Predator NON Hemi compression help

I have a Non-Hemi Predator 212. I opened it up today. It has never been run. The piston sits .020 in the hole (measured from piston edge to block face, NOT THE DISH)

The stock gasket measures .009-.010

I’m no mathematician but it seems that my stock engine has .030 piston to head clearance.

I want to install a billet rod and a mod 2 cam. I would like to increase my compression as well, but do not know the easiest and best path to take.

Gasket is a no go...factory is the thinnest already.

This leaves me with the rod (arc +.020 or arc +.040), milling of the head, and/or flat top piston.

Milling of the head is an option and desired but can anyone reccomend a good amount...I want to use 93 octane and I’m unsure on how far to mill it to have a good chamber volume and not go farther than 93 octane can handle (octane booster can be used if needed)

That leaves me with flat top piston. This would be same as I have now except no dish so a little more compression.

The DJ-1285PH I believe would be about .040 in the hole, and with a +.020 rod...we are back to .020 in the hole. ARC Racing made a +.040 rod to work with the DJ-1285PH specifically for the non-Hemi...that would put the piston level with the deck but with a .009 head gasket that would be too close right?

Do I have this correct so far?

I did read on here that one of the members used the hemi flat-top piston with the .040 rod and was at .020 in the hole...

I believe based on my readings here and other forums that my best plan of action is the Arc + .040 Rod with the DJ-1285PH piston...install and measure how deep, if any, it sits in the hole, and adjust piston to head clearance with the gasket. Does this sounds like a solid plan?

Sorry for the long winded first post and all the numbers. If I am missing anything or have messed up in my thought process please set me straight. I am including pictures of my measurements. I used a digital and a non digital micrometer. Both read the same .020 in the hole. I don’t understand the best way to achieve what I’m looking for as I don’t know if one way is better than the other.
 

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Last edited:

VolvoBattousai

New member
i pulled my HG and used copper spray a gasket. worked ok till i sent my cart a lil to hard and cracked the block
Edit: not sure about the rods/pistons but thats one easy/cheap way to up comp
 

alvin l nunley

Site Supporter
If I was contemplating all that you're contemplating, the 1st thing I would do is check my piston to valve clearance. Find out from someone who knows what the minimum should be after all the modifications.
 
Yep. The piston was about .004 in the hole with the longer rod. So I have the .030-.031 piston to head clearance...which is about .005 more than needed. Should work pretty well.
 

alvin l nunley

Site Supporter
Current kart engine theory suggests that a rod length to stroke ratio of 2 to 1 is ideal. No way to achieve that with the currently available 4 strokes, but getting closer, I would think, is going in the right direction. What compression ratio did you end up with? I like to say "compression is the holy Grail" lol
 

alvin l nunley

Site Supporter
That sounds good! I would think you would want a colder (colder than stock) heat range plug and maybe 93 octane fuel. Might even consider 100 octane. The octane is to prevent detonation, nothing else.
 
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