Posted By: elmor
360 Piston Choice - 11/09/12 10:13 AM
Getting ready to send my block to be machined and would like to get some input on pistons to use. I want to run pump gas and I'm using factory heads that came off my 85 engine. I would like to get an honest 9 or 9.25 compression ratio. The block will go .030 over and have the decks squared up. I looked at KB-107's, but I think they may put me a little higher than I really want to go. Speed Pro H116CP's look like they may be a little less compression, but still get me in the ballpark.
Just need some input from people that have done this. I appreciate any suggestions.
Posted By: RapidRobert
Re: 360 Piston Choice - 11/09/12 10:25 AM
If the short block is still together I'd measure the deck height & compare the OE piston compression distance to the CD of those 2 piston choices. If those heads are 302's I would shoot for .035"-040" quench which as you know will let you run the highest CR & fastest advance to get the most torque out of the lowest octane and when you choose the best pistons for this (I dont have an answer for your Q on that) then mock them up with a floating pin to find out how much to square deck the block to to get the CR/quench where you want it.
Posted By: elmor
Re: 360 Piston Choice - 11/09/12 10:42 AM
The heads are definitely not 302's, can't remember the casting numbers.
The engine is down to the bare block and the factory pistons and rods are sitting in a box. My machinist is a friend of mine and I'm hoping he may be able to help me get some measurements. I would think that even with the engine apart, we should be able to get a pretty good idea how far in the hole the pistons were. If we measure the deck height before it's cut, measure the compression height of the stock pistons, we already know rod length and stroke. Am I close to being right, or am I just whistling thru my butt? lol
Posted By: 70Cuda383
Re: 360 Piston Choice - 11/09/12 01:16 PM
If you have open chamber heads, the 107s are a great choice. if your deck height has been shaved and they end up at "zero deck" and gives you more compression than you want, then you can take those 107s and have some, all, half, etc. of the dome shaved off.
you can do it to create a quench pad by only milling on half the piston, you could mill evenly off the whole top, etc.
Posted By: 440newport
Re: 360 Piston Choice - 11/09/12 08:40 PM
I'd use the H116CP's. In my '79 360 they sit 0.015 in the hole. I'm using '345' 80's heads that have been milled about .030 to give 69cc chambers, I think it's good for about 9.6 compression.
The 107's have a high top ring land and can be sensitive to any detonation.
Posted By: 451Mopar
Re: 360 Piston Choice - 11/10/12 02:38 AM
The speed pro pistons will get you in the 9.2 to 9.5: compression area, but have no quench effect.
The KB107 is closer to a zero deck flat top which will increase compression over the speed pro piston.
You should CC the heads and that will really help in calculating the compression. I built my 9.5:1 engine with the KB-232 0.050" quench pistons, but it requires alot more machine work. The piston is designed for magnum rods pin widths so the machine ship had to mill the pin end of my rods, the block was decked to square it up and get the pistons near zero deck height, then the heads has to be decked between 0.040" and 0.050" to set the quench pad to the recess area of the head (zero clearance without gasket.) The gasket provides the quench clearance. For a simple 9.5:1 engine, I don't think it was worth all the extra pains just to gain a small amount of quench area. I think if I was doing a simple 360 with 9.5:1 compression, I would just use the speed-pro pistons.
Posted By: 360view
Re: 360 Piston Choice - 11/10/12 12:33 PM
Factory stock 1995 Magnum 5.9 pistons average
472 grams without rings or pin,
and average about 11 cc in the dish.
Compression height seems to be 1.626
Anyone know the
lightest piston available
in a 4.00 size?
Could a 360 be internally balanced
without Mallory Metal
If a light piston and aluminum connecting rods
Were used?
Posted By: HotRodDave
Re: 360 Piston Choice - 11/10/12 05:12 PM
I looked into that before and could not find a way, I did not look into aluminum rods but I don't think they are gonna get much lighter than a SCAT I beam, the lightest common affordable strong rod. I think if you got some custom ultra light pistons you could MAYBE do it but even then you would probably have to weld up the existing balance holes in the counter weights and grind off the casting protrusions on the pin side of the crank.
