new guy here with a question about kb421

[joshm]

ive searched quite a bit for feed back on the new (last year) KB421 pistons. Im wondering if anyone here has ran them yet. i spoke with a builder today and they said they have built 20 motors without any problems and sold many more kits. the only thing that came up in my search was from a year ago and a few members sounded leary of them. That said, any new feedback? and im glad to be here thanks for any input.

[Russ Pottenger]

What's not to like about it : )

It wouldn't be my first choice for a piston.
It's a Hypereutectic/Cast full circular 27.5cc dish piston that sells for over $300.00.

Comparing that to my piston which is machined from a high silicon aluminum 4032 forging. Rather than a full circular dish, I can make mine in a reverse mirror dish in any volume up to 28 cc in any compression distance for just $200.00 more than the cast KB piston.

You're welcome to contact me I'll be happy to email you more information on my Pistons or any of my other specialty kit components.


Russ Pottenger
Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California 91790
(626) 673-2203
Email/PayPal: [email protected]

[duck454ss]

His pistons are truly worth it....

[joshm]

Thanks for the feedback fellas. Yea I've considered a set of custom Pistons and the icons. It's a slippery slope if I go high dollar forged then I might as well go big valves and port the head. And if I go that route I might as well throw in a bigger cam springs header etc... just not the road I wanna go down with this engine. Maybe on the next build.
I was pleasantly suprised today when I tore down the two motors. The 4.2 had been recently rebuilt and the crank is cut 20 under and won't need anything but a polish. The 4.0 was all stock with minimal copper showing/ all standard bearings.

[Russ Pottenger]

If you're that budget conscious you might consider a 232 3.500 stroke "Mini" Stroker.

A reground 232 crank with cast replacement 4.0 Pistons will cost you less than your KB421 Pistons , and will keep you off the slippery slope.

[joshm]

I appreciate your input Russ, and i understand that you sell a far superior product, that would be a great option for a higher performance stroker build. What is your opinion on these pistons? from what i understand they are made specifically for the 242 258 stroker application, they are better than cast, have the correct pin height to allow for the longer 4.0 rods (better) and have a dish volume that will allow for lower compression ratio and reduced chance of detonation. seems like a win win unless there is something Im missing

[Russ Pottenger]

In my opinion it's just a horribly speced out piston.
I just don't know where to start.

First it's a bad idea to run a full circular dish piston with a closed chamber head unless it's absolutely necessary.

In a normally aspirated engine utilizing a cylinder head that has a close chamber the best piston design would be a flat top piston. In my race Strokers that's exactly what I run. The only problem with running that combination on the street is the static compression ratio is over 12.1:1
Obviously that combination is going to present a problem if you want to run on pump gas. So the next best option is to determine how much volume you need to add to drop down to your desired static compression ratio so you'll be able to run your desired octane level. The shape of the dish in your piston should be a reverse image of the combustion chamber in your cylinder head.

Next, at TDC you ideally want that piston to come as close to your cylinder head is possible without hitting it.
In creating this quench area where the flat part of the piston meets the flat part of the combustion chamber, it excites the air fuel mixture that's coming into the combustion chamber. Because of that induced stimulation, you're going to get a more efficient and complete combustion.
* More power/torque
* Able to run a higher static compression ratio for a given fuel.
* Potentially more MPG.

The other problem with the KB421 piston it's suffers from the same problem as the forged KB944 piston. It has a compression height of 1.353. Without decking the block the Pistons going to be about .030 down in the hole, over .070 minimum piston to head. That will absolutely kill any combustion efficiency.

While I'm sure there's been plenty of people running this piston, and plenty more will continue to use it.
Unfortunately if they would've put a dish in it similar to their 944 piston with a 26 to 28cc dish volume and a compression distance closer to 1.380/1.385, it could've been a potential big seller.

[joshm]

thanks for taking the time to answer my questions russ, im dropping the block off on tuesday to get cleaned and measured. ill check back with you about your pistons once its all measured out. thx again