Anyone tried 12.5:1 comp. piston???

[leasureryan]

I just got a spare cylinder back from GT Thunder having the heavy duty head studs installed. I think I am going to bore it to a 416 with atleast a 11:1 piston, but was actualy thinking of going ahead and running a 12.5:1 piston. Anyone had any problems with this? And what brand piston is the best. I am useualy a Wiesco guy....just always have been. What are the best?

I will be running race fuel...and thats not a problem for me. So, lets not have any of those "well if ya ran a 10.5:1 piston" posts please. I just basicly want the opinions of those who have had first or second hand experiances with HD studs and high compression

[drew416ex]

I have run both 11:1 and 12.5:1. My 12.5:1 was a JE that i got from sparks racing. It ran great. It had more lowend than the 11:1 had.

[leasureryan]

did you have heavy duty studs? And did it ever blow head gaskets?

[lilyamaharacer4]

From what i understand, over 12:1 you need hd studs and also a hd rod..

[Ruby Soho]

i blew gaskets at 11:1 (wasn't even a true 11:1)

installed the studs, had it milled to alittle over 11:1 and its been 100% fine for 2 years

[bjg696]

I had to have heavy duty studs and rod, when i installed my 12.5:1. it runs and performs great. but i have been through 2 head gaskets and i think i got to replace this one. I had that head and jug both did perfessionally and it will still blow it.

[drew416ex]

i didnt need the hd studs for the 11:1 but I did get them for the 12.5:1. I have never blown a gasket. As long as you torque it correctly, your fine.

[bjg696]

What are the torque specs and torque pattern for a 12.5:1?

[drew416ex]

The torque specs are them same for stock or anything else you put in it. Its 33 ft-lbs for the cylinder bolts and head nuts. Just lightly tighten each one a little diagonally until you get them all torqued. And to edit what I said before, aslong as they havnt been overtightened before and you torque them correctly you should be fine.

[GPracer2500]

I don't know exactly what cylinders and sleeves you guys may be running....but sometimes I wonder how much of a difference that makes when it comes to head studs. It must matter at least a little, I think. Specifically, I'm wondering if the tendency for the studs to pull could vary with different thicknesses of metal in that area.



I tend to go overboard sometimes and I had my cylinder o-ringed. HD studs too. The o-ring'ing deal is just a circular groove cut around the top surface of the sleeve--the same surface the head gasket sits on. You take a stainless steel wire and fit it into the groove. The wire doesn't quite fit flush in the groove so it creates extra pressure along the wire when the head is bolted down. I wish I had assembly pics--oh well. It's tricky to keep the wire in place during assembly (tiny dabs of super glue works) and the ends of the wire must meet perfectly flush. But it makes for a very secure sealing surface.

I did all that and I was using a JE 416 10.8:1 in the stock sleeve. After being run-in it pumped 175psi cold with an old version HC2 at 1300ft. It would not run under heavy load without deto on my local 91 pump. Since I was expecting it would be ok on 91 (regrettably, I never measured my gaskets or the squish) there was a dune trip where I had nothing but 91. I "rode around" the problem that weekend but it did knock here and there and got plenty hot. The head gasket held fine before I started running a proper gas. I sold it so I can only assume it has continued to hold. I sure hope it has considering the double protection I tried building into it.

BTW, the deto thing is relevant because an engine that pings or knocks occasionally is going to be extra hard on the studs and head gasket.

If I was building a 12.5:1 EX I'd probably do the o-ring and studs again. I mean, if I did that for 175psi I'd do it for 200psi or whatever. I couldn't say how necessary that really is though. I might normally associate steel o-rings with nitrous applications and other super high pressure stuff. But I guess I figured the risk of finding the limit costs more than doing the o-ring from the get-go, for me.

Just some food for thought and a possible solution for head gaskets that refuses to hold.