I've just sent a message to a seller on eBay about the compression ratio of his mild engine, he replied a compression test showed 215psi.

What the???

Is that the right?
Shouldn't it say... **:1?

_________________
Santo

"The Lone Ranger"
HI-HO Silver......AWAAAAAY!

nah, thats nice and high, which is good for POWA

Do you know how to convert that to **:1?

_________________
Santo

"The Lone Ranger"
HI-HO Silver......AWAAAAAY!

no, but 215 psi is very good

You cannot convert the PSI figure to comp ratio very accurately but you can guess.
My HQ race car used to give about 230- 240 on the gauge and it was about 12.6:1.

(useless tip) If you want the gauge to read higher tip some oil in the hole. The more oil the higher the reading. (/useless tip)

So you could probably guess it would be around 11:1 ratio.

Not bad i spose!

_________________
Santo

"The Lone Ranger"
HI-HO Silver......AWAAAAAY!

Or his gauge is stuffed! If it had 11:1 it would ping on nearly every fuel. And it would be hard on starters.

It is not really this simple- if the motor has a long duration (ie sporty) cam, this will reduce cylinder filling at cranking speed, the result will be lower readings than with a stock one, at any given C/R.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

My starter motor died recently and i had it replaced with a second hand item for $55. I thought my battery was sick since it would crank slowly and sometimes sound like it was struggling to turn the engine over. I tested the battery and it was apparently fine.

Could the sluggish cranking be a result of my higher than standard compression? I'm running 9.4:1 at the moment. Is that enough to make a noticable difference?

Sorry if this is considered thread jacking but i guess it's sort of on a similar topic.

_________________
- Simon -

At 9.4:1 it should crank fine. Mine is running 10.7:1 and spins fine with a factory recond Lucas and a 550CCA battery.
Could be your starter is dodgy, methinks- I had one like that, allegedly reconditioned...

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Difference is that i don't think it was reconditioned... should i have expected a reconditioned one for $55? That seems pretty cheap.

_________________
- Simon -

No, but it should spin fine under load. If not, take back if possible.
You can get an idea of how good the brushes in it are by spinning it with your fingers- if no drag at all, it needs new brushes fitted.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

My LS runs at roughly 10:1 I'm told. is that good?? im clueless at the end of the day when it come to technical mechacanic stuff

What you can run at boils down to fuel type, cam duration and intended use. 10.0:1 is reasonable.
I run 10.7:1 now on the street with an RE282, with this cam it could stand a bit more.

For an RE13 and street use with 98 octane fuel though 10.7 is about it, I found 11.0:1 a bit high... it pinged then.

For track work only you could go up more, as the motor never gets lugged.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I would also check/tighten all your earth leads and battery earth strap - you may have coincidently loosened one when changing over starters.
KB