Race Gas questions.

[Doc]

I am told that I can't run regular gas in the Duc. It has a compression of 10.5:1 (doesn't seem all that high) and I was told I HAVE to run C12.

Anyone disagree and can give me a good reason why?

Also, Since I HAVE to run C12... What kinda storage issues am I gonna have with this stuff? Should I drain it out of the Tank and Carbs between race weekends? How about over the winter. Will it be good until next year if I don't use it all or should I just throw it in the lawn mower/ snowblower?

[Scottg22]

Doc,

I was not they guy you spoke with at the VP truck the other day.... but I would recommend running the C12.

A bike with motor work, you should use C12. MS93 or pump gas will not have enough octane and may cause detonation in the heads and eat your motor up. I know this from Expirence. I lost 2 motors in my 06 R6 this season after 1 weekend each motor because I was determined to use MS93 as it was "just a supersport engine". Well I was miserbly wrong and its cost me 1000's of dollars and missed Yamaha Contingency Money !!

I spoke with the Yamaha guys (specific to my problem) and they felt I had a timing issue.... but after the last motor popped... there was missing aluminum inside the head, around the seats, around the spark plugs threads & 4 valves were eaten (missing chucks off the edges).

Anything with higher compression, for 6.50 or whatever they charge... do yourself a favor and RUN the C12 ! Plus VP pays contingency in 2 classes on the C12 vs. 1 class for running MS93.

As far as winter storage, C12 is unoxygenated so there is no issue with leaving it in your bike all winter. Best to fill the tank, add stabilzer and run the fuel/stabilizer thru the system. Bruce from BCM/Meyers Performance recommends FOGGING the engine as well.

Scott

[Doc]

Ohh.. Your THAT Scott G!

Thanks for the tip. I will run it and leave it in the tank. (and Fog it)

[Scottg22]

You guys have it all wrong.

I am THE ScottG

And Doc, you never came up and asked for help while at the LAPS day. Next time maybe?

[Evil_Weasel]

10.5:1 is fairly high for an air cooled motor.... wouldn't raise an eyebrow about it in a liquid cooled bike. best run the C12...a little extra (not excessive) octane is better than not enough. look at it like insurance...expensive, but i hear those duck parts are pretty pricey to.

[Doc]

You guys have it all wrong.

I am THE ScottG

And Doc, you never came up and asked for help while at the LAPS day. Next time maybe?

Hell yeah next time! Sorry I was kinda preoccupied with finding C12 to put in the Duc, (never did and ran 93 :oops: ) fixing my Hawk that Oxx crashed and dealing with Buddha's head injury.

Next time it is. Thanks again Scott.

[978chris]

10.5:1 is fairly high for an air cooled motor.... wouldn't raise an eyebrow about it in a liquid cooled bike. best run the C12...a little extra (not excessive) octane is better than not enough. look at it like insurance...expensive, but i hear those duck parts are pretty pricey to.

How come you're more worried about using it for an air cooled motor with said compression ratio than for a liquid cooled, yet Doc hasn't lost an engine yet and this other guy lost 2 R6 motors? The R6's were liquid cooled, no? What was their compression ratio(s)?

Am I misunderstanding something?

Under what conditions do these problems with low octane vs. compression ratio present themselves? Are we talking just for the track here? If so, what characteristics of riding a track vs. riding the street create these issues? RPMs and engine heat etc?

Or are you saying to run this gas in this bike at all times, street or race, due to the compression ratio?

I'm not trying to be an ass, I'm trying to understand the information being exchanged here. Streetbikes are about the only things on 2 wheels that I have not raced and I'm seriously thinking about giving it a try. Just trying to understand the why's of what you're saying here.

TIA.

[Trackday Guru]

You guys have it all wrong.

I am THE ScottG

And Doc, you never came up and asked for help while at the LAPS day. Next time maybe?

Jeesh! Here we go........LOL

(Scott- Kevin has your DVD)

[Doc]

I haven't lost an engine because it was run with C12 before. This is the Pit area so we are talking race engines. I would assume higher revs and heat. I hope that helps a little.

[Wishbone]

stock r6 is about 12.4:1

stock 900ss is about 9.2:1

docs motor is 10.5:1 so that is a significant chance over stock

were as a 10.5:1 compression on an r6 would be no big deal and run pump gas.

ANY engine running with to low an octane for it will cause pre-detonation and will make it one big paper weight. If you try to run higher octane than needed to make more hp then you will be "pissing up a rope" -PK

[Honclfibr]

Because "this other guy" is Scott Greenwood, the current LRRS lap record holder

What causes detonation? Temperature and Pressure. Liquid cooled engines more precisely regulate the engine temps, which reduces the chance of detonation. Air cooled engines, as the temperatures rise above nominal, become more susceptible to detonation and therefore need a wider margin of safety than liquid cooled engines, all things being equal.

How come you're more worried about using it for an air cooled motor with said compression ratio than for a liquid cooled, yet Doc hasn't lost an engine yet and this other guy lost 2 R6 motors? The R6's were liquid cooled, no? What was their compression ratio(s)?

Am I misunderstanding something?

Under what conditions do these problems with low octane vs. compression ratio present themselves? Are we talking just for the track here? If so, what characteristics of riding a track vs. riding the street create these issues? RPMs and engine heat etc?

Or are you saying to run this gas in this bike at all times, street or race, due to the compression ratio?

I'm not trying to be an ass, I'm trying to understand the information being exchanged here. Streetbikes are about the only things on 2 wheels that I have not raced and I'm seriously thinking about giving it a try. Just trying to understand the why's of what you're saying here.

