I'm kinda excited about this latest motor build, its really been treating me well and performing to my hopes and expectations. Well one of the things that is really intrigueing is that I am running the smallest jet ever in my TM45. Apparently the vacuum created by this piston is quite a bit higher, and its sucking more fuel through a smaller jet.
This is the rwr 14:1 with the gapless 2nd and axtel cams, carb mount filter and HMF.
Back when I ran carb mount with my previous motor, all things equal except a je 11.5:1 instead of the new cp piston, I was running a 150 main (on average, depending on climate). even at 5K' on the mountain at utah a 145 proved the best hp producer. now I am running a 140 at sea level. I've never needed a jet that small, no matter what the weather was like. the only time I ever ran a 140 was in walden colorado at 9,000 feet.

Well there's 3 things contributing to this, wonder which one is the biggest hitter, and how much the others really matter? higher compression, gapless 2nd ring, 110 octane leaded (used to run 93 pump with the old piston).

I used to have a lot more blowby than I do now, you could feel it puffing kinda hard out the breather, but now its almost nothing, undoubtedly due to the gapless ring. yeah you can still feel the air puffing in and out as the piston reciprocates, but nothing like it was. this has got to be increasing vacuum in the same manner - if combustion pressure was escaping from the ring gap then vacuum would be escaping at a comparative rate. not saying its a big deal or anything, but you know how it is - every little bit counts. two ways to increase flow to the head - make it easier for air to get in, or increase vacuum.

what kind of jetting difference does the 110 octane fuel make? I have no idea.

 

I think its the higher octane maybe burning a little slower.

Ive tested different fuels at dumont with my old stage 3 dune bike and when I dumped 112 octane in it , well it fell on its face on the top end. So that is an indication.

 

yeah its burning slower, and we need the slower burn to combat the heat produced by the higher compression, but I aint so sure that's it - just cause its burning slower doesn't mean the amount of fuel needs decreased.
if I was pulling in less fuel, and buring slower to boot, it seems counterproductive to go to high compression. but to pull in the same amount of fuel, or even a little bit more, and compress it more, would equal more power, and just cause she's burning slower well a burn is a burn either way and one is without preignition.
but to throw high octane into a motor that does not have the compression to require it, that's a HP robber right there, whether the a/f ratio was right or not.

 

What comp and PSI w/ out de comp lever?

It all depends what kind of fuel your running. Some higher octanes seem to burn faster than others. I will PM ya..

 

...Careful with those PMs, you might want to just send email instead!

 

you know the more I think about it the more I can see the fuel alone being a big factor - with the sunoco 110 race fuel I am running, its got more real go juice in it than pump gas - which is more than likely got plenty of other stuff that does not contribute to power.



I hear ya, tomorrow this is gonna be a big can of worms man...

 

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Hey Hightower! What kind of increased miles are you getting now? extra 25 miles on a tank?? makes it more worth wild to Pump up the DS

 

I have experienced the same thing in my Raptor when i raised the compression from 11:1 to 12.5:1.When i changed i could not run as big of a main jet as before the bump in compression.I also went from using 93 pump gas to 110 octane as you did and to get my motor to perform i had to go down 1 full step in jet sizes.I just assumed that the extra compression was possibly pulling fuel in at a faster rate than before and it seems that you have found the same thing.I am getting my Baja motor built right now with a stock bore 12:1 piston gasketed for 11.5:1 and with HR3 cams.I guess i will have to play with the Lectrons jetting when i get my Baja back since i assume it will do the same thing.I think that there is a lot to be gained in performance if you pay attention to detail with the air and fuel needs or at least i have found that to be true.

 

Vacuum Signal Increases:

When you raise your compression, you are raising your cylinder head pressure, which results in raising the temperature of the air/fuel mixture.
When you raise the temperature of the air/fuel mixture, the thermal effects of a better combustion will result in raising the vacuum signal. The same is true if you advance your timing. With advance timing or higher compression comes the necessity to run higher octane fuel so as to control detonation.

With the higher compression, have you also advanced your ignition timing?

I recently repacked my silencer and also had to lean down alittle. An overrev design silencer will draw harder at top and cause higher velocity through head, which also increases vacuum signal.