If you have a small airport in your area. They will sometimes sell it to you if you bring in a 5 gallon can. I purchase it at a small airport for use in storing my snowmobiles in the summer months.

 

Well the quad has a 440 wiesco piston kit in a 400ex. with and eddlebrock carb, stage 2 hot cam, white bros exhaust. do you think it should need a 100 octane mix.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Banshee1201

Well the quad has a 440 wiesco piston kit in a 400ex. with and eddlebrock carb, stage 2 hot cam, white bros exhaust. do you think it should need a 100 octane mix.</end quote></div>

It needs 100 octane if the compression is high.... I don't know what compression piston you have in there and so far I've not seen any compression numbers......

An engine's valves/cams, displacement, and intake have zero impact on octane......

You can have a 800cc engine with twin-cams, titanium valves, and a solid gold intake and it could still have a compression ratio of 8:1, and run 87 octane no problem.

Just like you can have a simple push-rod engine with 2-valves and a high compression piston that is slamming in at 13:1.... in which case you better be running at least 93......

If the octane is not right, then the other components like valves and cams can suffer stress. So it is important to run the octane you need.....

You can have two identical engines, same exact displacement, same components, and different compressions depending on the shape and contour of the piston. And of course how it relates to the shape of the head.....

If you can get your compression ratio you will know what octane you should be running.....

 

ok thanks and i belive the compression is 11.5 or 12 to 1. Is it bad to run to high of compression? Or could i just run 93 on this?

 

<div class="FTQUOTE"><begin quote>An engine's valves/cams, displacement, and intake have zero impact on octane...... </end quote></div>
This is not true at all.
Cam profile can make a big difference in whether an engine will get into detonation or not.
Many, many things can influence detonation. Timing, intake air temp, cam profile, elevation and even load can all have an effect on detonation.

To the OP, here is the deal. If the maker of the kit recomends 100 octane gas, it's a real good idea to use 100 octane gas.
Now, 11.5 is not that much compression for pump gas and "I" would try to get away with pump gas. BUT, I know the signs of detonation and how to look for them.
IMHO if you don't know what to look for, you had better use what the kit designers recomend.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Doctorturbo

<div class="FTQUOTE"><begin quote>An engine's valves/cams, displacement, and intake have zero impact on octane...... </end quote></div>

This is not true at all.

Cam profile can make a big difference in whether an engine will get into detonation or not.

Many, many things can influence detonation. Timing, intake air temp, cam profile, elevation and even load can all have an effect on detonation.



To the OP, here is the deal. If the maker of the kit recomends 100 octane gas, it's a real good idea to use 100 octane gas.

Now, 11.5 is not that much compression for pump gas and "I" would try to get away with pump gas. BUT, I know the signs of detonation and how to look for them.

IMHO if you don't know what to look for, you had better use what the kit designers recomend.</end quote></div>

Well as I said, those components can be affected by running the wrong octane, and in concert with a higher compression piston require higher octane. Getting to the compression is not the compression itself.

Those components can be run with lower octane if perfect compression is achieved properly by using that lower octane. The octane in the gas should not affect how the valves are closing off and when, if compression and ignition are perfect.....in theory.

But you're right when you consider the engine as a whole, I was generalizing to make a point.....the wrong octane will stress those valves and affect compression on the next stroke.

But at 11.5:1 compression you should not need 100 octane..... by all means it won't hurt anything running 100 octane so if you can stomach spending the cash go for it.....

But a z400 is just about the same compression as that, and running 91-93 octane in that DOHC engine is fine.... The 400ex is a much less complex push-rod engine and I would think at 93 octane for 11:5 compression should keep things in time.

 

I would get with your engine builder or the kit builder and ask them what they recomend.
Like Doctor Turbo stated thier are allot of differant things that can contribute to detonantion. I am running 13:1 compression on my Busa motor in my bike and I am running 91 Octane pump gas. I can do this becouse my engine builder set up my Motor and my Computer system mainley the timing so I can run pump gas and still get the horse power out of the motor. If you did this on most motors with out setting it up properly you would have massive detonation and probably melt a hole in your piston or valves.
Good luck with your bike.

 

<div class="FTQUOTE"><begin quote>Originally posted by: tramp

If you have a small airport in your area. They will sometimes sell it to you if you bring in a 5 gallon can. I purchase it at a small airport for use in storing my snowmobiles in the summer months.</end quote></div>

Thats AV gas and completely different subject. [img]i/expressions/face-icon-small-wink.gif[/img]

 

<div class="FTQUOTE"><begin quote>Those components can be run with lower octane if perfect compression is achieved properly by using that lower octane. The octane in the gas should not affect how the valves are closing off and when, if compression and ignition are perfect.....in theory. </end quote></div>
I don't understand what your trying to say?

What I'm trying to say is this. I can build a 12 to 1 engine and stick a high bleed high overlap cam in it and run it on pump gas all day long with no ill effects.
I can take that same motor and put a high capture cam in it with no overlap and blow the thing up on the fist past with pump gas.
The reason is the cam and the cam only. No change in static compression at all. Just more cylinder filling with a higher efficient cam.

Another difference "can" be the carb. If I put a little carb on a given engine and if it does not detonate, and then change that carb to a BIG carb, I will now have more of a chance for detonation to show up. Now you need a big difference in carb size for this to show up.

This is the same reason blown engines get into detonation so easy. It's all about cylinder filling.

 

Doc,

I'm agreeing with you..... I was just saying that if he does need the extra octane, it is mostly because of the piston.... The other components need to be tuned for said compression....... we are saying the same things but in different ways....