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BergRyder

Running Both HotCams with Pump Gas

18 posts in this topic

Is anyone running intake and exhaust HotCams in their 426/450 and still using pump gas?

Previously I just had the exhaust HotCam, and the bike ran great on pump gas. Now I have installed the intake cam as well and intend to try it with pump gas to see how it runs. I read an old post by a tuner (STM?) on the Dirt Rider web site, and he was saying because of the design of the combustion chamber, 5 valves etc., that some of the rules of thumb for the SOHC (Husky/Husaberg/KTM style) motors didn't necessarily apply. He was talking specifically about higher compression pistons with the YZF not needing race gas as he had experienced no detonation problems even with Mexican (Pemex) gas.

So what do you think, I'm racing Supermoto which is mostly at high RPM, according to Dyno charts that I have seen race gas performance gains are at the low to mid range and doesn't add much, if anything, at the high end. So unless there is a mechanical reason for me to use race gas I don't want to use it.

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92 octane pump premium from the quickie mart doesn't ping my 426 with both hotcams

I'm going to ride my bike (426) for the first time next weekend with both cams. How big of a performance change was it for yor bike?

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Not much difference on the bottom (didn't really lose any of the grunt)...a little bit more of a hit in the middle, and holy schnikies on the top end. The bike pulls a lot harder as it walks the big end, and gets to the rev limiter pretty quickly when you're really on it!

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Since you're not changing the compression I dont see why you'd any problems with pump fuel. As long as you never had problems with pump gas before the cams.

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Since you're not changing the compression I dont see why you'd any problems with pump fuel. As long as you never had problems with pump gas before the cams.

I thought I read on the HotCams web site to use race gas after installing their cams but I can't find the quote now....

BTW I have a post on another thread asking you how you like the 444 kit.

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I replied to the other post about the big bore kit.

As far as race gas..... I'm serously doubting the hot cams have radical enough durations to require race fuel. Usually high compression requires race fuel, not a cam swap. I'd try pump gas and if you get detonation then try a 50/50 mix of race and pump fuel.

Grayracer, where you at!?!?!?

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The most popular "race gas" for modern four-strokes is not any higher octane than pump gas. VP's U4 and U4E are 92 and 93 octane. Octane (detonation resistance) is not why Hot Cams would recommend the fuel. They probably said something on the order of "for best results", meaning that to help realize the full potential of the cams, you could use a high energy fuel, or "race gas" like U4.

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I can't for the life of me understand how so many "experts" on this forum poo-poo the use of good gasoline and recommend the watered down crap available from the pump these days. I'm no chemist, and I don't profess to be an expert, nor would I pretend to know what the truck driver dumped into the tank down at the local Arco station, but I know damn well what the seat of my pants tell me, and good gasoline makes a big difference in power in any high performance engine. It seems to me any aftermarket cam company would be well served to recommend not only high octane fuel for the reduction of detonation, but leaded fuel for the improved lubrication and protection of valve guides and seats. :D

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I've never used race fuel in any of my bikes, am I missing out on anything besides that sweet smell? I have always used 94 pump gas.

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Frankly I hate the smell. It's toxic as all hell. To me there's nothing worse than getting behing someone on a track who's burning some ungodly potion as if it's gonna help them go faster or break some kind of land speed record. :D Especially the two strokes. I have to pull over for fresh air when that happens or I'll get a headache. But as it's been said before, we ride these bikes because the power is fun! And if you appreciate the fun of a great running motor in top form and can discern the subtle characteristics that good fuel provides, yes you're missing out on something. But it's not gonna make your bike "faster". :D BTW 94 pump gas sounds pretty sweet. We sure as hell can't get that in Cali.

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BTW 94 pump gas sounds pretty sweet. We sure as hell can't get that in Cali.

Only Sunoco or Shell stations have it here.

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I can't for the life of me understand how so many "experts" on this forum poo-poo the use of good gasoline and recommend the watered down crap available from the pump these days. I'm no chemist, and I don't profess to be an expert, nor would I pretend to know what the truck driver dumped into the tank down at the local Arco station, but I know damn well what the seat of my pants tell me, and good gasoline makes a big difference in power in any high performance engine. It seems to me any aftermarket cam company would be well served to recommend not only high octane fuel for the reduction of detonation, but leaded fuel for the improved lubrication and protection of valve guides and seats. :D
U4 will provide a more or less instant 1-2 horsepower over pump gas if you jet for it, possibly more, depending on the quality of the pump gas you have access to. You certainly should be able to feel that in the seat of your pants. But once again, octane isn't a part of the question, since the bike won't ping on pump gas. But power is power.

The only strike against it is the expense. Even now, when the 10 gallons I haul with me to a day in the desert costs me $30 instead of $15, it's still a lot less than $100. Now for racing,that would be different...

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Be careful with U4, get it out of there when your done riding. Drain tank and carb and restart with good pump. I've had problems with U4 in some of my race engines. It seems to turn into aluminum eating gum. I've had it pitt valve stems and faces, plus it eroded a aluminum jet needle, the center of the needle was near pitted through. If you can afford it use MR1 or MR9, slightly more power, tons more money!!! (typical) VP has stated they have no problems with U4 (surprise) but in my experience the stuff is nasty. Have you seen any issues Gray Racer??

PS. I also have no problems with good pump, and the MR lines are also similar in octane to pump, but they make great power (approx 6HP in an inline four) :D

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Never seen the erosion problem, but I have seen complaints of the gumming issue. Valve faces get pitted just doing their job, but one of the two U4 blends is leaded, which may help, at least with the exhaust valves.

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