My engine build is coming to the end and im considering what to do about my exhaust, i can either get my current 3’ system modified to fit or was wondering if it’s beneficial to go for a new 3.5’ bore system, was wondering what others have done at this level? And if realistically the difference you would notice is minimal and not worth the bother, or its worthwhile. Thanks

 

I would have said 3 inch would be fine Steve

 

I was told 3" including baffles for more power than that so 3" is fine

 

Any decent performance exhaust will not have baffles.

And 550hp can easily be achieved on 3".

 

It's a long time ago now but I remember rapidcossie went upto 3.5" exhaust at 550 hp and there were good gains he had

 

I know that it can be done and the 3’ would be ok but as scooby says im wondering if going to a 3.5 would be quite beneficial, seems difficult to find an answer as most just use the 3’
I was under the impression that with turbo stuff and a decent power level you ideally want the least restriction possible from the exhaust, so bigger the better, especially the downpipe. I guess im wanting to know realistically if its worth the bother though or if its just throwing money away if you get me?

 

I've changed from 2.5 to 3" on cars around 500hp, and honestly felt no difference. Maybe a dyno will tell different though ?

Also have cars in the 6-700hp range with 3" without any difficulty. It isnt to say larger may not help...but the 3" certainly posed no problems, and these were proper systems with a couple of boxes so they were quiet so as not to flout any noise restrictions when racing ( Subarus )

One car ran 9.5 at the 1/4 with a full quiet 3" system. I think at testing it was in the low-mid 90's db range. Cant remember exactly, but it was quiet. Far quieter than most of the slower cars.

We did change the above car to a 4", and it did affect tuning and boost control, although didnt really affect times. It has run faster since, albeit with other changes too.

I think people get too hung up on thinking they need a huge exhaust or something. If you have the room for it on the car and it meets noise criteria etc...then absolutely bigger can do no harm.

But if the 3" fits better, is quieter, cheaper, whatever and is maybe off the shelf....it's a no brainer to just use one.

 

On the ma developments 2.2 engine I bought it was running at 670bhp on a 2.5inch system and Mark said it would do 700bhp on a 3 inch system if I remember correctly

 

It was mark that advised me 3' inc baffles

 

Probably meaning if any

 

i think it was just a matter of tight for space mate

 

5' drain pipes on mine

 

At 550hp you will notice virtually nothing, may free up a mininimal amount of hp but that’s it.
Your turbo will be more restrictive than the exhaust at that power.
Having said that if you need a downpipe made anyway then I personally would go for a 3.5 inch downpipe then leave the rest of the system at the normal 3 inch diameter.
That way if you do increase the power then you already have a bigger downpipe fitted

Cheers Paul

 

Up to 550hp a 3 inch is the correct size if it’s got a free flowing box’s after that a 3.5inch system is a better way of doing it even though a 3 inch will go to 700hp.

Mark