Is 2.5' exhaust piping good for boost or would 3' be better?

[aiixon]

This is killing me... It's " not '. the single line is for FEET double is for INCHES.

[lone_wolf025]

I am not an expert by any means, but I do believe there is a point of diminishing returns. Since all exhaust gases and pressure are directly fed into the turbo and need a path out, the larger the pipe may not necessarily affect bottom end numbers seeing as how the turbo is the biggest restriction in the line. However, with the turbo the scavenging effect derived from a properly tuned exhaust is a fairly moot point as the above atmospheric pressure air charge would push out remaining exhaust better than atmospheric pressure could. Also, with the spinning impeller blades a certain amount of momentum would serve to produce that effect as well. Granted it wouldn't be much but it'd still be there.

Regardless, part of the point AaronGTR was making was that if you have a small turbo the gains received from 3" piping as compared to 2.75" would probably be minimal at best. It all depends on the cfm of airflow.

[SilverGAGT2002]

Well the the turbo is a garret gt32

As far as the 3' how hard is it to get the 3' dp from the turbo back to fit in such a tight area?

[SpyhunteR]

Originally Posted by SilverGAGT2002

Well the the turbo is a garret gt32

As far as the 3' how hard is it to get the 3' dp from the turbo back to fit in such a tight area?

Don't do it on a v6?

[SilverGAGT2002]

Ok so the turbo kit im buying already coems with a downpipe that was custom made by a shop so would i only need to worry about the exhaust from the cat back? Does the size of the dp even matter? Something im confused about sorry...

[SpyhunteR]

Originally Posted by SilverGAGT2002

Ok so the turbo kit im buying already coems with a downpipe that was custom made by a shop so would i only need to worry about the exhaust from the cat back? Does the size of the dp even matter? Something im confused about sorry...

Yeh becuase was the downpipe made with a stock exhaust setup in mind or someone's custom exhaust setup?

[SilverGAGT2002]

I think it was a custom exhaust setup for his car. With that in mind what would i need to do as far as a dp? Im planning on buying that set of headers from mp racing not sure if that is gonna come with a dp already or not.

[shadowlurker]

Originally Posted by SpyhunteR

You can't go too large on the exhaust part of a turbo. The goal for exhausts on any turbo app is no backpressure. Ideally you'd have a dump tube going off the turbo and venting into the atmosphere and having the wastegate dump out into the atmosphere instead of being reintroduced into the exhaust.

Here have fun. This guy elaborates what's going on in my head.

http://www.tercelreference.com/terce...st_theory.html

Yes, your much better at wording it .

[AaronGTR]

Originally Posted by SpyhunteR

You can't go too large on the exhaust part of a turbo. The goal for exhausts on any turbo app is no backpressure. Ideally you'd have a dump tube going off the turbo and venting into the atmosphere and having the wastegate dump out into the atmosphere instead of being reintroduced into the exhaust.

Here have fun. This guy elaborates what's going on in my head.

http://www.tercelreference.com/terce...st_theory.html

Well yeah if you have just a dump tube then you have a short pipe so there is no back pressure and there really is no need to worry about it. If you are going into a regular exhaust though you still have a length of pipe then that the exhaust gas needs to travel through so you still need to worry about exhaust gas velocity.

[AaronGTR]

Originally Posted by SilverGAGT2002

I think it was a custom exhaust setup for his car. With that in mind what would i need to do as far as a dp? Im planning on buying that set of headers from mp racing not sure if that is gonna come with a dp already or not.

If you are going to buy the turbo headers from mp racing (if and when they are available) then don't even bother with someone elses down pipe they made for their turbo setup. That other persons manifolds wouldn't be the same so the turbo wouldn't be located in the same spot and the down pipe wouldn't even match up anyway. You'll need to have a custom down pipe made anyway once you get the manifolds and turbo in, so you can get it made any size you decide on.

[westerndragon]

Originally Posted by SpyhunteR

You can't go too large on the exhaust part of a turbo. The goal for exhausts on any turbo app is no backpressure. Ideally you'd have a dump tube going off the turbo and venting into the atmosphere and having the wastegate dump out into the atmosphere instead of being reintroduced into the exhaust.

