Marx Mcrae

iTrader: (4)

How much differance wiuld it make if I swapped my 2.5 inch exhaust for a 3 inch exhaust? My car is currently running a forged 2.5 with a 20g. Recently made only 325bhp but with over 400lbft on a rolling road, so was just wondering if it was the exhaust that was holding it back, and if the power figures seem right.

sy.

iTrader: (8)

most tuners say around 350hp is when to go from 2.5" to 3"
or at least andyf does..(quote taken from afp)
"A fully decated 2 ½” bore system is adequate up to 350 bhp. After this a 3” system is recommended. Sports cat systems are available but ultimately still limit power compared to a fully decated setup"

scoobiewrx555

The exhaust isn't holding you back from making a bit more bhp but FFS look at that torque figure....400ft/lb. That's not to be sniffed at and it's torque that makes for a quick car as well as a generally really nice to drive scooby.

There are plenty of cars running around with 400bhp that are making a lot less torque than you due to the bigger exhaust and the way it's mapped. Moving to a bigger exhaust will make it easier to yield bigger bhp but my guess is you'll start losing torque. Mind you having a 2.5L bottom end is a huge help.

I'd rather be driving your car aevery time, and i'm pretty sure you'll get 350/360bhp on your exhaust plus a bit more torque no probs.

Very nice one!!

kiranbaloo

iTrader: (9)

I had a 3"exhaust but with a 2.5"connection at the end of the downpipe and on a 2.0 with an md321t it made 424bhp I then changed the downpipe so it was 3"all the way and it now makes 444 and it pulls so much better the car feels slot more lively and wants to rev more

Marx Mcrae

iTrader: (4)

Im more than happy with the torque figure but was expecting nearer the 360/370bhp figure with the mods that the car has, so was a little dissapointed when it made 325bhp. Having said that eceryone who had there car on the rollers that day seemed to be between 10-15% down on power.

In the long run im hopefully gonna get a slightly bigger turbo to get the car to 400bhp, so is it gonna be worth swapping to the larger bore?

scoobiewrx555

A 20G will make 400bhp and spool like a nutter on a 2.5 bottom end as long as you have 550cc injectors running at around 4bar, or you use 650cc injectors at factory pressure.

You need to get back to your mapper to do some more work on your ECU or ask him if he's already maxxed out your injectors. If so then it's running just a bit too rich.

Marx Mcrae

iTrader: (4)

It was only recently mapped by JGM.

scoobiewrx555

Well, Simon has done you proud with a gob full of torque. Testament to his cracking mapping skills but no doubt but there must be a good reason why your car is making just 325bhp although that torque figure is top notch.

Your 20G is capable of a lot more than 325bhp. Perhaps he found your exhaust too restrictive to make any more, perhaps the injectors are maxxed out, could be he's mapped it that way on purpose.

You should really go back and ask him. I hear he is a nice guy and very approachable so should answer your questions no probs.

Marx Mcrae

iTrader: (4)

Cant fault Simons mapping at all! Will get back to him though and see what he thinks.

Injectors are 740's so are well within there limits.
The engine was built for well over 400bhp and is supposed to only need a bigger turbo to get the most out of it

71/200

iTrader: (2)

You dont list the rest of the spec? Does it feel good on the road, if the answer to the latter is yes i would leave her alone. As has been said 400lbsft is not to be sniffed at.

People get fixated with RR figures, myself in the past being one of them. My car feels great on the road and on my current set up i need more CC,s to make more torque. Mapped also by JGM

andyden71

I had my cat mapped today by bob rawl it's a 2ltr with vf35 turbo Sti injectors and Sti intercooler mine is running 335bhp and it's got a 2.5 down pipe and standard center section with a cat in tail pipe is a 3 inch iv got a 2002 bug

RoyPinhey

I hope you went gently on her, most cats hate being mapped