Omc 3 cylinder comparison

[Powerabout]

Hounddog
can you run 160 psi with pump gas in Canada?

[phillnjack]

what is with the talk of 160psi

is this what yourgetting on a compression test or what ?
in the uk when talking about cylinder heads we talk of different measures .

yes we do say things like high compression , but then it goes to the ratio.
so 160 to me sounds like your compression test.

such a big difference in the way things are described between usa and england.

and whats with the canada pump cause talk ? is that very high octane or low octane ?
in uk our average is about 90 octane.

phill

[Powerabout]

what is with the talk of 160psi

is this what yourgetting on a compression test or what ?
in the uk when talking about cylinder heads we talk of different measures . ( No you dont)

yes we do say things like high compression , but then it goes to the ratio.
so 160 to me sounds like your compression test.

such a big difference in the way things are described between usa and england.

and whats with the canada pump cause talk ? is that very high octane or low octane ?
in uk our average is about 90 octane. ( you need to know if you are talking RON or MON, Tesco Momentum99 is 99 RON 87 MON)

phill

phininjac
I'm from OZ so I know both systems,
compression ratio on a 2 stroke doesnt work like a 4 stroke as a 4 stroke is measured as a percentage of total cylinder volume ( useless when you have ports in the cylinder), hence the industry uses cranking pressure and even sometimes measures the cranking rpm to create a specification ( like with the ignition systems)

Pump gas
The numbers are different in different parts of the world as some use RON and some use MON ratings and they do not directly convert, I think Canada same as US, UK same as OZ
AV gas has international standards for obvious reasons and both are now called 100, 100LL ( has more lead than automotive ever had)its blue and plain old 100 its green has 3 times more lead (MON ratings)

PS ther are a few language barriers
torch = gas axe not flashlight
Beer = ??
box wrench = ring spanner

[Hounddog]

Hounddog
can you run 160 psi with pump gas in Canada?

We kept the rule very simple. Yes, we are talking 160 lbs on the compression gauge. The head we use is the spec head for the SST60 motor. On the SST60 motor that head produces 180 lbs compression. We tested different heads on different motors to find one that improved the performance and was easy for a racer to get. The motors have no problem running on premium pump gas. This is the head we use for the bridge port fishing motor. That motor had the 4 spline crank from 1986 until 1988 and it is the same spline as the 49, so racers do not have to change the crank. The later 56 fishing motor is an oval port motor and it requires different head.

[phillnjack]

so you are using a head with a smaller squish clearance then to give higher compression.
whats is or would be the problem of shaving off a couple of thou on the later 56ci to bring the compressin up higher ?

I would think anyone with a slight bit of damage to a head would have it skimmed to re-use anyway.

I get 145 compression with dry cold testing on a 56ci bog standard motor, if i was to skim the head by a few though
then this would probably be taking me to 160+ psi.
or is it that the later heads cannot take any skimming due to small squish clearance ???.

well what about doing a few improvments to the head on the later engines ????
or is something not right about them for modding ?

phill....

[Hounddog]

One last try.
Here is the SST60 spec sheet
http://www.apba.org/sites/all/files/documents/60.pdf.
The head is a cut head that measures 28.5 CC. Same stock fishing head shaved down to that spec.
That head on a 86 to 88 bridge port, non decompression, fishing motor gets you 160 lbs compression.
It will be different of any other block.
Since you have 145 compression then I am guessing yours is a later model oval port motor. For that than motor we take less off the head to arrive at the 160.

[tumblweed9999]

FYI for you guys ....I think I see the sought after "lighter 72 flywheel" on ebay today. Its sitting on a complete 49 cid powerhead in Florida. advertised as 1973 Johnson. I have both flywheels and I'm pretty darn sure thats the one. has the skinny teeth. http://www.ebay.com/itm/1973-Johnson...6e4946&vxp=mtr ... seller is leeannmcil can anyone confirm that?

[phillnjack]

"Since you have 145 compression then I am guessing yours is a later model oval port motor. For that than motor we take less off the head to arrive at the 160. "

How much is shaved off the head of the later oval port ? and what would be the limit that can be taken off ???

phill

[Hounddog]

We have only surfaced the block and the head on that model. We think? That is all it needs to be competitive in our T class.

[phillnjack]

But if one wanted to go to the extrem what can be done with the later 56ci.

is there any mods that can take this engine a lot further ? or would it then become unreliable.

would the 56ci later 70hp be a lot more powerfull than say a sst60 if these mods were done to it ?

i ask as in the uk, it seems that the later 56ci engine is the one thats being used for racing and it
is breaking some of the records.



phill