My local custom exhaust garage have offered to do me a full turbo back stainless steel system with sports cat for

I very much doubt you'll get 20bhp from just an exhaust.

My local custom exhaust garage have offered to do me a full turbo back stainless steel system with sports cat for

Blueflame reckon on a 17bhp gain using their system

There may be a 20bhp difference in a custom exhaust over the standard one when the vehicle is remapped at the same time.

A full turbo-back Milltek on my Fabia vRS (plus Cupra intake) gained me 7.5 BHP as measured on before and after RR runs.

There may be a 20bhp difference in a custom exhaust over the standard one when the vehicle is remapped at the same time.

But why does a bigger exhuast help achive bigger numbers? Does it allow the turbo to run more boost?

Only asking as I dont know.

I think it just allows more flow at the top end, when petrols produce their peak power. Not sure about on diesels. The little I do know is the best TDI exhaust is a straight pipe (fairly wide one too) - the idea being to get the exhaust fumes from A (turbo) to B (tailpipe) as fast as possible.

some exhaust claims are just silly! just a marketing gimmik to get you to buy

But why does a bigger exhuast help achive bigger numbers? Does it allow the turbo to run more boost?

Only asking as I dont know.

it isn't just boost that makes more power, it is just one of the factors!!!! as allready mentioned it allows the gas to escape more freely than the standard system....

A full turbo-back Milltek on my Fabia vRS (plus Cupra intake) gained me 7.5 BHP as measured on before and after RR runs.

are you comparing a nice new 'high performnce' system to an old oil filled coaked up, soot ridden standard one!

It wouldnt be Ascar that your on about would it?

If you do get one just make sure that its not a Corsa Special Think ill stick with my Milltek plan tbh

never gain that much from just changing a turbo, a sports exhaust can gain you power becuase they can flow more freely so let the engine rev quicker and better.

So if the gas is being restrited would that mean its harder for the turbo to spin up?

possibly, but i don't think it would make more boost just quicker

possibly, but i don't think it would make more boost just quicker

Thats what I'm thinking.

The bit I'm trying to understand is. If a mapper maps the car to say 1.2bar of boost and the engine/turbo can meet the requested boost. Why would increasing the bore of the engine help increase power? I can understand it might help the turbo spin up quicker results in more low down power but cannot see how it would help higher up the rpm if the turbo can already meet the requested boost. :confused:

I can however understand if the exhaust in the first place restricts how much boost a turbo can give. So by replacing it with a bigger bore the mapper can request more boost. If this is correct then you would need a custom map to make use of the exhasut.

Or have I got it all wrong

20hp isa bit ambitious from a system on a stock car that will give that figure. A sport cat and mid/rear with a sport filter and 20hp is obtainable.

As for the skooby yes as there systems are more restrictive on there cars and they have 2 cats plus bigger turbos so more flow means more power up the revs.

2.5" on 20vt is recommended for good power gains but on universal systems that garages weld up on site eg Powerflow/rage etc are not designed specific for a specific engine type so the back pressure may not be balanced to flow properly,

hence those systems are usually alot noisier with less power gains and in some cases minus power gains on non turbo cars.

I would stick with the Best Supersprint/MILTEC/Ansa/Jetex as these systems have been extensivly tested on dynos too make sure optimum flow rates are relised without comprimising on noise and gains

you only need to look at Star performance/ Jabba ect to see they only stock the best

One thing to note. where is this 20hp gain. Doesnt always mean at the top end.

Thats what I'm thinking.

I can however understand if the exhaust in the first place restricts how much boost a turbo can give. So by replacing it with a bigger bore the mapper can request more boost. If this is correct then you would need a custom map to make use of the exhasut.

Or have I got it all wrong

P.s i think your spot on, on that part,

takes to long to edit hence new message

One thing to note. where is this 20hp gain. Doesnt always mean at the top end.

On mine it was top end but did gain 15lb or so torque from low down so worked well but mine was Miltec cat and supersprint mid/rr

it would help power at the top end the same as a better flowing air filter would, its lets the car get the air in and out quicker so restricts the engine less

20bhp from exhaust alone on a vRS is absolute rubbish. Ask him if he will gaurantee the increase

I had a 18bhp gain with Carbonio CAI, 100cel race cat and Miltek cat back, Neuspeed TIP... This was noted on my rolling road result before it was remapped at AMD (198bhp) after mapping it was 237.1bhp.... about right for their claims of an additional 40bhp

20bhp is possible but not just with an exhaust change

HTH

Phil