GROUP K 845cc SuperJet Freestyle Tech Info

#ZERO

#ZERO

Beach Bum
Location
Florida - U.S.A.
A stock stroke big bore with Northwest sleeves would hit a lot harder than the Group-K 845 IMHO.

It appears they're using flat top pistons in the 88.5 and 89mm sizes very similar to the Riva flat tops made by Wiseco. They have a lower compression height which raises the port timing and when combined with the 62T cylinder it makes it even higher and more suited for racing.

Jared, the exhaust ports open right at or before 90-degrees because 180-degrees would be at BDC. :hitwithrock:

I've rarely seen any skirts bending inward on Wiseco pistons when the clearance is set properly, but I've seen a few new pistons having different measurements even with matching serial numbers. Also, I've seen some Wiseco domes collapse in the center area from overheating.

A new style Wiseco 83mm piston weighs approximately 332.5 grams and the older ones in the same size weigh 350.8 grams. The newer wrist pins weigh about 83.8 grams and the older ones weigh 59.4 grams. Also the newer style KD rings are 1.5mm thick compared to the older TD style rings that are 1.2mm thick.

They must be using some different alloy composition during the pressure forging in a mold to make them lighter and stronger; however, with the overall weight of the complete assembly, they now weigh more!!!
 
W

waxhead

wannabe backflipper
Location
gold coast
#.0 said:
A stock stroke big bore with Northwest sleeves would hit a lot harder than the Group-K 845 IMHO.

It appears they're using flat top pistons in the 88.5 and 89mm sizes very similar to the Riva flat tops made by Wiseco. They have a lower compression height which raises the port timing and when combined with the 62T cylinder it makes it even higher and more suited for racing.

Jared, the exhaust ports open right at or before 90-degrees because 180-degrees would be at BDC. :hitwithrock:

I've rarely seen any skirts bending inward on Wiseco pistons when the clearance is set properly, but I've seen a few new pistons having different measurements even with matching serial numbers. Also, I've seen some Wiseco domes collapse in the center area from overheating.

A new style Wiseco 83mm piston weighs approximately 332.5 grams and the older ones in the same size weigh 350.8 grams. The newer wrist pins weigh about 83.8 grams and the older ones weigh 59.4 grams. Also the newer style KD rings are 1.5mm thick compared to the older TD style rings that are 1.2mm thick.

They must be using some different alloy composition during the pressure forging in a mold to make them lighter and stronger; however, with the overall weight of the complete assembly, they now weigh more!!!
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depends on how your looking at it
Most people speak in duration not degrees after tdc
so 180 degrees is opening at 90 degrees after tdc
but when you see figures like 192 exhaust and 127 transfers you are talking in duration
Ethier one is correct just different ways of saying the same thing
 
W

waxhead

wannabe backflipper
Location
gold coast
I have tried all sorts of clearances on wisco pistons and had thrm all collapse in the skirt area

The fact that wiseco acknowlodge this themselves make its clear to me its not a clearance issue
 
the WaTeRhAwK

the WaTeRhAwK

fryin' up a/m electrics..
Location
okc
waxhead said:
lucky its not an issue with the cast pistons and only an issue with wiseco
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they should just make them thicker at the skirts.
as I mentioned before, the extra weight needed to improve their strength in that area shouldn't be an issue vs. as much hp as these engines make.
 
2

2XLR8

X-
I have seen pro-x piston break at the ring land. Basically seperating the piston in two. I have never seen it on the wisecos. The old wiseco would crack above the pin and would cause catastrophic failures on engines running over 7600 rpm on flat water. This means more than that over choppy water. This same old ones would collapse the skirts 3 times as bad as the new ones. The only good thin about the old ones were the pins. over 60 on R C scale new ones 57. The OEM pin is better. I would run the wiseco, just my opinion.
 
W

waxhead

wannabe backflipper
Location
gold coast
Each to there own
I have seen the wiseco break where you talk about as well
Not good

I would rather a sister in a whore house than to run wisecos

but thats my op
 
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H

HLS30

Location
surfcity
I know kawasaki 800 sxr engines running high rpms over 7800 in flat water which means the engine hits the rev limiter at much higher than that have been having skirts break with the cast pistons. You just cant compare a cast to a forging. Next time you have some old wisecos and old cast pistons put them in a vise and hit the skirt with a hammer and see which one takes more abuse. You will be amazed at the difference between the two.
Since I don't have a sister I am going to have to run wisecos.
 
2

2XLR8

X-
I think no matter what piston you use if you are making some horsepower they get stressed and fatigue sets in and there are many factors to look at. Po-x or wiseco Im sure there are advantages and disadvantages to each. You can't go wrong with either of them. Just stay away from SBT or WSM if you are builiding for top performance. Again it is just my opinion.
 
Polish jet pilot

Polish jet pilot

4aces4aces4aces4aces4aces
Location
Warsaw, Poland
#.0 said:
The cast pistons will crumble into a million pieces at the skirt before they'll bend.
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I had Pro-X in my 550. One day I open up the negine (would not start) and both pistons were cracked the same way! straight through the piston sleeves, on both sides of piston.. from that time I am sceptical on using PRO-X although I know a lot of folks love them beacause they resemble OEM pistons alot...

Is WSM any good for pistons?
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
All pistons can fail. I found the same thing once. But I had alot of time on the engine at that point, could have cracked from piston slap due to bore being worn out.
 
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