mjmoser

Hey guys,
Thanks for the input and comments! Valuable info and many things to think about. I'll start with compression and leakdown tests and see what may need to be done. I'm leaning towards a top end rebuild to fix the head gasket issue but that's not definite, depending on what the tests find. And, I'll also start by asking around at the different shops you've recommended for price and time.

As a further idea/question, does anyone have any opinions about doing a top end rebuild with either fixed/machined heads and cylinders vs new heads and cylinders? New seem to run around +$5k whereas fixed/machined are, of course, cheaper.

I'm also interested in increasing the hp with added headers/exhaust and maybe other additions to the engine. A Motec box seems to help, but not sure if new exhaust and Motec is the right direction to go.

Thanks!

eddieb4

Curious ... what are considered unacceptable leak down numbers?

tjb616

You definitely should not need new heads, just have yours sent to a good machine shop (Steve Weiner being a favorite.) New pistons and cylinders are usually done with a bottom end rebuild, but are not always necessary.

If you want to increase HP, Weiner heads with a matching cam and exhaust supported by a custom chip from Steve Wong is a good first step toward more power. Past that, you are looking at Motec or similar engine management and a whole lot more money. 9M and Steve Weiner are great resources for these solutions. Both provide lauded cam and exhaust pairings.

tjb616

Eddie, a rule of thumb good healthy motor should be under 6% across the board. I'm not an expert or builder, that's just what I've read and been told by the shops that have done leak downs for me.

Goughary

Important thing about a leak down- particularly in a non-head gasket motor- is that a cold compression test on that motor will likely result in terrible compression numbers. The heads don't seal when cold. Aka, the "oil leak" that's not an oil leak.

A leak down is done hot, and it'll show you not only if you have good compression, but it'll also show you where you may need improvement...aka, rings, valves, etc. this is why for a leakdown, you should be having someone familiar with these motors doing your leakdown. So you get the best interpretation of the data.

He will then be able to best guide you in terms of bottom vs top end. And then if course, once the motor is open, he can get more specific.

I'm still on the "fix the drips and drive it a while" camp. Instead of just throwing money at a rebuild...but...rebuilds are fun...so if you go that route, lots of pics and info here please!

mjmoser

Thanks again for the info and tips! Good to know about compression test variance and how to do a leakdown test. I'm having the clutch, valves and suspension/height adjusted this next week at Performance Automotive. They'll also do compression and leakdown tests. So, I should know which direction to go in, in 2 weeks. I'm away until then.

Also, thanks for the tips about how to improve performance and who to go to.

tjb616, when you say Steve Weiner is good for matching heads, exhaust and cams, do you mean machined heads with gaskets? Also, I suppose Steve would have recommendations for which cams and exhaust? I know some people like Fabspeed exhaust, but they're a little too raspy and loud, to me. I prefer Brombacher exhaust, from what I've heard. I suppose Steve could recommend cams and chip to accommodate Brombacher exhaust?

Thanks,
Michael

Navaros911

Michael,

Something to think of or search for... I believe the heads and cylinders with and without head gaskets don't mix.

So I think you are looking at both or not at all.
I think cylinders come with pistons... which will get pricey, especially if you don't really need it.

Perhaps retrofitting is possible. Just adding this as something you may want to look into in advance.

mjmoser

Hey Navaros911,

Yeah, that's what I meant. From my understanding, either the heads have to be machined to allow gaskets and then fit to the existing cylinders, or new heads and cylinders (which fit together, of course) can be bought. Correct?

But, I'll look into this more.

Thanks

Navaros911

I believe the heads can be machined to accept the gasket. The existing cylinders though, I'm not sure that is possible. The lip that mates with the head is very thin and now one needs to create a groove in this to hold the gasket.

I'm no expert on this, since my heads were ready to accept the gasket... and I purchased new cylinders at time of rebuild so nothing had to be modified for gaskets.

In any case both the head and the cylinder needs to be able to accept the gasket. However you get to that point is up to you and the mechanic/machine shop.

John McM

My cylinders were machined to accept the older sealing ring. It left a very thin edge which cracked. I replaced all the cylinders with originals. No seepage yet.

jimonycricket

Since you're somewhat local to me. I had my top end rebuilt a few years ago at Performance Automotive in Malvern. They specialize in air cooled Porsches. Mine is an 89 so They reused my heads and machined them to accept the updated gaskets. As far as I can tell they did a great job. Pete and Paul are no strangers to doing engine rebuilds. I hope this helps.

Goughary

Just to put this out there. Machining the early cylinders is silly. It doesn't resolve the actual issue. It only solves the drip on the garage floor and offers zero actual performance value. Resolving the fact that the early cylinders, when cold, can experience a compression leak, can be done without a head gasket. And the heads when properly installed, Mate perfectly.

If you really want a head gasket, get the new style cylinders.

But again. If you are doing this solely based on seeing an oil weep in that area, you are going to spend a huge amount of money to resolve a problem that is not a real problem.

Further- anyone who panics over seeing a little weep of oil w these cars, truely needs to chill. Cuz you are going to see a lot of wetness over the time you own the car. And if you "have it fixed" every time you see oil, it'll live in a shop and drain your accounts.

So...be careful to not care too much. Take it easy. Stay informed and aware. And make good solid choices that are for the right reasons. There is no need for 964 ownership to be expensive.

Ralph3.

mjmoser

Thank guys, for the advice.

Yes, I'm not sure about having the heads machined to accept gaskets. I'm also looking to improve some performance. So, if there's any issues with the compression and/or leakdown tests, and I'm leaning towards a top end rebuild, I've thought that new heads and cylinders would make sense.

Yes, I'm having some work done on the C4 now at Performance Automotive. They seem to have a lot of experience and know what they're doing. Thanks for the extra plug.

Thanks,
Michael

mjmoser

An update on the process. Just got numbers from leakdown and compression tests:

Leakdown:

Leakage
#1 5%
#2 10%
#3 22%
#4 8%
#5 15%
#6 15%

Compression:

#1 220 psi
#2 225 psi
#3 215 psi
#4 215 psi
#5 215 psi
#6 220psi

My interpretation: Compression looks good. Leakdown shows expected leak past pistons.

Or, does anyone have another take on these numbers? Since I'm not stepping on oil in the garage, not sure if these leakdown numbers justify a top end rebuild. I kind of expected less-than-optimal leakdown numbers. However, are these numbers worse than you would expect for a 1990 964 with 95k miles?

Michael