Planet Minis

Freddie

Can I still run premium pump gas with a 12.5:1 piston?

dood

you can run premium pump with 14.3 to comp. It depends on the combustion chamber. If it isn't detonating, then you can run pump. Just make sure it's fresh pump gas and not some cheapo stuff you find out in the middle of no where to save a few cents.

Freddie

Thanks, Dood. I appreciate it.

dood

I've built a couple 150R's with close to 14:1 CR and the fuel we ran was Ultimate 4 which is only 93 octane. It didn't ping and the only reason I ran that fuel is because I couldn't get a hold of any MR-9 which is only 89 octane. I normally run MR-9 in alot of my RoadRace engines which have nominal CR's in the hi 13's with no issues.

firepower354

You bought a $150 piston and don't want to spend an extra $2 a gallon for race gas? Not such a good idea. With the high comp, it will make more power and live longer on race gas.

cyclerider57

You'll make the most power with the least amount of octane that allows you to burn the fuel at the right rate. I've ran 89 on 12.5 engines and 91 on 13.5 engines. If you are not detonating then extra octane is useless and actually creates less power.

__________________
The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

firepower354

-ish...
Until the local gas station can guarantee the exact same blend, clean and without contaminates, I'll pass on drawing fuel for MY race rides from the common well. The varied levels and types of octane increasers, aromatics, differing specific gravity, oxygenation, and a dozen other variables all make pump gas a gamble. Spend thousands on a bike and mods, then save a couple bucks per ride on horse whiz?
What gets poured in to the big orange tanks of your XR750's?

RcWannabe

Hell yeah, down here vp 110 cost 4.85 and premium gas is 3.50 + anywho long story short as little gas as these eat up I use all race gas in all of my bikes.

dood

Ok so to clear up the whole gas thing. Maybe I should have said you don't have to run 110 octane fuel. Most fuel companies do sell a low octane race gas like 100 or 104.
The benefit of running race fuels is the fact that they are more consistant as opposed to regular pump fuel. That is why I said go to a highly popular gas station to make sure you have at lease fresh gas vs driving to bum f*** to save a few pennies on gas.
I tell alot of my clients that if they are insistant on running race gas, find the lowest octane you can, and you'll be fine and make more power doing so, unless you wanna purchase real race fuels like MR10 or PRO V-1 which are all in the low 90's in octane.

Highside

Ho do you figure that you are getting close to 14:1? According to CP the stock setup only specs out at around 10.7 despite what honda claims. You can safely take off .020 on the stocker but that doesnt get there. The cp 13:1 piston puts the valves at .050 from the piston. How close are you running it? More displacement maybe?

cyclerider57

VP only for our race bikes. Buy it by the 55 gallon drum.

__________________
The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

dood

That too. Alot of guys just deck the head and throw in a Hi comp piston and call it good.
I mill the head, deck the cylinder, modify the chamber, sink the valves but also unshroud them, modify the piston to match the head mods, I could on and on.
The things I do are the same things that the factories do to their engines (because I used to work for a few factory teams) and that is the reason their engines are faster than the normal throw together engines.
Ask Cycle 57, or any other engine guy who knows his stuff. It Just takes time and patients and alot of testing.

Highside

Your the man if you can improve on that piston. .035 from deck. valves .050 and .045 from piston. 13:1 The valves take up 75 percent of the chamber so sinking them would really hurt compression. Unshrouding, yes. But there goes quite a bit of compression. This motor should not be compared to the norm though. I haven't fully figured it out myself, I have flow numbers saying that the engine should make almost 30 hp but it doesn't. HP per cc this thing stomps 450s though.

Attached Images

150 piston.jpg (51.7 KB, 35 views)

dood

You can go .023 piston to head. And as for the flow numbers, Try welding up the floors and shrinking up the ports. Intake is wrong shape, and the exhaust is just plain to big. You can make a CRF150R make 30hp pretty easily if ya mod it enough and the right fuel.
I build alot of RoadRace bikes and most ports are too big. ( except most the of the Kawi's ) You reduce the exhaust on a Yamaha R6 and you'll pick up almost 5 hp alone doing the intake to will net you another 5. I do it all the time.
And as far as the piston you are showing, It's nice but make it 3 mm bigger in bore, do some mods and measure your compression.

Highside

Sorry to jack the thread, I think your bike will run fine on premium pump with your 12.5:1 piston. As far as going .023 squish, hope its a brand new motor. I have had them hit at .025 once they get some wear. I just cant put them together like that and tell people to came back and see me next week for a refresh

dood

I build engines depending on what the client wants. I explain the reasoning behind what I do, and tell him ( or her ) the benefits and the woes of what I do. I ask where they are racing or what kind of track and also talk to the rider to see how they ride. Then they get the full spectrum of what is going on in their engines and can make the decision from there.
I'm sure every other engine builder does the same.