I am ripping into my motor and am thinking of going with the low comp je pistons which yields 9.5 to one comp with no head shiim. I currently have a pw stage 3 kit and stock pistons with the head shim. What I am wondering is if i run the je's will my compression go up or down. I am not exactly sure what the comp ratio is from daves head shim, and I do not want to raise my compression in my motor any by going to the je's in order to save on race fuel.
je pistons vs head shim
- Thread starter boost4life
- Start date
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Zipperno
Well-known member
You dont say what sled you have, Im guessing Nytro with the powderlites kit.
I do not know what CR the powderlites headshim gives you, but Impulse and MCX uses a headshim with 9.1:1 CR.
I also find it strange that most aftermarket pistons have a CR around 9.5:1 when the shim on most kits are 9.1:1
Anyone with more info?
It is a nytro. I am getting coontradicting numbers from different sources. i think the pl kit uses a 60 mil shim, and the impulse uses an 80. With the pl kit you have to split a head gasket and put half on either side, and with the impulse paul puts on a full gasket on either side. I am not sure what the mcx kit uses. i don't know how this corresponds to comp ratio.
I would just save money and do another shim. The pistons are not the weak spot on the motor, it's the rods and rod bolts. If your just trying to get a certain cr just use a shim. If you plan on running pump and running on the edge of detonation, just know that by getting je's it's not going to save you if you get detonation because a rod will fail before a stock piston.
I have to buy pistons anyways and the je's are around the same price when you factor in everything. I just figure if i can get rid of the head shim, and have the same cr then i am that much more ahead. This way there is less chance of problems later running big boost. I am also buying the carillo rods for strength.
I ran both ways. I have JEs in my personal sled and a head shim and 2 gaskets in a buddies Nytro. My sled was alot snappier on the bottom end. With low comps you have less chance of a blow out if you over boost. Low comps are much lighter so there's less mass to move by the crank. Low comps also create a more ideal combustion chamber. I would never split a head gasket. In 08 that was the thing to do until every one and their dog was blowing them out. Gaskets do not work right when you split them other wise Yamaha would save the money and use them that way stock. Thats just my opinion from experience. FYI I ran 50/50 110/92 up to 19lbs with the JEs and never had an issue. I did have Carillo rods.
Funny, back in 03, the trick was to stack 3 headgaskets on the TRX1's. As there was no low comp pistons yet, yes wisceo came out very soon after. I ran 3 stacked to give 9to1, now the engine got je 9to1 with 1 headgasket. Never had any issures with stacking gaskets, but its kinda redneck like spliting gaskets & spray painting them.
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SylvanLaker
Well-known member
Motelyone is right, the main benefit is response in the bottom end. Both pistons are reliable, however there are weight differences, if you have the money so the pistons..
do you have any oil consumption using je 10-1 pistons.how is trottle response compared too same sled/turbokit with 9,5-1 headshim?thinking of putting the 10-1 je in my apex but have not heard of anyone running them,most guys do 9-1 je
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TApeX_07
Active member
So true. I have had two different rod failures in two different motors. Both Apex motors on 10-15lbs. 50/50 mix too. If I was building it, I would do rods and piston.. with GOOD hardware!
Rods seem to fail around 17-18 lbs. of boost on the Nytro. I would either do the head shim or go all the way and do rods and pistons. As stated above the stock pistons are really good, the detonation shock seems to have a more adverse effect on the rods. Also, remember that if you detonate with any piston it is bad. From my experience, I would do everything you can while you are in there. It is not fun to pull a motor and split it down to the crank, so do it once, do it right......then RIDE!
How many have seen or heard about failed rods in a nytro? I'm curious cause I no simmons have been running 22-26lbs for 3 years now on stock pistons and rods.
I have seen three cases here.
Regardless of what you do make sure to run the fuel required, or better yet run even better fuel. Like mentioned detonation is the killer so dont cheap out on proper fuel. With good fuel stock pistons and rods will last a long time, unless you are planning on 19+ lbs of boost.
Happy boosting.
Happy boosting.
The low comp pistons are usually heavier, same with the Carrillos, they are heavier. At least the ones for the Nytro. So faster reving isn't going to happen with these internals changed out alone. Keep in mind heavier also "sometimes" means they are stronger. You can have failures with either if you are not matching your engine specs with the right tuning and octane.
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HANDSOME
Well-known member
I believe that is because they are running propane. No deto and everything is good in the hood.
friend of mine runs propane, cracked the head and cracked the piston @ 26 lbs, rods survived
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wilbilly
Active member
nytro boost
I put rods ,pistons ,and arp head studs in my engine and everyone that i have talked to has told me my engine is good up to 18/19 lbs . on 100% fuel .After that there is a good chance of my head lifting and statring to leak coolant . My question to the form is how many people have went above 19lbs. without oring cutting the head with no problems .
I put rods ,pistons ,and arp head studs in my engine and everyone that i have talked to has told me my engine is good up to 18/19 lbs . on 100% fuel .After that there is a good chance of my head lifting and statring to leak coolant . My question to the form is how many people have went above 19lbs. without oring cutting the head with no problems .
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HANDSOME
Well-known member
Ouch, it probably was not detonation though if the rods are ok.? Years ago people were buying propane heads for ford 351 and 350 chevs which had stelite seats and valves and that was stock engines, so would it be heat ?
