I am going to order a rotating assembly for a sbc 400. The kit I want comes with 2 choices of forged flattop pistons for 6 inch rods - KB forged (# KB755 http://kb-silvolite.com/forged.php?action=details&P_id=328 ) or the probe forged flattop ( # 12339-030 http://www.probeindustries.com/Pistons/Pistons_SRS/Chevrolet/Chev_400.htm )

Both wiegh about the same, have about same valve reliefs, I think KB has some funny ring gap issue? is the good or bad? While the probe has a weird 1/8" bottom ring and the KB has the usual 3/16". ??

What you think? Can I go wrong with either choice?

Edit: I noticed that the KB has a 1.333 compression height while the probe has a 1.125, What does this mean. (Both are listed as about the same compression ratios

I am going to order a rotating assembly for a sbc 400. The kit I want comes with 2 choices of forged flattop pistons for 6 inch rods - KB forged (# KB755 http://kb-silvolite.com/forged.php?action=details&P_id=328 ) or the probe forged flattop ( # 12339-030 http://www.probeindustries.com/Pistons/Pistons_SRS/Chevrolet/Chev_400.htm )

Both wiegh about the same, have about same valve reliefs, I think KB has some funny ring gap issue? is the good or bad? While the probe has a weird 1/8" bottom ring and the KB has the usual 3/16". ??

What you think? Can I go wrong with either choice?
i like the probe they have always been a good piston.The kb forged are fairly new to the forged world, and i haven't heard much good or bad about them. I do like the probes small 1/8 oil rings.

I noticed that the KB has a 1.333 compression height while the probe has a 1.125, What does this mean. (Both are listed as about the same compression ratios

Braden,
I have only seen one set of the very early KB forged pistons and they did not appear to be finished very nicely. The Probe ones are very nice looking. I know appearance does not mean as much as actual performance/durability, but it tends to bias me towards the Probe ones. I just got a set for a customer the other day and they are very nice. I was also impressed as all of the pistons were within one gram, weight wise. Says somthing about quality control in my opinion.

I noticed that the KB has a 1.333 compression height while the probe has a 1.125, What does this mean. (Both are listed as about the same compression ratios

The KB's have a C.H. of 1.133" and the Probes have a 1.125". The KB's will sit slighly higher in the holes. Read on:

The better of the two here is the Probes. You've got lighter pins, 2.500" 118 gms as opposed to 132 with the KB's, lighter rings, 1/16"-1/16"-1/8" and they've got a decent track record behind them already. Both are on the 2618 material platform.

Not sure tonight about the oil ring positioning on the KB's but the Probes are fine with the 1/8" rails. No rail supports should be required.

The only issue I have with the Probes is the fact they don't incorporate "direct-pin-oiling". I feel this is mandatory on high HP units. We have run them with .0015 pin clearances to date however with no issues!

(Add) The ring gap issues would affect only the "Hypereutectic" (cast) pistons, not the forged!

Thanks, Gary in N.Y.

P.S. If you're going after "serious" HP I would recommend drilling those pin-oilers, it's not that difficult for a shop. With clearances under .001" (piston/pin) and any power-adders like Nitrous, and you will risk having pin issues!

the forged KB don't have the design deal that causes the HT to need the big end gap on the top ring. They're a conventional forged piston.

on the height diff, the short piston won't have as tight a quench area.

stroke radius of 400 crank is 1.875

1.875 + 6.0 + 1.333 = 9.208???? block is only 9" tall? piston sticks out out of block .200? something wrong there, maybe a typo.

1.875 + 6.0 + 1.125 = 9.0 this is right.

Probably is supposed to be 1.433 CH for a 5.7 Rod, maybe?

I just had a DeJaVu moment.

Im running the Probes in my 408sbc. great so far!

probes and srp are great stuff and pretty light.

I've had excellent results with JE/SRP stuff. Been using their stuff since the mid-eighties, never a problem.

Ahh crap, The 1.333 CH for the KBs is a mistake its suppose to be 1.133. So it will the deck will end up being 9.08 I beleive with the KBs ?? so with probes the 1.125 it will be 9.000. Meaning it is zero decked? good for qunch ? I am kind of confused now with the deck, I had always thought that to change the deck you mill the block.

If the block is stock deck height..it's around 9.025. The probes would be down in the hole around .025 with the KB's around .017" in the hole.

I've only had one experience with probe pistons....and That is the only experience I will ever have with them....

If the block is stock deck height..it's around 9.025. The probes would be down in the hole around .025 with the KB's around .017" in the hole.

I've only had one experience with probe pistons....and That is the only experience I will ever have with them....

So acutally the KBs will give better quench given the block is not milled correct? What was your problem with the probes?

To be fair. it was when the company first started making pistons. I had a set of dished forged 383 pistons. The valve reliefs were wrong. I called them and they said I was wrong. I relieved the VR's but I wasn't happy with them. We orderd another set for the speed shop and they came with the proper VR's. I took pictures and sent them to Probe. They told me to basically F&%k off.

I wrote ROSS a letter and told them what I wanted, paid my money and several weeks later had what I ordered fine!!

Beautiful pistons!! Kind you wanna make into ashtrays and sit on the coffee table back before PC!!! That pretty!!!!

pdq67