Check my maths :)
Turbo Mini Forums

can someone double check if i got this right, used two CR calcs which gave two slightly different results.

1293cc
27cc chambers
8.4cc dish (21251's +20)

Head and block have had a slight skim, not sure how much this changes things but i was getting a result of 8.18:1

If this is right, is it good for 10-12psi?

i run 15psi on 8:1 so yeah i'd say it was fine. Although i've heard the 21251's aren't really up to turbo use but i'm probably wrong :)

http://www.afracing.com/cr.xls

Alex

AlexF

The 21251 pistons are horrible, as they have a LARGE oil drain slot behind the oil ring... I would NOT use those in a turbo-engine whatsoever. I've used them in high perfromance N/A engines, and they didn't like that either...

bloody useful that cheers alex, i got roughly 7:1 should be fun!

oops think i got that wrong, how do you find out deck volume?

you measure it :S

or work it out...

pie x radius sqaured x height


Alex

AlexF

no I mean chicken and pea....

AlexF

easiest way is to get piston to tdc then fill with parifin from a syringe this will give deck volume then add gasket and head cc this will then give total volume. more accurate then other way.

always looking for them bigger bunches of bannanas

so how accurate are you with a syrine then .. dial gauges woul d easier and slightly more accurate

Everyone knows that instructions only have to be read if the thing doesn't work....

with a medical syringe you can be bloody accurate!

alex

AlexF

Mike, did you check that piston dish cc for real? I'm building a street engine with those pistons now, and was wondering about the CC of the pistons.

I make it ALOT higher than 8.1!!

Depends on your deck height though? To get 8.1:1 with those cc's you would have to sit the pistons down the bore about 1mm.

im using 12cc pistons, 1293, 28cc head and its 8.3:1.

Ive always put a cd on the top of the piston with a smidge of grease and used a syringe. It kind of illiminates any surface tension you may get.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

If your only going to be using 10-12psi then you can run CRs much higher than 8.18 with safety!

The engine for Candice's car is going to be running about 10-12psi over a CR of about 9.2 - 9.4:1 which will be fine with an efficient IC and MegaJolt handling the sparks.

Remember, the higher the CR the better it will drive off boost and the less agressively the engine will come on boost ..... both important in the real world of driving on UK roads!

just my 2p's worth

Every day is a school day ...........

How fast and how expensive ...... the same question...