wesam

I have TT C5z06 with all supporting mods
now running 10 PSI and want to up the boost to 18-20 PSI
but i want to keep an eye on exhaust back pressure as my axel back is 2.5" ( all the pipes after turbos including x pipe are 3" )

I want to know what is the acceptable ratio between back pressure and boost

Thanks in advance

Blackpanther99

iTrader: (8)

Well, the closer to 1:1 ratio the better but honestly not everyone ever sees a 1:1 lol 2:1 or such is a good ratio.

Not sure what size cubes or turbos you are running. Any BP at 10psi?

wesam

Still no BP at the moment I'm waiting to fit the gauge in the car
370CI with 6265 turbos

wesam

SO at 20 PSI of boost its is acceptable to see 40 PSI of BP ?

Forcefed86

iTrader: (4)

There is no magic acceptable BP number. 1:1 or better may make the most power and choose the most radical cam. It also won't spool up near as fast. Most find a happy place int he middle.

With a twin setup you should have great BP ratios anyway. (I'd guess under 2:1) I wouldn't worry about it.

I ran as high as 2.8:1 at 25psi. The less overlap you have on the cam the better for high back pressure setups. What are your cam specs?

wesam

So a cam shaft with negative overlap will be best for TT

Forcefed86

iTrader: (4)

Not really... If you have known high back pressure, neg overlaps cams tend to work better IMO. (like my setup) I doubt you have high back pressure. Since your setup is already together it doesn't really matter. Put a gauge on your setup and report back what you find.

TT setups generally have less back pressure than singles. (one of the reasons they tend to make more power) So you can usually go with a more radical/higher overlap cam. Depends what your looking for.

Mongoose350

iTrader: (1)

You could always throw a pair of cutouts on it, that way when you up the boost, open them up and BP problem solved.

Forcefed86

iTrader: (4)

A 65mm wheel should be fine with the 3" downpipe. Back pressure is measured preturbine and will depend mainly on the AR and wheel size of the turbo.

Blackpanther99

iTrader: (8)

Yes sir, shouldnt be an issue whatsoever. Lots of guys go over 2:1 but at that point there factors that cause it.

As forceded mentioned, a cam and downpipes have alot to do with this.

I know quite some ppl when they have these BP issues they throw in cutouts to relief the BP. Then again theres no point of a true dual system and running with cutouts open all the time soo thats when changing things around are a must if the BP is bad.