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this has been on my mind for awhile.....wouldn't open DP flow as well as a (full) 4 inch system due to its early exit? if not better? eliminating the need for a costly 4 in. exhaust-and dont say things like "emmisions" -this is simply performance wise
 

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i've read something on this somebody else posted, they were saying 4inch exhaust is too little backpressure and with 3 inch you are way better off. so im guessing open dp would be worse than 4inch from that perspective.
 

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i knew i knew-i should have also included in the 'dont even say section': "because its too loud" i made it pretty clear though, esp. stating quote:"PERFORMANCE WISE" :p
 

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Go read the new exhaust post in the FAQ section. Open DP would be better, complete free flow. Back pressure is needed for NA's to force the rest of the cumbustion out (Don't know if I worded that right, no bashing fellas ;)), but with a turbo it is not needed. Go open DP :D
 

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iheart6bangers said:
i've read something on this somebody else posted, they were saying 4inch exhaust is too little backpressure and with 3 inch you are way better off. so im guessing open dp would be worse than 4inch from that perspective.
Backpressure is an enemy on a turbo car, and is highly debated on a n/a car. Open downpipe is always going to be better then any size exhaust you can fit on.
 
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Open Downpipe is to annoying to run trust me
just get an electric cutout if you really want to do it,
its a Y pipe with a butterfly valve, when the valve is closed it is stock exhaust, when you press a buttont open it, open DP
 

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My friend ws gonna do that with his but he got too lazy and just made a side exhaust. Yea I imagine the sound would get annoying (Freeway drives, hehe yea 4agze got annoying as fuckin hell and our ears rang afterwards).

Performance: Yes
Comfort: NO

:\
 

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4" pipe vs 3" downpipe dump. I'd take the downipipe with a cutout shorter no restrictions like a muffler...

You really want as little back pressure as possible..


You may loose some torque (not much with a turbo) with a large downpipe in the lower powerband but you'll gain heaps of power and torque anywhere over 3500 RPM
 

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I would get an electric cutout. Its a lot easier to change rather then my cutout/dump. It only takes me a minute to reach under my car and change the flange for a noticable increase in power.

As for backpressure, on the turbo, it feels like there is a little loss in low end torque but that is made up by how fast your turbo will hit full boost. hits nice and hard too. for an na, I ran a full 3'' cat back off it. The power increase was good and I didnt notice any loss in the low end.
 

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hatchback19 said:
Backpressure is an enemy on a turbo car, and is highly debated on a n/a car. Open downpipe is always going to be better then any size exhaust you can fit on.
I really dont know why you would say backpressure is debated on a NA car. without the lower exhaust size of a NA (2.5 or 2.25) thier is practicaly no scavenging effect in the cylinders. this scavenging effect pulls the exhaust gasses out, and helps suck in the new air/fuel charge. without this. this is lost. and what you MIGHT gain in high rpms, your gonna LOSE at low RPM (where 95 percent of us drive all the time)

Theres your expert opinion.
 

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^ still not entirely correct. Na's dont need small exhausts for 'backpressure' they need them to keep exhaust gas velocity high to facilitate scavenging.

Secondly, pressure drop depending on pipe area is not intuitive. The pressure drop is not actually proportional to 1 / (area), its closer to 1 / (area x area) . (this is an approximation, its impossible to express for air without knowing everything about the flow).

IE pressure drop for 3" exhaust is proportional to 0.02
pressure drop for 4" exhaust is proportional to 0.006

The pressure drop for a four inch exhaust will be 0.3 times the pressure drop of a 3" exhaust, all else being equal.

Conclusion: A 4" DP and catback would flow better than a 3" DP, assuming the DP is half of the exhaust (close)
 

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mullenc525 said:
^ still not entirely correct. Na's dont need small exhausts for 'backpressure' they need them to keep exhaust gas velocity high to facilitate scavenging.

If you notice... I talk about scavenging. I just used the terms "smaller pipe" to make it easier for the little kiddies...
 

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NA's like scavenging. to have this, you need to keep up your exhaust velocity so the negative pulsewave remains strong.

with larger diameter pipe, you improve volume and decrease velocity which causes the negative pulse/pressure wave to diminish. the scavenging effect is minimized on exhausts that are too large of a diameter.

turbo engines typically have about as much pressure INSIDE the exhaust manifold as they do in the Intake side of the manifold... so dont worry about backpressure in the exhaust system. post turbo, you want as LITTLE restriction as possible.

and the fancy mathmatical formulas only apply to straight pipes. on the MK3, running a 4" exhaust can be challenging and will require a few bends. it DEFINITLY requires a few bends on a MKIV, that i know for sure. running an open 3" on a car with a 4" exhaust with multiple bends is unlikely to flow better thru the exhaust.

open DP isnt THAT bad. i ran my car open DP for about 7 months. it made the coolest noises. it turned so many heads at the local meets, it was amazing.
 

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I was running a open 3" DP for a week or so... From Idle to Low RPMs the turbo whine was very apparent and sounded very cool.
Anything above mild acceleration became particularly loud, but from within our heavily sound dampened cabins the sound wasn't uncomfortable... I wouldn't be able to say as much for the pedestrians walking by, though. They along with the local police did not find it entertaining.

Oh.. and it goes without saying the power increase from stock exhaust to open 3" DP was MASSIVE! But honestly I did not notice any significant decrease in power once adding a SS catback and Apexi N1.. but the exhaust sounded 1000x better.

...my .02 cents.
 
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