dede944

Hi !

I read a lot of topics on that but still got a few questions...

If I shave the head by approximatly .020 to .030''
(still not sure of what i'm gonna do...),
is it gonna give a hard time to the bottom of the engine ??

My car is a 85.5 with a cp of 9.5:1 and from 87 the cp
is up to 10.2:1 and adds up 8hp. http://944central.com/lna/specs.asp

Are these hp are only comming from the cp ??

And is anybody had find out how much needs to be
shaved to go from 9.5 to 10.2 ??

I'm actually doing a DIY port job on a spare head and
tought about shaving it a little bit to complete
my head work...

thanks !

Eyal 951

You can no problem, I milled mine .050 (on a turbo) for an NA its great to increase compression, but doing it with pistons is better.

M758

Don't shave the head.

Just shave it enough to make it flat. Power gains are non-exisistant. They are lost due improper cam timming since the distance between the cam gear and crank gear is shorter.

Also many spec racers have tired to do it and this has netted zero hp or many blown headgaskets.

So shave it enough to make it flat, but don't shave it for hp. It is just not worth it.

BTW.. the 88 cars used pistons with smaller dish to get more compression ratio.

Mongo

Bore and stroke. There is no replacement for displacement.

L8 APEKS

I completely disagree, *if* and *only if* you add a cam gear after shaving the head.

I had my head shaved .030" and the car was a pig afterward...it was slower than before. Until I installed the adj cam gear, that is, and set it to 6 deg advance. HOLY CRAP, the car spun tires like no tomorrow and pulled like a raped ape! It was a very, very noticeable improvement. I haven't seen many N/A's shred healthy 225/16 tires thorugh 2nd gear until then. Ask Legoland, he was in the car too.

However, if you can't afford the ~300 for an adj cam gear, then don't shave the head...just have it resurfaced. You will lose TQ and response, and raise the powerband out of daily driving range.

hosrom_951

The beauty of English vs Metric unites

Well, there are three grooves that Porsche placed on the head, to record the amoun that should be removed.

Now, .020 inches is equal to 0.51 millimeters, when we measured those grooves, we found them to be at 0.5mm, which is the limit as the factoru manual specifies. You would need the thicker 1.4mm headgasket ($$), you only need to skim the head of you have a bend/not flat.

Did you get a straight bar and a feeler gauge and checked? you are allowed 0.05mm

Geo

An alternative to an adjustable cam gear is an offset key.

Oddjob

This discussion has come up several times in various past threads.

Just keep in mind that there not an entire consensus on this.

There are plenty of p-car and race shops that will shave heads to increase the compression ratio.

If you get up to the 0.04 and greater, sure I buy that its retarding the cam timing enough that you may want/need to adjust it (by cam gear or offset key). But taking .020" off the head will not significantly alter the cam timing to the point of needing an adjustable cam gear. And the manufacturing tolerances of the cam belt, the stretch under load, the age, and the range of tension adjustment will give greater variation in cam timing than shaving 0.02" off the head.

hosrom_951

What is an offset key?

Chris_924s

ask Dales944 about head shaving. He wore a stocking cap for months...


OOps wrong thread.

dede944

Thanks guys for your answers

Still not sure what i'm going to do, but one thing
I know is that I wont spend 300 US on a cam gear...

It's kind of confusing, everybody have different opinions

I'm leaning toward resurfacing to avoid futur troubles,
a Porsche is already expensive on maintenance...
even more when your track it

Geo

The cam and crank pulley are located by a Woodruff key.

An offset key is a Woodruff key that fits in the same slot, but the locating portion of the key (the part that sticks up) is offset slightly. Using basic math you can calculate how much offset you need to attain a certain number of degrees.

Peckster

The real reason they do it is so they can bill the customer more.

Save the shaving for when you have to fix a warped head or one that needs a new mating surface.

Do it for no reason and you might regret it later when you need that metal.

Whoever said they had better power when they added the special cam, that would have happened without the shaved head.

Legoland951

You are not going to regret the metal when you can get a core head for $20 to $40.

Mongo

shaving the head with a more aggressive camshaft will also yield a gain in power.