Maximum head milling

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eestatic

eestatic

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Maximum head milling, how much, (safely) on a set of 1974 Dodge Dart 2BBL 318 heads would yield what kind of compression with what/best/type of head gasket (safely) used..
Pistons stock..what ever consensus here..
Do not wish to attend to rocker geometry
Will go back with next size larger than stock exhaust valve, maybe..

Thanks
 
Well, looks like no one is gonna help you and I don't have the answer. Lot of variables here I think. Too many to give a straight up answer.

Do you want to avoid taking material off the intake side of the head? Is it going to have the stock cam? Do you want to spend mega bucks for super thin head gaskets to achieve this? What cc/compression ratio are you looking for? What year are the heads(different years yield different cc's)? How far do the pistons sit down in the heads(my understanding is that there is some variation here)?

Anyway, I can only tell you what I did with no changes or ill affects to anything. I was able to take 0.040 off and use a FEL-PRO Part # 8553PT gasket on a 70 318.

Maybe others could tell you what they have safely done and give you something to go with.
 
Do yourself a favor - If you are rebuilding it anyway (which was how I read that) it will be similar money to replace the stock type pistons with a set of performance hypereutectics and have it balanced and the rewards will be huge. Milling the heads a lot requires milling the intake flanges of the heads and/or the intake itself to match. Then you have a "matched set" and can't swap anything. Plus, it will require custom pushrods because you're affecting the distance between the lifter cup and the rocker cup so much. Milling costs a bit and it's multiple passes. So - if you're rebuilding - spend the extra $200 plus balancing for a piston that will get you 9.5:1.
Rocker geometry is not affected by milling. It is affected by the valve job on the heads, and the position of the rockershafts. So if you mill a lot but don't want custom pushrods you will be shimming anf messing with geometry.
 
1974 ~ 318/170 HP {2-Barrel}

These engines had an 'Advertised' Factory Compression Ratio of 9.20 - 1.

* That is with the Piston measured at .056 {Below the Block Deck}.
* .032 Factory Head Gasket
* And the #2843675 Open Chamber Cylinder Head with a 61.5 CC Level.

But, when those 318 Engines left the 'Factory', they were nowhere near close to
those Specifications.

Since most of the Blocks left the factory with the Piston deeper in the Cylinder
than the (Factory Listing of .056"),,,,,,,,,,

You should be able to to take an 'easy' .030" off the Cylinder Head.

For every .0053" removed off the 'Open Chamber' Cylinder Head, it will reduce
1 CC from the Cylinder Head Combustion Chamber.

Taking .040" off the Head (lowering the CC level by 8 CC's) should increase the
current Compression Ratio by approximately {.6}

We have gone up to .050" off this Cylinder Head with no problem, but we did remove .020"
off the Intake Side of each Cylinder Head to insure alignment with the Intake Manfold.

Also, the Fel-Pro #8553PT is an excellent Head Gasket at .040" Thickness.

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Example,

On a recent 1974 318 Engine Rebuild for a Customer, the Factory Pistons measured
at {-.076} below the Block Deck.

Our customer didn't want to go for new Pistons or Block Decking, and only wanted to
go for an inexpensive 'Piston Ring 'refresh' Engine Rebuild'.

But, he wanted the Compression Ratio back to the 'Factory Advertised' ratio of 9.2 - 1.

To make up the .020" in Piston Depth 'difference' and thicker Fel-Pro Head gasket .008" thicker
than the Factory Listed .032" Gasket, we had to do the following,,,,,

A) We first brought the Cylinder Head Combustion Chamber to 61.5 CC {which required a .022" Mill}.
(Most of the #2846375 Cylinder Heads left the factory with a Combustion Chamber with a minimum 65+ CC level.)

B} We then milled the Cylinder Head an additional .028", which gave us a Net Compression Ratio of {9.2 - 1},
which is what the Factory Advertised.
 
No open chamber 318 head ever came 61.5cc's
Every stock 675 casting I've measured came in at around 68cc's.
Factory steel head gaskets were more like .019 thick.
Op, you mill can mill them to the 50's cc if you want-.064=12cc or 56cc's starting from 68cc.
 
Pistons are the best way to go, how much compression ratio you shooting for?
 
1972 thru 1974 {318 Engine} Cylinder Head Gaskets were .032" Thickness from the Factory - for the #2843675 Cylinder Head.

Factory Steel Head Gaskets (.019" Thickness) were not used after 1968 on the 318.
 
The stock gaskets aren't gonna used anyhow.
Most likely some .046 crushed felpro8553's will be used, and even then who's to say till he makes his choice, none the less...the open chamber heads never came with that small of a chamber and he really should measure them to start if he wants to do this accurately.
 
I know my 1970 318 was unmolested and it had the .019" steel shim gaskets and the pistons were sunk .078" in the block. All the dimensions that were quoted in the day were just what they were shooting for but rarely any of them built to those specs. I worked in the auto mfg. industry during those years and know how they operated.
 
Yes,

Never take anything for granted with Mopar Specifications.

1970 and 1971 {318 Engine}

Was supposed to have the Pistons set at .060" Below the Block Deck, and .028" Thickness Head Gaskets.

