Does size matter?

[turbomike]

I am getting a full system made in t304 stainless for my march turbo and i was wondering what size it should be i had decided on 2 and a quarter inches diameter or can i go bigger?Also i would like to fit an intercooler where could i get one and would this cause lag even if not front mounted?

 

[RIK]

sometimes bigger isnt always better,smaller tube give more backpressure=more torque

but im not sure with turbo setups,if its different or not so ill leave it ther

 

[Ed]

Rik that’s wrong. Its a common misconception due to people oversimplifying or not understanding how exhausts work.

Backpressure is ALWAYS a problem – period. What people are saying about creating a back pressure is more to do with exhaust tuning, the idea is that the trailing pulse creates a vacuum in the pipe which actually sucks the next along and so forth, this is how 2 stroke engines work by creating the common 2 stroke style expansion chamber. In performance 4 stoke systems you want to aim to merge all the pulses at equal delays in time, so that one does not disrupt the other so you have fairly long collectors of 4-2-1 or 4-1 directly if your more interested in how the top end flows.

Turbo cars are different. They only care about one thing for power that is NO restriction. In an ideal world the outlet of a turbo would be a big horn, that basically acted to slow down the exhaust gasses as they met the atmosphere to cause minimum restriction (Its an impedance match basically). It would look as funny as anything, but is part of the reason performance back boxes open up. Every little helps.

As for the March turbo, If the ST can make 110bhp (and more) from a stock 1 ¾inch exhaust, you would be good at most to go for 2 inch. Anything more on that kind of power will just cost you more and do little. As it is the HT-07 down pipe is very restrictive and you would be better going for less on the exhaust and spending what you save there.

Ed

 

[Craig]

If the ST can make 110bhp (and more) from a stock 1 ¾inch exhaust, you would be good at most to go for 2 inch. Anything more on that kind of power will just cost you more and do little. As it is the HT-07 down pipe is very restrictive and you would be better going for less on the exhaust and spending what you save there.

Ed

Says theman with a 3" pipe
Next question for you is though, how does backpressure create low-end power (or is it torque if it even does) in less than 50 words please

 

[Ed]

Its not so much making back pressure different exhaust designs are more efficient at different airflow rates. Its all todo with tuning, so for example a 4-2-1 is better at flowing air lower down rpm than a 4-1 which is better flowing towards the top. There is always a compromise you cannot realistically have low volume/freeflow where you want it.

A torque curve represents engine efficiency. If you have max torque at 3000 rpm that is where your VME is at its greatest. Its obvious that if you had the most back pressure here, all else being equal (which of course they are not) you would have the least power, so this must be the point of least exhaust resistance...

Ed

 

[Craig]

Interesting stuff, so that is why race cars have a very high peak torque then?

 

[Speedle]

any pics of your car mike?

 

[Ed]

Interesting stuff, so that is why race cars have a very high peak torque then?

A minor reason, there is much more going on than just exhaust design.

 

[Slim]

racing cars have very high peak torque because of the way they are tunes. They have very high flowing heads, lair cams and don't tick below 2000 rpm otherwise they'll stall, unlike a k10 which you can make idle at 250rpm if you wish.

And as for backpresure in the standard exhaiust system, its not rally the thikness fo the tube that does it, as a standard k10 system is 1 1/2 thick anyway, its the silencers that cause it.

 

[Craig]

Yes I phrased it badly, should have said that it allows them to tune max torque higher up in the rev range