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xflow optimum squish
Supergoose - 29/4/12 at 10:09 PM

Could some one please tell me the optimum squish for a locost xflow, I'm used to working with bikes with much lighter rods/pistons but they rev much higher but I don’t know what you need to account for,for elasticity?

Please help as i want get the gasket and get racing!!!

snapper - 30/4/12 at 07:22 AM

Crossflow has chamber in piston and a flat head so squish is not relevant as pistons will be down the bore.
In a pinto squish is a minimum .75mm with .9 recomended for 8000 rpm
Basically you are building in a margin for rod growth and piston rock

[Edited on 30/4/12 by snapper]

mcerd1 - 30/4/12 at 01:33 PM

a few more details about your engine spec / size might help...

is this a 750mc car ?


quote:
Originally posted by snapper
In a pinto squish is a minimum .75mm with .9 recomended for 8000 rpm
Basically you are building in a margin for rod growth and piston rock

yeah, I've got my pinto's pistons flush with the top of the block and a 1.0mm gasket - hope it works

[Edited on 30/4/2012 by mcerd1]

Supergoose - 30/4/12 at 07:35 PM

Sorry yes it's a locost and I don't agree with the comment that squish isn't relevant with a flat head, focusing the burn to the combustion chamber is key regardless of weather it's in the head or the piston

Richard Jenkins - 30/4/12 at 08:03 PM

This from the 750MC Locost regs - "Gasket: The cylinder head gasket must have a minimum compressed
thickness of 0.85mm and a minimum cylinder aperture of 82.5mm"

mcerd1 - 30/4/12 at 09:02 PM

quote:
Originally posted by Supergoose
Sorry yes it's a locost and I don't agree with the comment that squish isn't relevant with a flat head, focusing the burn to the combustion chamber is key regardless of weather it's in the head or the piston

I think snapper is just talking about piston / head contact, where as your thinking about compression ratio....


but like richard says there isn't alot of options if you've got too meet the 750MC Locost regs

Supergoose - 30/4/12 at 10:09 PM

not at all, surely the closer the non combustion areas of the piston are to the head the more accurate the burn is focused to in the comustion chamber and not seeping across the whole face of the piston. but maybe im understanding it properly?

Supergoose - 30/4/12 at 10:10 PM

true about the regs mind you

snapper - 1/5/12 at 05:37 AM

My comment about not being relevant should of perhaps said "not achievable" if you look closer at my post i also gave pinto squish distance.
You can't get that close with a flat head unless you have very deep piston bowls therefore the edge of the pistons will not be close enough to the head to create any squish, if the piston bowl edge was close enough there would be very little squish as not much of the piston is close enough.
The swish on a pinto is where the chamber, which has large flat areas and flat top piston get really close as said 0.75 to 0.9mm is the target.

How far down the bore are your pistons?
Standard 1600 pistons are further down than the 1300 pistons would be that are used to increase compression.

Supergoose - 1/5/12 at 06:13 PM

Nearly flush

procomp - 1/5/12 at 06:40 PM

Hi

As mentioned there is the min compressed thickness for the gasket IE using a Payen or similar standard type gasket. Copper or similar reduced thickness ones are non compliance with the dimensions stated in the regulations. Piston not to protrude above block face. Piston dimensions as in bowl depth / dia and radius in the bottom off the bowl + valve cutout dimensions are all checked by the scrutineers and comparisons are made to standard parts with the correct dimensions.

Also the valves have to remain as STD. The scrutineers have pattern parts, as some have already tried to take the mick with that area of the regulations already.

Matt ( Locost drivers rep )