12:1 piston questions/compression

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jasonp said:
spark knock is detonation. detonation can occur from advanced timing.
Pre ignition happens before the spark.
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We agree they are two different issues correct?

Im also familiar with to much advance being able to knock with the added pressure due to the added time to burn before the power stoke, this is a spark knock. Which can be cured by higher octane fuel. And yes a a extreme to much fuel can cause extra heat, but also remember that with higher compression the motor is not straining as much to lug the heavy chassis around, so you dont run it as hard so its cooler. I know that not all carbs will need retuned with a timing advance but mine benefited best after a re tune. But changes in engine temps will be minimal as long as it is in proper tune with adequate octane fuel.
 
duneracerweston said:
We agree they are two different issues correct?

Im also familiar with to much advance being able to knock with the added pressure due to the added time to burn before the power stoke, this is a spark knock. Which can be cured by higher octane fuel. And yes a a extreme to much fuel can cause extra heat, but also remember that with higher compression the motor is not straining as much to lug the heavy chassis around, so you dont run it as hard so its cooler. I know that not all carbs will need retuned with a timing advance but mine benefited best after a re tune. But changes in engine temps will be minimal as long as it is in proper tune with adequate octane fuel.
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Not really.
As you go up in compression heat and stress on the internals of the engine go up. The reason why most manufactures use a lower compression piston is because it will allow the engine to basically last longer. It puts less stress on everything and thus will wear things out slower. So higher compression piston will cause more heat. And your engine will run hotter. There is no question about that. As heat rises inside the combustion chamber both pre ignition and dentonation can occur easier.
Basically with higher octant fuel you can run more ignition advance because it burns slower and has a higher ignition point.
Burn rate speed of the cylinder pretty much equals how much ignition timing you throw at it.
 
advancing timing and more compression adds to bottom end power and might lose a little in high rpm, but def will make the bike more rideable. Does anyone know the octane rating of E85? I don't know if id run that crap or not. ethanol sure does screw up alot of carburetors nowadays.
 
Looks like taking out the base gasket would add .5 to compression but is it worth the risk of the silicone blowing out and having to pull the topend to fix it?
 
i do not use silicone on my motor i use loctite gasket eliminator .. we use this stuff on hydraulic pumps on backhoes and have never had problems with it
 
The only reason I say that about the engine heat is because I found mine ran cooler after the higher compression. Maybe I had something off before that. Idk.
 
headache said:
advancing timing and more compression adds to bottom end power and might lose a little in high rpm, but def will make the bike more rideable. Does anyone know the octane rating of E85? I don't know if id run that crap or not. ethanol sure does screw up alot of carburetors nowadays.
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When I added +4 degrees on the bottom end with my JE 10.5:1 engine it spark knocked with 93 octane. But if you are talking typically when you do add timing to the bottom end yes I agree it gives the engine a little snapper feel to it.

You can see that the stock curve peaks at 33 degrees at 5000 rpm and falls off. If you could hold that much advance till red line you won't loose so much in the upper rpm. I tune to 34 degrees till red line.

Typical octane rating of E85 is around 105... You have to tune for 30 percent richer so it doesn't get as good as gas milage but produces more hp. It burns clean and cooler. I would do a search on the internet as there is a lot of benifets to runing this type of fuel in high compression engines.
 
headache said:
Looks like taking out the base gasket would add .5 to compression but is it worth the risk of the silicone blowing out and having to pull the topend to fix it?
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I don't think taking the base gasket out would even add that much more like .25 or .15 more compresssion. Boring from 83mm to 85mm can add up to .55 more compression.

I would make sure and check deck height when removing the base gasket. JE pistons will stick above the deck .15" if you remove it.
 
the reason i was wondering about E85 is that we have a station locally that is selling it for around 3.19 a gallon where as turbo blue 110 race fuel is up to $8 a gallon. and if it does help cool some on the motor would be great. The other motor i built with the 10.5 85mm je piston ran hot as hell. I mean it literally bubbled paint off the head and cylinder. I ended up running an oil cooler, d9ea spark plug and mixing in race fuel to help keep it cool.
 
ok what from the calculating i've been doing, i should be right at 11:1 with a wiseco 83.5 piston, zero deck clearance and taking 1 layer off stock headgasket, which gets it down to roughly .02". i measured the stock 350 raptor head at 36cc chamber, give or take a half cc
 
jasonp said:
I don't think taking the base gasket out would even add that much more like .25 or .15 more compresssion. Boring from 83mm to 85mm can add up to .55 more compression.

I would make sure and check deck height when removing the base gasket. JE pistons will stick above the deck .15" if you remove it.
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When I built mine last (.040 wiseco10.25:1) and removed the jug gasket I did the math and at 84mm it was actually 11.02:1 compression. And on a 12:1 je80 over its actually closer to 12.6:1 if it has the same dome as their STD bore 12:1 piston, so if you dropped the jug gasket on the 12:1 80 over its actually closer to 13.6:1 so really you can go as high as you want comp wise. It all comes down to octane and amount of spark advance you have.

Im not a huge fan of e85, the octane ratings are wrong, if tested with a octane motor its actually close to 96-98 range. Also you cant let it set long and it collects moisture. I'd rather run race fuel but thats my .02
 
headache said:
ok what from the calculating i've been doing, i should be right at 11:1 with a wiseco 83.5 piston, zero deck clearance and taking 1 layer off stock headgasket, which gets it down to roughly .02". i measured the stock 350 raptor head at 36cc chamber, give or take a half cc
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I'm not sure you can get 0 deck with the wiseco with just gaskets as I've never owned it. I don't like that piston as much because of the large skirt and lack of wrist pin oilers. Also was told that it sits down in the bore the same as stock?

.035" is about as low as I would run for total clearance.
 
duneracerweston said:
When I built mine last (.040 wiseco10.25:1) and removed the jug gasket I did the math and at 84mm it was actually 11.02:1 compression. And on a 12:1 je80 over its actually closer to 12.6:1 if it has the same dome as their STD bore 12:1 piston, so if you dropped the jug gasket on the 12:1 80 over its actually closer to 13.6:1 so really you can go as high as you want comp wise. It all comes down to octane and amount of spark advance you have.

Im not a huge fan of e85, the octane ratings are wrong, if tested with a octane motor its actually close to 96-98 range. Also you cant let it set long and it collects moisture. I'd rather run race fuel but thats my .02
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I think you need to check your math and do some more research on E85 because your opinion is incorrect.
 
jasonp said:
I'm not sure you can get 0 deck with the wiseco with just gaskets as I've never owned it. I don't like that piston as much because of the large skirt and lack of wrist pin oilers. Also was told that it sits down in the bore the same as stock?

.035" is about as low as I would run for total clearance.
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I'll machine the top of the cylinder to get the piston as close to top of deck as i can. I'll also machine the sides of the skirts like the Je pistons are. The new Wossner piston is machined even more than the Je. I just wish the wossner had higher compression. They are incredibly nice pistons
 
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