what octane? 20cc Domes.

[POORBOY350]

i have a 421 cub with 20cc domes and +4 timing. was wondering if i could run 93 octane fuel in it. i usually run 111 but it is a long way away when there is a store right up the road i could go grab some 93 ya know. would it be better to stick to 111 or what. thanks for any input.

[Wildcard2]

what is your compresion?

[rtcc]

Yeah you are gonna have to check your compression. I run 93 with 20 domes but I dont know if a cub changes anything or not. Im pretty close to the edge of running pump, but I am at 1000 ft or more. If I was at sea level I think I would have to do something different.

[POORBOY350]

DONT know what compression is. dont know how to do a test. do have a tester. i am on gulf coast. im prob at sea level or lil about not much. right on the coast. also rtcc love your bike dude.

[Snopczynski]

Your gonna need to check the compression, also checking the squish would be a good idea too. No way of nailing it down without the compression check because your obviously running a stroker that could have about 5 different ways of being setup. All these different ways will effect compression and squish.

[POORBOY350]

thanks alot everybody. but im going to bring it to a guy i know who will prob have a comp test and can tell me the sqush. i will get bakc with yal. i'd like to get it dialedd in good obviously.

[05.Banshee.SE]

At sea level 20ccs are odd.

 

I've seen some 20s that need race fuel, and some that don't.

 

 

It changes from bike to bike....we'll see what your numbers are though!

[dajogejr]

Seeing as how cubs are prone to deto and you don't know your compression ratio....run the 111.

[2001Stroker]

I have 18cc domes at sea level, with stock cylinder 421. My compression is 180psi. So, I run 110. You might be able to get away with mixing 50/50 93 and 110. I don't know what kind of different gasses you have around there, but here we have 100, 105, 108 oxidized, 110, and 113. All are off-road, leaded gasoline. You might consider trying to find some 100 or 105 around you somewhere. Call a local race track, or racecar shop.

[Snopczynski]

This is going to vary by crank manufacturers, piston brands, spacer or dome cnc tolerances, and base gasket thickness. So the only real way to answer this is, check your compression first.

[Bansh-eman]

there are so many variances. On my cub with 20cc domes i had 185 psi and 40 thous squish, I sent it to be drag ported by K&T and no have 18cc domes and 42 thou squish and my comp is 165... dont try and ball park it based off someone elses motor, get a tester and check it. differant piston and dome angle will make a differance. not somthing that your going to be able to make a calculated guess just basing a few general numbers off of.

[THE GRIM RIPPER]

What he said.... But at the end of the day, more octane isnt gonna hurt! Run what ever high octane you can get.... Fuck pump gas

 

(I spoil my banshee)

[rubberneck]

My 421 Cub with 20cc domes at sea level pushed 185-190 PSI depending on the tester. Yes you need to check squish and compression, but im betting the farm, you will NOt be able to run pump gas on that motor. I would stay with the 110. If you do the math on that combinaton the uncorrected compression is about 14:1 too high for pump.

[J-Madd]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[POORBOY350]

as long as 111 wont hurt it or is better for it i have no prob rinning it. i like the smell lol. but i still have alot to learn about these bikes. thanks for all the info its great.