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Rebuild Pt2


Scot
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Ok guys,

The reason why i havnt posted much these few wks, is because ive been busy!

DSC02482.JPG

DSC02483.JPG

Ive just been to the work shop where we buretted the chambers to find out the compression ratio....and the news is.............BAD

On the first attempt with a used standard Head Gasket it comes out at 13.46:1, with 2 H/G's it was just under 11:1.

So we though sod it, and tried my new H/G that we planned on using which gave me a reading of 12.42:1

So the answer is to somehow source a 2mm thick headgasket to reach 11:1, failing this a 1.6mm will work, but will the require machining of the valve reliefs on the pistons/and taking metal out around the spark plug hole!!!

If any of you dont follow what im saying heres the gist. Each chamber (in my case) has approx. 500cc, and when the piston travels up on its compression stroke, it forces all the air and petrol (500cc's of it) into a much smaller mass before ignition happens. In my case it squashes just under 500cc into a space of 42cc which equates into a ratio of 12.42:1, with our c :censor: p petrol this would destroy the engine in a small amount if time due to detonation.

So i need, instead of a 42cc combustion chamber, a 48cc one. With our calculations, on a 78mm stroke, and a 88.5mm bore, using a 2mm thick head gasket i'll be able to gain an extra 6cc in the chamber. Happy Scot.

All i need to do now is find one :crybaby:

it could be a few wks or a few months :eek:

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Looking good Scotty boy, she's going to look stunning when completed. Shame about the compression ratio's but am sure you'll find away to get her working as soon as you possibly can, I can't wait to hear her ticking over again...

Those photo's don't do her justice when you see her in the flesh....

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Shame about the compression ratio's but am sure you'll find away to get her working as soon as you possibly can

Did the explination make sense then mate???

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Dont take this the wrong way as im sure you know exactly what your doing but have you taken into account the overlap on your cams as this lowers your compression :thumbsup:

No i havnt taken it the wrong way :D

You'll have to explain.....

ok, so the overlap is when both valves are open at the same time. but this would only happen early on in the stroke right? or wrong? but by the time the piston has traveld up, and is near the point of ignition the valves are fully closed, and full compression is reached....so how does this effect it?....

or does it happen on the exhaust stroke....... then what happens??? :D :D

Dont forget this is my first time, so any help is great. And hows the celica going???

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Celica gr8 havent stopped grinning yet :D as for overlap have too look it up :bookworm: but kinder works that on "hot"cams you get overlap on the valves due too them being open longer so inlet is still open as exhaust opens.Because of this you lose compression so the "hotter" the cam(s) the higher comp you need too retain standard comp.All i know is on my racecars we were running near 13:1 compression with race cams you had nearer 10:1.If you got a kent cam book think they explain it better or maybe worth talking too an engine builder.I had a 2.0 pinto running a 1300 head with 49cc chambers and was told it would be ok with the rally cam i was using!

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Hey peeps,

i should be getting my full gasket set for the engine by this weekend.... had to come from japan!!!

And ive ordered a 2mm H/G from toysport, which should be here in a couple of wks........ and thats it :-)

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  • 1 year later...

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