High Compression Numbers?

hell, pour some 110 octane in her and see how she rips, just make sure you have some cold plugs in it :woohoo:

Thanks for all the input guys - I picked up a new compression tester tonight and will run some tests again tomorrow.

I think it is probably true that the gauge is just not correctly calibrated, but I would like to think that she's been shaved, ported, etc. Performance would suggest otherwise though...

Whatever the numbers, I guess it is at least encouraging to know that there is only around 5% discrepancy between the cylinders. I'll post my test results in the near future. I am also planning to do the WiredGeorge coil mod as mentioned in some other posts - sounds like it may be just the ticket to some of my problems.

-Pete

steell wrote:

KaZooCruiser wrote:

220 psi / 14.7 (atmospheric pressure at sea level) gives a 14.9, almost 15:1 compression ratio.

I'd use another gauge.

The bikes are listed at 9.5:1.

Only the GPz750 is 9.5:1, the others (650 and 750 fours) are 9.0:1.

And you keep forgetting to factor in heat to that equation, air does get hot when it is compressed, and when it gets hot it expands.

150 psi would be a 650 with really good ring and valve seal, as in freshly broken in. The low milage 650's I have checked averaged 135 PSI hot.

Steell is correct as usual.

I put the compression guage on my motor 2 weeks ago and they all came in around 145-150. The motor has 2000 miles on the 810 rebuild with 10.25 to 1 pistons and a 0.010 haircut on the head. It makes plenty of power:)

Cheers-Colin Firth-Ontario Canada

steell wrote:

KaZooCruiser wrote:

220 psi / 14.7 (atmospheric pressure at sea level) gives a 14.9, almost 15:1 compression ratio.

I'd use another gauge.

The bikes are listed at 9.5:1.

Only the GPz750 is 9.5:1, the others (650 and 750 fours) are 9.0:1.

Not often information is helpful, but sometimes it is. . .from KZInformation here on the board. . .

1978 KZ 650 SR
Written by kzrider
Sunday, 03 September 2006
Identification
Letter designation D1
Color Candy persimmon red
Frame # KZ650D-000001 ~
Engine # KZ650DE000001 ~
. . .
Engine
Type 4 stroke, DOHC, 4 cylinder, air cooled
Bore and stroke 62.0 x 54.0 mm
Displacement 652 cc
Compression ratio 9.5
Maximum horsepower 60 hp @ 8,000 rpm
Maximum torque 5.8 kg-m @ 7,000 rpm

my bike makes 180psi with the wiseco 1171 kit rated at 10.25:1

that estimates to 12.24:1

Doh!:pinch:

If the compression is really that high I'm surprised the battery will crank the engine when all spark plugs are in. Ed

steell wrote:

KaZooCruiser wrote:

220 psi / 14.7 (atmospheric pressure at sea level) gives a 14.9, almost 15:1 compression ratio.

I'd use another gauge.

The bikes are listed at 9.5:1.

Only the GPz750 is 9.5:1, the others (650 and 750 fours) are 9.0:1.

My 650 B2 owners manual says compression is 9.5:1