rebuilding pinto - need help on piston height

[bogape]

I'm rebuilding a 205 injection engine to use in my RS2000 with twin 40s, ported but std valve head, and RL30 cam. Its from an 89 sierra. I've measured the pistons and they're around 1.1 mm down from face of the block. All info i read is that they are normally 0.5 mm down. I'm sure its not a low CR engine. I want to get to around 10.5:1 CR and will measure the head volume to work it out, but i had hoped to take about 1.5 mm off the head. i need some advice. Has anyone seen pistons 1.1 mm down? i don't really want to have to get the block machined....

[racing escort]

You have to machine the block, otherwise combustion is not good and the head should be skimmed to much to obtain 10.5 CR

[snapper1]

I have looked at the piston pin to piston deck heights and it looks to me that you have low compression pistons, probably easier and cheaper to get a standard block, then use a Felpro gasket that crushes to 1mm, this should give 9.7 to 1 then skim head for the 10.5 required.
Or you could bore the block, fit bigger standard pistons, skim the block so the pistons are level with the block deck.

[capri dave]

on my 2.1 pinto (205 block) the pistons are, as snapper1 has already pointed out.....flush with the top of the block.

[sierra3dr]

This might interest you

I've also been led to believe that on standard specs,the pistons would sit above the block deck. As I've just installed YB pistons in a Pinto block and they did exceed 0.07mm above the block deck

[snapper1]

The engine I have almost completed, uses Cosworth rods and 2.8 V6 pistons machined to take Cosworth wire circlips.
With this combination the pistons sit 0.38mm below deck, this + 42cc chambers and a Rienz gasket gives me 10.6 to 1 on cast pistons

[bogape]

Thanks everybody! This is a great forum...
Excellent help and info.. It gets more complicated as time goes on!
I checked my original rs block and that's about flush... will take a piston out of the sierra block to see the compression height
Another point, general info says a standard head gasket is 1.6 mm compressed, but both the one on the rs and the sierra are 1.3 uncompressed and 1.2 compressed..
My compression ratio calcs have gone mad - about 12 options of piston height/gasket thickness/head volume
My head volume is currently 38cc so at least that bit seems normal, nothing else is

[snapper1]

Head volume for a standard 2,L should be 48cc, 38cc is a 1600 head in my book or a very heavily skimmed 2 L.
I have been struggling with getting compression down to 10.6 static with the parts I have amassed

[bogape]

i meant to say 48cc head volume not 38cc... (maybe wishful thinking!)
got the pistons out now so will have a measure up of compression height

by the way, with your details I calculate you have 10.9:1 compression assuming crushed gasket height of 1.2 mm and 93 mm bores

[snapper1]

1.3 crushed gasket
92.8 pistons
Add 1cc for piston top ring volume
I know I am right on the limit for cast pistons and 97 ron
I even found 1/2cc with the recessed plugs.
The Reinz gasket was cheap and thicker than the Adjusa, if I have det problems then it's a Cometic one for me

[Legend]

I've also been led to believe that on standard specs,the pistons would sit above the block deck. As I've just installed YB pistons in a Pinto block and they did exceed 0.07mm above the block deck

I don't think they do protrude as standard, i don't think Ford would have run their squish clearances that tight back then, and i did an engine for a pro-sports 2000 car a few years back and the rules stated that standard pistons must be used, and that they must not protrude above the block. This is the rulemakers way of limiting compression ratios.

[Graham]

your right as std the pistons do not protrude out the block, they are normally about 0.5mm down the bore and low comp about 1.5mm down

[sierra3dr]

I don't think they do protrude as standard, i don't think Ford would have run their squish clearances that tight back then, and i did an engine for a pro-sports 2000 car a few years back and the rules stated that standard pistons must be used, and that they must not protrude above the block. This is the rulemakers way of limiting compression ratios.

I will add though,that the crank is a standard 2000cc,as we know the stroke on these is 76.95mm. I've got different information on the YB stroke,77mm and 76.95mm and the con rods are 1.5mm longer than standard 2000cc rods.
Oh yes,I haven't fastened down the big ends ,I need a socket set for the bolts,don't know what they are called...splined?

[Graham]

Oh yes,I haven't fastened down the big ends ,I need a socket set for the bolts,don't know what they are called...splined?

they are not splined, you just need a 12 point socket 7/16th from memory

and the con rods are 1.5mm longer than standard 2000cc rods.

yes yb rods are 1.5mm longer, but yb pistons are also 1.5mm shorter than pinto

[snapper1]

The reason I used Cosworth rods with V6 93mm pistons was two fold, the rods are good for more revs than I will ever use and they give the right compression height, and that little bit longer rod gives better rod angulation I am led to believe

[radjay mk1]

just read the thread and i have the opposite, i have a 205 block,standard crank,cosworth rods,cosworth pistons and the piston sticks out about 0.5-1mm!
anyone any ideas why?

[Graham]

the block has been skimmed

[radjay mk1]

great! only bought the engine for the block! was supposed to be standard.

[racing escort]

Cosworth rods are longer then pinto ones, therefore the pistons should be shorter

[radjay mk1]

but as graham said cosworth rods are 1.5mm longer and the pistons are 1.5mm shorter than standard pistons.
so they should be the same height as standard rods and pistons.

[racing escort]

So pistons should be machined down, or a new block ?

[Graham]

you can shorten the pistons no problem

[radjay mk1]

I do have another set of cosworth pistons and they are are slightly shorter than the other set? When I put them in they came 0.5mm under the block.They are both standard & had no machining done to them.Both supposed to be 2wd pistons.Did they come this different c/r?

[Graham]

maybe different manufacturers?