But, it was not uncommon to see 1969 thru 1971 {318's} with {.019" Thickness Steel Head Gaskets}.
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1972 thru 1974 {318 Engine}

Was supposed to have the Pistons set at .056" Below the Block Deck, and .032" Thickness Head Gaskets.
 
If the pistons were typically too deep in the hole, was it because the blocks were too tall? Or was it because the pistons/rods were too short?

The reason I ask is because if the blocks were too tall, then milling the block or head to compensate should make the intake manifold fit better, shouldn't it? Wouldn't it also correct the valve geometry? Same thing with milling to compensate for thicker head gasket right?
 
Thank y'all for contributing!

As far as what cr I'm shooting for, the most I can get away with using pump gas I suppose.
I'm sure the picture will be clearer once I tear down and see what the 318 yields.

I'm working on an assumption that i will not need new pistons, but that is still unknown.
I am trying to evaluate a "side-by-side" build of not touching the pistons and what would be max potential power vs using the KB167's ? and factor in money spent either way for what kind of potential gain??? I am excited about porting the heads (never done before) and if I get gung ho enough, was pondering building a flow bench.
 
Mr. EE-Static,

I'm assuming that the 1974 {318 Pistons} are probably at a depth of approximately
.080" 'below' the Block Deck.

If you are going to use a Fel-Pro PT-8553 Head Gasket (.040" Thickness).

To achieve a {9.2 - 1} Compression Ratio,,,,

You will have to get the Combustion Chamber in the #2843675 Cylinder Head
down to 55.5 CC's.

As a 'general rule', Milling .0053" off the Cylinder Head, will reduce 1 CC level.
 
Before you decide on CR what cam are you gonna run, most street cams only need 9:1-9:5, Each compression point will give about 4% power increase so on a 300-400HP engine would Give 12-16hp no point pressing your luck unless your cam choice requires it but since your running a stock short block, I'm assuming your cam gonna be around 268 so 9:1 is probably all you need.
 
The 268 cam is the one I have considered, but ultimately will see what gels with what I discover when I break into the rebuild process. I want to make each area complement each other for optimum satisfaction.

Mr. EE-Static,

I'm assuming that the 1974 {318 Pistons} are probably at a depth of approximately
.080" 'below' the Block Deck.

If you are going to use a Fel-Pro PT-8553 Head Gasket (.040" Thickness).

To achieve a {9.2 - 1} Compression Ratio,,,,

You will have to get the Combustion Chamber in the #2843675 Cylinder Head
down to 55.5 CC's.

As a 'general rule', Milling .0053" off the Cylinder Head, will reduce 1 CC level.
Click to expand...

If one were to use the "zero deck pistons" in lieu of the above milling, in this scenario, what would be the CR?

Also, the KB167's? : Are they lighter than the stock pistons [any performance
there]?
 
Mr. EE-Statc.

The Stock 318 Piston = {593 Gram Weight}
The KB -167 Piston = {507 Gram Weight}

The KB Hyperuetectic Piston clearly better than stock, and has a higher
Compression Height {1.81"}, compared to (1.72" to 1.75" for the Stock 318}

If you utilize the KB-167 Piston with a 'Zero Deck', and a Fel-Pro PT-8553 {.040" Thickness} Head Gasket.

Cylinder Head 'Combustion Chamber' levels.
* 60.0 CC = 10.0 - 1
* 61.5 CC = 9.8 - 1
* 63.0 CC = 9.6 - 1
* 64.5 CC = 9.4 - 1
* 66.0 CC = 9.2 - 1
 
KB's zero decked and a .040" gasket
60cc chambers 10:1
64cc chambers 9.5:1
68cc chambers 9.1:1
 
Nice info..!

OK, so what are the power differences between, say 9:1 cr and 9:6 cr, using 268 cam?
 
.5CR=5-10hp
Not that 318 heads are bad and can't be made to perform well and if you don't want to go EQ I'd go 340/360 heads ported and blueprinted to 68cc for 9:1 with a high lift voodoo or comp cam 268, Airgap, 650, headers with a zero decked shortblock
 
Assuming CR equal, does an engine perform better w/pistons at zero deck vs say, .080 in the hole, and the lighter pistons (167) should offer merits with regard to weight/mass?
 
since there's no quench either way all that matters is final CR but it hard to Build good CR with small displacment engines, zero decking just helps, plus latter if you want to step up in power latter you could go 10:1 closed chamber magnum type head with .040" quench with a 285ish cam
 
In this imagineering stage, what are expected cost with head milling (approx) to get low 9's cr?

What is reasonable safe cr for pump gas?
 
You can either mill them till you hit coolant, and then back off a bit,

or...

Just buy the damn pistons and do it right. You won't make any power with a clapped-out bottom end and warped heads.
 
Mr. EE,

If you want to do this Engine Job on the 'cheap'.

Go the way Mr. 273 stated,,,,,,

Have the Cylinder Heads milled, to a 58.0 CC Level, and go with a Fel-Pro
PT-8533 (.040" Thickness) Head Gasket.

You should be around 8.90 - 1 Compression.

The 'thinner' {.025" Thickness} Head Gasket is also an option, which could give
you a liitte more 'boost' at 9.15 - 1 Compression.
 
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