That's why I asked what the KB162's weigh. Looks like 738 gr. The 2315's are 786 gr. about the same as OEM.

Looks like balancing or machining heads if you're looking to bump the CR, or going back with what it was before if the budget is tight.

Do we know how big the cam is?

The crank was not balanced to the KB and the goobers that did the last one job, ruined the cly for these KB162 and made them too rough, too big, put a .0015 taper in the cly and did not use a plate. We have to have pistons. They are taken care of and we are going .040 over. Have not chosen a cam yet.

i'm going to take a stab at piston/pin weights. a 2315 will be very close to 1000grms. a stock is around 1000grms. kb162 about 930grms. the last 383 I did had 8:1 cast in it and they were replaced with 2315's. I don't know the weight of those 8:1 pistons. we didn't re-balance, which I would have preferred, but there absolutely was no money so it went together. I was dumbfounded by how smooth the engine ran. actually noticeably smoother than my balanced "properly put together" 440.

So, 2315's in a 4.290 bore sounds like the best solution without blowing the budget. As mentioned, these pistons came out as a forged replacement for stock pistons, so balancing wasn't an issue supposedly. Be nice to find a set of heads without the huge combustion chamber, but that can be changed in the future. Good luck and hope it all works out.

This.

The 2315 and the factory pistons were the same within their respective tolerances, probably +/- 10 grams. The 2315 comes with a factory-like pin as well, total right at Lew's 1000 gr.

factory piston is 770grms. .040" 2315 will be close to 790. I wasn't trying to get the OP to spend $400 on new pistons. balancing for the kb162's is cheaper. it's my understanding balancing is not an exact science. I was just trying to layout some differences and how some perceptions fool us. either way it will work.

Mopar made some embellished "factory blue print" information to NHRA back in the late 1960s and early 1970s, the 1970 383 motors being one of them, No stock 1970 383 motors made had anywhere close to +.005 piston tops above the decks, none of them The standard stamp steel head gaskets for the 361,383 413 and all of the 426W where all .022 thick I use to keep dozens of them in stock until you couldn't buy them anymore
Ford said that the 1968 428 Cobra Jet motors had 335 HP, just like the 1966 and 1967 390 HP had Hence the Mopar response in 1969 for the 1970 model year

We can’t use the kB now. We’re getting the 2315f. I just have to figure out the heads. Now that I think about it, I have a original 70 383 hp short block at the shop. I’ll measure the C.H. of a piston.

Do you mean deck height of thosestock pistons?

I can measure the compression height and figure out what the deck height would be. I could install it but it’s a std bore piston in a .030 hole. I don’t know if I can get the old motor to turn over easily.

I’d just forge ahead on repairing the current motor, instead of starting all over again.

If nothing else...... the heads should be good cores with new parts.

It really shouldn’t be that expensive to fix them up.

I ran the 2315 pistons .030 over - 906 heads - Mopar 284/484 cam - For 20 years in my numbers block with zero issues


Then I got greedy , and installed the E Street 75cc heads on that same setup a few years back Looking for more

Motor ran awesome , 6,000 Rpms came on really really fast on the highway running 3:91 gears if you weren’t paying attention

Right up until I kissed two intake valves , took out the pushrods , lifters , and camshaft - Again greedy

Then I decided to build my 432 Stroker

So watch your camshaft selection and valve clearance - Only disadvantage , no valve reliefs

performance 383's need valve reliefs in the pistons. I've busted a lot of parts with flat tops, no reliefs, 4spd and 383.

I've built plenty of budget street .070" 383s using these or similar for my customers, the deck height is almost identical to the 68-69 383. At one time I had a barrel full of stock standard 72 440 style pistons and found a good use for them. https://www.summitracing.com/parts/slp-424np?rrec=true a .040" over makes a budget .020" 400.

Looking in my service manuals and another source I have, the 383 CR has varied.
62-65. 10.0 closed ch
66-67. 10.0 and 9.2 closed ch
68. 10.1 and 9.2 open ch
69. 10.0 and 9.2
70. 9.5 and 8.7
71. 8.5

I assume all of these CR changes were made by pistons changes. As far as I know, mopar only used .023 shim steel gaskets from the factory. I have three 383s at the shop. One bone stock oem 69 non hp that’s too nasty to turn over and check. I’m sure it’s a pass car 9.2 CR. One 71 hp with oem pistons and one 70 with aftermarket .040 cast pistons of unknown CR. Both of these later 383 have had non factory cams installed at one time because both of them have valve marks on the pistons from hitting valves. So that is a major concern for sure on these 383 pistons with no valve reliefs. I will have a cam with less than 230 degree of duration @.050 because I need my power brakes to work. I may have to go even less. At least his first motor did not have that problem with KBs. He had big cam with 241@.050 but the KBs have hugh valve reliefs. My other issue is all the cost of rebuilding the 452 is fasting approaching new stealth head price. Cleaning, mag testing, good three angle VJ is $400. $100 for cutting cutting for better seal and seals. Then new springs and setup pressures and were getting close to new stealths. All the cheap crappy machine shops have vanished from poor work work like we got on these heads. These heads he has at least have new hardened ex seats and new valves but they appear milled some and still have 92 cc chambers. I’m going to measure some more heads I have and make sure it’s not my measurements. I’m going to order a new burette.

the difference in compression ratios were different chambers and 2bbl vs 4bbl pistons. using stock hydraulic cam valvetrains may be the biggest culprits to piston to valve collision. when the springs would float the tappets would pump up (keep in mind .100+" pre-load on the tappets) and the intake valve is into the piston. tight lobe separations, added duration, aggressive lobes, increased lift just makes matters worse. keep in mind that the intake valve is chasing the piston on it's downward motion and the valve is moving faster than the piston. valve reliefs are the only true answer to the problem. a stock magnum cam with slower ramps and wider lobe separation is safer but like all hydraulics needs pre-load reduced. aftermarket rockers usually have higher than advertised ratios so using them may not be the cure.

the 2315's are easy to use but can set you up for piston to valve collision when revving the engine up. the kb162 is safer and lighter. another thing; big valves will give you a little less piston to valve clearance. advancing the cam will reduce clearance, AND, don't over cam a 383.

FWIW, I don’t pay any attention at all to what the factory CR specs are.
Pretty much useless info for the real world.

Measure everything...... and iiwii, regardless of what any spec in any book says.

And yes......... it’s easy to spend Stealth money on fixing old heads...... even refurbished ones, if they’re screwed up enough.

Zero valve lash and triple springs, no valve float or kissed pistons, shifted my 383 @6800 all day long, MP 509

I really don’t think V/P clearance will be an issue at all for the proposed build if an “appropriately” sized cam is used, and the heads/block are not excessively milled.

2315’s with the heads/block/gasket situation set up for low 9’s CR shouldn’t present any problems with a suitable street cam.

The stock eliminator guys get it done without valve pockets(pistons have to be stock configuration) and much bigger cams than what this build will get.

stocker guys don't run .100" preload on their tappets. ain't apples to apples.