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QUOTE (billy d @ Aug 9 2009, 10:35 AM) index.php?act=findpost&pid=52654detonation...several culprits...to much timing..to low octane..tight squish...wrong domes?...need more info
It is definately detonation. Does it do it only after you run it hard back to back? Gas motors detonate easier of course easier than an alky motor will.
 

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Discussion Starter · #6 ·
QUOTE (Kawiking @ Aug 10 2009, 10:34 AM) index.php?act=findpost&pid=52731my plugs backed out on mine because i threw alittle to much timing at it.

alky or gas ?
what size motor and carbs ?


16mill Cheetah on alky timing is at 7 compression 190-200 It only does it after one hard pass. I let it cool down for atleast 30mins in between passes. Oh yeah 45mm Lectrons.
 

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Streetking there are a lot of things that all contribute to detonation.
Dome design
Compression
Squish angle, clearance, mean squish velocity
The pipes ability to not let too much heat build and be sent back into the combustion chamber.
Lean A/F ratio.
Too much timing or even too little timing sometimes let's heat back into the cyl.

There's more than these but these are common reasons for detonation.
It doesn't sound like you have too much timing but your 200 lbs of compression is definately suspect.
200 lbs would lead me to believe the dome setup might either be too tight squish or too small of a dome.
Other than just tell you to run it richer which would be the easiest way to get rid of detonation I would check the squish clearance and if its not .048 to.055 or more on that big of a motor I'd either check the base gasket thickness and see if its supposed to be that thin or I'd go up a CC or two on the dome size like from a 23 to a 24 etc and try that,get your domes cut a little, or get new domes.
Most bikes run better at 180 psi rather than 200 IMO and that's a high $ motor I'm sure you don't wanna cheap out over $100 on domes.
Nate Mccoy is great on the big motors and for probably less money than you'd think will check it out,cut domes,tune,dyno etc that thing and get the last 10% out of it.
 

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QUOTE (Radar @ Aug 10 2009, 04:09 PM) index.php?act=findpost&pid=52795Streetking there are a lot of things that all contribute to detonation.
Dome design
Compression
Squish angle, clearance, mean squish velocity
The pipes ability to not let too much heat build and be sent back into the combustion chamber.
Lean A/F ratio.
Too much timing or even too little timing sometimes let's heat back into the cyl.

There's more than these but these are common reasons for detonation.
It doesn't sound like you have too much timing but your 200 lbs of compression is definately suspect.
200 lbs would lead me to believe the dome setup might either be too tight squish or too small of a dome.
Other than just tell you to run it richer which would be the easiest way to get rid of detonation I would check the squish clearance and if its not .048 to.055 or more on that big of a motor I'd either check the base gasket thickness and see if its supposed to be that thin or I'd go up a CC or two on the dome size like from a 23 to a 24 etc and try that,get your domes cut a little, or get new domes.
Most bikes run better at 180 psi rather than 200 IMO and that's a high $ motor I'm sure you don't wanna cheap out over $100 on domes.
Nate Mccoy is great on the big motors and for probably less money than you'd think will check it out,cut domes,tune,dyno etc that thing and get the last 10% out of it.

number 1 reason for deto on a full pull that I see is lack of fuel,, fuel consumption at higher levels of compression is pretty high,,, I run engines at 200+(not all of them though lol) but strict perimeters are followed,, one thing that happens when you lower Comp. is the MSV rises so if it is a velocity problem it will get worse, the problem with deto is you dont want to just try things , you want to reverse engineer it , find it, fix it.

very good advice on the Squish clearance, that should be known on that much compression or any build for that matter imo along with Comb.Chamber volume. Next thing is relief on squish angle,and squish width, which can be checked from the squish test. there are suppliers out there that use generic domes and use the same squish angle for just about every dome they sell. this just simply wont do, not only is the angle usually wrong but the percentage is wrong also
 

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Nothing against Nate, but I would personally let Tim Bond (Titan Racing) do some replacement domes.
 

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Discussion Starter · #11 ·
Thx for all the info guys. The bike is at my mechanics shop now. I was told that this was a common problem with the Cheetah cylinders and the head I had on it. There's supposed to be a new head out to correct the problem so with that and all the info I got on here we should be able to correct the problem.
 

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QUOTE (dajogejr @ Aug 11 2009, 06:47 AM) index.php?act=findpost&pid=52881The guys I see running the Cheetah cylinder use the original head cast by CP (the maker of the cylinder)...

the cheetah dome is now replaced by the DM dome and you either have to machine the shell to accept it or use a DM shell. not that there is a problem with the cheetah head, it is a good head just easier to have one sized dome for both heads. the problem is the marketer for the cheetah stuff sells a generic profile
 
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