piston question

I have a 406sbc that was assembled with hyputectic pistons (keith black). Now I have heard conflicting stories from different engine builders about how reliable they are at high rpm. Has anyone had any problems with these pistons? Any help to ease my mind would be appreciated, thanks.

 

hmmm....the negative stories I usually hear from hypereutectics are related to the rings---gotta run bigger end gaps because of the thermal expansion.

logically though, they are cast, and would have a lower piston speed threshold than a forged piston.

 

I would say how much time will it spend at those speeds? You have a long stroke so that isn't in your favor either. I have them in a 350 with Total Seal rings, and no problems for about 40K miles. I do flog it a bit, but nothing in the twilight zone either.

 

Yet hypereutectics expand less than forged, so no concern there about gap. And any educated 406sbc owner knows he's not to rev these motors anyway! Right.
So unless you are planing on runing a turbo, supercharger, or lots of spray you have no worries, other than finding a better informed engine builders in Minnesota.
I have those exact pistions in a pair of 406s (one race only motor with several hundred passes on it) and a street motor with no problems at all.

 

All I have heard is you don't want to go nuts with nitrous with them.

 

i never liked them and refuse to use them now, but if you do go with them ring gap needs to be a bit wide

 

I've got a buddy that does some dirt track racing and has had them come apart at high rpms. But with your stroke you may not need to worry about it, just depends how you drive it I suppose

 

Follow the KB instructions on ring gaps.

High Silicon alloys expand less, but hold a lot of heat.

 

Keith Black hypers require more end gap than other brands of hypers, cast, or forged pistons. As long as you have enough gap, the rings will be all right. If you (or your builder) just gapped the rings at the standard width then there WILL be an issue.

Hypereutectic pistons are better than regular cast pistons, but they are still a type of cast piston. They will break easier than forged, but they are fairly durable for the cost.

I guess my question to you is, what rpm is high rpm? 5000? 6000? 8500???

Hypereutectics also break when the engine detonates, rather than deform like forged pistons. BUT, if the detonation will harm hypers it would also harm forged pistons just as easily.

To put your mind at ease, make sure you have the correct ring gap, the correct fuel, and correct timing and you should be just fine.

Adam

 

Im not racing the car, just a crusier. The engine was built to run on E85 and develop 500hp. We got 480hp and 505ftlbs tq. After I posted this question I called the one builder and asked him what exactly he didnt like about the pistons and he said it was a timing/detonation issue that cause the piston failure. He had built a 406 for a friend with the kb pistons and the engine failed because of operator error but he still got blamed for it. Advised him to get a new friend. thanks for all your imput!!!!

 

As a former dirt track racer for many years. None of the engine builders use them in a high hp, high compression, high rpm situation. they seem to not be as bothered for street use. The cost of a 383 stroker kit could not be any cheang for the buck on street use.

 

Great street pistons. I had them in a 393W stroker for several years, that motor saw 6300 rpm many, many times.
All the pistons looked great when I tore the motor down after I cooked a couple of rod bearings.

I can say they're between a forged and cast as far as strength and price. If you're building a pump gas motor with reasonable compression and keep the RPM's under 6500, they're ideal. Quiet and pretty light.

 

Like many have said already, they're great for street use. They lie somewhere between a typical cast piston and a forged piston. They are indeed still cast, but with a stronger alloy than previous cast pistons. For your application, I would have no worries.

 

I have Speed Pro Hyper's in a 390 Ford .060 over and reading the instuctions was suprised to read the near normal ring gap so I called thier tech guys and they said that was correct for thier piston, as stated earlier, they agreed the KBs need a wider gap. I have 6 years on a set in a 383 and no problems.