Anyone know what the safe compression is if I helicoil one of cylinder heads(spark plug)?? Im running 11.3 right now and since I was going to helicoil the head I messed up i was thinking of running a thinner gastket. Thing is I dont know what the safe compression is for this!! Any help is well appreciated.

 

I used them on a SS/A 68 Hemi Cuda with 12.5 to 1 compression ratio with no problems. Actually it was not a helicoil it was a threaded insert that I installed into the aluminum head for the spark plug. I do not remember the brand name but I am sure that they are still available. It was a better piece than the helicoil. That is what I would use in that application.

 

Thanks bud. I will try and do some research on that

 

Heli-coil pull out strength is based on two things, one is the parent material (the aluminum head) and the second is the length of the heli-coil. If you use a heli-coil that is nearly the same length as the spark plug thread the strength will likely be more than the stock head. Careful that it doesn't protrude into the combustion chamber though. The heli-coils are available in thread diameters so that a 1 diameter heli-coil for a 5/8 thread is 5/8 long whereas a 2 diameter is 10/8 or 1-1/4 long, etc.

 

from everything i have ever learned about helicoils, a helicoil is stronger than the original thread.... if done correctly.

 

Vettenuts and Darkcloud: Thank you for ur imput!!

 

I stripped a plug thread on my old heads in '03 and used a threaded insert kit from Pep Boys to fix it with the head on the car. I know, not the best way, but I had no choice and it worked well up to '08 when I put in my new motor.

 

My friend put a helicoil in his supercharged cobalt when a plug blew out. Been a year and still going strong.