Question, from reading past threads it seems that you can get away with lower octane at higher altitudes.
Now I am going to be replacing my stock piston here pretty soon with a high compression model and my thing is since the altitude here is around 4800-5000ft. could I get away with a 12 to 1 piston on pump premium, my better judgement says no. Every thread I have read says a max of 11 to 1.
If this not possible what sort of mix would be safe to run(race gas-pump)?

 

Help please

 

I would not risk it. Even if your comp dropps at higher elevation Your motor will last linger with a cooler burning fuel. Avoid detonation.I would Pay the extra $ for the better fuel and higher octane... JMO

 

I totally agree with ANNIHILATER. You will be playing with a bag of snakes. Are you going to get bit? Maybe, maybe not. There are a lot of things that will contribute to detonation.
If your really set on doing this, keep a CLOSE eye on your plug. If you don't know how to read a plug your going to have to learn real quick.
The harshest your engine will see is when it is hot, dry and with a heavy load. Keep a really close eye on your plug when under these conditions. If you see any signs of this, start mixing a gallon or so of race gas with a 5er of pump gas.

 

Thanks for the replies gentlemen. I am not dead set on being a cheap a$$ it is just from what I have heard you want to run the lowest SAFE octane for best performance. What are some of the better fuels available? Thanks again!

 

VP has a whole list of vuel as you know. The thing you want to look for in these fuels is the spec gravity. The VP chart will tell you what fuels that are designed for 2 strokes or 4 strokes. There is some good 100ish octane unleaded fuel that makes good power. You may not want to get above 100 if your truely 12.1. See what psi you are running and go from there. Even with the sleeved 720/730s the heat is what will pop a head gasket loose. I check my temp after every run LITERALLY. You should be fine with 100, especially from VP. I would also get an in-line temp guage from ESR. The temp guage can tell alot IMO even if its a water temp.




Pick your poisonnull

 

Annihilater thanks man! Im just running the stock bore nothing major. Just one more question do you run leaded or un? whats the pros and cons of each? I am going to be starting her up this weekend for the first ride in well over a month[img]i/expressions/face-icon-small-smile.gif[/img] this rebuild Im adding 12:1 comp piston from MRHP and a lectron also porting the intake. OK so I lied I have another question how do YOU break-in your DS after a rebuild I have heard so many different things. And many thanks for the link!

 

ATK's run 12.5-1 stock. My friends and I run on 91 octane. My motor has 100hrs and it hasn't had a problem w/ our 11,600rpm redline.... We ride at LS, Utah 5000ft. I run mx races also on 91 octane..

 

Mongo--I break my motors in kinda slow in the beginning. Many may argue this opinion. I tried to break a 400ex in hard and it ran like a dud throughout its life. Many will say ride it like ya stole it. They can think what they want. With new pistons and rings and sleeves etc.. IMO breaking it in slow and easy for the first few hours might prevent some probs. Of course you can go through the gears and blurp the throttle and let it get to operating temp. Do a few rides and let her cool off a few times. Watch the temp and make sure you dont have any bubbles in the coolant system.
I run leaded fuel specifically designed for 4 strokes. It seems to keep everything lubed a little better.

YA ya ya People say a top fuel dragster run hard on a fresh motor, But do you really think they have time to break a motor in. NO, If they make a pass in a 1/4 mile and blow something up they have no time to break a motor in anyways.

Just dont hold your bike at high rpms in the beginning. Just to be safe. Run through the gears and all but dont open it all the way up untill the rings are seated after a few heat cycles. This is how I broke my last motor in and it has held up strong for 2 years. Thats a fact...... (knock on wood) I can get through a few more months of running the hills.

Ya some bikes can handle lower octane w/ 12.1 comp like the yfz. Thats probably due to a different chamber that is designed for lower octane. Just be safe with it and youll sleep better at night, OH and check your oil res filter!! Make sure its clean totally.

with my testings, c-14 burns nice and cool, and unleaded may fire faster than some leadeds and burn a tad more hot.
I also change my oil after every weekend.

 

ANNIHILATER said:

>>I break my motors in kinda slow in the beginning

Mario, I'm still trying to build the visual of you riding slllooooww. Not happening.....I keep seeing 100lbs of sand flying into the air when you hole shot. You must do the break-in at Armogossa or something...

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