Fuel quality and compression

[4stroker]

Ok guys im from australia, so bear with me!

 

what octane do you guys consider to be "regular pump gas"?

 

here in aus, our regular fuel, that every tom dick and harry fills there cars up with, is 91 RON.

 

Premium is 95 RON. Then most fuel companies have their better version again, which are commonly 98 RON.

 

Whenever me and my buddies go riding we use the 98.

 

But what needs to be said is that our octane ratings are advertised differently to yours. Long story short: our 91 is equivalent to your 87, our 95 your 91, and our 98 your 93.

 

What is smallest size noss dome i should put in my bike? (stock bore, stock port, +4 timing). oh yeah im at sea level.

 

can some of you who actually know their dome size and compression get back to me with what fuel your using?

 

thanks, mark

[Bansh-eman]

i ran 21cc domes on my mild ported stock bore 4mil and had like 150 psi at sea level. 87 octane or your 91 is what most people run in thier daily drivers, but when we run "pump gas" its premium or 93 octane your 98

[tgbanshee]

Every bike is different so you really need to grab a compression tester and see where you are at once you put the domes on, then decide what fuel to use from there. I have a 4mm stroker, 21cc domes, and NO porting with a spacer plate so the extra crankcase volume I have gives me 180psi compression at sea level. Yours should be lower because of the porting. I run a 50:50 mix of premium 93 and VP C-12 which is 108 MON. MON (motor octane) will always be lower than RON (research octane) and in the U.S. the pump octane rating or R+M/2 which you see at the gas pumps is an average of the RON and MON (retarded, yea I know I blame the politicians). I agree with Bansh-eman you will probably be in the 150-160psi range, and might want to consider mixing a little higher octane race gas with your normal 98 pump gas or using straight race gas if you can find it for a reasonable price and want to be on the safe side. If you aren't getting any detonation on 98, then you could run straight 98 all day long without a problem, it all depends on the bike.

[Animalman294]

Totally agree.............

[4stroker]

get this, my buddies play bike has the following:

 

66mm wisecos

FMF SST Pipes

Clean up port on intake and transfers, polished ex port (no actual timing changes)

32mm Mikunis with pods

slotted stock timing plate (prolly advanced 2 deg at the most)

 

and most importantly : Noss head with 19cc domes

 

he has run this bike like this for years on our 98 RON, (your 93). it has never had any problems, we call it "ol reliable".

 

pull the head off every now and then for a re-ring and there are no signs of deto.

 

even more interesting, the other weekend we accidentaly poured 91 RON (your 87) premix into it, and it ran like a champ all day, flogging the absolute guts out of it! (he didnt know till after he had put 91 in it)

 

oh yeah and we are at sea level!