I'm running a 268H cam in my engine with headers, stock heads, performer manifold, demon carb, TH350, etc. Do you guys think I should slide a set of 10.2:1 HyperEutectics from Keith Black in my engine or not? Has anyone heard anything good about them? :cool: :chevy

 

I have not heard any bad comments about the hypereutectic pistons.

Better than cast, and don't need to be bored larger like the forged pistons.

Best of both worlds. Not as strong as forged, but unless you are running an insane amount of NOS, supercharging, turbo or anything else, they will be just fine.
The new ZZ motors from GM come with them. They call them something like "high silicon content" pistons.

 

sounds good. :D I like the cost of these too! $143 from Jegs. :cool:

 

No. Get some heads. Al. for 10 C/R. A lot to lose w/ little to gain by raising C/R too high. Replace pistons at rebuild.

:cheers:

 

"xfactor"----

Hypereutectic cast pistons (i.e. high silicon alloy pistons) are used in the Corvette 92-96 LT1 engine, the 96 Corvette LT4 engine, the 90-95 LT5 (ZR1) engine, the 97-2002 LS1 engine, the 2001-02 LS6 engine, all of the ZZ-series crate engines including the 430 hp ZZ-430 engine, the current Dodge Viper 488 cid engine and the upcoming Dodge Viper 500 cid, 500 hp engine.

They represent the best COMBINATION of strength, durability, and oil control for a STREET engine. That's why the major manufacturers use them for most MODERN high performance PRODUCTION engines. If you have a racing-only engine, used forged pistons. If you have a street engine or street/strip engine, use hypereutectics. If you have a "grocery-getter"/"beater", use conventional cast pistons.

 

I am also running the XE268 comp cam. I have a 1980 L-82. As part of my rebuild I selcted KB-119 Pistons after much reseach. As Joe indicated, they're pretty dam good (well he didn't use those words). The machinest I used for my block work didn't think much of them and warned me about paying close attention to the ring gap. I guess he had to buy someone an engine, or something, after the rings desentigrated on a rebuild he had done for someone. I have decided he must not have payed attention to the instructions that come with the pistons as they inform you that ring gaping for Hyperutectic pistons is differant than most other pistons. They provide a formula for you to determine your ring gap by multiplying your bore by a factor. Mine came out abour .027 for the top ring. The point is, read the instructions and you'll have no problems. Go in like you know it all and don't read up and you will pay the piper. I'm glad now that I went this rout. Would I do It again? In a heart beat! Would I change pistons just to be changing pistons? I don't think so! I would need more reason than that to tackel that job. If I had other reasons to replace my pistons, I would do a complete overhaul, or at least freshen up the hole lower end.
Good luck! Bill Pike

 

Gayney's correct on this one, over 9.5:1 (rule of thumb) on iron heads without very high octane fuel is problematic. If you want to run 10:1 or over, get aluminum heads which generally allow a point higher CR on the same gas.

In addition the benefits of flow over the factory heads will certainly provide more power for your money than just a little over a point of CR.

All that said Hypereutechics are fine pistons and I wouldnt hesitate to use a set in a rebuild, I wouldnt go out of my way to tear down a motor just to install a set.

 

"Strike3"-----


Yes, I strongly suspect that the problem which your machinest encountered had to do with improper top ring gap. With the KB hypereutectics, the top ring gap setting is CRITICAL. Sometimes folks get used to just taking the piston rings out of the package and assuming that they're properly gapped. With pre-gapped rings like most machine shops use, they're USUALLY correct. However, the pre-gapped settings don't work for hypereutectics.

Hypereutectic pistons run hotter at the piston crown than other pistons (thus the need for more ring gap for ring expansion). The reason that they run hotter is because they keep more of the combustion heat in the combustion chamber where it can produce POWER than if it radiated THROUGH the piston.

 

I would agree that with stock iron heads, I would not run 10.2:1 CR. You will have serious detonation problems. That being said, I have KB 10.5:1 on my Z28 383 with Trick Flow aluminum heads. I like them. However, this point is moot in your case unless you are getting new heads, and in that case, you can raise the CR that way.

 

Yea Joe! Thats the same reasoning I used to blow off his advice. I took my time and fitted every ring to the cylinder it was going into. Darn little work, but a lot of patiants.

 

You might want to look at the plain Speedpro hypereutectics. They manufacture the KB pistons and my machine shop showed me examples of the same piston in a Speedpro version and a KB version. They were identical. I think the only advantage the KB's have are there are more radical versions available.

 

Why does the iron or aluminum heads make the difference for what octane I can use? :crazy: I'm not seeing any reason why it would make such a difference :smash:

 

I believe it's related to heat dissipation. Someone will likely correct me if I'm wrong:D

-dath

 

In addition, old high compression engines with iron heads ran on leaded gas. The lead worked as an anti-detonation additive. That is why they were able to get away with it. Now, there's no lead in gas so you have to run lower compression, or higher octane. At some point, the higher octane becomes restrictive as to where you can buy high enough octane to feed your high compression iron head engine. There are additives that you can use, but I don't know how effective they really are.

I totally agree with Ganey that new heads make a lot more sense. 1) You don't have to tear the engine completely apart. :smash: 2) It will allow you to go to a higher compression without all the other stuff you'd have to worry about (octane, additives, etc.). :crazy: 3) They'll flow better than your stock heads, most likely giving you a better HP increase than higher compression with stock heads. :D

My $.02 (I guess that makes $.04) :cheers:

 

hey! I have to thank you guys for the response. I think that the heads are going to be a good idea now. I'm looking into the Sportster II's from World products. The aluminum ones of course. By the way, no one mentioned how high of a CR I could run with aluminum heads. :cheers:

 

I personally would not go over 10.5:1 with aluminum heads. 10:1 might be even better because the few ponies you get for that 1/2 point probably aren't worth the problems you could develop. You can still have detonation problems with aluminum heads, just not at as low a CR as iron. 10:1 might be safer. I run 10.5:1 on my 383 and initially had to deal with some detonation issues switching over to an adjustable vaccum advance to remedy.

 

This is a very interesting topic since I know very little about the new engine stuff that is out there. Is there a good book on building a small block available? I need to do a rebuild on the 73 and I'm not sure if I should return it to stock or if I should make it go faster. Thanks, Craig

 

Make it go faster. It's much more fun :cool: . To start off with you can get rid of those early smog heads.

 

I have heard that the KB's have a 7000 rpm limit on 355's. I ran them hard for years. they have some better sealing properties over cheap forgings like TRW. they come with two valve relief at -6 cc so with a 355 you can get up to 10.7 with a 64 cc chamber. They also have nice pockets that clear .580 lift with 238 duration @ .050 with 2.055 intakes. They can not do 2.08 valves.

I should add that I did run iron heads with 10.7 You just have to have proper cam and ignition advance. It runs fine on 92-93 gas


[Modified by gkull, 11:21 PM 8/9/2001]