From Sterlings to Silv-o-lites......need source

[Dr. Righteous]

My 360 Ramcharger consumes too much oil for a fresh engine.
I suspect the Federal Mongul pistons because they felt a bit on the loose side when I installed them, but I was assured by the machine shop and Summit Racing that they are suspose to be that way and they would have the proper clearance once it was up to tempature. My gut feeling was to ditch the pistons for some Keith Black pistons. But I went cheap. Paying now.
Since this is just a truck there is really no need for race pistons. Some cast Silv-o-lites should do.
The problem is I can't seem to find anyone that can give me a price on a set of 0.030" over flat top 360 pistons.
The KB part number is 1273-030.

[6 packin]

Just wondering?
What was your ring end gap? And what rings did you use?

[cuda66273]

Doc..email me off the board and I'll get you a price on those pistons.

bigdaddy@4secondsflat.com

[Dr. Righteous]

I set the rings up for Hypernutectic pistons. The rings were speed pro molys. I set the top gap at .026" I believe. NOW,if you read the "rebuild kit snafoo" thread the quesiton I have is are those even hypernutectic pistons at all????
Bad news. Will post more information as I tear into it and replace the pistons.
I also have a different set of heads I am going to install.

[jelsr]

Like 6 packin, The ring end gap for KB's is outrageous by normal standards. I tend to follow Mfg's specs (they made it so they should know how to fit it) but that is a big gap. I've heard stories about using .016-.018 with no problems but I wonder?

[451Mopar]

Just to clearify, only the top piston ring gets the larger gap when using KB pistons, the second ring and oil rings are stock gaps.

The 1273 piston is supposed to be right at 9:1 compression using 65cc heads.

[6 packin]

There is your problem! If you set the ring end gap for those pistons as if they were Hyper pistons you have way more end gap than you need. If I recall the end gap of the top ring is almost twice of the normal setting! Those are NOT Hyper pistons, there cast pistons. You got to watch them. Sivolites and kieth black makes stock cast pistons too, besides ther line of signature series pistons like the KB #107's which are Hyper and require spiecal end gap. These will be very noticable the top ring land will be much higher on the piston (not spaced evenly compared to the others). This puts the piston ring higher above the water jackets in the block which it tends to run hotter, which calls for the loose ring gap for expansion. If NOT done the ring ends will butt, do to the expansion and pull the top of the piston apart.

The engine will disasemble about 10,000 times faster than U put it togather!

[6 packin]

Here is a pic of a hyper piston, take a good look at the top ring land!

[Dr. Righteous]

The pistons in the engine now are Federal Mongul H405P at .030" overbore.
That is what I ordered in the kit. I installed them and assumed they were the right pistons. It turns out by all my checking that they are the wrong pistons. They are not KBs of any kind. I want to switch to KB Silv-o-lites because for my application I really don't need hypernutectics.
The real problem is the pistons in my 360 now are a total mystery. I don't know what kind they are because from my reasearch they are not really FM H405p pistons.

In other words. The box the pistons came in said Federal Mongul H405P hypernutectic pistons. But they looked nothing like what I hypernutectic pistons should. They may be stock cast pistons. If that is the case the top ring gap is way way way to big and it is robbing compression.

[6 packin]

Ok my bad!
One other thing, the hyper pistons worked ok for my application, there better than the stock pistons for sure. There not race pistons also, they will not stand any detnation at all, no NOS too! For a good track/street car I will go with Forged. Thats my opinion.

Good luck!

[Dr. Righteous]

Well, maybe when I say a "Race Pistons" that is too broad a term.
Better said is that they are an excellent Performance Piston.
Hypernutectics do have some advantages over Forged.
They are much cheaper, they don't cause the engine to consume oil like with forged pistons, and they are much lighter.
For what I have seen most of the failures people complain about with hypernutectics is improper application or installation. The top ring gap varies depending on what your type of racing is or whatever.
My next RACE engine will use hypernutectics. The main reason is I can build it much cheaper and get just as good as performance as using forged. I would be nervous running forged pistons if I had stock rods. You need race rods with forged pistons because of the weight. VERY EXPENSIVE. Out of my league.
Yes, forged pistons is the ULTIMATE, but for us budget racers, we have to save as much as we can.

[jelsr]

I guess I missed something on the forged pistons needing aftermarket rods due to the weight. I am running JE's in my 451, which are 25gr lighter than the KB's for the same application. The Ross' were only about 3gr heavier than the JE's and both offer .990 pins which save another 50+ grams. Got the JE's off the net for $320. Guy ordered .050 over for 451 instead of 440 and they wouldn't take them back, .050's were special order. Got lucky there! The KB's are good pistons but they are not "race" pistons, they are more brittle than regular cast pistons and will not stand any detonation.

[Dr. Righteous]

Sorry, I didn't consider some of the newer forged pistons out there. There have been some improvements in the weight.
I remember that the TRWs (back in the good old days) were way heavier than the stocker pistons and racers would break stock rods using them.