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Discussion Starter · #1 ·
If I remember correctly the standard size pistons are 87mm, but will check that from the parts that are on their way to me - thanks Shrew, :thumbs:

Without doing all of the maths of pye R squared H x 4 etc (for 1712 to 1830) can someone tell me is it 88.5, 89 or even 90mm?

Would be interested in some pistons specifications if someone has them. I spoke with JE and Arias and they will make some - but they need to know what I want :rolleyes:

Probably going to get some higher lift cams to go with so need to be mindful of the pocket depth and compression ratio, so if anyone has some piston specs that would be a good starting point....

Cheers. E.
 

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1712cc is 87mm bore and 72mm stroke.

Thats 4 cylinders of 428cc each.

1830cc is 4 x 457.5cc per cylinder.

1cc = 1000mm^3

cylinder volume = radius^2 x 3.1417 x Length

457500mm^3 divided by length 72mm = 6354mm^2

Bore surface area = half of bore size squared x 3.1417

6354 / 3.1417 = 2022.5

square root of 2022.5 = 45 (radius)

x 2 for diameter of piston = 90mm.
 

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Discussion Starter · #4 ·
Thanks Pud :thumbs: I followed pretty much most of your workings out there.

If the pistons are 90mm say - what diameter (out of interest) do the bores in the block need to be? I presume they need to be 90mm+. Clearly the 3 rings need to be in there, but I was just curious how much bigger the bore is over the piston size, or is that something the engine builder somehow works out??
 

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Now thats the million dollar question - it depends on material of pistons/liners/rings, the expected operating temperature of those components. I would ask you engine builder and if he sounds like he knows what he is talking about then I'd go with his recommendation.
 

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Discussion Starter · #6 ·
Wow! Now that is an interesting response. :cool:

Certainly a very interesting comment and much appreciated. One small point is that the block is a solid lump (so no liners) and 90mm would probably be a tad extreme, but it is what I think I had last time. It may be worth getting two blocks cut at the same time, but if one breaks then I could transfer, but then who's to say that a second one wouldn't do the same? Fun, ehh!
 

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Pistons are aluminium so they grow a lot more with heat than steel, so bore clearance isn't strictly fixed, you need to state what the bore clearance should be at a specific temperature, then you can work out what the clearance will be at say normal operating temperature. EG there'd be typically more clearance on a turbo'd car as its expected they'll be hotter, you don't want it seizing up if the bore/piston clearance is set for normal aspiration. Similarly you don't want the engine to be too tight at normal operating temperature cause it'll drag down your power figures and wear out faster.

Same story with V6s, the ally blocks grow more than the steel liners so when you're machining the blocks to take bigger liners its important to get the height of the liner correct, they need to protrude slightly out of the block, otherwise when hot the block will have grown more than the liners, lifted the heads up and your head gasket leak between the fire rings and tops of the liners.
 

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Discussion Starter · #10 ·
Yes JB, i'm not rushing into anything as far as ordering parts go.

It would be really helpful if you could measure the pistons for me.

Silly question - but why are they not in the block, with heads bolted on top ....:confused:
 

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Discussion Starter · #11 ·
Just had a very quick working out from the numbers that Pud supplied above and if my back of a *** packet calculation works out correctly an 89mm piston give about 1790cc.

Would anyone care to confirm?
 
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