32 replies to this topic

[Captain Vimes]

I'm new to vx ownership and the snow outside means that I've spent more time reading this site than driving the car.... which inevitably means that I now want to mod the car. I'd like to keep the car na but would like to add a bit more sparkle at the top of the rev range. BUT I would also like to be able to take the car to Bedford autodrome without blowing the sound meters as its one of my favourite circuits. Many of the modded NA's only seem to make a little extra power until the exhaust manifold is swapped for something decent (tullet) which makes me wonder whether the back box is really that bad. See dyno in this thread for what I mean: http://www.vx220.org...d-so-which-cat/ So now I've waffled for ages.... Has anyone replaced the individual bits of the exhaust and measured the effect they have on power (manifold, cat, back box)? When does the Standard back box start to become a bottle neck? P.S I've had aftermarket turbos and sc cars before and don't want all the hassle of remapping and the constant niggles that come with it. Plus I ride a 1000cc bike so get acceleration kicks there - the car is about handling.

[smiley]

You can get better results on air intake part then exaust part. Read up i would advise.

[Captain Vimes]

Sorry, I should have mentioned that I'm not looking to only replace the manifold/cat. Let's assume that the intake side is as good as it can be, the head is ported, cams are swapped etc. and we focus only on the exhaust for now.

[fezzasus]

Sorry, I should have mentioned that I'm not looking to only replace the manifold/cat. Let's assume that the intake side is as good as it can be, the head is ported, cams are swapped etc. and we focus only on the exhaust for now.

But... It's not, so it seems a bit pointless to hypothesise otherwise.

[Captain Vimes]

I appreciate you're trying to help. Not sure how else to ask a simple question.... The standard exhaust restricts the performance of the engine even with the standard intake system; both courtenay and thorney tuning kits replace the exhaust system without really touching the intake side with proven power increases (even if it's not the cheapest first step - it shows that it IS a restriction in standard guise). So the question I have is, which part of the standard exhaust is most restrictive? From all the reading that I have done my guess is that the standard manifold and cat restricts more than the exhaust box.

[Captain Vimes]

Fezzasus - off topic but the heater you've produced looks great. I may have to invest in one if you do another run later in the year....

[smiley]

Yes, 4-2-1 or 4-1 outlet manifold, and precat out at least. Cat section (default 400 cells) swap for 200 or 100 cells. Weather or not swapping default 2" to 2.5" sort of depends where you´re aiming for.

Edited by smiley, 23 January 2013 - 12:20 AM.

[chris_uk]

Buy my full 2.5" exhaust system. Its a 4-1 tullet manifold and piper downpipe/backbox.

[vocky]

the standard manifold is rubbish (you could gain 5-10bhp changing it to a 4-1), the downpipe is too small and the standard cat restrictive (you could gain 2-5bhp changing it to a sports cat with 2.5" pipework) and the U bend is very restrictive (you could gain bhp by changing that to a 2.5" pipe) I was quite surprised by how much difference the 2.5" U bend made.

[slindborg]

The bits that most of the 'chooooners' change on the exhaust do very little in the grand scheme of things (particularly when you compare gain VS cost), The key is the manifold and U bend, everything else is just minor increments.

[oakmere]

If you don't want to change to a 2.5" exhaust I would remove the cat section and remove the pre-cat then cut out the main cat and weld in a 200 cell sports cat. I did this at an early stage of tuning and it made a noticeable difference. The cat should cost about £80 + welding. Manifolds cost much bigger money but it is worth keeping an eye out for second hand. Also look on z22se.co.uk for info and parts.

[JohnTurbo]

I have a 2.4 inlet and remapped ecu in parts sale section. Coupled with decent exhaust it dynod at 170ish bhp. Pretty cheap gain - im surprised it hasnt neen snapped up.

[fezzasus]

A few people have swapped the NA backbox for the turbo version which is a straight swap, but should have a better flow rate. Not much you can do about the rest other than directly swapping them out. A common mod early on was removing the pre-cat. I've done the same and can't say i've noticed the different, but in theory it should help.

[tommobot]

Does the Turbo backbox fit straight on to the standard U-bend or is a custom piece required?

[oakmere]

You need the turbo u bend then it bolts straight on.

[Winstar]

Does the Turbo backbox fit straight on to the standard U-bend or is a custom piece required?

use the turbo one as it's bigger Diameter and has the flange in the same place

[Bargi]

I'd like to keep the car na but would like to add a bit more sparkle at the top of the rev range.

I have a 2.4 inlet and remapped ecu in parts sale section. Coupled with decent exhaust it dynod at 170ish bhp. Pretty cheap gain - im surprised it hasnt neen snapped up.

^^^^This, if you want more get up and go in the top end the 2.4 manifold is what you want.
I had one without a remap and compared to standard cars I've driven it's much more exciting in the top end of the revs.
Grab this mapped ECU and you should get the extended rev range as well as you'll find yourself hitting it a lot more when you're on it with a 2.4

Edited by Bargi, 23 January 2013 - 01:36 PM.

[Bargi]

It's not uncommon to see 240-250bhp with standard manifold and Milltek exhaust with SC'd cars. Also I thought Nev or someone checked and the std flows to >300bhp or so, the Dave H airbox still uses the standard filter doesn't it? But I guess it's different with an NA compared to forced induction?

[Kev S]

Buy my full 2.5" exhaust system.

Its a 4-1 tullet manifold and piper downpipe/backbox.

I'm still interested in some / all of this system Chris if it's still for sale? Thought you sold it tbh

PM me!

[Captain Vimes]

Thanks for all your responses. Sounds like my ideal setup would be:- - 4-1 Manifold (Tullet looks good but piper is £200 cheaper...) - 2.5" downpipe with sports cat (these seem ridiculously expensive for what they are - I'm sure my local exhaust place could fabricate one for half the price) - 2.5" U-bend (B&Q seem to have a nice range of u-bends...) - VXT exhaust box / modified N/A (pipo style) Coupled with intake mods along the lines of: - K&N filter (already on car) - Straight intake wih Samco 90 degree bend - 2.4 inlet Hopefully this should free the top end up whilst maintaining a nice OEM sound. Any thoughts/experience on whether the equal length Tullet manifold is worth £200 more than the piper?

Edited by Captain Vimes, 23 January 2013 - 09:13 PM.