U4.2 ?'s about jetting

[Hillclimb#42]

Hey guys,
 I tried to search for some answers, but came up short. If you have already explained this please point me out to the old thread.
I contacted VP about running one of their race fuels in our bikes. One guy on our team already runs U4.2 in a 79 H2 Triple(and a Banshee). Also have several friends and competitors who run the U4.2. I, of course was initially interested in the Q16, as Stewart highly recommends it. Their Rep seemed surprised that I would be asking about it unless my bikes were very high compression. We actually have 9 bikes that are going to run on the same fuel. The Rep gave me a quick education on bang for the buck, and I came to the conclusion that C12 is the best all-around fuel, and U4.2 is better power than that. The down side being that(according to the sales Rep) the U4.2 is harder to jet. He said that every 20 degrees of temperature change, I would be adjusting jetting. I am a little discouraged about those prospects, but am hopeful that this is already worked out by some of my kxrider buddies. We often have the first round of racing during the peak temps of the day, and the second round under the lights finishing up sometimes 11:30- 12:00 at night.
 Now, I have heard plenty of varying stories, philosophies, and comments, from guys not on the web, but I am having some issues with making a common sense approach out of them. Most competitors are not changing their jetting between rounds. BUT, I have heard plenty of mystery jetting sounding issues in the hole, that seem to be better on the Sunday race. I've heard many things. Bikes smoking, sounding as fat as any bike, while in neutral, then dump the clutch and be like a rocket, so doing the norm with the U4 is difficult, I guess is what I'm saying.
  Anyone have a technique for staying on top of jetting issues with U4.2? Jet to a middle ground?
 Alot of guys know its a problem, but the Lectron's are too much work to swap jets quickly. So the guys that have those, must be a little rich during the day, ya think?

[Friar-Tuck]

 Nobody else chiming in I'll throw out there some thoughts..

 U4.2TM       http://www.vpracingfuels.com/tech_tune.asp
The latest generation of our U4 based fuels, this fuel is a direct pour-in replacement for pump gas, with little to no jetting changes required - +2 main jets and +2 pilot jets at the most. Makes power equivalent to U4 with no sticky residue and a less pungent odor. Designed for stock and modified 2-stroke and 4-stroke applications. U4.2 passes AMA amateur fuel rules and is perfect for club level racing, CCS, WERA and AFM. U4.2 makes up to 6% more power than pump gas.

    * Color: Blue
    * Oxygenated: Yes
    * Motor Octane 102
    * Specific Gravity: .784 at 60? F

Says little to no jetting changes  +/- 2 main and or 2 pilot. 
   It says makes up to 6% more power than pump gas, but are the engines built with that much compression and etc. to actually make that 6% ?     You could add more timing, I guess...
 I'm no expert just thinking this through my own self...

 Full read: http://www.popularhotrodding.com/tech/0901phr_difference_between_pump_race_gas/index.html
Pump Gas Versus Race Gas
Octane rating is defined as the resistance to detonation a fuel has in an internal-combustion engine. The higher the number, the more resistance it has. That is why engines with higher compression require higher-octane fuel. As a result of its resistance to detonation, it has a resistance to burn as well. This resistance to burn is a non-issue in motors tuned to the edge; the edge being just before detonation occurs. When a pump-gas engine is subjected to a higher-octane race fuel, it may result in a decrease in power from an incomplete burn.

Oxygenated Fuel
The theory is the more fuel you can pass through an engine and completely burn, the more power you can make. The fuel has to be matched with air to create a burnable mixture. Without a power adder such as a blower or a turbo, air is hard to add. That is where oxygenated fuel is helpful. It contains a higher percent of oxygen, creating a quicker, more efficient burn. In the state of California, 91-coctane pump fuel is oxygenated, so the gains between the two fuels due to oxygenation wouldn't be notable.

The Results

91 Octane Versus 100 Octane
The first test was to compare the difference between 91 and 100 octane without making any changes from the 91-octane baseline. The engine, with pump gas, responded the best to 37 degrees total advance, and 71/77 jetting. The same tune, with 100-octane fuel, showed no change. Through the same tuning processes used to find the most power from 91 octane, we were able to get up to 7 lb-ft of torque between 3,800 and 5,000 rpm. Horsepower gains were similar from 4,600 and 5,500 rpm. The only change made was going from 77 to 79 jets for the secondaries. At $60 for a 5-gallon can, I personally think that 7 horsepower worth of extra acceleration can more cost effectively come from lightweight parts.

100 Octane Versus 118 Octane
The first test we did with the 118-octane fuel was with the settings that worked best for 100 octane. We saw an across-the-board loss in horsepower and torque. Again, using the same procedure, we found that the 91 octane's best settings were the best for 118 as well. That meant returning the secondary jet size to 77.

