360 rebuild with a 343 rebuild kit?

deadironrat

I'm looking to rebuild the 360 in my 79 J10 and I want a little more performance. I know 343 pistons will bump up the compression some, my question is if I was to buy a 343 rebuild kit with pistons would all the gaskets and bearings from it work in my 360? The reason I ask is because it would be little cheaper to buy everything in one kit instead of buying pistons seperate.

JERSEYJOE

YOU WILL NEED TO REBALANCE THE ASSY DUE TO THE WEIGHT DIFFERENCE IN THE PISTONS. FIGURE ABOUT $300.00 TO REBALANCE.

AMX69PHATTY

As far as I know, Yes, all the gaskets, bearings, freeze / pipe plugs, and rings are the same.

Significant Differences between 343 and 360:
Deck Height - 343 = 9.175 ... 360 = 9.208
Stroke - 343 = 3.28 ... 360 = 3.44
Pistons - 343 4V had flat top with valve reliefs. 2V had small dish
......... - 360 had a "large" _28cc dished piston '72 & up
Exh Port - 343 = rectangular ... 360 = dogleg
Chamber - 343 = 50.60cc ... 360 = 57.92cc late '71 & up
Crank Flange - 343 = BW flange ... 360 = TF Flange '72 & up
Dampener - 343 = 3 bolt ... 360 = 4 bolt '73 & up
Flexplates were different for C.I. and Trans Type
As mentioned, the 343 rebuild parts should all work with the
360 dampenr, flexplate, crank, block, rods, heads, etc.
but re-balance the rotating assembly.

May I ask, are you considering a 343 Kit from www.egge.com ?
If so the pistons may have a ~.030 shorter compression height than stock.
Info Egge provided to me was 1.570 Compression Height for their 343 pistons, both 4V & 2V.
Stock 343 & 360 Comp Ht is 1.601 nominal calculated from info in PAS.
Be sure and consider that when calculating CR and deck clearance.
Some of that can be "re-gained" by offset grinding the 360 crank, and/or deck milling the 360 block.
If Con Rods are re-conditioned they will get a few thousands shorter.
Using nominal values,
3.44/2 - 1.72 throw + 5.875 Rod + 1.57 CompHt = 9.165
360 block Deck Height = 9.208 - 9.165 = 0.043 Deck Clearance.
Understanding is the egge 343 4V piston has _3cc valve relief volume
and the 343 2V piston has _14cc relief / dish volume.

deadironrat

So would I be better off sticking with 360 pistons? I'm looking to build the motor for both on and off road use. I pretty much only play in the mud off road so my RPMs are almost always high, I'm a senior in high school looking to build a motor for my J10 that will last me through college. When I bought the truck the PO told me it had under 10,000 miles on a rebuild but it just sat for about 4 years before I bought it. I checked the compression in one of the cylinders and it was 120 PSI, I put a little oil in it and it only came up to 125 PSI so I'm pretty sure it needs head work. I can't check the PSI in the rest of the cylinders because the next day I broke the dizzy gear. I guess what I'm getting at with this long misorganized rant is, what would you (the experts) recommend I do to build this motor up for good performance and reliability?

Dusty

These two threads might serve you well the first one was a good discussion

http://www.bulltear.com/forums/viewtopic.php?t=2653

http://www.bulltear.com/forums/viewtopic.php?t=7010
:lo1l:

AMX69PHATTY

Check out the Keith Black SilVoLite web site. To avoid detonation you need Quench. To make power you need CR. Determine the desired power rpm range, choose components, mainly the Cam. Cam's Intake closing angle determines Dynamic CR. Max Dynamic CR for pump gas is about 8.0 to 8.5:1 CR. Choose heads and pistons to get enough Static CR to get ~8.3:1 Dynamic CR. Good Quench means 0.000 deck clearance, ~.045 piston to head clearance (head gasket thickness). Off the shelf 360 cast pistons usually have a deep dish, about .20 inches deep & 24 to 28 cc's. The lip of the 360 dished pistons can give the desired 0.000 deck. But not easy to get enough Static CR with that large of a dish with 58cc heads. The 343 pistons are flat, 4V, or small dish, 2V, so make more CR, but may not have as good quench, like .030 deck clearance. One solution, use 343 pistons, offset grind the crank, mill the deck for zero deck, and open up the chamber in the heads to get desired static CR. Another, use 360 pistons, get zero deck, use early closed chamber heads, and mill the heads to get desired static CR. Another, spend the cash for custom forged pistons made to your specificatons of compression height and dish volume to get zero deck for good quench and with a dish volume to give the desired CR with the combustion chamber volume of the heads. It sucks no one offers a 360 piston that gives 9.5-10:1 CR with zero deck and 58cc heads. The Egge 343 2V pistons are real close but the block deck must be milled for zero deck and the combustion chambers opened a little bit which aint bad since that allows for unshrouding the valves. But the Egge 343 2V cast pistons are not cheep, about half the cost of forged. BRC offers pretty nice custom forged pistons made to your specs. From calculations what is needed to do this is a piston with 1.605 Compression Height and a 15cc dish. +9.208 deck ht -1.730 crank throw 360 crank offset ground .010 for 3.46 stroke -5.873 Con Rod - reconditioned -1.605 Piston Comp Ht =0.000 deck clearance = good quench 4.110 bore - 343/360 bored .030 oversize 3.460 stroke - 360 offset ground .010 15cc piston dish volume 58cc combustion chamber volume 10:1 Static CR There are many other ways to get there, mill deck and/or heads, etc. In the end what is needed is: 8.5 max Dynamic CR based on chosen cam's intake closing angle appropriate Static CR to achieve the Dynamic CR 0.000 deck clearance for good quench Deep pockets :mrgreen:

deadironrat

Thanks for the advice, I think I'll just stick with 360 pistons to keep it simply. Has anyone run a comp cams 270H in their 360?