Arno - best way to reduce Comp Ratio on LET

[JohnA]

We know that if we are to keep the safety margins intact, then a rise in boost should be accompanied by a further reduction of the Compression Ratio. There are other modifications needed as well, but let's stick to CR for now.

One of the major detterents for detonation built in this kind of engines, is the combustion-chamber shape, which is designed to stir up the charge right before it's about to be ignited (so that the spark stands a good chance to light in an area with decent Air-Fuel ratio, etc..etc...)

There are several ways to reduce the CR, but almost ALL of them change the shape of the combustion chamber - as a result any squish, swirl or tumble motion will not be as the manufacturer intended.

I know from experience (different engines) that you may reduce a CR from 8:1 to 7:1 and end up with MORE detonation because of this altered shape of the combustion chambers.

Question for Arno:
-----------------------
Having done destruction tests on LETs, and having experimented on these engines more than most of us ( :lol: ), which method have you found best?

 

[ASH]

Hi !

We tested many ways !

1) two C20LET original gaskets : stupid solution , too many problems!

2) re-desighn the piston shape , we tryed many versions , one had the most reduction , and the highes ignition angle , so the most power !
But the reduction is limited down to 8.5:1 !

3) use a tower made of Z20LET gaskets , some cars drive fine , no problems !

4) full metal gasket : highest possible way of reduction , when somobody need this , he can use this !

regards ASH

 

[JohnA]

..so you're happy with a thick (say 1.8mm) steel gasket.
No absolute need for changing the pistons then, eh?

 

[yunis]

arno you made the point about spesso gaskets not being very reliable for p3.5, so what are the other alternatives? the z20let on is 1.1 mm and offers not change in CR, is there someone who make s a thicker metal gasket is a 1.6mm?

 

[rds]

Yunis SBD make them to what ever you want
BTW great power output from a std LET in TV mate :wink:

 

[yunis]

Thanks rob!!

yeah not bad eh? man i tell u what im glad i did it my way, and Daves Andrews head work certaily paid off well, but that was with out the IC, once fitted i took it down to a local place and it made 273bhp and 285lb/ft of torque running .9bar boost. now i just need to find a engine management solution...Autronics thread on mig, well that is really getting me excited!! :lol:

 

[JRS]

Yunis, i'm currently looking at the Autronic software through Graeme at ATC, and agree that it looks pretty impressive!! are you looking at the one with launch and traction control or without. These kits also run antilag

 

[yunis]

well with out i guess i have 4wd so there is no point in having tc or launch control and anti lag is not really suitable for a road car.

yeah the ecu does look demon!! together with a t4 turbo...woooo properly setup your lookig at 400bhp (with a few other mods inc fueling etc)

 

[JRS]

I'm trying to resist but i don't think that i can, can you imagine a 400BHP Astra Mk3!!! one word springs to mind; SAVAGE!

 

[yoyo28]

i'm making an mk3 astra who have 2 bar pressure
i have an c20XE turbo with c20LET reworking piston for a 8.2:1 ratio

 

[jackb77]

In a phase3 with a standard engine and turbo, it's better a 1,6mm headgasket or 1,9mm???

 

[David Dixon]

So your recomendations are a 1.8mm steel gasket and leaving the standard pistons? and is this ok for a phase 3.5 and 4?

 

[yoyo28]

u can work u'r piston
i have do that
look piston 4

 

[pacifier]

I reduced CR by pistons.

 

[DD]

If these were the original ones, they won´t last very long!

 

[yoyo28]

why ?
on phase 4 there are original piston with this work on the head