Head Gasket

palaxdad · 03-06-2001, 06:33 AM

I need to have the head gasket replaced in a '78 924na. As part of his normal procedure, my mechanic will send the head out to be inspected (and planed if necessary) before reinstalling. Does it make sense to consider a port and polish since the top is already torn apart for the head gasket replacement?

porscheboi928s/c944t/n · 03-06-2001, 06:49 AM

Palaxdad..
There are two answers about port and polish..
what is your plan on the 924?? for keeps,race or just a regular daily driver?? if your answer is just for a daily driven then i suggest you just keep it stock and no port polish...but if ur racing it for for keeps then do the port and polish..but before you do that what other power adders ur planning or have on the car??co'z this also can play a big role on the p/p..also match the intake and exhaust manifold with the P/P....my 0.02 cents.

palaxdad · 03-06-2001, 06:56 AM

porscheboi, this is my son's car. It is his daily driver and in the fall he going to be taking it to school (10 hours away). So far the car has been very reliable and I have been concerned about tradeoff between performance and reliability. So far we have replaced all gaskets (except the head), belts and hoses, replaced most of the ignition system, installed K&N air filter and installed dual straight out exhausts from the cat back (no mufflers). The car breathes very well and we are considering headers and an Audi 5000 throttle body.

porscheboi928s/c944t/n · 03-06-2001, 07:23 AM

Well, if your considering on getting the headers and a big throttle body i guess go for the port and polish..why not go with the bigger valves too??since ur aim too is unleash the power of the engine...shaved the head too(bump compression a little bit)..also since the head will be out of the block why not re ring the pistons too???...my 0.02 cents...

palaxdad · 03-06-2001, 07:33 AM

Is there a tradeoff between power gain and reliability with a port and polish? As the father, actually I am far more concerned with reliability than power. From what I've read, the headers will help breathing but the cat is still a bottleneck, and the throttle body upgrade will yield marginal results without head work. If he's going to get 5-10 hp and flirt with reliablilty issues, then this is a bad idea - right?

Obin Robinson · 03-06-2001, 07:57 AM

i rode in a friend's 924 that had a port and polish done and i thought it was a turbo! the car could make short work of my 944, 924, or scirocco.

get the p&p done. no reliability issues. fuel economy drops about 1mpg, if that.

obin

palaxdad · 03-06-2001, 08:08 AM

Obin,
Thanks, always good to hear from you... Since he's going to have the head inspected and planed if necessary, how much more would you guess for the p&p?

porscheboi928s/c944t/n · 03-06-2001, 08:20 AM

u should gain a good 20 to 25hp....reliability is still the same but power is upped.almost entire powerband will be flat..about gas consumption u should be about the same if not better..

AMCPorsche924Powerhaus! · 03-06-2001, 10:00 AM

In fact the modifications you mention will most likely improve reliabilty.
Headers are less likely to crack, port and polish is letting your engine breathe better.

Headers won't make much difference anyway unless you get the p&p.

Shaving the head more than you need to may not be a good idea, i would just put a 931 head gasket on, that should improve reliabilty also, since it is a stronger gasket, but it will also raise your compression half of a point, and compression is a very good way to increase power, and half of a point is a lot, maybe 10 HP if you have the otehr modifications done to let it get you 10 HP.
If you just have one thing done, like only the head gasket modification, then results are always not as noticeble, do them all and you will notice like 10 hp just with the gasket after the port and polish and headers say giving you 10 (a guess).
You might only get 5 HP with the gakset and no otehr mods, and you might get only 5 with just headers and a polish, but with all it done you might end up with 20.
With all done each mod will be more effectve, each one helps the other, they aren't seperate things that all have different HP ratings, not like a bolt on or something.

So the only thing that might not be reliable in my opinion is shaving the head more than you need to to get it flat, and I wouldn't shave it more then you need to IF you are using the turbo gasket, but you could.
Keep in mind that 0.1mm = 0.1 points of compression
So if you shave the head 0.004 inches (0.1mm) then you up the compression 0.1 points.
So the gasket is getting half a point, and if you wanted to (if your head has never been shaved) you can shave it even 0.016 thou if it will allow it, that is the max you can shave on the turbo. That would get you 0.4 points plus the gasket is 0.5, and you almost have 1 whole point of compression.
Myself I would just go with the gasket and the minimul amount shaved off the head, since you might have more timing belt problems (tensioner maybe not allowing it to be tight enough), you may warp and/or distort the head easier with too much compression or too much weakening from the shave, etc.
From what I have heard and sean these heads aren't that strong, if you new it was strong then I would do the 16 thou shave.
But that is me, you might want to do the 16 thou shave.

[This message has been edited by AMCPorsche924Powerhaus! (edited 03-06-2001).]