998 Turbo Build - Update
Turbo Mini Forums

This question has come up before with opinions both ways....

Most OEMs put it before the intercooler, and that's where mine is going (although mine is a recirc. type)

EDIT - I should add...... looks good :)

I did do a double take on the intercooler seeing the crimped plastic ends before I actually read what you had posted (bearing in mind previous posts about alloy welding) !!!

Edited by Rod S on 4th Jul, 2009.

Schrödinger's cat - so which one am I ???

I'll leave it where it is then, saves time. Just need to get some aluminium bends to fix the kinks.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I have often wondered why dump valves are fitted.
I can only think it is to stop pressure waves when the throttle is shut from causing compressor blade damage.
On small compressors this is very unlikely to happen.

I am sure it will slow the compressor down more quickly than not fitting one due to the extra pumping work required to flow the air out of the valve.

Of course it will make a boy racer noise which I find tiresome compared to compressor stall noise but that is my preference.

Can anybody enlighten me?
I have never bothered to fit one.

Edited by matnrach on 4th Jul, 2009.

when the throttle shuts the air coming from the turbo (as it is still spinning due to momentum) has nowhere to go so you will get a pressure spike, this can damage the turbo, hence the dump valve.

Yes this is what I thought but with small compressors, the blades are quite stiff and natural frequency is very high so I doubt they would fail.
I have seen this happen but only on large compressors.
All the engines I have run have never had a dump valve and not failed but I guess it is a trade off in reliability v performance.

The main thing it does is let the turbo continue to spin so that as soon as you are back on the throttle it's ready to boost.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I think the opposite. The extra work done in pumping the air will cause the wheel to slow down more quickly.
With a closed pipe there is no net work done on the shaft hence the speed will reduce less.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

If that were true then all turbo race cars would have a valve and they don't.

If you change gear fast enough, ala race cars, you don't need one, is my thought.

You never ever hear mine when I'm competing.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I realise that there will be a power consumption with a closed ended pipe but without doing the sums I'm not sure it will be less or more than the work done in flowing the air throught he valve.
I guess it is quite a complex sum a bit beyond my spreadsheet maths ability.

So it is maybe dependent on the actual installation.

Certainly when I was doing rallying a few years ago, most people blanked the valve off as they felt it reduced lag.

It would be interesting to see the calculations anyway.

Why dont you start a new thread about this rather than clutter up mine?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."