I want to jump from Trinity 25percent to Mugen 40percent. I know I would have to reshim the motor. I hear from local experts that the mugen 40 was the way to go. As long as I pick a fuel with good lubricity I should be good right?

i wouldnt do it... i have tried 30%, 25% and 20% on .21 engines... i now like 20% best coz i can still get good power and run reasonably cool. but i save about $1 a litre on nitro that i dont need

What size engine are you running? Are you running offroad or onroad?

My idol......

I'm gonna be using it in my STS D5 mounted in my Prospec.

To be safe I would put two .1 shims in the motor.

you cant get a better answer than that (mike)

but doesn't 40% kill microcast piston motors.

i busted a brand new rex rer12s3 motor last vegas race. two practice runs with 40% byron and the motor lost compression and was gone. (motor had extra shim also)

motor was broken in properly of course but with 30%.
i used 40% in vegas to have that extra edge but unfortunately, i lost the motor.

i spoke with dennis richey about this and he said i wasn't supposed to use 40% on my motor. but if i had the older piston style (not microcast), they are safe to use with 40%.

No, from what JP has told me that it is safe to run up to 45% nitro. I run 30% for runtime issues but the guys on are team that use 40% do not have a problem.

are the jp motors equipped with microcast pistons?

you know it may be the byron fuel also. i've never liked byron fuel. but i used it for a while earlier this year to save some money because they are cheaper. but now i'm back to using odonnels again which i've used consistently since i started racing rc cars. but i'm going to try the mugen 40% with my microcast motors.

Yes, The JP's are with the microcasted pistons.

Mugen fuel and Byrons fuel are the same.

there must be some other factors i did wrong when i was in vegas then. i'll do more research and testing and hopefully i don't spend too much in the process.
anyways, thanks for your quick replies.

Hey Mike did you use the new Jaco's for the Nat's? I want to see a picture of them.

i run only 15% in my RBC4, i tryed 25% but it ran crap like it was to rich,
so i thought what is the point of shiming to go higher in nitro, just to keep the engine cooler? it has heaps of power already and is running cool.
a colder plug helps with higher nitro as will dosn't it?
it seemed while it had 25% in it it needed to be leaned up quite a lot, but i was not to keen on doing that because this reduces the engines lub
what do you guys think?

No, I ran Kawahara tires at the Nat's.