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chevyelc81 01-27-2005 01:58 PM

Keith Black 121 pistons
How much BOOST and HORSEPOWER can the KB 121 Dished pistons handle? They are 28cc dished and say they are suitable for blower turbo applications. With 64cc heads they make 8.6 to 1 compression. They are for a 383ci stroker engine with 5.7 full floating rods. Will they handle 10 or 11 lbs of boost? They are hyperutectic. Thanks

Cstraub 01-27-2005 02:28 PM

If properly set up in the block, yes. The problem is most don't give these pistons enough clearance in the rings and you need to run alot less timing in the engine.


k-star 01-27-2005 05:32 PM

These pistons got a bad rep when they first came out, and it stuck with them for some time. As chris pointed out you need to pay real close attention to the gap on the top ring. I fit mine .002" or so over the top gap they recommend. All these pistons that i have seen destroyed have been for 2 reasons. The top ring lifted ( because of a small end gap) Or detonation. They will not tolerate any detonation at all.... I'LL REPEAT THEY WILL NOT TOLERATE ANY DETONATION!!!!!!

So if your a good tuner and pay attention to what is going on inside your engine your ok..... if your new at this or don't pay attention i would spend a few extra dollars and get the forged..


camaroman7d 01-27-2005 08:32 PM

I personally would NOT use those pistons in a blown application. If you were talking 4 lbs of boost I would say go for it. Hyperutectic pistons are CAST pistons. If you do your research they DO NOT suggest running cast pistons in blown engines that are being built to make power. You said 10 or 11 lbs of boost. For a roots blower that is going to make a ton of torque and power. Don't confuse that boost with the boost of the turbo cars or centrif blowers. Roots blower will also make more heat and be more prone to detonation if things are not set-up correctly.

Cast pistons are good to maybe 5lbs of boost. You will no doubt break those pistons if you run boost on them.

Before you throw a blower on anything make sure you do lots of research. While it is possible to just slap a blower on an engine and it will make power, there is a right way and lots of wrong ways to do it. If you want to make power and want the engine to live do it right.

I have forged pistons and 8.47:1 compression I run 12lbs of boost on pump gas, that is REALLY pushing the limits on 91 octane. Make sure you check into what boost does to your "effective" compression ratio. If you need help finding this info let me know I will try to post some links. Actually go to and browse the FAQ section, along with the rest of the site. That will not be all the info you need but, it will get you started in the right direction. I also HIGHLY suggest picking up (and reading) a book called "Street Supercharging" by SA Designs. Lots of good info in there to get you started.

Not trying to rain on your parade but, I would hate to see you throw money away.

Check out my site and you can see a little of what it took to build my engine

Hope that helps some.


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