80’s 318 compression ratio figuring out where I’m at.

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WTF is graphite steel?
not a shim but about as close as you can get except Cometic and???
 
Purpose of vehicle is for just for fun, bit of drag racing. Plan to do a 408 down the road, but for now the 318 in the duster will do, but don’t intend to dump a bunch of money into it. I’m going to see how much my machine shop wants for balancing and for bore and hone. Might go to 0.040 over if it’s not too much more.
 
OK well there is typically a pretty big difference between doing a whole balance job and just balancing the crank. That is why I am giving the details of how to just balance the crank' you're not going to like the price of a whole balance job for a project of this level.
 
Whole balance job involves:
  • Weight matching the pistons & pins to each other
  • Rings and pin locks, if used, are weighed
  • Then weigh the rods to find the 'small end weights' and the 'big end weights'; this takes a special weighing jig
  • Then the small end and big end weights are matched to each other.
  • The above processes can take some labor time, which is where a lot of cost is for the whole balance
  • The next step is to take the final numbers from the above steps, and compute what is called a bobweight
  • Weights, called bobweights, of the above computed value, are fastened to the crank journals, the crank is spun in a special machine, and the crank and bobweights are balanced.
If you are doing a true performance build, you'd prefer to do all the above. If you are doing a cruiser build or need to cut corners, like in the case of putting in KB167's in a 318, and you just need to get back to factory quality balance, then:
  • The KB pistons come closely wight matched out of the box, and the pins, rings, and locks (if used) have very small variations that you can live with for this. You just weigh a couple of pistons, a couple of pins, and a couple of ring packs and use those weights for the bobweight computation.
  • The rods have some variation in weights but weighing the small and big end is the most complex part, so for cheap, you just live with the variations, and use the nominal small end and big end weights for the bobweight computation.
  • You use the numbers from above and compute the bobweight, and hand that and the crank to the shop to balance. That is as good a process as the factory process.
 
Okay. Yes I don’t need a fully blueprinted and balanced bottom end. I do have a scale that is accurate to 0.1 gram so if there a way for me to balance any of the components myself I don’t mind doing that. Or at the very least try to match pistons and rods to get the weights close between the 8 assembled rods/pistons/pins/rings/bearings.
 
I'll suggest taking the scale to the local machine shop with a piston and making sure your scale is close. (Or use some other calibrated weight in that range to check the scale accuracy).

Then just carefully weight the pistons, pins, ring packs, and rod bearing pairs (and locks of being used) with your scale to get average weights for each item. Then you can take those weights and use these small and big end weights, which are what I have weighed for a couple of sets of unmolested heavy rods:
  • Small end: 240 grams
  • Big end: 518 grams
(And if anyone has other such numbers, I'd like to hear them.)

These get pulled in to the standard formula for bobweight.

Make sure your shop is OK with this procedure; one fellow on here had his shop refuse to do it this way.

I'll PM my email and phone so you can contact me direct if you like.
 
How much do stock 318 pistons and pins weigh? I did a bit more research and found some sealed power speed pro hyper pistons for cheap $125 for a set way cheaper then kbs. They have a 1.755 compression distance so that would put me 0.067 in the hole and with a 0.030 mill to each cylinder head that get my compression back to 9.35:1. They supposedly weigh 761 grams with pin. How close is that to 318 stock pistons and pins? Maybe this option is cheaper and I can skip the balancing if they’re close to stock weights.
 
Pin weight is 154 grams for LA318, 340 and LA360. I have 748 grams for a stock original bore 318 piston from some direct measurements.

761 sounds like a weight for a mild oversize piston. So it will balance out reasonably well. It ought to be fine for non-hi-po use.

It looks like your static CR will be around 8.5 at best with the 63 cc chambered heads, not 9.35. That is about the best you will do with stock replacement 318 pistons. If you do another .030" mill on the heads to get down around 58 cc's, and use the thinnest head gasket then, you are getting up near 9.2-ish.

Question? Is the 63 cc's that you measured on the 318 heads or the '596 heads? 63 cc on '596 will take around .050-.060" of milling.

If you indeed end up with .060" total milling, then you're likely going to need to mill the intake side for the intake to fit, and probably will have to change pushrods to a shorter length (assuming you are running the stock stamped rockers and shafts).
 
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I’ve got 596 heads on it (that’s the way the motor came). I cc’d two difference chambers and got 63cc both times. So these may have already been milled in the past (not sure how much). So if I’m starting with 63cc chambers another 0.030 shaved will put me at around 57 cc’d and at 9.3:1 which should work out on 91 pump gas. If my intake doesn’t line up I can always mill the intake side of the head no? The car came with the adjustable 273 rockers and what looks to be beefy pushrods Didn’t measure but way thicker than stock pushrods). Cylinder heads also have upgraded springs as they have dampers in them (not sure what springs). A couple members thought the cam may be a 220 @ 0.050 cam with about 470 lift. I’m still trying to confirm the specs with Crower but I think it’s a super old grind and nothing they’ve sold in decades.
 
OK, that typically would be .050-.060" of milling to get that chamber size with the larger open chamber heads. Maybe your machinist can comment on going further, and others here who have done so. It seems like there have been a few cases of going that far reported here.

Maybe the pushrods have already been shortened. IIRC, the adjusters would have to be turned about 2.25 turns to accommodate a total of .090" head change (if the cam's base circle was the same as stock); that might get some of them pretty far backed out. A thin shim (just 1 thin shim) under the rocker shafts on each stand would help that a bit.
 
as nm is trying to say overadjusted- too long-- to many thread showing adjusters
BREAK
if you have roller tip rockers consult with B3racing industries
 
I looked at the heads again and the edge of the intake valve is fairly close to the deck (bottom of the head). With a straight edge I got maybe 0.035 clearance. So if I milled an additional 0.030 from the heads there may not be enough piston to valve clearance with flat top pistons with no valve reliefs which is one option I was investigating. Especially if my cam has Approx .470 lift. I may have to go with the kbs which have large valve reliefs and wouldn’t require further head milling. I may have to steal some of my daughters play dough and see what my current piston to valve clearance is.
 
How deep is the depth of the open flat area in chambers? Stockish unmilled numbers run around .100-.120" deep.

PV may be OK... it all depends on the cam durations and lift. Folks have been running milled heads for quite a while. And it sounds like you are going to try to keep the low RPM torque up by making he cam too big.

But the KB's are gonna give you a whole lot more flexibility in cam choices as you are not as limited in the duration.
 
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