11 replies to this topic

[coople]

Hi just wondering what sort of power levels you can get on the standard exhaust.. I have basically all the parts now for a good performance step to fit ... Top hat and intake pipe, vxr turbo, stage 4 intercooler, paddle clutch, vxr injectors, uprated side engine mounts. However I have the standard exhaust. I may buy the first decat stage.. To improve it. What should I expect?

[siztenboots]

just fitting the largest diameter decat downpipe will make a big difference. In 2007 , as a test at Courtenay Sport, we changed just the back box for a prototype 2bular 3" 7x18 with an adaptor U section to mate to the original exhaust catback flange with the main and pre-cat still fitted. We took off the TMS stage 1 map and put on the CS map, that made 290bhp with a standard LET turbo and black LET injectors, but without any safety factor so running lean. I then drove home with factory map for full safety, before a months later fitting the chargecooler setup and going to stage 3 with a full 3" exhaust system which I still have on today, but stage 4.9 So the backbox does play a big part , and the decat downpipe takes away the first big restriction and source of heat.

[SteveA]

As Sizten says it's all about heat, you can map it as high as you want but you will eventually kill something. Most respectable tuners wont want to map it past 230bhp on the standard exhaust for safety. I would heed their advice.

[G-Bob]

People run 250-260bhp on supercharged cars with a tubby exhaust but not sure if that's any different for turbo power?

[SteveA]

Just tubby backbox IIRC bob, plus they don't have the downside of a red hot turbo inline.

Edited by SteveA, 11 March 2015 - 11:50 AM.

[coople]

What's the size of the standard exhaust diameter? 2.5? I think in the miltek blurb it says an extra 10bhp for the back box. But I don't see why a tuner will say you must stop at 230 Bhp. Especially as mine is not a track only car. Your probably never full throttle for longer than 10 seconds on the road especially if your around stage 3 -4 levels of power unless you want to be locked up. Surely if it's mapped correctly so it's not knocking etc and maybe fuel a fraction more top end you can go past 230 safely.... A stage 1 is 235 bhp and that's everything standard.

[coople]

I thought the big power stopper was the intake temp rather than exhaust..

[G-Bob]

Standard NA exhaust is 0.25 inch smaller.

 

Think it's 2" for NA and 2.25" for turbo as standard.

[SteveA]

Remember that the turbo supplies the air to the intake so the hotter it is the hotter your inlet temps will be. Not allowing the turbo to exhaust efficiently will heat everything up.

 

IIRC the standard exhaust is 2.25" (edit, beaten to it by Bob)

Edited by SteveA, 11 March 2015 - 12:42 PM.

[2-20]

NA is 1 7/8

 

I think  Turbo has different diameters . Pipe to cat being 2.25'' and then  2'' at backbox level .( TBC )

[scw02102]

I thought the turbo had a 2.5 exhaust? I must be wrong going my the above

 

the precat is restrictive on the turbos so that is the hold up then the 400cell standard cat then the backbox (as far as im aware anyway)

 

I wouldnt expect 10bhp from a backbox but maybe from ditching the precat

[Lev]

if you do not care about db regulations you may simply bin the whole system, replace it with a 2.5" pipe and enjoy..mind you, this will not be significantly noisier than a 2.5" system with a 200 cell cat and a backbox, but kinda adds a TVR like tint

 

 

i have just dropped off all this stuff so my "sport exhaust system" is pretty much like a 2.5" straight pipe

 

measured 330bhp/410Nm with a busted hose at ~1bar boost with the above exhaust. btw, my car is a turbo converted NA.