360 Piston Choice

Been researching piston choices for the 360 I'm building and it looks like it's either KB107 or Speed Pro H116cp. With the heads I'm using and a .039 head gasket, the KB will give 9.82:1(.012 in the hole) and the Speed Pro will give me 9.51:1(.027 in the hole). Not a huge difference, but a little. My question is which piston will be most reliable? I've heard several stories from guys that have had the KB's come apart on them. My old boss at the machine shop I worked at said he would use the Speed Pros because he knew they were a quality product and never encountered any problems with them. What are the pros and cons of each? Would love to hear what kind of experiences you guys have had, good and bad.

The KB's are popular due to price. They break easy due to bad ignition timing and/or poor state of tune along with bad ignition timing. I have used the KB-107's several times. My machinist doesn't like them much.

The Speed Pro C116hp I have used once before and currently I am using again on the currently being built engine. I also had a create engine with these pistons within. My machinist likes these pistons.

What my machinist likes and dislikes just seemed to be preference by him.

I have not seen, felt or measured any difference in performance between the two oistons. The SP116 has the coated anti friction skirt. Some around the net complained when it wears off with "I don't want that crap floating around my engine as it wears off the skirt."

I say your oil filter takes care of that and if it doesn't, you need a better filter.

The SP116 will work a little better in a iron head solely due to the slightly lower compression height that makes it easier for a lower ratio to work easier with a iron head. While it is true you can have your deck surfaced for an any thickness MLS gasket, the finer points of your build and how it gets done is your call.

I found both Pistons to be just fine. Perhaps you may want to look into there weights? Or bang for the buck cost wise. The SP116 can be found at summit being sold with rings for less than a separate purchase of each. I do not know if the KB's are available like this in cost savings or cheaper than the SP116. Perhaps one has deeper valve notchses, if you actually need it.

I dont see a problem with either choice as far as integrity goes but I would get quench if you have closed chamber heads or mill the recesses in the open chambered heads then work with plateau pistons to achieve it if you want to go that far (its time/money but worth it). #1 quench (if you can) #2 cam choice (one that you can live with) (3) octane choice) (4) SCR to get the DCR in a good range so you can run a fast ign curve & be under the pinging line. As said detonation will kill any of em (not to mention any names but some quicker than others!).

Had KB 107 in my 360 for over two decades of street abuse now. Couple hundred thousand miles, bad pinging problems for a lot of those miles, three tear downs, three different sets of rings. Zero issues. I would use them again in a heartbeat.

Think hard about your CR, timing, and fuel choices. The 107s with unmilled j heads and a Mopar Performance distributor, I could get the thing to NOT ping even on premium. Changed to a stock distributor last spring and now it runs as just as good on 87 octane.

First of all, let's get something straight. Any Sealed Power or Speed Pro piston with an "h" in front of it is a hypereutectic piston. So the H116CP as well as the H405CP are both hypereutectic pistons.

Second, what heads are you going to be running? That's a huge question. Open chamber heads and closed chamber heads have different needs.

One major advantage the KBs have is they are light. The 107 is 507 grams and pin is 132. Sealed Power/Speed Pro pistons are usually stock weight which in this case would be 584 grans, plus the thicker wall pin is at least 152 grams. That's at least 87 grams off the piston/pin assembly.

I'd suggest going to the United Engine and Machine website and look at the choices and their weights.

Keith Black pistons do require larger ring gaps, especially the top ring. This gap is usually big enough that one can use regular rings and file fit them.

Do look around on ebay and other places. For example I found a set of forged pistons for 4" stroke 360 for $315.00

Good Luck!

R.

I would likely use the lower compression speed pro pistons with rings, only $275.99 (kit with rings is cheaper than pistons only?):

http://www.summitracing.com/parts/slp-8kh116cp30/overview/make/dodge

Either piston could work, but I would not push the compression too high on a non-quench engine. I think the KB pistons run the top ring higher on the piston which requires a bit more ring end gap.

I'm using mid 70's factory open chamber heads. Also using Comp XE268 cam.

Didn't realize the Speed Pros were close to stock weight. KBs are definitely lighter and will necessitate a balance job on the rotating assembly. Something else for the OP to keep in mind.

The KBs definitely need the larger gap on the top ring. I've read elsewhere this is a lot of the source of negative feedback in KBs, user error. People put them in with stock end gap, ring s heat up and ends contact, ring keeps expanding until it wedges into the cylinder wall, top of piston cracks off. I've always used off the shelf rings and hand filed the gap on the top ring myself. Just takes a little measuring and some careful work with a fine file. Formula for necessary gap is on their website.

(1) very user friendly calculator for SCR (they have DCR but I would not recommend it) (2) 0.0065" gap per inch of bore on top ring (street/normally aspirated). 2nd ring same as normal (I go with 0.003" per inch of bore) but KB wants .004 per inch on the 2nd ring on their pistons

I suggest you go to the Silvolite website and look over the KB piston selection there. IIRC there are 5 different Keith Black pistons. As you have an open chamber I think it would help to have one with a "quench dome". If at some later time you decide to go closed chamber the quench dome can be machined off.

Actually as you have an open chamber I would suggest Magnum heads and a reverse dome piston set close to the top of the bore..

R.

Most of the KB hyper failures can be traced back to improper ring gap (ignoring the instructions and doing what you have always done) or severe detonation. I have had real good luck with the KB107 and really like how you can get tight quench easily with it.

If the SP H116 is close to the same weight as factory pistons, I think that's the way I'll go. I'd rather not pay for balancing if I don't have to. It all comes down to MONEY! lol I found a set of new H116CP pistons in Australia! With shipping total price is $213.00

I'd Google it & see what the gram spec for em is. My balancer has a limit of 20 grams (iirc) & thats on the recip part of the formula so it is cut in half when added in so its actually pretty limited on the leeway. Do ya feel lucky? well do ya

Did a little digging and found that factory piston weight is 584 grams and Speed Pro H116CP is 567. Is that enough of a difference to worry about re-balancing?

I had many people tell me KB pistons were junk and I could never spray with them. That is a wad of crap. They were fine. I did break one in half when I got greedy, but that wasn't KB's fault.

Yee, do open up tye top ring gap or the top ring will butt and blow the land up. On a 3.45 bore I had mine as wide as .035.

I would talk to your man but it sounds good from here

IT'S A STOCK REPLACEMENT PISTON. Or a high perf version of a stock replacement piston.

Thousands have been installed in 360s without rebalancing. It's not an issue.

People on this board will tell you 95% of the time that anything and everything needs to be rebalanced. That's bull. But it's easy to spend your money.

Chrysler balancing specs had to be the widest in the industry because the anecdotal evidence is huge. Yet, there weren't customer complaints about engines running rough. Chrysler engineers were very, very good at figuring out what corners to cut to get costs down.

I'd go a different way as outlined above, but do a search and you'll find an article by Steve Dulcich about a 360 with those pistons making 417 hp with stock heads.

R.

PS: Weird but true, the Oz seller appears to be low. Their dollar is worth $0.76 US so there is a set for $150 Australian that comes out to $114 plus shipping. I'd be looking at UPS or DHL for the delivery.

Close chamber heads with (your favorite brand) D-dish pistons is the only way to fly. If you want a pinging iron headed motor then by all means go with 9.5:1 flat tops.

FalconGlobal has'em for less than $300.

http://www.ebay.com/itm/Speed-Pro-Chrysl...=item2c8f42cbc9

R.