Conclusion
Filling your tank with high-octane fuel, when your engine runs fine with 91 octane, is a waste of money. In this engine's case, minimal gains were achieved after a dozen dyno tests were made, and would be too small to notice at the track. The higher 118-octane fuel made less power than both the 110 and 91 octane. It would be interesting next time to see what effects the fuel has on a boosted engine. We would expect to see more impressive changes there.

Tuck\o/

[Hillclimb#42]

 Thanks Tuck. All good info there. I read most of that already and have been reading about fuels for a couple months here and there. I have caught up to that point, and just short-handed my findings, in my post. That is the best point to take home that you are making, and shows your wisdom, as that is basically the same message that the Rep from Vp was making. Actually spending more on high octane fuel, may cost you performance too, unless you have a high compression cylinder. Actually pointing out that the least octane that your motor can use is the best, because the resistance to burn(octane) is the resistance to release energy.
 Theres no chance to convince me that 91 octane pump gas has the same power as VP's c12 or U4.2. I agree that they can run on pump gas, and for the extra money, I may be able to redirect the extra cash to other performance parts, but have to believe in a company that is developing, producing and posting many results. All backed with high regards by Stewart's Dyno. Also many champions using VP on the Hillclimb races. You may also be making a good point that the added performance may be hard to notice, but these races are often decided by a couple thousandths of a second. Small margins in performance are noticable.
Actually I was mostly concerned about how much jetting may need changed from a high temp of say 90* with 90% humidity during the day, to like 70* with same or less humidity. I would have already increased my jets a size or two for the basic set-up, but once it leans out at night, I'm not sure I want to swap slow jet, main and needle setting every evening. I'm not sure if I would need to be set-up a little rich during the day, so at night it wasn't too lean, or be ready with my nightime jetting set-up. Hopefully someone on here is running it and has tackled this issue, and save me some trial and error. Once set-up how often do you re-jet, and what are you changing, both jets and the needle or just one adjustment?

[DoldGuy]

#42,

You stated that you will be using this in "9" different bikes. That is alot of bikes to use the same fuel, and have it perform the best in all. You also mentioned the VP rep stated that Stewarts fuel is for High compression (Think I read he is running 15:1 Uncorrected Comp) and Tuck (The typing Encyclopedia) posted the Pros & Cons of different fuels with a Base line motor. Are ALL of the bikes "Tuned" the same (Comp, Timing, RPM, Etc.) What carbs are you running? Powerjets? Adjustable P.J.? Some of the Carbs are more sensitive to temp, Humidity and altitude changes. I ran the U4 in my 250F (jetted just a little on the fat side) and could get by with just a quick adjustment on the Fuel screw, But I found a very little benefit versus C12, which has a Much wider tolerance range on jetting. Also you noted that some of the Bikes on the Line sound Real Fat until that drop the hammer, most of the bikes here running Nitro sound the same until a "Load" is put on the motor and then it is shredding. As a side note, I run a KX125 & a KX250, and they like different fuels which I Blend for each (Have not experimented with the Big K5 Yet).

DoldGuy

[Hillclimb#42]

 Great post. Thanks. Thats true and all points and exactly the voice of experience that I was looking for. It is alot of bikes, and obviously, no, not all the same tuning. We run stock carbs for the most part, except the triple and banshee, moderately modded bikes with stock compressions, mixed with a Trinity Cr500, a Stroked 85ktm, and now a full mod kx250, also a freshly rebuilt and ported KDX200. None of the bikes are the same in every department, so I was also leaning to the C12 as the final plan, but now that you mention it, U4 for the modded cylinder higher compression bikes, and c12 for the modded, but stock compression does make alot more sense. How did you get to that conclusion that one bike preferred one fuel over another, just riding them?
We have ran CamII in the past and have been satisfied, but are on the quest for innovations and celebrations, thanks for your opinions.

[Friar-Tuck]

 42,
 I don't see how you could avoid re-jetting if you're temp/humidity swings are that broad without Fuel Injection.
  The lectron has the ability to adjust jetting .25 per click. how much can you "dial" in?   
(I should have been more specific/concise but there were lots more people looking at your thread than answering.)
  The race fuel should be more consistant, I think running it in an engine that could use it and mix it 50/50 or so with pump premium on stock /slight modded engine.
( I believe what D-Old guy was reffering to).   Like you stated post #4
  Tuck\o/

[don46]

Kyle,

I've ran/run both, I think the q16 make more hp than the u4, both are oxygenated and like alot of jet for example on pump gas my  450 runs 170-175 main, on the q16 I'm at a 185-190. On my gas 500 I'm running a lectron carb and q16, again it likes fuel and I don't have to do much jetting it runs pretty consistent. 

Don