young olds

In bill traVato's book he said he has ccut heads as much as .1, I think that was that was on big block heads. Wonderng if small block heads with take that much as well, not that I'm trying to go that far.

MDchanic

Sure, but you will have to account for the valvetrain being slightly longer (change to shorter pushrods, use adjustable rockers, or shim rocker pivots if it's not a highly stressed engine) and for the loss of combustion chamber volume (depending on pistons, original chamber size, etc.).

- Eric

young olds

i wanted to mill quite a bit to get ok compression with the standard fel pro replacement gasket, .045. will the lifters not be able to take up the difference?

drop top olds

Why use the Felpro's? You can purchase Cometic head gaskets and avoid milling the heads (if that is the only reason you have to mill)? Cometic gaskets come in various thicknesses, most certainly less than the Felpro's. Seems like I recall Cometic making a .028 thick head gasket for Olds..

80 Rocket

Depending on piston dish sizes, the only way to gain more compression is by milling heads.......even when using the thinnest possible gasket.

I know you can go .060" on either big block or small block with no sealing issues. I have personally never went further than that, but I have heard of others doing .100" with success.

MDchanic

If all you are doing is taking up for the change in gasket thickness, then you're not really changing anything.
Original gasket ~0.016", FelPro Gasket ~0.043", if you mill the heads 0.027" you're right where you started.

- Eric

wr1970

My question is if you go .028 gasket how much compression are you gaining over the .043 gaskets if you are using flat top pistons at zero deck? Is it really that much of a difference?

MDchanic

I don't know enough about the engine in question to do meaningful calculations here.
Your profile shows a '68 Delta Custom, which should have a 455, and a couple of earlier F-85s, which should have either 330s or 215s (I don't recall the years you listed).

Figuring a 350, if you have a 1968 high compression (10.25:1) 350, it should have a 6cc dish and a 0.016" head gasket, with about a 0.020" deck height and an average 68cc combustion chamber, which would give you an actual static 9.78:1 compression ratio.
Changing the head gasket to a 0.045" FelPro will change the CR to 9.16:1, a change of about 0.6:1.

- Eric

young olds

I'm trying to gain compression. I already have the felpros and I can get the heads milled for about the price of smitty's .011 gasket which won't give me as much as milling with the felpros.

MDchanic

Pistons? CC volumes? Engine CID (330, 350, ???)?, Cam plans?

- Eric

young olds

I do thanks you for your help, but I'm not asking for help building an engine I just want to know how far I can safely cut a pair of small block heads. But it is a 350, I have a cam but will only use it if I can get the intake I want, which will also be the deciding factor on pulling the heads to get them milled

young olds

It's not that I don't need or like help, I just already know what I want and have most of the pieces. I just need to know what the safe limit is on cutting sbo heads so I know If I can get what I want out of what I have

MDchanic

Sure, cut 'em down.

There comes a point where you will also have to mlll the intake (or mill the intake side of the heads, up to a point), but if I recall, you can usually get away with 0.100".

Just be sure to re-measure and re-calculate valve train length, and be sure that you've got enough valve clearance if you're going high crown or high lift.

- Eric

young olds

thank you for your answer and insight.

odddoylerules

Wow isn't .1 a LOT?! Makes me feel better about the.050 I have planned after they weld my divider into the exhaust port

young olds

Didn't end up doing it, I have cut big block heads quite a bit though.

Octania

"Wow isn't .1 a LOT?! Makes me feel better about the.050"

can we please use thousanths of an inch to discuss such things? All three decimal places, even if they are zeros.

.050 [fifty thou]
0.100 [a hundred thou]
0.030 for pistons, etc. [thirty]

thanks

odddoylerules

Of course, I did it for emphasis I mean its a freaking TENTH

wr1970

Why? A tenth is a tenth

BlackGold

Ever hear of "significant digits?" 0.1 is any amount from 0.05 to 0.1499999. Whereas 0.100 is any amount from 99.5 mils to 100.499 mils.


Besides, most machinists like to talk in mils or thousandths, not tenths.

odddoylerules

Aaaanywho, can anyone link me in the direction of these "Smitty's gaskets" because they are talked about all over these forums and I'll be damned if I can find them googling.

MDchanic

If you're saying a tenth, I'll just say 3/32.

- Eric

wr1970

Ever work aircraft? .10 tenth also .100 hundred thousandths i don't care how you slice it dice it!! You guys need to quit being so condescending.

young olds

I bought a set from smitty, called him and ordered. He asked for my bore size and took my card info, didn't charge me for a bit but all was well and I got my gaskets.

young olds

Mjproformance is his website I think, site didn't work but had his number

odddoylerules

Haha first search "proformance" was money.

I think I might be better off getting the thin gaskets, I just read some #4 heads are more towards 61cc than 64+ you'd expect w factory tolerances. If this is the case they may be worth more in the end uncut.

