boost ; meltdown; co ; ignition
Turbo Mini Forums

Ok
I appeal to the egg heads here !!

I have been pondering and pondering and pondering

More boost means piston meltdown ; unless you lower the compression and then more boost is safe ...

On my car I have the CO at 10 PSI set nice; and a intercooler fitted ... so in terms of boost am I right on the limit as to what my pistons can take ?

How are these things worked out ? I mean how do we know how much boost is safe ? I know I am burbling but I am knackered I just dont understand how we can possibly know how much we can push things without lowering the compression

Durrrrrrrrrrrrr

s

TurboLessTosser

The standard Metro Turbo pistons will handle a lot more boost than 10psi. But it's not just a matter of lowering the compression, fuelling & ignition also needs to be altered when the boost is raised. If not you'll run into trouble ........

Phil.

WWW.TURBO-MINI.COM

Its all about control and peak cylinder pressures. ...

Think of CR in two ways:

1) static CR... your calculated compression ratio (you know the swept volume into combustion chamber volume one.

2) dynamic CR... if you boost an engine you pump more air into the cylinder than it would achieve in a nat asp form. That is to say a NA engine will fill its cylinders to atmosphric pressure (1 bar), a turbo adds to that.

For example you might have a static CR of 8:1... so assumning things are prefect... you get a compression pressure of 8 bar. Now if you turbo your engine and run a bar of boost you get a compression pressure of 16 bar!!


ok so thats the 1st half... next next bit is that the higher CR you have the bigger the bang from your fuel air mix. This is the control thing I mentioned. You need to run an engine in such a way that you extract the maximum amount of power from the fuel and air via a controlled burn... the problem comes when you get an explosion rather than a burn.

With better control you can run closer to the point were an engine detonates (thats a whole subject in itself!!).

The typical method for more power is more boost and in order to run it safely without det most tend to lower the CR.

Alex

AlexF

and how does one know when your jsut about to hit the point of detonation?

can you do it LIKE advancing the ignition til u hear pinking then retard it a bit? i do understand detonation is very destructive, so how do u know ur running the max boost you can safely?

Edited by evolotion on 29th Jul, 2004.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Det is not the same as pinking...

pinking is pre-ignition and you can hear it, were as Det is scilent.

Alex

AlexF

thanx for the useful replies !!!

HOwever I am still lost as to what to do !!

With my intercooler fitted and only running 19 advance .. and co at 7 on 9PSI should i risk tweaking up a bit more then ?

I know i sound like a w@nker but am really in the dark still

S

TurboLessTosser

I have fitted a bleed valve in the car and I think I will relocate tis to under the bonnet somewhere, I know myself, This is very dangerous and a positive meltdown. I see my hand go already.

no dont steve!

unless you know what your doing you'll blow the engine!

alex

AlexF