[steve25]

A factory cast piston will run a tad longer than a hyper when tuning factors go off the rails since they are not as brittle.

This does not mean I would not use them in a build, but I would not use them in a short block that would be approaching or topping 400 Hp unless my wide open throttle tuning skills where very good.

To me Hyper’s are not a material to hone your tuning skills on, especially so with todays pump fuels.

I would sooner run a common 5/64” ring Speed pro piston and stuff far lighter wrist pins in them.

Also I need to mention because I forgot that total seal makes a shim to go from 5/64” rings to 1.2nm.
This changes things in a big way, and they claim a 12 Hp gain.
Taken with a grain of salt let’s say a solid 8 Hp gain.

It’s a bit of a learning curve to heat a rod for pressed pins.
I learned on 5 junk rods before I got the hang of it, but I gotta say that if a shop leaves this task to the lowly shop Gofer then the odd’s of taking the needed temper out of steel rods goes way up!

The best way to do that job right every time is with a Thermal gun.

[tooski]

Originally Posted by Cliff R

Most of his new KB HT pistons were missing from the bores and piled up in the oil pan. They shattered like glass and left the rods and pins moving up and down in the bores void of any pistons on them.....NO THANKS!
.

Wow!

[steve25]

Unfortunately for them a lot of folks don’t know how much the timing needs to be backed down even with just a 150 Hp shot of that stuff!
If you don’t have a programmable ing box then that’s not easily done .

[Kenth]

Originally Posted by tooski

Wow!

That's why KB does NOT recommend nitrous shot for the hypers.
But racers are racers, they will ALWAYS run their stuff until they break, one way or another.
(This is the "Street" section BTW).

[tooski]

Originally Posted by Cliff R

The cast piston options for the 400's are absolutely pure bovine excrement and always have been. I still remember mocking up an engine I was hired to assemble decades ago using those pistons. They were WAY down in the holes at TDC and already taking over 15cc out of the squish area like using a dished piston. Team that up with a 4X or 6X-8 head in a 400 build and you'll have about as much compression as a Briggs and Stratton lawn mower engine, and left wondering why it doesn't idle or run for chit once placed in service......

I had them in a build that was done in '82. I asked the machinist to do a zero deck. I found out he did not and was glad for that as the pistons were .040 down. Swapped heads to a 6X-4 to alleviate detonation. Resulted in a CR of 7.6. Engine still ran ok . Swapped pistons to the heavy SpeedPro which brought the CR up to 8.2. Still not great but the engine runs much better.

[PAUL K]

Originally Posted by Kenth

Hardly the pistons fault if the mechanic is ignorant.

Agree 100%

When you build engines for a living you don't want your customers having an issue. I've personally run KB Hypereutectic pistons in my own build and was happy with them. They were in a 1971 HO that ran bottom twelves on motor and high tens with spray. Never had an issue. May not be as good of a story with a 9:5 build and the guy gets a tank of 87 octane that's marked 93. The piston might launch into orbit before the driver here's any pinging.

KB hurt themselves when they first introduced those pistons. All their advertising was spent promoting the product and talking about how great they were. Little was ever mentioned about the increase in top ring gap needed and they never talked about them being octane intolerant. Folks were ripping the tops off those pistons more often than not due to using a standard ring gap. It took quite a while before they highlighted the ring gap issue and had advertisements make note of it also.

[ponchjoe]

Originally Posted by Kenth

That's why KB does NOT recommend nitrous shot for the hypers.
But racers are racers, they will ALWAYS run their stuff until they break, one way or another.
(This is the "Street" section BTW).

Thanks Kenth. Seems like every post goes to drag racing/max effort somehow somewhere, that’s why I posted the build of a 9ish:1 street cruiser. Sounds like KBs might be an option I’ve never considered. My builder is well versed on Pontiacs so I’d just have to reminds him about the clearance.
Do you know how much weight difference there is between the KBs and the Speed Pros?

[Joe-Touring]

Originally Posted by ponchjoe

Do you know how much weight difference there is between the KBs and the Speed Pros?

Per the Speed Pro website: 589g/783g with pin

KB’s website does not list weights, from CNC motorsports website: 541g/704g with pin

https://www.drivparts.com/part-detai...rand_code=BHVW

https://uempistons.com/product/647/K...TM.030?sflag=0

My personal recommendation is to go with the speed pros. They were the go to for many years, I haven’t seen many examples on here of them failing. Multiple local machine shops have said the KB Hypers have issues even when you open the rings up to their specs. The shops said you wanna go REALLY big on the gaps

Of note: KB’s website says they sit 0.025” under the deck. Quite a bit of deck to trim off

[ID67goat]

Originally Posted by Joe-Touring

Per the Speed Pro website: 589g/783g with pin

KB’s website does not list weights, from CNC motorsports website: 541g/704g with pin

https://www.drivparts.com/part-detai...rand_code=BHVW

https://uempistons.com/product/647/K...TM.030?sflag=0

My personal recommendation is to go with the speed pros. They were the go to for many years, I haven’t seen many examples on here of them failing. Multiple local machine shops have said the KB Hypers have issues even when you open the rings up to their specs. The shops said you wanna go REALLY big on the gaps

Of note: KB’s website says they sit 0.025” under the deck. Quite a bit of deck to trim off

In my opinion, it is hard to compare a hyper piston with a forged. But just for info here, I have a set of the KB 2618 forged pistons (+.030 428 piston with a dish) and they weigh 714.4 grams with pin and 567 grams without the pin.

[Formula8]

I have used ICONs and Autotechs from PK. My understanding is the Autotechs are all 4032's while the Racetech's are 2618. No issues with either ICON or Autotech. Both were accurately machined and my current Autotech's are doing just fine. Thanks PK!