I know guys run these all the time and most new car/truck engines have hyper. pistons. I just purchased a nice GenVI to reassemble. The motor had hypers in it. It will reassemble at std. 4.250 bore. I want to run a CR in the mid 9's. Not too many options for std bore pistons. And most of the forged either require cutting the heck out of the block and heads to squeeze out 9.3,maybe 9.4 or jumping up to 10+. The plan is to reassemble with about 9.5/1 CR, use the ZZ502 cam with factory rollers and bolt on my Merlin 119CC heads with a dual plane intake.

By nature of the valvetrain and intended use, the self imposed RPM limit will be less than 6k, so I would think the hypers would be quite suitable. I also like the fact that the hypers are tight fit in the cylinders. And then the other big advantage is a broader selection of piston dome volumes.

Joe,I run hypers in my 454..10.5 to 1 compression as well.
10K + miles,and no problems.

For a modest rpm mill that won't see power adders, imho, they're a good choice.

Chris, I had completely forgot that you run that high of a CR. Now, just for clarification, did you have the deck cut to any certain depth to control the quench? On an uncut deck, the quench is going to be .064 (.025 Comp Ht for the hypers and .039 gasket). That's a lot more quench than what I have read is recommended, but from what I can gather, every crate GM is putting out has the same/similar quench. I don't think this will cause much of a problem at 9.5/1 with the 502 cam (224/234 @ .050),I would expect the factory cam ramps are fairly gentle, I have not found the seat/seat specs anywhere, but if I had to guess I would peg it at 284/294. I did run several different options through the DCR calc and came back with a DCR of about 1 point less than static using the 284 and Int C/L at 106. Should give me about 7.5 - 7.8DCR then.

Joe,the block was decked on a previous rebuild before me,and the piston measured about .010 down in the bore,with a .039 head gasket.
Heads are 101 CC's and verified

To make matters more confusing, I have a set of L2399-060 (13.8CC) already hung on rods that I could install. These will only get me into the low 9 CR range with "0" deck and cutting the heads. I actually considered just boring the block out, putting it together and living with the lower CR. The only downside is, the GenVI production blocks are not recommended to go anything over .060, so if I hog it out to save on pistons, I am basically out of luck if I ever/when have a problem.

So you are running .049/.050 quench with 10.5/1 and a 280 adv cam on pump gas. Anybody ever told you that's not supposed to work? What LSA (110?) and ICL (106?) does the cam have?

Joe,cam is 112 LSA installed straight up,not sure of ICL,but I can check at lunchtime
Is it not supposed to work due to high compression?
I have no detonation issues with up to 40* total
The motor has about 205-210 lbs of cranking pressure.
On a side note,another Tcer (cmt454) built my motor identically,same pistons,cam,etc. but used 2.19/1.88 valves

Hi joe,
I ran cast TRW replacements in my 454 for about 5 years with many many trips down the 1/4 mile. RPM often hit 6500. They worked great and looked like new when they came out. So I would have to say that hyper's would be even better.
Ron

We chose hypers for our 350. It has been run at the track many times and shifted at 5800RPM - a few over that as well. Still holding up nicely.

Chris,
UD cam -112LSA, you probably have 106ICL. But that may compare to about a 110 for a symmetrical cam like a Crane or even a stock GM. I must have read 100 articles that claim "9.0 - 9.5CR" with iron heads, quench set at .035 - .038, no more or you will experience detonation. Maybe this just happens under certain atmosphere conditions. Must be all the "good" air we get to breathe on the East Coast. I guess if we lived in a heavy smog area like the West Coast, we would get stuck running low compression truck motors also!

Ron,
How ironic, the L2399's are your pistons, but you knew that. BTW, when I had them and the rods checked out, the machinist told me whoever did the flycut and balance had done a nice job. The original plan was to use those with a MKIV block and my 290 CC ovals. Of course, then I got sidetracked on the 496 motor, right up until we found the crack down the length of the block. At least the rods will be put to good use.

From what I have been able to find out, other than lighter wt. pistons like SRP's, the hypers (TRW/SpeedPro) that I want to use are simliar in weight to the forgings. And from what little comparison I did, even standard 454 pistons are about 50 - 70+ grams lighter than stock 427 pistons - benefit of the higher pin ht and slightly shorter skirt I would assume. That may explain the durability issue at RPM.

I found a dealer on Ebay 'Mad Dog Racing' anybody here of him? He is advertising new TRW hypers in the box for 210.00/set. The pistons I that I am leaning to are the H693CP 22CC dome, 1.640CH. These would place me right at 9.54 with .010 deck w/ 119cc head. The other option is to go with a forged TRW L2465F, 27cc dome, 1.640CH. These will get me to about 9.9 w/ .010 deck and the 119cc heads.

Not to sway anyone, but if date correct is not important,let me tell you how much easier it is to start with a new/near-new GenVI block.

Hey Joe,
My guy will be glad to hear he does good work. He cussed those pistons from the word go but just because the TRW's tend to be heavy and all over the place balance wise.
Those were the second set in my rat, the cast TRW's were the first. Well not including when it was stock. Now it's on it's 3rd set and is .070 over.
Hope you find a good use for the old TRW's, they served me well!
Ron

Apparently balancing is another big play for the hypers. Actually Ron, when I was headed off into the 496 build, I was going to sell the pistons/rods to someone from the site. I wound up keeping them once I found out the block I had was cracked. Not knowing where I was headed, I just figured I might want to economize wherever possible. As it turns out, I am going with a GenVI block and a budget is a budget, what can I say. So those truck rods will be put to good use. The pistons will probably wind up on the For Sale board or spend the the next 20 years on a shelf in the garage - when one of my kids or by then grand kids gets into them and wants to know "what are these for?"!

Hypereutectic pistons are plenty tough. I've run for long periods (10-15 minutes at a time several times a day)@ borderline detonation +4 degrees. Pulled the heads later, never a scratch on them. I've also had them up in the 6000-6750 rpm range for over half an hour at a time.

Mike

Thanks for the responses guys. From what I had gathered there were far more positives than negatives - severe detonation being about the only negative. I really like the idea of having the tight fit in a fresh build. I don't know what the actual effect is, but if it is 10% reduced blowby, that equates to a fair amount of power with a given set Comp Ratio.