Hello All, I am about to have a rebuild done on a 70's 390 and would like to know what pistons will get around 9.5:1 compression for the least cost? Here are the parts I am going to order for the rebuild:

Part Number Description
EDL-1407 Manual choke, 750 cfm, Carburetor, Performer Series, 750 cfm, Square Flange, Manual Choke

EDL-1483 Ford: 1968-99 with cable-operated throttle, automatic transmission (except AOD), throttle lever adapter

SUM-G1300 72 in. long universal choke cable for manual choke carburators

EDL-2696 Square bore carburetor to spread bore manifold, .850 in. four hole carb adapter
"
EDL-2105 6-72 332-428 FE, non-EGR, dual plane, square bore, aluminum, Performer intake manifold

CRN-52308-1 Ford: 352-428, 260/272 advertised duration, hydraulic, PowerMax series, cam and lifter kit

EDL-7808 Ford: 1963-76 332-428, timing chain set

STL-381P30 Ford/Lincoln/Mercury: 390, truck only, .030 in. oversize, 4.080 in. bore, 3.780 in. stroke, 6.480 in rod length

FEM-1445M Ford: 352-428 FE, cam bearings

MEL-M57HV Ford: 330-462 FE engines, high volume oil pump

ARP-154-7902 Ford: 360-428, chromemoly steel, black oxide finished, oil pump driveshaft

ARP-155-6002 Ford: 390-428, 3/8 in. diameter, high performance, connecting rod bolts

FEL-KS2307 Ford: 332-428 FE, complete engine gasket kit

CRN-99042-1 3/8 in., 7 degree, single groove locks

CRN-99822-16 3/8 in. valve stem diameter, .531 in. guide O.D., .620 in. seal O.D., Hi-Performance Teflon valve stem seal set

Thanks for the help, Doc.

 

You didn't specify which heads you are using, which makes it very difficult, without assuming, what kind of compression you'll have.

Example, though, I've got KB150 hyper's in my .030 over 390, using C7AE-A heads that were cut .005 on the deck. The pistons had the dishes cleaned out just enough to get me 9.2:1, and no, I do not know how much the machinist cut out of them. One reason, among a few, why I would never recomend him again.

At any rate, if you're running the D2TE-AA heads, which a 70's truck *should* have, that will raise your compression using those pistons. Take a look, and check the values on these pistons (KB150) for the CC's of your heads (D2's should be a nominal 68cc, but if you want to know your CR, you gotta cc your heads and measure/calculate everything!) Shop around, and see what others have to say. I'm far from an expert!

You also have to take into account lift from the cam, as these pistons are 0 deck height, so you need to make sure you have room for your valves. Can't say for *sure*, as I had to take others advice from their knowledge, but your cam doesn't look like it's going to be an issue.

Hope this helps some!

 

I was just looking at that page before I got here. They look like a pretty good piston. Your heads will have around 68cc to them like he said as long as they haven't been cut. There are very few specs on them. Why did you have to have them cut? They have a 20cc dish to them which is twice that of the L2291F series. The L2291 Pistons also leave .020 deck clearance. They say with 68cc heads they will yield 9.4:1 compression. This might require a mid or premium grade gas with your cam. I really like those pistons. My deck has been cut a little and the crank was moved up a few thousandths during the line bore which all together pus them at 0 deck clearance. These must be newer pistons. I never knew KB made hyper pistons for the 390. I can't find a price on them though. What did they set you back and where did you get them? Optimally your piston would come up to zero deck clearance and will be dished to give desired C.R. This will let you run the most compression possible without detonation problems.

 

To be honest I'm not sure how much they cost me, as they were part of the short block price, which also included the crower cam, lifters, bearings, gasket set, machine work etc. I could probably find out on Monday how much they were, as my machinist ordered them himself. This is a local chain, based in Seattle (which, by the way I'll never go to again for several reasons) All told, with line bore, rod- recondition, pistons and parts it came out to just over $1500.

I'll try to dig up a price on them if I can, and get back to you.

As for having them cut, the heads were shaved and so was the block. After the heads were remanned, they were cc'd and the engine was mocked up. Machinist said he calculated it out at about 9.8:1, so he cut it down for me as I wanted to stay under 9.5:1. According to him he cc'd a piston in the block mockup and came out with a 9.2:1 compression. This is using a felpro blue gasket, btw.

I think KB's figures take into account for the original thin head gaskets that were factory. Not sure, so don't quote me on it!

 

Thanks guys, I think I will have the let the engine guy get the pistons, because deck clearance, cutting and the like really doesn't mean anything to me. So, I will have to depend on him for that. At. this point, I am up to about $1100 on the parts, so it's starting to get too expensive anyway. I said I was going to quit at $1200 and I am almost there. If I change to eight $20 pistons, I am there. Still have to get pushrods, a starter and maybe manifolds or headers (will figue this out when the time comes). I will think about what you have said and ask the engine guy Monday.

 

This all looks good -very much same parts list as many built 390's, except I'd not use the 750cfm carb, unless you plan on doing the equal of jetting it down, I had 750 EBrok and it was very ill mannered on street, it has to be wide open and that sounds like fun, but where I live they have stop signs and stop lights and 35 mph speed limits. Went back to 600cfm EBrok for several years. And it was great. I'm going to a 670cfm Holley Avenger to try that.

 

CAC, actually, I have changed the carb to the 600 cfm edelbrock, manual choke. I have been told enough times now that the 750 is too big. I will post a final list in the next few days to get final opinions. Thanks for your input, Doc.

 

you dont need the spreadbore adapter. I'd go with a midsized 670CFM holley-type too. I have a 600CFM edelbrock and I'm pulling vacuum at WOT on my 360 sometimes, but it's probably a tuning problem...

 

Thanks FE427, took the bore adapter out, that made my pockets feel better!

 

Good catch man. I didn't see that. Quadrajets are spreadbore carbs. Regualar Holley and carter/edel carbs are square bore.