Race gas or High test ?

[rigger]

What kind of copresion numbers should you be at to run high test and what should you be at to need to run race gas?

I have not run the motor yet due to a starting issue but a quick compression test showed her at about 195psi.

Does anyone know what stock compression number should be at?

[rsss396]

I would have to say race gas, I bet stock is about 150

[IcutMetl]

That is incorrect. 150 is pretty low and time for a rebuild. The Honda service manual states compression should be 170psi +/-15psi.

After 180-185psi range, you should start thinking about mixing race fuel with premium pump gas, and 210+ is regarded as straight race fuel range.

I tested at 195-200psi and have been having great luck with 50/50 mix of 110 and 92.

[thedeatons]

Yeah, I agree with that last post. 173psi has me running 91 safely. Some of the guys run mid 180s with 91, but that seems a bit risky.... :)

James

[deathman53]

my honda manual says to do the compression test when fully warmed up. It says between 170-199. I do them cold and my motor read 200 psi. I haven't tried it hot, I would imagine it would be somewhat higher, as the rings/piston expand, cylinder does somewhat also and there is oil in the top end sealing around the rings. There is more to race/pump gas than compression, squish band, angle, timing adv/retard and port timing also matter.

[rsss396]

didn't realize static pressure was that high but it would make sience the exhaust ports are pretty low stock.
if you have had port work done and the exhaust has been raised then I would have to believe race gas would be needed.

My 175hp arctic cat 900 in my snomo quad has only 150psi static pressure brand new from the factory but they have pretty high exhaust numbers

[1promodfan]

With 195 PSI.......running 50/50 can be a little risky in my opinion. I'm not saying it can't be done. Just don't cheat yourself now to save money, because it'll cost ya more in the long run.

[rockingkfarms]

With that compression, I would run race fuel just to be on the safe side. Another plus is it's more consistent than the gas you buy at the pump.

[rigger]

Thanks for your input guys.

[Ruf Racing]

I have 180psi and running 93 octane, with no problems.

[86 Quad R]

Originally posted by Ruf Racing
I have 180psi and running 93 octane, with no problems.

here aswell. on all of em.

[Honda 250r 001]

Originally posted by thedeatons
Yeah, I agree with that last post. 173psi has me running 91 safely. Some of the guys run mid 180s with 91, but that seems a bit risky.... :)

James

hmm, ive been gettin away with 195 and +2 timing advance on a 310 with premium 92.

[86 Quad R]

Originally posted by Honda 250r 001
hmm, ive been gettin away with 195 and +2 timing advance on a 310 with premium 92.

now your pushing it young man :eek:

[pdxbigfoot]

Originally posted by 1promodfan
With 195 PSI.......running 50/50 can be a little risky in my opinion. I'm not saying it can't be done. Just don't cheat yourself now to save money, because it'll cost ya more in the long run.
Thats just it...dont cheat yourself to save a little money. At the shop all of Arlans engines are built to run race gas, its key to getting a 2 stroke to make some #'s.
I see guys drop 3-4K on their engine build and turn right around and run 90 octane lousy pump gas.
Its totally insane to me!!!
Why would you even think about putting your hard earned money at risk??
Thats like trying to run coleman camp stove fuel in your lamborghini....somethings going to happen.
To me its worth the piece of mind to spend the extra $5 a gallon and not have to worry about all the low octane worries.
You ever try to jet a high compression engine with pump gas?? especially the 10% ethanol blend garbage that Oregon has.
Its just not good logic!!!

[250r grave yard]

i have a service manul saying 110-130 psi and tested a stock 250r and got 130 psi and it was 15 years old never touched ?

[fulltiltrider]

Going off static compression #'s is bad practice imo. I've seen drag engines with 180 psi that would deto on race gas, setup for alky. You should be figuring your uccr for octane requirements

[deathman53]

how should I test compression for a true reading? Right now, I use my gauge, screw it into the spark plug hole, hold throttle wot and kick away until it doesn't read any higher. I'm reading 200 psi, doing it like this, on a dead cold motor too.

[deathman53]

Originally posted by 250r grave yard
i have a service manul saying 110-130 psi and tested a stock 250r and got 130 psi and it was 15 years old never touched ?

I want to see this manual, my honda and clymer say very different.

[rsss396]

Originally posted by fulltiltrider
Going off static compression #'s is bad practice imo. I've seen drag engines with 180 psi that would deto on race gas, setup for alky. You should be figuring your uccr for octane requirements

I agree 100%

[rsss396]

Originally posted by deathman53
how should I test compression for a true reading? Right now, I use my gauge, screw it into the spark plug hole, hold throttle wot and kick away until it doesn't read any higher. I'm reading 200 psi, doing it like this, on a dead cold motor too.

this method does not check compression it checks the static pressure of the motor.

to check compression there is a couple ways but the easiest is to get a degree wheel and put the motor at top dead center.
fill the cylinder with a light oil using a burette that measures
cc's.

I won't go into detail unless you really are going to do it, let me know and I will help

[250r grave yard]

Originally posted by deathman53
I want to see this manual, my honda and clymer say very different. here you go

[250r grave yard]

the book cover

[IcutMetl]

What manual is that??? The FACTORY Honda service manual that's actually for a 250R says on page 2-2:

"Cylinder compression- 1,177+/-98kpa (12.0 +/-1.0kg2, 170+/-15psi"

Is that manual for a Foreman?? I think you have incorrect information; at that kind of psi, I think you'd have problems getting it to run or even start correctly.