TIA.

[TLRMan]

Because "this other guy" is Scott Greenwood, the current LRRS lap record holder

What causes detonation? Temperature and Pressure. Liquid cooled engines more precisely regulate the engine temps, which reduces the chance of detonation. Air cooled engines, as the temperatures rise above nominal, become more susceptible to detonation and therefore need a wider margin of safety than liquid cooled engines, all things being equal.

There's a little more to it than that....but you are on the right track...
So why is it I can run 91 octane safely in my TLR with a comp ratio figured at 12.8 to 1?

[Kurlon]

I know of street 944 kitted motors with some silly compression running pump gas. Did you cam that motor at the same time Doc? If so your dynamic compression will likely be far lower than the static compression listed for the piston. (Cam overlap sneaking into the equation here.)

[Wishbone]

ok stupid question.

I want to bump the compression on my 02 fz1 since the jet kit I am running says it worked best on 87 octane soooo...what is the best way to go to bump compression so that I would run 91? I know thinner head gasket, how about decking the block and heads? If so where could I take my motor to do that? what else would you guys suggest?

[Kurlon]

If you can find replacement pistons, I'd go that way, that way you can revert later on if you want. No custom work, no milling too much by accident and then having to flycut the valve reliefs on the pistons, etc.

[Wishbone]

Pistons alone can bump compression???

If so why not just get over sized pistons?

and if you milled to much then had to fly cut the piston wouldn't you loose the extra compression you just gained by decking the head?

[Honclfibr]

There's a little more to it than that....but you are on the right track...
So why is it I can run 91 octane safely in my TLR with a comp ratio figured at 12.8 to 1?

Do you mean compared to a car, which at the same compression ratio would require higher octane gas?

I've often wondered that myself. The only answer I could come up with is that the smaller bike engine generates less heat and has more efficient cooling compared to a car engine?

[TLRMan]

Do the math and figure what clearances can be had 1st.
Most engines with stock cams can afford a bunch of squish pulled out, and still miss. I did several things with the TLR, on my 2 cycle engines, I remachined the heads including shapes, and squish angles.
The TLR and all engines for that matter run BETTER when you can get the piston as close to the head as possible. Several things happen here. End gasses that would normally fall out of suspension won't, because of the added squish velocities. Detonation (or auto ignition) can occur when the flame front compresses the pockets of fuel that end up on the edge of the piston. Larger diameter bore engines with short strokes will have more of a problem with this, because of flame prorogation, and how long the piston resides at or near Top dead center. I solved one problem with piston velocities by actually making the connecting rod longer, NO NOT STROKING, it required the placement of the wrist pin to be higher in the piston, which in some cases will require fabricating pistons to relocate the oil rings....anyway...with a longer rod, (less angle now) the piston resides longer at TDC, and takes a little more advantage of cylinder pressure as well. With higher RPM engines (Scott G's), the use of Shower injectors are a MUST if you are going to count on that fuel to TOTALLY vaporize once in the cylinder...Fuel not in an atomized state will cause pockets, and detonation. Race fuels are formulated to atomize faster than typical pump gas, and can support higher RPMs.

Back to TLR..with squish clearance set tight, Yup, piston is missing the head by about .035" , you can then figure how much if any you want to skim off the heads...Did I say the cylinders are machined at the base to deck it?
You must have a way to measure the TOTAL VOLUME inside the engine, pistons aren't flat, and heads aren't either! To come to a reasonable compression ratio...If you are running cams with more overlap, like mentioned earlier, that will have a play with corrected compression ratios.

So by getting correct clearances, OH! BTW... cam timing retards when you deck engines, so go out and buy your cam degree kit and sprockets, cause you are gonna need those too....You can get a reasonable amount of power increase, and get away with running lesser octane fuel than you would if not setting the squish clearances tighter...so I can, and will run 91 Octane in my 12.8:1 TLR without a problem....

See simple huh?

[OreoGaborio]

but how much octane could an octane chuck chuck if an octane chuck could chuck octane?

[Wishbone]

See simple huh?

Yeah I was just gonna post the same thing

So if I brought you my mota could you measure and then tell me how much I can deck the block and head? Then do you know or are you a machinist that could do that? Also was looking at porting and polishing my heads while there.

[TLRMan]

but how much octane could an octane chuck chuck if an octane chuck could chuck octane?

Octane does not horsepower make...Octane corrects issues related to timing, compression, and poor head designs..but not so much poor, it all has to do with round valves and where to place them...it's a mechanical issue as well....

[TLRMan]

Yeah I was just gonna post the same thing

So if I brought you my mota could you measure and then tell me how much I can deck the block and head? Then do you know or are you a machinist that could do that? Also was looking at porting and polishing my heads while there.

One of the BIGGEST mistakes is to port too big!
Bigger doesn't mean better...you have a race bike that needs to still have power to drive out of the turns..Going bigger may make the engine perform worse...
BTW..NEVER polish the intakes... you can go nutz with the exhausts..but you are asking for it if you make the intakes all nice and shiny! You should work on velocity of air instead of volume of air...

[Wishbone]

Very good to know! If I couldn't find a shop I was gonna polish the crap outta them

[OreoGaborio]

Very good to know! If I couldn't find a shop I was gonna polish the crap outta them

I'd polish the rest of the bike, first if I were you

[Wishbone]

I'd polish the rest of the bike, first if I were you

Yeah thats the problem, I care more about the go and less about the show