I am getting all the parts together to rebuild my 5.7 in my 89 GTA.I hear alot about these pistons .Do any of you have them? What are the best Rod and main bearings?? Thanks

I have these pistons in my car. They are stronger than cast pistons because they put some sort of silicone in with the metal when it is a liquid form. Since they are harder than cast pistons they can crack with the use of too much nitrous. Too much pressure in the cylinder and these things will crack. If you are going to use the spray go ahead and get forged pistons. They are the strongest. If not just use hypereutectics.

I think I used Federal Mogul bearings in my rebuild. They seem to be good. I turn this motor 6500 rpm's with no problems. Stock rods and rod bolts.

I'm running a set of keith black hypereutectics. A hyper piston is in the middle of the pack, between cast and forged, when it comes to quality. What makes the difference between the three isn't only how it is made, but what its made of (hyper's are mostly silicon). The nice thing is that the hyper's will fit really tight in the bore. The problem with the hyper pistons is that they aren't that knock accepting and therefore if later on you wanted to add nitrous, a turbo, or a supercharger you'd have to be careful to make sure that everything is tuned properly. I put my hyper pistons on the stock 5.7l rods and just used some clevite bearings.

the pistons are good, I like them cause they're light. But it hinders my custom turbo that I want to add...

Good luck,
Mike

Why does everyone knock something that they don't know much about?

Hyper's are safer to use with nitrous than cast pistons are.

They have more heat transfer, and are less likely to shatter.

They are a great middle-of-the-road piston.

No, they aren't as strong as forged, but a lot of people use forged when they aren't needed. They can handle 450-500HP.

Stay away from 250HP spray, and they'll do fine. And a blower will be fine as long as you know how to figure the comp. Forged are a lot more forgiving for those kinda mistakes.

BTW, you can run tighter piston-to-cylinder clearances with them than forged also. Due to the fact that they don't expand and contract as much. Actually not much more than cast.

AJ

Yea like AJ said they will do fine on a small shot of N2o as long as you keep the fuel mixture high when you spray they work fine. Ive seen one guy blow chunks when he dident get the correct mixture, melted 4 pistons 4&6, 3&5 with KB pistons and a 250 shot on a fogger plate. The pistons are sitting at the machine shop on a plaque that reads "Nitrus is for dentists, keep it off the track"
SSC

The best bearings is debateable, but the Clevite 'Vandervell' bearings are up at the top somewheres. I usually just get the normal Clevite bearings, havent had any problems.

As for the pistons, they are more brittle than other pistons but are alot stronger than cast pistons. I have heard stories about breaking off the ring lands and beating the cylinder bores to death, but at 9,000 miles the KB pistons I used in a 350 werent showing any trace of those problems. I would say most of the problems associated with them are user error.

I hate to say it,but dont even bother with KB pistons.I had a well know engine builder use these in my 350 and they had oil control problems from day one and the top of the pistons cracked.
Theres not alot of strong meat there from the top of the piston to the first ring.

Some time Later,I took the motor to another engine builder.I told him i had it rebuilt by so and so ,and it had been burning oil.The first thing he asked me was,"When you had the engine rebuilt,did they use KB pistons?".He seen this many times already...I was suprised he asked me that but wasnt sure why, and he then showed me a box FILLED with old KB pistons from former rebuilds.They all had cracks on top and all had the same syptoms my motor had.He will not use these pistons in his rebuilds.He saved them to show his new customers.

They were the rave for a while..maybe alot were done incorrectly and lead to problems,but When I saw that box and even exmained my KB pistons when removed, I saw what he was talking about.

I knew not to take a chance with those again.
Maybe some of us got a brittle bunch..I dunno,bt I wouldnt touch them again and with different pistons in my engine now,she burns no oil and runs real hard.

For those that run them and have no problems, Im glad to hear that.Not trying to put your car down. Just wanted to share what i learned and found out.These pistons are designed to fit tighter in their bores,maybe the machinist installed them too tight.

What ever piston you decide to use, be sure to follow the
manufacturers guidelines as to ring gap. All high performance
especially "poweradder" applications will need increased top ring gap. When under power they expand and end up with a normal
seal. This extra ring gap is not enough to cause oil control problems. But if the gap is too small and the rings butt under
heat/power, the ring seal will be lost resulting in loss of power
and oil burning. KB pistons, because of their higher silicon content
tend to run even hotter, therefore they require even wider top ring gap than others. They have specific top ring gap guidelines
that must be followed. Cracked piston tops are usually the result
of detonation. KB says their pistons require less ignition advance than other pistons because they are more thermally efficient.
Forged pistons are stronger, and will take a little more abuse
before they fail.

They've been in my car since 1994. For the last 5 years, the car has been running 42 degrees total timing (or more). I dont have any oil consumption, compression, or oil getting dirty too fast problems. I just followed the directions in the box and havent had a single problem. Like I said, I think the problems are due to user error.

i don't have a catalog in front of me, but i beleve hypers have a higher tensil strength than any other piston and are lighter than the common trw forged piston. they are also more brittle. hyper pistons transfer more heat away from the combustion chamber and to the piston causeing the rings to expand more and possiably butt up, for this reason end gap is very important and every hyper piston i've used i had to file the end gaps larger. also hyper pistons can't take much or any detination or knock.

Read this month's Car Craft (tech advice at back of mag.) and you'll be as smart as these guys on the subject

Well, since there have been a few negative KB comments, I'd say look at the Speed Pro's from Fed. Mog.

Somebody already said something about them, but I can tell you a bit more.

Well actually, here's the link........

http://www.federalmogul.com/speedpro...speed_pro.html

Pay attention to the fact that the rings don't need a larger gap with these pistons. That's important in the long haul.

AJ

I'm running the FM H631P hypereutectic 2 valve relief flat-tops in my current engine, no complaints here after its second season. This season's racing has been ~11 trips to the dragstrip averaging 6 runs each, 2 days at Pocono Raceway road courses, 1 day at Nazareth Speedway, 1 day at Lime Rock, 2 days at Memphis Motorsports Park. Daily driving in hot/cold weather, too.

Amsoil 10W-30 in the Summer and on the track, then 5W-30 from end of racing season to first track event...it spends the snowy weeks in the garage.