spooled just slightly faster with the larger pipe...
so mkivtt03 doesnt ditch a 4" unnecessarily...
a good 4"@bpu doesnt = lower power than a 3", right?..
thanks again
brian
cowboy... i knew there wasnt really any hp to be gained up top from a 4" at bpu... however, anything worth doing is worth doing right (the first time)... no need to buy a 3" just to turn around and want a 4" when you go single... at around 700whp people have seen nice gains in hp from the bump to 4"... why not just go there from the start (if you can afford it)... then you wont see gains going bigger til youre pushin 1200whp... and i still think my car spooled just slightly faster with the larger pipe...
so mkivtt03 doesnt ditch a 4" unnecessarily...
a good 4"@bpu doesnt = lower power than a 3", right?..
thanks again
brian
and the energy goes into creating heat and noise as oppose to increasing flow
a large exhaust pipe will hinder flow in that the turbos can't push the air through smoothly, resulting in more turbulence. The turbulence being small whirlpools and eddies, don't evacuate the pipe, they clog up the system.
I'm sorry guys. There is no way I will believe a 4" exhaust will not outperform a 3" at any of the power levels we are talking (400+) w/o some proof. The difference may be very small at 400hp, but I can't swallow that it will be less. I am not a flow expert by any meens, but I have stood behind a supra on a dyno and the stock turbos did not seem to be having any trouble with the 4" exhaust. I know that isn't scientific in the least, but please enlighten me with some data. I for one would never hesitate about going 4" with the stock turbos if you were planning on going single someday.
Daniel
Daniel
Ask Mr.5" himself- Johnny Bahn! :tongue:
Based on the findings of some others who live by me, the problem was actually controlling high boost, not stock levels of boost. Those of us who choose to run stock twins have settled on 3" exhausts as a result of those experiments. Stu Hagen is one of those who can shed some light on this if interested. 
Steve T.
Steve T.
steve... i think youd have a slight problem running the factory 12psi but if you can live with the 16psi or so you get from the free'er flowing 4" you can accurately regulate from 16 up...
I am running a 4" on the stock twins with a 3"dp, and to tell you the truth I really dont like it. The car does not realy sound that great, it sorta lost that Supra exhaust tone that we all love, unless you are WOT. Either way it will be single soon at which point I am hoping a 4" dp/ mp will not hurt my performance.
Good question OP.
Good info. I guess this would explain that when I bolt on my Veilside Titanium exhaust to my Tananbe 3" DP, I feel like I lose power like the OP has stated. For a while, I thought it was all in my head, until I switched the exhausts back and forth a few times. WhenI go back to my 3" no name exhaust (came with car) the car pulls like a MOFO. I'm bummed I can't enjoy the ever so light and awesome Veilside Ti exhaust.
Too much exhaust flow no, too large an exhaust pipe, yes. Contrary to conventional thought, a large exhaust pipe will hinder flow in that the turbos can't push the air through smoothly, resulting in more turbulence. The turbulence being small whirlpools and eddies, don't evacuate the pipe, they clog up the system. An exhaust pipe should always be matched to the turbos being used. Fwiw, I made 891rwhp on a 3"OD exhaust, 2.75" ID. The stock twins aren't outflowing a 3" exhaust anytime soon.
Eric
Good info. I guess this would explain that when I bolt on my Veilside Titanium exhaust to my Tananbe 3" DP, I feel like I lose power like the OP has stated. For a while, I thought it was all in my head, until I switched the exhausts back and forth a few times. WhenI go back to my 3" no name exhaust (came with car) the car pulls like a MOFO. I'm bummed I can't enjoy the ever so light and awesome Veilside Ti exhaust.
You are talking about a 25% increase in surface area that should give you a hp increase but *likely* only at higher RPMs. What cowboy refers to is gas velocity and increasing the surface area of the exhaust and creating a reduction in back pressure will affect your power below peak.I'm sorry guys. There is no way I will believe a 4" exhaust will not outperform a 3" at any of the power levels we are talking (400+) w/o some proof. The difference may be very small at 400hp, but I can't swallow that it will be less. I am not a flow expert by any meens, but I have stood behind a supra on a dyno and the stock turbos did not seem to be having any trouble with the 4" exhaust. I know that isn't scientific in the least, but please enlighten me with some data. I for one would never hesitate about going 4" with the stock turbos if you were planning on going single someday.
Daniel
In essence, the larger pipe you use, the more you will choke your engine's ability to evacuate gasses at lower RPMs for an increase in higher RPMs. In the example using the Veilslide Ti exhaust, it's probably a terrific exhaust provided you're producing power levels to generate enough exhaust volume to take advantage of the increased diameter.
I have little understanding of the 2JZ, yet. I can only therorize what your butt dyno tells you without seeing the dyno test results back to back to understand how the same engine behaves.
If dyno results from a 3" diameter exhaust tell you anything, a 5" exhaust is good for bragging rights but not much else without the rest of the setup to take advantage of it.
I'm with him. The exhaust gas is coming out at pressure, and that delta p alone will move it down the pipe. The bigger the better. Just keep extrapolating: how about a 5 inch exhaust, 8 inch exhaust? Thats pretty big. Its turning into almost no exhaust at all. I dont think anyone will argue with me that no exhaust pipe at all is best.I'm sorry guys. There is no way I will believe a 4" exhaust will not outperform a 3" at any of the power levels we are talking (400+) w/o some proof. The difference may be very small at 400hp, but I can't swallow that it will be less. I am not a flow expert by any meens, but I have stood behind a supra on a dyno and the stock turbos did not seem to be having any trouble with the 4" exhaust. I know that isn't scientific in the least, but please enlighten me with some data. I for one would never hesitate about going 4" with the stock turbos if you were planning on going single someday.
Daniel
You're absolutely right, open air is best. That's why nitro dragsters that accelerate to 300mph in less time a stock TT Supra takes to get to 60mph have open headers and expel exhaust gasses in excess of six thousand degrees.I'm with him. The exhaust gas is coming out at pressure, and that delta p alone will move it down the pipe. The bigger the better. Just keep extrapolating: how about a 5 inch exhaust, 8 inch exhaust? Thats pretty big. Its turning into almost no exhaust at all. I dont think anyone will argue with me that no exhaust pipe at all is best.
2JZ engines aren't dragsters and designed with a certain amount of back pressure. Without the hardware up front, your larger exhaust is good for little more than bragging rights.
You will notice more of a difference on a stock engine doing a run on on a cold morning than a warm afternoon on the same track in the same day.
Factory exhausts are extremely well tuned and also legal. I would be surprised to see a double digit gain by changing a bone stock TT's exhaust to a 1" larger diameter and any gain at all under the curve.
I'd be happy to be proven wrong!
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