Dump valve anyone??

[M15ley]

I'm getting my Audi S3 Superchipped on Tuesday and wondered if it's worth getting a dump valve fitted and what will it do for me??

[Currymonster]

I was considering the dump valve option for my A3. Binned the idea when a VAG specialist told me he had heard reports of a TT that had lost about 15bhp by fitting a dump valve. I think a better option would be a sports induction kit and exhaust. Apparently a Cat bypass pipe gives a whopping power boost but this is obviously not allowed on the road (no shortage of people that will fit them though!) let us know how you get on... CurryM

[M15ley]

Hmmm, power loss, I think not!! On the CAt side, do they actually remove it or do some fancy pipework stuff to bypass it?

[Dave_H]

Don't laugh but I used to own an MG Meastro

I got chatting to a well known tuner of the turbo version of this fine car (they are very quick/tunable hot hatches) he told me that his experimentation of fitting dump valves proved that they do nothing for performance whatsoever, just another bit for bolt-on-boy to buy for the hiss hiss gear change sound effect.

Go for the induction and exhaust mods for real performance upgrades.

The cat is removed (big difference) but you'll have to re-fit before each MOT for it to pass.

With the cat removed, you should notice an increase in MPG.

Cheers,
Dave.

Edited by Dave_H on Sunday 16th December 20:54

[ATG]

Doesn't the dump valve allow the boost pressure to drop quicker when you come off the power? I thought it was supposed to give the turbo more life, not to enhace performance?

[GuyR]

Dump valves operate when the throttle is closed when changing gear. Since the turbos are spinning and building pressure, when the throttle is closed the pressure builds up and without a dump-valve the turbo will stall. This causes pressure on the turbo and may prematurely wear the turbo fins, also it means it loses the inertia and has to respin again when throttle opened.

With a dump-valve this pressure is released, so the turbo keeps spinning giving a faster spool-up time in the next gear.

In short therefore it does not add a single bit of power, but boosts engine response and aids turbo longevity.

As for the whoosh noise, dump-valves come it 2 types, re-circulatory and external. Many cars have standard re-circ ones that send the air back into the intake system and are silent. The external ones (often with loudening horns) and the ones you hear make the noise.

I have had both types at different stages of tune on my Nissan Skylines.

Guy

[numlock]

Car & Car Conversions is doing an article on tuning the TT this month (and next I think). I can't quite remember what the details are but you DO get a power loss if you fit the wrong sort. Buy the mag and I guess all your tuning questions will be answered.

[Mark Benson]

The standard S3 Diverter Valve (since that's what Audi call them, I guess because it's recirculatory rather than vent to atmos.) has been a common failure point on all 1.8T engines for some time - the housing and valve are both made of quite cheap looking plastic, the diaphragm seems to fail quite easily causing a loss of power and a chirruping noise.
Audi are well aware of this and will replace the OEM part under warranty, however many people are fitting aftermaket ones (Forge and Bailey are the most common).
After several failures in my A3T I gave in and bought a Forge for £100 - no noticable difference in throttle response or pickup but at least it didn't fail all the time.

[Stig]

If dump valves are of no benefit, why do all the WRC teams use them?

www.locost-racing.com

Car No. 13

[M-Five]

You could get a sports cat which is a lot less restrictive than a standard cat, and will pass the MOT.

I believe AMD www.auto-amd.com in Bicester do them for Audi/VW etc.

One of the owners has an RS4 (or S4) and TT - both a lot more powerful than standard!

[trefor]

Std Audi 'diverter valves' fail on 1.8T as has been said - no power gains from replacing them, but some (Forge and Bailey I think) give a smooth on/off boostiness particularly noticable when changing from first to second gear (6 spd box, very short first gear and dodgy boosting = jerkyness).

Fitted a bailey to the girlfriend's TT and it's been fine for 24,000 miles (the OEM part started to fail while we were still running the car in).

I don't think removing the DV will give a performance gain, AMD et al will know best ...

T/.