Exhaust Bore on Custom System

15th December 2010, 21:03

Hi,

Gonna be going to get a pipe made up and fitted on Saturday. They have recommended using a slightly biggger bore than standard to help "Free it Up". It's a MK2 Saxo VTR (2001). The pipe will go from the down pipe to my backbox.

Should i maintain the same bore or go a bit larger? What do you guys think? Is there a risk of loosing performance? The pipe will be removing just one silencer, this in itself won't make any difference apart from louder... will it?

Cheers again guys

15th December 2010, 21:08

2" seems to be a good bore size mate. unless its turbo'd where a bigger bore would be required you will actually loose power because of loss in backpressure. might see a gain on a dyno if a silencer is remover but only 1bhp perhaps. you'd never feel it.

16th December 2010, 08:44

why get a custom one when ones like the supersprint and our stainless steel centre pipes are available off the shelf and better as they are mandrel bent?

16th December 2010, 11:47

If its all standard keep same bore it should be cheaper

16th December 2010, 11:55

Quote:

Originally Posted by KamRacing

available off the shelf and better as they are mandrel bent?

all decent companies that do custom exhausts will have their pipes bent using a mandrel bender, only comes down to price really, if its cheaper then go ahead. Personally I'd get one of Kam, less of a hassle and priced competitively too

16th December 2010, 11:57

Quote:

Originally Posted by johnr32

all decent companies that do custom exhausts will have their pipes bent using a mandrel bender, only comes down to price really, if its cheaper then go ahead. Personally I'd get one of Kam, less of a hassle and priced competitively too

Not true. Most powerflow places havent got mandrel benders. I know, i used to work there.

You geniunely cant beat an off-the-shelf system from a good manufacturer!

16th December 2010, 12:44

Quote:

Originally Posted by johnr32

all decent companies that do custom exhausts will have their pipes bent using a mandrel bender, only comes down to price really, if its cheaper then go ahead. Personally I'd get one of Kam, less of a hassle and priced competitively too

Most 'high street' garage places do not have a mandrel bender. This is why they either get thinner at the bends, are enlarged at the bends or have a horrible crinkle effect. Our are made on a fancy computer controlled one and the bore is perfect all the way through.

16th December 2010, 13:07

I had a btb system on my car (2.5 inch bore), then I fitted a saxsport system (2 inch bore). It seems to go slightly better with the saxsport fitted, I think this is down to the fact that my engine just couldn't produce enough gas to fill up a 2.5 inch system.

A slightly larger bore will be beneficial on a vtr, but dont expect to notice it. You'd see much better gains by fitting a aftermarket manifold which will decat your car.

16th December 2010, 13:24

Even a manifold, decat and full system will only see you 5-8bhp on a good day anyway.

16th December 2010, 13:33

On the VTR a manifold and full straight through system seems to regularly get 12-15bhp. The standard manifold and cat seem to restrict these significantly.

16th December 2010, 13:52

My 98bhp vtr made exactly 98bhp at Northampton M.S, then i did the following mods:

Janspeed manifold (wrapped)
Decat
Straight through centre section
Magnex back box
BMC enclosed filter with cold feed.

It then made 107bhp on the same R.R. Pretty shit really! Lol

16th December 2010, 14:06

9hp is pretty good to be fair. And why get a custom one, when the supersprint etc have had a lot of development and actual maths put into them to work efficiently

16th December 2010, 14:26

Cheers for the feedback people. Well the reason i am getting a custom one is it's a lot lot cheaper. £75 made and fitted (mates rates). For that price i can keep either the same bore or go for a slightly larger one, he said its my choice which is why i wanted the advice. I do understand that supersprint mayber a better exhaust due to all the effort gone in to making it work perfectly, but for £75 i can't leave that offer lol.

Think i will stick with the same bore though to be on safe side.

16th December 2010, 14:35

Quote:

Originally Posted by 5trudd3rs

for £75 i can't leave that offer lol.

At that price you cant really complain.

17th December 2010, 10:03

Or, my other alternative for £50 is to have a small piece of pipe welded in place of the silencer. Is this recommended? I imagine it will give the same noise as a full pipe just less fancy looking. Is that right?

17th December 2010, 10:20

what other mods have you got? are you planning on going any further with the engine? If you are i would go 2 inch.

17th December 2010, 11:13

I may be but not for a while. What is the standard bore, do you know?

20th December 2010, 13:55

Hi people.

Went and got the pipe made and fitted on Saturday. Got a 2" pipe made up going from down pipe to back box (cat Back) for £60

. Sounds brilliant, i think its the same level of noise as just having a back box but with a much deeper note. On the way home i noticed the noise is there all the way through the rev range wheras it used to be between 1000 - 3000 rpm.

Also, the guy who fitted it pointed out that saxos original pipe reduced in bore size going through the centre box to enable the cone shaped baffle to work properly. So i prosume this must be restricting the flow slightly?

As for performance it feels a little sharper but i think that may just be due to the different exhaust note making it feel quicker.

I would deffo recomend this over a decat as you get a great noise without the loss of torque low down.