goingnsane34time

I WAS WONDERING WHAT PEOPLE HAVE HAD THERE 86' 944 CYLINDER HEAD MILLED DOWN FOR MORE COMPRESSION AND IF ANYONE HAS HAD ANY PROBLEMS WITH INTERFIERENCE THANKS FOR YOUR HELP

CPR

That is what my wife wants to do to me.....

Van

Doesn't work that way... because you're taking off a small percentage of the chamber volume...

Head gasket is about a mm thick - eliminate that, and you gain almost a compression point.

Machine the head down a mm, and you might be lucky to bump the compression up 0.3 of a point.

goingnsane34time

well it dose work when you take off enough thats why i was wondering if anyone had taken alot off and had problems or what the max was i was planning on taking off like .125"

V2Rocket

thats wayyyy too much...

i had mine milled i believe .020 just to give it a clean surface for the new gasket...

Weston

Aside from sealing ability, how is taking 1mm out of the head any different from taking it out of the head gasket (once compressed)? It effectively changes the dimensions by the same amount either way.

Anyway, I'm told that shaving off somewhere around 0.045" - 0.050" will bump an early car (9.5:1 stock) up to about 10.5:1, not accounting for other variables. If it is shaved enough that you can no longer see the squish area behind the spark plug (ie it's level with the rest of the head surface), then you should be close.

goingnsane34time

i am lookiing for more power not too just clean up the head thats the reason i was asking whats the max people have gone with out trouble and and any amout you can take off the head will help for power its just its basicly free power if you are doing the head gasket anyways

white924s

its not free power - milling that much won't be cheap unless you're very good with a bridgeport-style mill and can do it yourself. Not to mention that you'll have to adjust your spark timing and fuel map if you change the CR significantly. Not to mention, taking a lot of material off the head will change the shape of the combustion chamber. You might have better luck going with high compression pistons, but good luck with whichever road you take

Alex 944S2

To know exactly how much you can mill down the head you have take it off.
You need to know the drop hight of the valves in relation to the valve lift and the pocketsize and position of the piston.
The pistonoverhang is important too.

Van

The combustion chamber component in the head is called your head volume - this can easily be measured and you can calculate what your new head volume will be after shaving... Do some searching - I'm sure it's been covered. BUT, I can tell you, I've done those calculations, and the head volume per 1mm cross section is a fraction of the volume at a 1mm cross section of the cylinder bore.

Machining down the head to the minimum thickness (the measurement Porsche deems safe) will only raise the compression a negligible amount.

I'm sure you can get up to a higher compression ratio by machining 4 or 5 mm off... but that's going to compromise the head (might machine through the oil/water passages) and will causes fit problems for your manifold and timing belt. And, or course, you'll need to fly cut your pistons more to clear the valves... which will again lower your compression.

The power gain from machining the head to the minimum thickness is negligible. Either tear the engine all the way down and put in euro pistons (or custom pistons) or do something else to increase your power.

Simply put, rarely is there such a thing as "free power".

goingnsane34time

i am a machinist and a mechanic

lee101315

I shaved the head on my old 944 .5mm when I had the head off. Im sure it raised the compression a little bit, but the car wasnt much quicker. However, keep a few things in mind

You'll have trouble getting the timing marks to line up

If you ever overheat and warp the head, you may as well just throw it away.

goingnsane34time

i have a spare head sitting in my garage right now thats why i wanted too try this on the old one tooo see what i can get out of it

TedA

for an na, $$ squared = still not a lot of hp. I have a dyno sheet to support the hp, I refuse to comment on the $$$$$$$$$$$$.

schwank

If you are a machinist and keen to mess around on a street car I imagine you will free up more power by lightening the flywheel and crank than by decking the head. The crank in these things is immensely heavy.