Contour Enthusiasts Group Archives Forums Modifications Forced Induction CR with boost....

Came across this the other day which may help acessing your engines CR (simulated) under various boost levels.
Final Comp ratio= [(boost DIVIDE by 14.7)+ 1] X existing CR.........

Hmm that means roughly 14.5:1 on the 3L S/C with 9 lbs boost. Sheesh, that's gonna be hard on things. At least I don't plan on this motor lasting forever! Hopefully the trans will, right Terry?

Rick

If you start with a lower cr more of the engine range is in a 'progressive' boost above atmospheric.Once you are over around 10:1 on say a 91 octane at stoichometric a/f ratio (14.7) you need enrichment to go higher re det etc......

so if I did this right under 10psi boost I have 16.8:1 C/O?

-Mark

With a 10:1 Cr on the motor yes @ 10 psi it will be 16.8:1 CR, hence the need for ign retard /enrichment and H20 to reduce det...but then again no one ever works out the 'stoc' cr correctly (ie the intake valve is still open as the piston accends on compression so the swept volume is less!!!!)

That's right Terry, completely forgot about that. Thx!
That's another nice input for perfecting my calculations...
Need to look up those valve timings....
You wouldn't happen to know them for the 1.8 Mondy, would you?

Further if it has any interest, I have (and am still) looking into turboing my 1.8 Zetec (115hp, CR10:1).

A Mondy fellow overhere is running with 200hp@4800rpm, only with a Fuel Pressure Regulator, otherwise stock.
Above 200hp@4800 the A/F ratio leans out.
The guy is still working to improve it further..


AFAIK these cars do work with high CR turbo:

The Focus 2.0 has a 9.6:1 with some 8-10psi boost (Aerocharger)
The Audi TT 1.8L, 180hp has 9.6:1 and a 11.8 psi boost....

It should be possible.