Spacer Plates And Compression Ratios?

[Guest Dan_Beeston]

I've been looking at methods of reducing the comression ratio on my Pinto Turbo, and out of low comp pistons or a copper spacer plate between the head and block, the spacer plate sounds simplest!

 

By my calcs a 0.8mm spacer plate should reduce the 9.2:1 compression ratio to around 8.4:1. Can anyone verify this?

 

Are there any other pitfalls I sould be looking out for?.......................

[richyb66]

Dan,

 

I assume 90.8mm bore, 76.95mm stroke and standard 2 litre head with 50cc chambers. I can check your calcs but need to know what thickness head gasket your planning on using - and presumably your going to try and get away with just one head gasket ( I have known them to be doubled up

 

You could use the 93mm Cologne V6 piston which has a lower compression height than the pinto piston which would also take your capacity up to 2.1 and don't bother with having the block decked like you would with a naturally aspirated 2.1. Obviously you'd need to bore the block and I'm guessing you don't want to drag the engine out which is why you're considering a spacer. I you don't already use one you'll need a vernier cam pulley if you alter the deck height with a spacer.

[Guest salty_monk]

If he uses a spacer plate he'll need to use 2 head gaskets. 1 on each side of the spacer so their thickness would need to be taken into account.

 

The P100 & the transit both had low compression variants, I wonder if it was a different piston in the same block, probably.

 

Dan

[Guest Dan_Beeston]

Yep, I was using 91mm bore, 77mm stroke & 54cc chambers (I was working on the principal a standard headgasket was included in the factory compression ratio spec, so effectively adds to the combustion chamber size (over what you would measure by pipetting it))

 

I'm already using a vernier cam pulley, so that end of it's sorted.....

 

I've heard of people replacing standard head gaskets with solid copper gaskets, so I was hoping a wouldn't need a normal head gasket either side of the spacer plate. Can anyone confirm or deny this?

 

I guess I could just use a couple of head gaskets instead, but I don't like the sound of this somehow? Are there any pro's or con's to this method?

[richyb66]

0.8mm thick spacer works out OK to drop the compression down to about 8.4:1. Is this going to be a low enough CR if you start to wind the boost up?

 

Trawling back 20+ years me and a mate put a RO34 blower on an Essex V6 and headgasket life was short to say the least despite having pistons machined for a lower CR. A number of solutions were suggested including solid copper gaskets which work well if the head is machined for Wills rings but in the end we just had the head machined for Wills rings and used decent quality (Reinz I seem to remember) head gaskets.

 

I think the issue here is how many things you're prepared to try to get something that works reliably. If you only want to do the job once then get 0.8 turned off the piston crowns, have the crank balanced, get the head ringed and use a genuine Ford head gasket.

 

This would neccesitate pulling the engine out but is guaranteed to work. Cost TBA...

 

 

Ok, spoke to my pinto guru and 4 Mahle or Schmit pistons machined to suit is going to cost around £200 and then another £100 to get everything lightened and balanced - but he also suggested the Transit low compression pistons which are designed with a lower crown height but he's not sure exactly what CR these give but in terms of fitting this would be an easy job. They're probably not a forged piston like Mahle so wouldn't be the best if you start to crank the boost up but you could fit them with the engine in situ. If you're thinking of investigating this further I can put you in touch with him which means you could speak to him directly and get some more info (he's local to you too).

[Guest ticeysoft]

how bout skiming some of the top of the pistons.... it would prob be easier than messing around with compression plates/gaskets

[Guest salty_monk]

Transit is about 8.2 or 8.4 CR from memory. Might not be too hard to get hold of a Transit block & pistons but likely to have a lot of Mileage. P100 used the same. I think some were 202 block, some 205.

 

Dan

[Snapperpaul]

Bore to 93mm adds compression because you now have a larger area being compressed into the combustion chamber space counteracting any gain made by the 93mm V6 pistons lower deck height.

Cometic do a very thick gasket, crushes to 0.125" which is somewhere around 3.2mm.

I have been trying to reduce compression ratio on a 2.1 engine to fit a head with 40cc chambers to get 10.5 to 1 but the same calcs should work.

 

You will need to check these calcs/formula's so here we go..

 

A. Bore x Bore x 0.785 x stroke divided by 1000 = volume of 1 cylinder

Bore = actual bore diameter not piston size, every thou helps.

 

B. Bore x Bore x 0.785 x height piston top is below block deck = volume to add to chamber volume.

 

C. gasket bore x gasket Bore x 0.785 x crushed thickness. add to chamber volume ( gaskets for standard bore are 92.5mm and crush to 1.62)

 

D. estimated top ring to piston top volume = 1cc add to chamber volume

 

E. actual chamber volume, should pipet to find real volume but can be between 48 and 50 on a 2.0L pinto head

 

to calculate compression ratio.

 

Cylinder Volume + Compressed volume divide by Compressed volume = compression ratio. all figures nominal

A. 500 + B. 3 + C. 7 + D. 1 + E. 50 = 561 61 9.1967 to 1

 

There are loads of Cometic gaskets only 2 of which will reduce compression ratio over standard.

If you are going for big boost then the standard cast pistons can give out.

Cosworth rods and pistons come up on ebay for reasonable money but need oil to the underneath of the pistons for cooling, cosworth has an extra oil spray bar.

 

Have to stop now my brain hurts

[Guest Ian & Carole]

Have to stop now my brain hurts

 

 

Mine hurts just reading it