Here have fun. This guy elaborates what's going on in my head.

http://www.tercelreference.com/terce...st_theory.html

Great article

[SpyhunteR]

Originally Posted by AaronGTR

Well yeah if you have just a dump tube then you have a short pipe so there is no back pressure and there really is no need to worry about it. If you are going into a regular exhaust though you still have a length of pipe then that the exhaust gas needs to travel through so you still need to worry about exhaust gas velocity.

velocity is already provided by the turbo takin' a fat dump. You can't go too large on an exhaust after a turbo. You will get diminishing returns in power gains due to the size becoming null at a certain point, but you won't lose power by going larger on an exhaust, nor should you.

[Shock24Z]

Originally Posted by SilverGAGT2002

Well the the turbo is a garret gt32

As far as the 3' how hard is it to get the 3' dp from the turbo back to fit in such a tight area?

It's not that bad. Just make it with two pieces. It'll fit fine.

[SilverGAGT2002]

Alright but i still need a 3' mandrel bent exhaust thats the hard part to find around here since nobody around here does mandrel bending

[AaronGTR]

Originally Posted by SilverGAGT2002

Alright but i still need a 3' mandrel bent exhaust thats the hard part to find around here since nobody around here does mandrel bending

That's why you buy pre-bent sections and have them welded and assembled. Almost no one does have a mandrel bender.

[AaronGTR]

Originally Posted by SpyhunteR

velocity is already provided by the turbo takin' a fat dump. You can't go too large on an exhaust after a turbo. You will get diminishing returns in power gains due to the size becoming null at a certain point, but you won't lose power by going larger on an exhaust, nor should you.

I didn't say you'd lose power. I said you wouldn't gain any after a certain point, but you would lose low end torque... in which case makes my statement true that you CAN go overkill on the exhaust. Whats the point of going bigger if you aren't making any more power? Why not just tell him to use 6" piping? It will have less back pressure and thats your justification for it right?

[Shock24Z]

Originally Posted by AaronGTR

but you would lose low end torque... in which case makes my statement true that you CAN go overkill on the exhaust.

Regarding the downpipe?

How do you figure?

The only thing a larger downpipe is going to do is increase the pressure differential between the manifolds and downpipe and increase spool time... which if anything will help low end power.

Originally Posted by Aforementioned article

For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

The performance you gain going from a 2.5" to 3" downpipe is arguably worth the time and money spent on it.

Obviously, the performance aspect begins to plane out soon after 3" for a lower level build like this so going from 2.5" to 6" is a lot more time and money for not a major gain in performance. However, short of cost vs hp gained aspect of 6" pipe, there's nothing wrong with running it if you so desire. Though I could see some strange flow characteristics coming from a 2" outlet turbine to fill that void...

[SpyhunteR]

Originally Posted by AaronGTR

I didn't say you'd lose power. I said you wouldn't gain any after a certain point, but you would lose low end torque... in which case makes my statement true that you CAN go overkill on the exhaust. Whats the point of going bigger if you aren't making any more power? Why not just tell him to use 6" piping? It will have less back pressure and thats your justification for it right?

Anything lost in the low end is laughable considering the gains.

Actually a small dump pointed at the ground would be better than a 6inch pipe.

Backpressure = the enemy of a turbocharged vehicle. Backpressure = hurting potential.

Why do you think turbo cars gain so much going from stock to 3inch - 3.5inch - even 4inch bazooka tubed monstrocities?

Personally I would go with this. Any car that is turbo'd on this board in grandma land looking for anything up to 400hp, I would 3inches = good times. If you're going big dog style and wanting more power. Then I would recommend a cutout or just a fat non-street legal dump tube right off the turbo for getting the most out of the setup.

For you supercharged guys just listen to AaronGTR, he knows all apparently. 2.25 is perfect for ya'll.

[GT_turbo]

Originally Posted by AaronGTR

I didn't say you'd lose power. I said you wouldn't gain any after a certain point, but you would lose low end torque... in which case makes my statement true that you CAN go overkill on the exhaust. Whats the point of going bigger if you aren't making any more power? Why not just tell him to use 6" piping? It will have less back pressure and thats your justification for it right?

Give up a 3" exhaust is better than a 2.5" exhaust in ANY case... weather you have a catalytic converter/resonator/muffler... It is making you sound stupid, which your not, I know you have alot of knowledge with the GA, just trying to help.

[SilverGAGT2002]

So a 2.75' downpipe to a 3' exhaust would be better than using a 2.5' downpipe to a 3' exhaust? Would adding a cutout also be a smart idea?