Speedmaster, Edelbrock LA, or magnum cylinder head MILLING LIMITS & common Milling Optimization

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StreetSleeper

StreetSleeper

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When planning an engine build,

How much can SBM heads be milled?

(Closed chamber heads)

to reach 10, 11, 12 to one static compression for stock stroke 318 or 360 engines with:

Keith Black 167 +.020 (318/ 5.2 magnum piston Compression Height: 1.810 inch

Stats: https://www.summitracing.com/parts/...ENBFZ3ymXmnpBaYZqxu4a4s-V2Z520kMaAiNPEALw_wcB


OR

Keith Black 107 +.030 (360/5.9 piston
Compression Height (in.): 1.675 inch

Stats:



I guess one would be assuming
stock (9.599” for LA)
OR
previous experienced deck milled heights, combined with

stock stroke, and available gaskets.

I am considering what compression I can run with the camshafts that I have on hand, the 90 octane nonethanol locally available, and 600 foot local elevation.

Google says:
The deck height of a Dodge 360 engine block is typically 9.599 inches for pre-Magnum A-series blocks, while Magnum versions measure slightly less at 9.585 inches

I am working with LA blocks, (I bet others would want to know magnum blocks as well)

How much can I safely mill the block deck height?

Which would you mill first or prefer? Block or Cylinderhead

If the combustion chamber is smaller, does that make the combustion significantly more efficient? (Which makes me lean towards head milling)

Or is this what racers split hairs with in order to achieve those last few horsepower numbers?- am wanting 180 or more cylinder psi if possible.
If 10 to one is 147 psi at sea level, I am wondering how to achieve this.

Thanks very much!!
 
With 4 head screws or studs per cylinder, I would remove a minimum from heads and/or block. Buy the correct pistons to get your desired compression ratio.
 
You can remove .125 off a passenger car block. You can remove about .200 from an X block. An R block or Ritter can take .300 plus off.

I’m begging you to NOT buy a KB piston for anything. The ring package is just junk. Saving money on those pistons is a bad way to save.

A 5/64 ring package is obsolete. If they would just use a 1/16 ring pack it would be different. But they will not do it.

Really they should all have an .0394 ring package (1 millimeter) but that would be asking them to move from the horse and buggy era to the ballistic missile era in one step. It just won’t happen.

There is nothing wrong with those pistons other than that garbage ring pack.

At any rate, the block should be machined because it’s not flat, unless it’s already been done.

I’m not a fan of milling the hell out of a head for compression.
 
StreetSleeper said:
am wanting 180 or more cylinder psi if possible.
If 10 to one is 147 psi at sea level, I am wondering how to achieve this.
Click to expand...
My stock 71 340 with what I believe is the stock cam and stock pistons and 2.02” valve J-heads was giving average readings of 175-180 psi when I pulled it down. Are you sur ed about that 147 number? Seems low compared to other results I’ve seen over the years.
Get the piston to the deck level and you should be getting close.
 
I'm also against heavy milling for compression. Just mill the block and heads to assure they are flat and use an appropriate piston.
 
gzig5 said:
My stock 71 340 with what I believe is the stock cam and stock pistons and 2.02” valve J-heads was giving average readings of 175-180 psi when I pulled it down. Are you sur ed about that 147 number? Seems low compared to other results I’ve seen over the years.
Get the piston to the deck level and you should be getting close.
Click to expand...
Atmospheric pressure is 14.7 ( at sea level) ten to one would 147psi to 14.7

I think that the high compression 340 engines had dome pistons which negated. the disadvantage of an open chamber cylinderhead to some degree.
 
Last edited:
ch1ll said:
With 4 head screws or studs per cylinder, I would remove a minimum from heads and/or block. Buy the correct pistons to get your desired compression ratio.
Click to expand...
Forged pistons look to be the same compression height when shopping.
They say a KB-107 is still .012” down in the hole-hence milling needed to begin with.

I want to optimize compression, not just let it go-compromise the compression with simply putting everything together as is.
 
Newbomb Turk said:
You can remove .125 off a passenger car block. You can remove about .200 from an X block. An R block or Ritter can take .300 plus off.

I’m begging you to NOT buy a KB piston for anything. The ring package is just junk. Saving money on those pistons is a bad way to save.

A 5/64 ring package is obsolete. If they would just use a 1/16 ring pack it would be different. But they will not do it.

Really they should all have an .0394 ring package (1 millimeter) but that would be asking them to move from the horse and buggy era to the ballistic missile era in one step. It just won’t happen.

