fbekholden.com

Ok thanks Rob.

SbC the same cool.
I prefer NGK in my other performance engines.
Still have not worked out heat range yet.

I punched the numbers into a Compression ration calculator but using 53 cc as the combustion chamber to account for the too long thread of the spark plug.

It came back at 11.8 to comp ratio.
Now I still want to run the milder cam.

Playing with the numbers in the calculator, by changing the cc of the head to 62 cc will change the ratio to about 9.6 to 1 ratio (increasing chamber by 9 cc).

Also removing sharp edges which I think I was told by another builder can encourage detonation

The added benefit of this is the combustion chamber shape can be improved to a more modern shape somewhat, anything has to be better,provided the water jacket allows this but I think it will be ok.
It could expose the electrode to a larger volume of charge speeding up propagation of the flame.....I think.

The plug end is shrouded by the dome of the piston.

I want to run 98 pump fuel.

Any thoughts.

I am waiting for Galloway's to call me back as they were busy when I rang.

Any thoughts from anyone please advise.

You need to check your dynamic compression ratio vs your inlet valve closing angle.

Thanks guys,
I managed to get through to David at Galloway's, had a good chat.
I told him that my calculated compression ratio was 11.8 to 1, immediately, he believed the calculation appeared to be too high, he believed is should be 11.2 to 1.
David checked his records as he built the engine previously, possibly with a different head.
David informed me the Ross piston dome size in my engine was 20cc not 22cc as per my shite measurement.
He banged in the figures into his calculator and his calculation was 11.2 to 1.
I adjusted my dome height to 20 cc from 22 cc my calculator spat out a new figure of 11.2 to 1, great.

David then said he could only increase the head combustion chamber size safely about 3 cc without breaking through to the water jacket.

I also have the J motor head I had done by David earlier, to roughly the same specs but slightly larger Intake ports.
The J motor head still has the Thumbprint still visible.

The Race motor head has gone past the thumbprint.

Running new figures through the calculator, if we do the chamber work to the J motor head, we should get the compression ratio down to 10.2 to 1.

We also discussed smoothing out sharp edges to inhibit detonation initiation.

Clives Cams said 10.5 to 1 would be the upper limit and under 10 to 1 would be preferred.

So that seems to be the plan... at this stage.
I will cc the j motor head tomorrow.

Craig, I will have to do some research on what you exactly mean.

Cheers Ed.

ardiesse wrote:Ed,

That is definitely the wrong spark plug. Waaay too much reach. You want something like the Champion J12Y (13/16" hex, 14 mm thread, 3/8" reach). Grey motors take the same plugs as small-block Chev V8s, but with a different heat range.

ETA: 3-1/8" bore, 3-1/8" stroke equals 143.8 cubic inches.

Rob

Maths went wrong somewhere but using the 79.5 bore and 79.4 stroke I recalculated at 144.3cui so I assume your figures are rounded from imperial.

I calculate your head gasket volume to be 7.5cc assuming 1.5mm or 0.060” compressed height. Still don’t know deck height.

Assuming zero deck height then compressed volume = 50-22+7.5=35.5 cc. Using this I get 12.2:1, so obviously your deck height is not zero……..


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