Cylinder head thickness vs chamber CC

[Fordy]

So I am lead to believe the stock head of 73.5mm cc's around 44cc

Anyone know the head thickness vs cc?

Looking to get my comp ratio up to around 8.5:1 without skimming the block or pistons, so need to loose around 5cc's.

[Ian S]

Is there any useful info in here:

https://www.rtoc.org/boards/showthread.php?t=4750

My cylinder head has 1.5mm skimmed off.
Between 2cc and 4cc trimmed out of the the chamber in the head, the head has been buretted at 39cc.

[Fordy]

Yeah most of that has been useful, might take it 0.5mm at a time and see what the cc's are

i know most say anything 72mm is bad, but dont think anyone measured it to see what ratio compression it gives.

Not liking the idea of stripping a good block just to skim 1mm and feck around with it massively

[Ian S]

Regarding the block skimming, I was there at the moment the idea happened and was discussed with Big Jim and CTM. I had uneven piston protrusion, which is normal for these C1J's. And measuring the block top for flatness revealed it to be worse than a head that was in need of a skim. So Jim made the logical step and dealt with that. The problem with, and at the same time skimming, the lose liners had to be overcome and was, I forget how. Later the idea progressed to a deeper skim to create protruding pistons. IIRC, the intention was to reduce det'ing by minimising the 'squish' area. Those piston tops are about 13mm thick, IIRC, so you can do what you want with compression ratio by varying the depth of dishing. The dishing being to try and reduce det'ing by improving swirl, and therefore, mixing.

The last step was to change the shape of the combustion chamber in the head to again improve swirl.

I think that Phils engine may have all of that, which would seem to work quite well if it can utilise 32PSI and make 300+BHP, I presume without NOS.

[Fordy]

Well I have ordered a bigger valve set which aren't metro turbo valves and after lots of research with pictures of collet locations and valve lengths, I shouldnt need spring seats machining down

Playing genie pig a little but could potentially open a door for more budget big power c1j's builds

[philr5t]

Ian is bang on and yes I've had lots of block and head work done made the numbers quite well and I'm intending to make a higher hp hopefully a lot safer to by March time my engine also produces a nice amount of torque as well and high comp is lovely for drivability

[Fordy]

Phil, are you still using standard valves? or have you gone for bigger exhausts?

Think i've seen some pictures when searching of your head chamber, bit extreme for my budget atm

Also trying to find titanium caps on a budget, potentially found a cnc set for £80-90 new but need to find out the degree of the c1j collet's as they list 2 different degrees for twin groove and triple groove

[philr5t]

Yes mate I had bigger inlet and exhaust valves fitted which I can't really get any bigger in there as there nearly touching lol

[Trevhib]

There was a lot of talk about cc's calculation and measurement between Andrew Cooke and Scoff on here a few years ago. I don't know what the thread was called and if it's still on the server but it might be worth a search.

I'll have a look too. See if I can spot it.

[Trevhib]

https://www.rtoc.org/boards/showthread.php?t=12570 - Not really what you were after but some interesting flow figures (CFM) on the inlet side by Mr Cooke.

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https://www.rtoc.org/boards/showthread.php?t=17543 - Again, not really what you were after but this is useful information worth refreshing:

http://www.wallaceracing.com/dynamic-cr.php

Standard GTT figures to put into that calculator, based on that thread:

Number of Cylinders :4
Bore in Inches : 2.99
Stroke in Inches : 3.03
Rod Length in Inches : 5.039"
Static Compression Ratio : 7.9(:1)
Inlet Valve Closes ABDC : 28º (standard cam, 39 deg for a 285)
Boost Pressure in PSI : 17
Target Altitude 100ft

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From this thread: https://www.rtoc.org/boards/showthread.php?t=18542

There is a calculation for compression per mm of change in head height. It's for a 2l engine but could be easily adjusted for the C1J:

Well, we know we have 499.5cc of swept volume per cyl. IE, 1998cc in total.

standard CR is 11:1 so from that we can calc how much volume is in the standard combuistion chamber (including gasket, valve depressions in piston, etc etc):

swept vol
------------
cr-1


499.5
-------
11-1
= 49.95cc

If we want to get to 9.5:1 we need to calculate the new combustion chamber volume:

499.5
-------
9.5-1
= 58.76cc

That tells us we need to add 8.81cc's to each chamber (58.76 - 49.95).

using pi x r2 we can work out that 1mm of piston height is worth 5.37cc's of volume, so you need to remove (8.81/5.37) = 1.64mm


Also see post #8 in this thread: https://www.rtoc.org/boards/showthread.php?t=21497

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Compression calculator here:
http://www.csgnetwork.com/compcalc.html

From this thread: https://www.rtoc.org/boards/showthread.php?t=25398