How far can you mill a Mopar flathead!

Looking to get about 14 to 1 compression outta my '48 218 Plymouth sixbanger. How far can you SAFELY mill the stock head? thanks....

 

why so much lower end will go first unless you are running alcohol

ken

 

Find a spare head and saw it in half I've got a head I want to mill apart, but can't find anyone who will let me play on their mill

Although I'm sure you know already, milling the head that far will cause more shrouding of the valves which may negate any affects the compression may gain you. now if you mill it, and offset it to the valve side of the block slightly, you may have something....

 

Geez...I was KIDDING!?!?!?! But I still need to know.....

 

bttt..

 

kROOSER
First I would ultra soud the head surface for thickness. I would ***ume they a awfully thick.
Then i would put a piston in the hole measure it from the deck surface.
You will find You probably have room to deck the block first. Then cc the piston with the (500) down method.
Then cc the head - add the thickness of Your head gasket. Figure you compression.
The only thing that will limit You excessivly milling the head would be valvelift. So you will have to clay the valves to check valve to head clearance. So You should have the cam Your going to use installed.
You can unshroud valves easy. Just try and keep as much quench area as possible. And alcohol WONT make your bottom end last any longer. FEDER

 

Thanks...I'm not really getting too involved with this thing..I'm fixing one hole and maybe doing bearings.

I figured as long as the head is off, I could mill it a bit for a little more compression.

 

I know someone who said he milled the head on a Packard so much he had to double washer the spark plugs to keep the valves from closing up the plug gaps.
Another consideration if the plugs happen to be above the valves.

 

Remove the head and gasket. Clean head and deck surfaces. Put clay on the valves and pistons. Reinstall head with no gasket, snug down bolts & leave plugs in. Rotate crank 4 revolutions. Remove head and measure clay thickness. Find thinest piece of clay and subtract 0.100". Difference is clearance to be milled. If this is a big thickness it may not work as you may strike water!!!!

 

Okay..If I strike water, how far 'till it's drinkable?!??!

 

On the stock iron heads I've run, I've taken upto .040 off and no problems.
That's with a high lift cam too. Definitely check your valve clearance after though.

Are you looking for headers or an intake?
http://homepage.mac.com/rmccombs/StumblinIdles/PhotoAlbum49.html

 

.040 sounds about right. Thanks to all who've helped answer this question.

 

My 1952 copy of Hot Rod Your Car says .070 for Mopar sixes in its head milling chart.

 

Really! I guess I would have stopped at .040...I'll have to check clearances and see...Thanks.

 

years ago I ran a 230 with .060 off the head. Never had any problems.

 

Back in the 60s, .060" was the rule of thumb for any flathead motor.

 

Back in the 60's we cut a 46 plymouth six head .125. Didn't hit water but smashed the **** out of the plugs and had to use washers under the head bolts. .040 should give you what you want.
fred

 

I've been told .070 would be fine but an old timer by the name of George Asche has been messing with these engines for a long time told me to take .090 off. I would be inclined to do it.
Good luck on your decision.

******Knuckles

 

In earlier post I mentioned alcohol with hi compression
and the lower end I know for a fact you cant get the lower end to hold up if it is stock running gas and hi compression I have had stock bearings in vw running 16 to 1 compression with hilborn fuel injection on menthanol and lower end held up fine= went away with gas plus had lottsa cooling problems hope this clears up alcohol wont help lower end

 

when it comes to Mopar flathead sixes, if George Asche says "go .090"
I'd go .090