Short compression height pistons
Turbo Mini Forums

Ok, bare with me on this one

How is this achieved with mini pistons? Is this by moving the gudgeon pin closer to the crown, reducing the distance between the crown and the top ring, or a combination of the two?

The reason I ask is because looking at mini pistons they seem be rather top heavy, which obviously cant help stability at high rpm.

If the short compression height is achived through moving the pin closer to the crown could these be of benefit for engine longevity at higher rpm. The next engine I'm building will be a 1380 turning to 8k

There would need to be a element of skimming involved to then bring the pistons flush with the deck. Would this have a implicaiton on the angle the rockers sit at due to the head being sat lower in relation to the push rods?

Or is simply not worth the effort for negligable gain, and just less hassle to use ordinary 73.5mm pistons?

You are right, mini pistons are top heavy,

really to do the job properly the pin needs to move up toward the crown, There are JE pistons available that are made like this, you need to run them with a 6" rod or skim 1/4" off the block to get them flush.

the other alternative is to find pistons from something else, but it will be hard to find anything with the right crown.

If you take a load off the block you can use 998 push rods.

To do the job REALLY properly, you need longer rods. Longer rods, and lower pistons are they way forward!

21251s sit really low, ive had a set in a decked blocked before. Altho there made from chocolate

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

I was looking at these in the short compression height, but as I''m not sure what the std compression height is its hard to call it.

http://www.med-engineering.co.uk/product_d...62&vlang_id=106

The unfornunate thing is to do it properly would involve a mass of cost that I don't think can really be justified in any case really (well unless you can afford to just throw money around then why not).

std compression height is pretty much 1.5" so those arn't much shorter really.

longer rods slows piston acceleration also, improves gas flow around tdc, such tiny improvements for massive costs though!

Just a thought, if the pistons are approx 2mm shorter? it would make them effectivly a 17cc dish? that could help out a lot if you trying to get lower comp on a big bore without doing to much to the head.

Ruins squish though, and maintaining squish is the current way of thinking