Lowering compression,,,

[TUFFY]

I am working on a 1.6 for a pulling tractor. What is the best way to lower the compression some? I have not checked how far the pistons are above deck yet. I have a 3 notch head gasket.

If I was to mill the pistons for a .000 deck height with a 3 notch gasket would that be to low? I am using a 1.6 head.

[745 turbogreasel]

If you get aftermarket pistons, they usually set down deeper on the wrist pin.

[bajacalal]

I wouldn't mill the pistons, they seem to have a specific shape cast into them to direct the combustion a certain way when it comes out of the prechamber.

You could run the thicker head gasket, the three notch one, or even get one machined out of copper.

I have to ask why lower the compression ratio so much though, considering people run these at high boost without lowering the compression, I think it would be fine especially for an engine that isn't going to be used for thousands of miles. Excessive sustained EGT heat is what kills these, for 10 second bursts it would probably do OK.

[Jetmugg]

I'm curious to see how the pulling tractor plays out.  It's not too far removed from my 1.5L land speed engine.  If you have a target value for compression ratio, it's fairly straightforward to figure out how much to remove from the piston top, or how thick of a HG will be needed.

Are you aiming for a specific CR?

Steve.

[TUFFY]

Nothing specific, Just looking at keeping the head gasket in it at high boost.

So say when I check piston popout it comes out where it would call for a 1 notch gasket, How much would it drop compression with a 3 notch gasket?

[bbob203]

Why not use head studs and an aaz metal headgasket and you will have a higher tolerance for boost and the compression will be a tad lower.

[carrizog60]

what turbo do you plan to use?at what pressure?

[8v-of-fury]

Why not use head studs and an aaz metal headgasket and you will have a higher tolerance for boost and the compression will be a tad lower.

Use an entire AAZ head while you are at it, identical to the 1.6 head.. they'd never know

Usually drops CR to like 17.5? or similar.

[TUFFY]

The engine I have is mechanical lifters.

[8v-of-fury]

Does it need to be? You can put a hydro head on the mech bottom eh.

[Blownoiler]

I'm not familiar with this particular engines layout, but have in the past lowered the compression ratio on an IDI by "selectively" unshrouding the inlet and exhaust valves with a drill and selection of grindstones. How much meat does the cylinder head have around the valve area is the question! If you're desperate how about taking out the glowplugs and replacing them with a blank to increase chamber volume!

[theman53]

The CR I would not worry about. I would worry about the precups. If you stud it and use the AAZ metal HG people have ran plenty of boost and no issues. IIRC zukgod and 53 willy's were right at or over 40 psi and zuk went through many turbos without having a HG issue. If you have fuel to match the boost I would worry more of the precup failing than the head lifting.

[TUFFY]

I thought the AAZ gasket won't work on a mechanical engine.

[theman53]

I ran one 40,000 miles. You just block off the extra port. I used 3/8" teflon joint seal, some used oil cap material. Search for MJF an Audi 80 *same guy* as he was the first one that did it IIRC. My pics are on myspace and I cannot access myspace anymore bc my browser is too old. Works fine. Also if cost isn't an issue measure the gasket size you need and contact this guy. http://www.gasketstogo.com/faq.htm#stock

He will make you whatever. The aaz in a mech valve engine, no sweat. 120.00 each then shipping IIRC. But if you go that route let me know as I may get one and he does deals if you buy multiples. I might get 2 just in case, so if you got one that would be 3 and I think the price goes down to around 100 each plus shipping.

[RabbitJockey]

1588/4=397cc

397/23=17.26cc

Each head gasket notch size=.1mm difference in thickness

76.5/2= 38.25

Pix38.25x38.25x0.2mm=919mm^3

919mm^3=.92cc

17.26cc+.92cc=18.18cc

397cc/18.18cc=21.8:1 compression ratio

Or is my math wrong,  the part that seems wrong to me is the compressed volume I though the precups hold more than 17cc themselves