112 replies to this topic

[debkar]

If it hasnt been shaved much its probably around the 9.5:1 mark.

Head definitely aint standard, has had a bit of work done to it, should be good mate.

Cheers.

Thanks Bomber, memory is a bit hazy, it's a good bolt on performance upgrade.

My quick calc was using 42 cc combustion chamber size, may well be wrong

Input Parameters Are the Following:

Cylinder head Volume (CC) = 42.00
Cylinder Bore (Inches) = 3.625
Cylinder Stroke (Inches) = 3.00
Head Gasket Thickness (Inches) = 0.020
Computation Results:

Computed Compression Ratio is 11.1 to 1

Edited by debkar, 04 October 2009 - 10:14 AM.

[debkar]

If motor is 202 will be higher comp though

[debkar]

Where did you get 42cc's from mate???

I cant remember off the top of my head what an untouched high comp combustion chamber is but it should be a bit bigger than that. Closer to 48 or 50 i think, i may well be wrong there as well. If i get bored later i might cc one of the ones i have laying around out of curiosity.

Also you will note that the combustion chamber of that head has had some deshrouding work done around the valves which would have added 1-2cc's.

Also that calculation doesnt take into account piston dish and deck height. Standard 202 piston has about a 2cc dish and they never come right up the bore so theres another cc or so there.

This is all assuming the bottom end of the motor has never been touched, or if it was rebuilt at some stage was rebuilt using standard type parts.


As i suggested way further up in the thread its probably worth getting the lot cc'd before bolting it together just to check.

Cheers.

Hi Bomber,

As I said from memory. Job from a engine build way back in 1985. Be interested to see the cc of the head, if you get a chance to do it. I don't have any heads lying around to check.

That program is pretty basic, uses default deck height of .030, but doesn't allow for piston dish.

Best to get it all checked, before it's out together,

Regards Simon

[rodomo]

I think Debkar might be correct as mine has been machined and is 40cc.

[debkar]

I think Debkar might be correct as mine has been machined and is 40cc.

Hi Rodomo

Thanks for that, I was working from old old build notes and fuzzy memory. Ah, that is small , for a 202 even with dished pistons,and if it's bored oversize, comp will be higher again

These guys have a pretty decent calc for compression ratio

http://www.maverickracing.co.uk/

Edited by debkar, 04 October 2009 - 05:30 PM.

[debkar]

Just randomly plucked one off the pile and cc'd it three times.

Frist time, 46cc

Second time, 45cc

Third time, 45cc.

I dont have the proper type stuff, i just have a piece of perspex with two holes and a 60cc horse seringe, but everytime i have gotten something checked by the pro's its usually within one cc.

Cheers.

Thanks 45 sounds better, hope his head is same cc should be a good performance mod

Regards Simon

Edited by debkar, 04 October 2009 - 05:59 PM.

[debkar]

Hi Josh, Not standard, looks quite good. What's the part number?

Regards Simon

[debkar]

Hi Josh

7420109 is 149 cylinder head. I believe 7420108 is standard 149 head and 7420109 is 149 high compression head. High compression was 8.8 to 1 in the 149.

What is the cast date on the head, ?

Edited by debkar, 04 October 2009 - 08:04 PM.

[debkar]

Hi,

Same side as the part number, further back between 5th and 6th head bolt, will be something like E6 0

[debkar]

Hi

May 22 1964, EH 149 head, as far as I'm aware

[debkar]

Hi Josh

Probably best to get the head off and have a look at what you have. Especially if you are looking to increase power, check bore condition, piston movement in the bore. Then if all is good, you can go ahead and fit the new head.

See if the engine has been bored out, as oversize will impact on compression ratio. You don't want to end up with too much compression or you'll have problems. At worst , it will cost you a few gaskets, an you get to see how things work.

An old, but dodgy trick was to fit 2 head gaskets to lower compression on motors, so no need to change pistons. The other way was to machine piston tops, lots more work.

I think best to pull the head off and have a look. I think whatever you do, you'll need to run premium unleaded though (maybe you do already.



Regards Simon

Edited by debkar, 04 October 2009 - 09:03 PM.

[debkar]

This is the chamber of the head on my motor. Motor is 186 block with 202 crank. Compression ratio is 10.2 to 1, after some machining of piston tops. The head had been shaved quite a bit.

Well i know my engine or head has been reconditioned at one point, because it has a reconditioning sticker on the rocker cover, so i might discover some more surprises with the car... The plot thickens.

If i can get it all sweet, this should be a fast little rocket, hope i don't run into any issues with it though... Just want to bolt it on and get it going!

And yeah i already so run it on premium unleaded.

Hey, half the fun finding out about your motor. I think it will go very well actually , great combo. What Crow cam did you end up with?

[debkar]

Sounds pretty good, keep the updates coming and some pics would be great as well,

I'm sure you'll be happy with the increased power, well until you break some axles,

Keep up the good work

Regards Simon