Plus with a thin gasket I'm still getting a compression bump.

Only question.... Will Smitty's gasket seal 100% on a used block w the fresh heads. Felpros will.

cdrod

Are these the MLS Cometic gaskets you're looking for?

http://www.shopengineparts.com/parts...403+%26+455+V8

They come in .027, .030, .036, .040, .045, .051, .056 thicknesses to tailor your compression ratio.

odddoylerules

Stock is 0.19, Smitty's seem to be the only thinner.

Hey, have uguys ever heard of splitting a head gasket? Import guys do it on N/a builds

MDchanic

It's nitpicking, I know, but I've measured my own at 0.016" (just in case it's important to someone reading this later on).

- Eric

odddoylerules

The stock one? Sheesh, maybe I WILL mill.

odddoylerules

If I mill to 60cc chambers, w flat tops, a .040 gasket, and the slugs .020 in the hole the cr would be around 10.8:1. Sounds like milling them WONT make them useless for anything but a smogger. I was worried

MDchanic

Yeah, between the very thin head gasket and manufacturing tolerances that tended to make the combustion chambers on the large side (higher-than-specified compression = detonation, early engine destruction, and warranty claims, while lower-than-specified compression = no problem at all), there is generally plenty of room to mill the heads, so long as you then adjust for the needed change in pushrod length.

- Eric

odddoylerules

And pray tell, how does one do that? Is there a procedure I can look up to learn more about it?

W my pistons .028 deep and all things set I will be just right about at 8.9:1 w the mill job. Totally just what I was going for in the first place when I got the 64cc heads

MDchanic

I assume you're talking to me.

The simplest way would be to simply calculate the difference in the height of the heads considering the milling and the thickness of the new head gasket.
If you aren't changing other aspects of the valve train, this will probably work well enough.

The right way is to use an adjustable checking pushrod with weak testing valve springs to measure the right height, and, if you are using roller rockers, to get the center of the rollers' contact point in the center of the valve stem face.
There are instructions for this all over the internet, and recent discussion of it on this board.

- Eric

odddoylerules

Not going w any other valvetrain mods aside from a mild 212 cam on a stock size base circle though

Looks like time to read up

odddoylerules

If the stock height is .016 and my new height will be .040 minus the .055 cut then the difference in height is now (-).031.... Is that a correct way to figure it? Maths aren't me strong point

MDchanic

If the stock head gasket was 0.016" and the new head gasket is 0.040", and you mill the heads 0.055", then you are adding 0.024" (0.040-0.016=0.024) in height, from which you are subtracting 0.055", so 0.055-0.024=0.031" lower, which, if you are using stock hydraulic lifters and valvetrain, may not require any adjustments...

... BUT, since you are installing a new cam and lifters, even though they are theoretically the same dimensions as the originals, you would be wise to check.

Since the dimensions should be close, you may be able to get away with just assembling it, running it to get the lifters properly pumped up, and then using the known thread pitch of the rocker pedestal screws (18 per inch or 0.556" per turn) to indirectly measure lifter preload. Considering the 1.6:1 rocker arm ratio, every ⅓ of a turn of the rocker screw will correspond to 0.029" of movement at the pushrod, and since the desired lifter preload is usually given as 0.030-0.060" (I've never seen any one "definitive" number), that means that:

If you place a cylinder at TDC compression and you loosen the rocker screws, then tighten until the pushrod is just making contact with the rocker, then tighten another half a turn or so until the screw bottoms, that valve is adjusted correctly.

If it takes over ¾ of a turn before it bottoms, your preload is a bit deep, indicating a need for a shorter pushrod (or, if you're not going to overstress the engine, shimming the rocker pedestal).

If it takes less than ⅓ of a turn, it's a bit shallow, and you need a longer pushrod (milling the rocker pedestals is possible, but doesn't make much sense unless you've got a milling machine).

- Eric

drop top olds

FWIW- I have a set of #6 W-31 heads. They were bare when I got them. I milled the heads 0.030" to clean up the head gasket surfaces. The combustion chambers were cc'd after all work (new valves, guides, welded center dividers, etc). My set measured 60 cc combustion chambers.

odddoylerules

OK Eric, roger on that. We did that on my dad's Starfire back in the day.

So if I put some petroleum jelly along the valves to seal em closed and I level the sealing surface of the head then if I fill the chamber w liquid from a 100cc syringe I should be able to measure the chamber volume, correct?

I've heard some 4 heads error on the side of being smaller, multiple sources (2) claiming 61cc stock production volume, the opposite of what you'd expect from a production tolerance. (64 stock)

I got .31 too guess I remember SOME maths though

odddoylerules

Wait I was crossed up from too much reading. Scratch that last bit the heads are already 60cc huh. I need to take a break from this car thing my head is spinning.

Good thing tomorrow is a work day all this theory is buggin me out

2 sources did quote 61cc which makes perfect sense