There is nothing wrong with those pistons other than that garbage ring pack.

At any rate, the block should be machined because it’s not flat, unless it’s already been done.

I’m not a fan of milling the hell out of a head for compression.
Click to expand...
I can run H116cp hypereutectic pistons in 360, but they require even more milling. They are heavier, Rusty likes them.

I have not found a comparable hyper piston to KB-167 for the 318. There is merit to your views on KB. I have had a cast piston break apart in a 73 340 and simply replaced the piston and ring while cleaning up the bore with a home, changing the oil, a scraping off aluminum shreds and chunks from the bore and combustion chamber-I don’t think that the hypereutectic pistons would have given me as good of recovery (piston broke apart from the lean condition of the 600?cfm 4160 feeding 100mph driving with a coolant leak.

At least with forged, the bearings will probably fail from detonation before the pistons do.

Most 318 pistons are even lower compression until one eclipses $650-$700++ for the several forged options, all with 1.8 compression height as far as I can tell.
I did consider the DSS piston and ring set, they have the reduced ring thickness that you and yellow-?dart? Talk about.
 
Last edited:
if i were attempting to build a 360 bumping 10.5+ then i'd be looking real, real close at a mahle powerpak piston kit. lighter than KB, forged, updated ring pack, and with a close chambered head (*cough* magnum *cough*) you're easily there. wanna get frisky? cut the block so the pistons are positive deck and dial in your compression ratio with headgaskets.
 
StreetSleeper said:
I can run H116cp hypereutectic pistons in 360, but they require even more milling. They are heavier, Rusty likes them.

I have not found a comparable hyper piston to KB-167 for the 318. There is merit to your views on KB. I have had a cast piston break apart in a 73 340 and simply replaced the piston and ring while cleaning up the bore with a home, changing the oil, a scraping off aluminum shreds and chunks from the bore and combustion chamber-I don’t think that the hypereutectic pistons would have given me as good of recovery (piston broke apart from the lean condition of the 600?cfm 4160 feeding 100mph driving with a coolant leak.

At least with forged, the bearings will probably fail from detonation before the pistons do.

Most 318 pistons are even lower compression until one eclipses $650-$700++ for the several forged options, all with 1.8 compression height as far as I can tell.
I did consider the DSS piston and ring set, they have the reduced ring thickness that you and yellow-?dart? Talk about.
Click to expand...


I have personally used DSS pistons and they are very nice. And they should have a 1/16 ring package.

If UEM would fix the ring sizing I’d never have an issue using them.
 
Newbomb Turk said:
You can remove .125 off a passenger car block. You can remove about .200 from an X block. An R block or Ritter can take .300 plus off.

I’m begging you to NOT buy a KB piston for anything. The ring package is just junk. Saving money on those pistons is a bad way to save.

A 5/64 ring package is obsolete. If they would just use a 1/16 ring pack it would be different. But they will not do it.

Really they should all have an .0394 ring package (1 millimeter) but that would be asking them to move from the horse and buggy era to the ballistic missile era in one step. It just won’t happen.

There is nothing wrong with those pistons other than that garbage ring pack.

At any rate, the block should be machined because it’s not flat, unless it’s already been done.

I’m not a fan of milling the hell out of a head for compression.
Click to expand...
So a 340 or 360 is safe to mill the block deck 1/8"?
 
LO23M8B said:
So a 340 or 360 is safe to mill the block deck 1/8"?
Click to expand...


Yes but that’s the very most I’d take. I’d rather a small dome than doing all that milling.

The most I’ve ever taken off a passenger car deck was .100 and I had to do that to get the pistons about .050 out of the hole.
 
StreetSleeper said:
Forged pistons look to be the same compression height when shopping.
They say a KB-107 is still .012” down in the hole-hence milling needed to begin with.

I want to optimize compression, not just let it go-compromise the compression with simply putting everything together as is.
Click to expand...
You need to call other piston manufacturers and find the right pistons for your desired compression ratio, it may take custom pistons as these days there is not a big selection to chose from for these older engines anymore, most large selections are for newer engines like G3 hemi’s.
 
ch1ll said:
You need to call other piston manufacturers and find the right pistons for your desired compression ratio, it may take custom pistons as these days there is not a big selection to chose from for these older engines anymore, most large selections are for newer engines like G3 hemi’s.
Click to expand...


Yup, that’s true. These engines are getting to be the flathead of the 1980’s and on.
 
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