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MG Midget and Sprite Technical - CCs in 1500 HG

Does anyone know the compressed volume of a 1500 head gasket please? Ignoring the recess if present.
Thanks.
Peter Burgess Tuning

If you don't know Peter, we're all in trouble!
Jeremy MkIII

Peter,
I might have this wrong but is this what you mean -

"Head gasket volume: (0.040") x (pi) x (2.92"/2)^2 = 0.268 cu in * (2.54)^3 = 4.4 cc"

"The thickness of the new Payen-brand headgasket (0.040") was measured to approximate the volume between the head and block.
Similarly, the thickness of the old compressed head gasket was also measured. Somewhat surprisingly, both gave the same value of 0.040". It was expected that the old gasket would be somewhat thinner due to compression between the head and block."

From - 1973 Triumph Spitfire 1500 Project - http://73spitfire1500.blogspot.com/2016/03/engine-rebuild-part-13-combustion.html


Nigel Atkins

You might have already seen this with the 1500 spec missing but the Spit Mk3 and Triumph 1300 are shown as 4.48cc - https://www.teglerizer.com/triumphstuff/spitheads.htm
Nigel Atkins

Just measured up my old, used Payen headgasket. Approx 1.7mm around the fire rings +/- a few 0.01 of a mm.

Fire rings on my clean block seem to measure 30 thou (0.76mm).

So gasket volume ~ 0.94 x (pi x (73.7 / 2)squared) = 4011 mm3

4cc give or take a nats nadger.

Malc.
Malcolm

Measuring other bits of the gasket, away from the rings are anything between about 0.82 to 1-ish mm. It's a bit all over the shop depending where you measure.
Malcolm

Thank you everyone, I can now work out the CCs for a race midget engine. Trouble is I only have the head and the info flat tops and flush at TDC :)
Peter Burgess Tuning

I think this is only about the third full race Midget 1500 head I have done. The chambers measured 43 cc which worked out std 9.1:1 CR with 4cc for gasket. The new ccs required is just over 30, the maths says 158 thou off, will stop at 140 and burette again!
Peter Burgess Tuning

What's the target compression then? Something like 11:1? I remember taking a hefty chuck off mine just to get it to high 9s.

I would love to see the build spec and resultant output figures. But I wish people would stop building cool 1500s before I get chance to finish and show off mine for a bit! ;-)

Malc.
Malcolm

Hi Malcom
Target 11.8:1 slightly oversize engine, allowing 1 cc for annulus on piston to bore. It ended up we skimmed 150 thou off the head. Sadly I will not be involved with the build or rolling roading as far as I know :(

The ports are round about 31.5mm at smallest point so enough theoretical flow for 170+bhp. I think that may be quite a target though!
Peter Burgess Tuning

This thread was discussed between 13/02/2021 and 17/02/2021

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.