Needing some input on these kb hypers im using on this current project, consider it a simple bracket type build.

Iron heads, 4:56 gears and probably driven to track so the motor is going to make and hold heat.

Ive got the cylinder to walls at .0035 and im thinking .030 on the top ring on a 3.95 bore, maybe .026 on the second ring.

I know they say dont spray these but some do so id like to use a 50-75 shot possibly, remember on a tenner build a extra 50-75 is a good bit.

Any input would be helpful as the ootb top rings are at .019 so thats not even close to where I need to be.

THANKS.

I don't use any cast pistons on any of my Hi Po builds ever
Especially with a power adder

Good luck, wider is better on any ring gap than a tiny bit to narrow

On my little turd we ran the top rings at .032" on a 3.445" bore. For me hypers were great at a 150 shot, but 175 seemed to be the breaking point. I was always warned they would shatter. Never rid that, but I did break one in half. We didn't notice it untill we took the rings off and it fell apart.

My dad and wife have both have had KB hypers come apart and ruin darn near everything on the engine. Both were mild builds and weren't sprayed. I'd be careful how hard you beat on em...

I have a set in a 360 that I beat like a rented mule, 4 drag weeks, lots of street miles and a good amount of passes. I do not recall what I have them gapped at but it was whatever they recommend for street/strip NA. On a good day it made 500HP according to ET and wieght.

I will say this, I had some KBs in a 340 ages ago and I broke one of them. It cracked right across the top down to the pin but didn't come apart. It just picked up massive blow by. They had been ridden hard through high school with lots of abuse and lots and lots of passes.

Great Feedback! Thanks.

This is one of those "I got them cheap" deals but im pizt at myself when I passed on some new wiseco forged this past winter off ebay at $400.

I will use a .030 feeler and keep it on the loose side of that.

I dont think id spray it often at all but it can make a difference if the other guys got a fender or so on me.

I am hard on parts.

But this is a good reason not to beat this build, easier said then done.

THANKS!

My buddy built his cousin a 360 with hypers and told him not to spray it, cousin decided to work up to a 250 shot and bracket raced it for like 6 years till a rod bearing gave up.

I had a nitrous addiction with a junk forged piston 360 shortblock. One of the reasons I put the hypers in my 360 was so I wouldn't do that anymore those bottles go quick and aren't cheap to fill.

They work fine for mild applications. Where they fail is not having that top ring opened up. just follow the end gap factor for the top ring, error bigger than smaller and you'll be fine. Should be around .032 I believe. Id have to consult my book to be positive.

I ran a set of hypers in my 366 bracket motor for 14 years with no spray and not a failure, keep the gaps wide and don't let it detonate that is a sure killer of these pistons, and yes I have seen them in the bottom of the pan that looked like dust from a sb chevy roundy motor.

I got them wide .032 and its very mild. Im counting on the proper vert and rear gears to make up low power on this one.

built a 440, .590 cam, ported 906 heads, with KB pistons, raced it 6 years before it broke a rod. Follow directions on ring end gap, cylinder wall clearance, and ignition timing. The alloy of the pistons project more heat into the chamber, instead absorbing it like a cast piston, this also makes them expand less. I shifted about 6,000 rpm it ran 10.90 in a 3200lb car. Pay attention to the quench in the head, a tight quench helps stop detenation. I remember KB made a special piston for the open chamber head that you milled to adjust the quench. I would not recommend nitrous. Did build a SBC with 671 blower and KB pistons which held up well.

Read what KB insists on for end gap for nitrous race engine - it's bigger than you think: .0095" per inch of bore.
That's .038" for a 360, .041" for 440, and .043" for 4.500" bore.

Tight ring gap is the #1 reason for hyper failure: READ THE DIRECTIONS.

https://www.uempistons.com/installation_instructions/kb_installation.pdf


Thanks Poly, your correct, I think they mean that spec for full time spraying, im going by there street nitrous spec since the only track or the amount id run this is the 1/8 and never until out of low gear (oem cast crank) on a 3.95 bore.

But ive got them filed at .032 but could go more, I m not putting thim in till tonight.

But im open to go wider if needed.

.0035" piston to wall clearance seems too loose for a hyper also...unless I'm reading op wrong

If you look at the link above I posted that has the KB charts they say you can go as far as .0045

https://www.uempistons.com/installation_instructions/kb_installation.pdf

There is alot of info, good and bad on the KB brand hypers, I cant say this will be a learning curve for me because all I do is either stockers or strokers and this is sorta like middle ground and although different and semi fun at times im not liking some of it.

Ive beat oem cast pistons in the past, broke skirts, ect but it took 60k hard street beating miles to do so, my good builds always got forged.

With the pitfalls of the KB brand im wondering if it is really worth the bs in piston choice when its only a couple hundred bucks.

But maybe hypers have there place in class racing?

they are light.cant remember balance numbers but machinist cut alot off crank. stock ly rods

Id be more worried about the rpm. Everyone always told me to keep it under 6400???

I ran them in my old 906 headed 440 that was in my 63. I used the MP .557 cam and it is a street car but I raced it about twice a year. It ran a best of 11.49 in my 3725 lb 63 and I set the ring gaps as they said which I believe was about .025 on top and .022 on second. But as stated run the proper gaps and piston to wall clearance and timing. I ran my old 440 from 2006 to 2011 and its still running good in a Duster right now. It did have a little piston slap when cold but I knew it would from the extra piston to wall clearance you run with them. Ron

The alloy expands less than 2618 and 4032/VMS75. So they can go in tighter than forged.
It's kind of funny saying there's a difference between hypereutectic pistons and cast pistons. BOTH are cast. The reason a cast aluminum piston doesn't expand is because it has steel inserts that prevent it from expanding much. The KB pistons don't have these "autothermic struts" like a standard cast piston.
Over the years, KB pistons have been quite successful. They are quite unforgiving if you don't follow the book. It's worth noting that many/most of the OEM pistons in passenger cars are hypereutectic. Sealed Power has been switching over a little at a time. So there's nothing inherently wrong with hypereutectic pistons. You just need to follow the directions.

Some KB pistons are as heavy as stock, some quite a bit lighter. IMHO if you're looking for a light piston I'd suggest a custom forging supplier like Wiseco or Ross or Diamond or JE. Or Mahle.

Sounds to me like you're going to be fine. Just keep reading the instructions.

R.