Hi Guys

I was just wondering how much effect would a 3inch exhaust have on turbo spool up?

Just drove my friends car with a 3inch freeflow compared to my 63mm freeflow and it feels a lot quicker at lower revs. I can only equate this to the different exhausts.

Is this accurate and why would a bigger exhaust diameter effect the spool up?

Thanks

Edwin

 

would be interested to know about this too, as im looking at ways of getting my MD304 to spool a bit faster, currently on a H&S 2.5 inch exhaust.

Dan.

 

Recent back to back tests I have completed showed a specific 3" high flow exhaust system with uprated panel filter achieve full boost (1.5bar) @ circa 2800rpm opposed to a standard MY05 STi system with standard panel filter that produced the same boost @ circa 3300rpm.

Car was a Spec C using stock turbo with no mapping changes post exhaust and panel filter change.

Hope this helps.

Regards,
Shaun.

 

Better boost control and mapping, depending of course on what is already in place.

Shaun,

Nice result, twin scroll turbos rule!

Paul

 

Paul,

It would seem so in the driveability stakes!

Regards,
Shaun.

 

Personally i noticed a huge difference at lower reves when i changed from a 3" Blitz to a 2.5" TSL system....

Though the 3" was connected to a 2.5" downpipe!

Power running 319bhp with a front mount and TD05


--Sam

 

I think a lot depends on what your final power goal is. If both systems are identically free flowing apart from the size. The the 2.5 inch exhaust sytem would have a higher gas speed than the 3 inch system. This should lower the point at which required boost is produced. But the 2.5 inch system will not ultimatly be able to flow as much gas as the 3 inch system. so would become more restrictive at a lower power figure than the 3 inch system. I think someone on here mentioned the 2.5 inch system doesn`t become restrictive until you aproach the 300Hp region.


Jase

 

Jase,
The testing I have done on a Twin Scroll setup does not substantiate the fact that a 2 1/2" system makes boost sooner than a specific 3" system I tested, it was in fact the other way around (albeit with a change in panel filter as well).

Regards,
Shaun.

 

Have had 3" APS Cat system fitted to my bugeye STi along with Gems ECU I already had fitted FMIC and tubular headers. What a difference 360bhp great performance. In 6th pulls from 65mph effortlessly and with increasing gusto. Shame the 3.5" system didn't come with a Cat.

 

what excatly is a twin scroll? and what model no is it ?and will it fit in a uk99 ? and is it better spool up than a td04?

sorry for all the questions but at the moment im thinking of of a hybrid td04 and the twin scroll sounds good.

oh and sorry to hijack the thread.i also have a 3" all the way through

 

The twin scoll requires an up pipe, headers and down pipe IIRC and it will not fit a MY99 without these. The twin scroll has 2 exhaust entries for better spool IIRC.

F

 

I know but I did say it depends on the Power output you were aiming for. Also the twin scrolls work better low down anyway. So maybe negating the need to run a smaller pipe to keep gas speeds high. Us mere mortals who are running TD04's might see a differance as the the gas speed entering the turbo will be higher. And as the 04 will just about make enough horsepower to make a 3 inch system better than a 2 1/2 for outright power it would most probably lose some spool up time because the gas speed will be lower.

Jase

 

Paul

Three port and ECutek mapped by Bob so i don't see any problems there.

Currently dynod at 322bhp at powerstation so i think the bottleneck is either the exhaust of the standard airbox.

I have removed the resonator and got an STI panel filter in but it's still in the standard box.

Dan.

 

where do you find this resonator too ?

 

airbox rather than exhaust, but I would stick with the standard airbox until such time that you can make a partition to keep a cone filter seperated from the hot air of the engine bay.

A good 2.5 system will be better than a poor 3" system, especially 3" jap boxes with bungs fitted that have a 2" exit.

Paul

 

Thanks Guys
Well the reason for my question is because I recently drove my friends MY99 and I have an MY98 only difference other than that was I have a 2.5 vs his 3 inch and his car had a much better pick up down low...

Therefore I am thinking it can only be the exhaust!!

 

Shaun,
Which 'specific' 3" system did you test. PM me if you wish

 

V5-APS,

I am presently testing a multitude of products and theories, and as soon as I have come to a point that final testing and conclusions has been completed I will be publishing an article (hopefully within the next month). Unfortunately until then I do not want to give away any specifics.

Regards,
Shaun.

 

Still a bit hesitant about a cone filter as the MY99 MAF prob wont hack it for long, i'm hoping someone will come up with a way to use the new age MAF combined with the ecutek to make it more robust, i know a few people are working on it.

Dan.

 

what about the 3" roger clarke downpipe and a 3" revolutions centre and backbox.
is that any good??