irover

As on the Carrera 3.2 the surface mating the cylinder head on the top of the cylinders has no head gasket. This is also true on the turbo 3.3L cars. The carrera 3.2 cylinders are tapered slightly to seal better, and this mod is possible to do on the 3.3 cylinders as well. Do anyone know how much the taper should be, like how many degrees or how many hundreds of mm difference on the inner and the outer edge? I would like to do this and want to pass this information to my machinist so that he can perform the modification for better head sealing.

Thank you.

Peter

PorschePhD

To be honest, take a set of 3.2s, rebore them and have them replated. This is the best of both worlds. What is the other world you are asking, fully finned. The 3.3 cylinder is only partially finned and the 3.2 is fully finned. The taper can be done, but honestly the effort is probably not worth the expense for the outcome.

irover

Well it's the same expense as doing it straight as i have to do anyway due to previous compression leaks. Just have to angle the tooling setup a bit. Boring out a set of 3.2 cylinders would need a Nikasil treatment afterwards. Do you really think this is going to be cheaper?

And about the finning, i think Porsche did this deliberately to have the cylinder expand equally on the upper and lower side. So that isn't a bad thing. The Turbo also has Dilavar studs on both rows whereas most other 911 has steel on upper row.

Pete

rickc

Start with the 3.2 's as Stephen is trying to say very nicely. The concensus from the "free world" is to stay away from modifying the stock 3.3 finned cylinders if you can avoid it. I am in the same situation.....but I found a good used set of Nikasil 3.2 's. They were cheap!
Have you looked into Nirisist or the crush gasket type of setup from
Performance developments? Don't waste your time on a tapered setup....it's not really proven effective on a high hp turbo.
Rick
'78 930

PorschePhD

Pete ,
Like the Dilavar studs that was not Porsche's great designs. In fact the half fin creates an uneven cooling process that will warp the head to cylinder mating area. In 1991 Porsche realized that the design with the added combustion heat and HP was simply not going to work anymore. The only design that remains through Mahle as well as if you were to order replacement cylinders from the dealer is the fully finned versions with a shim between the matting surface. I have a box of cylinder if you want them What you will find also they are very prone to ovaling as well.

As far as the Dilavar, well those have proven to be completely inadequate and carry the "when" not "if" they break disposition.

irover

Excuse me, but are you saying that Porsche between 1977 and 1989 was doing it all wrong building crap engines by using the half finned cylinders on the Turbo? 12 years of manufacturing and they didn't realize their mistake? Sounds very strange and definitely not the Porsche way of doing it. They had full fins on the SC so that wasn't a problem either if they wanted to fit them on the Turbos. Why did they do that and why did they use Dilavars up and down?

Also i bought 993 Dilavar studs for my engine. About half people i talk to are saying no dilavars, and the other half say Dilavars please. some even say raceware and ARP are crap and not worth the money, they work out of the case etc etc. If you read the book by Mr Dempsey he says steel studs on all engines. Well, the 993 studs is a factory recommendation for the turbo since you can't buy any other studs for that engine from Porsche (a least not in Europe). Also factory studs come with loctite on them wether you want it or not.

I'm not doing any tuning here, just rebuilding to stock 300 hp. I'm even putting in stock cams! (probably makes you all throw up) I don't need more power what i need is a 100% stock 930, there aren't many around these days...

Peter

Geoffrey

Mr. Dempsey also says to put red loctite on the rod bolts...

I would backup what Stephen says that the 3.3 half finned cylinders do tend to become oval and you can measure them with a dial bore gauge.

irover

I did mine are fine.

Peter

PorschePhD

Yes, I am saying it was deficient after time and when HP started to go up. If you look at the range of Porsche and their development and the amount the cars are actually driven the need for a new cylinder was evident by the time they brought out the 965. A fully finned cylinder was accessible, somewhere in their engineering they thought it to be appropriate. In time, they realized that the same designed engine needed to change. Hence the lack of ablity of any half finned cylinder through Porsche or Mahle after 91' and at the present. Things occur around data and demand. The amount of time given to collect "real" data on the 3.3 turbo took time. Heck, most of the cars running around still have not seen 100K miles. In fact many issues were present, such as the need for valve guides every 50K miles. It was a TSB at the time that a full 50K check up included said service. Any of the 3.4 turbo cylinders in the era as well as now were fully finned and we have not and do not see the same issues.

In regard to the head studs. I build apx 4-5 turbo motors a month. So I get to see all sorts of things. It took Porsche nearly 10 years to make a design change on the studs, or to openly admit they had a problem. The result was the fully threaded 993 style. Like many I ran out and started installing them since this was the fix!! A year later a motor we built snapped a stud. So much for that great design. So we moved over to Raceware and ARP. To which we have never seen an issue with either stud. Once again this is from the data of building motors for some time. To farther along that theory of what works and what doesn't is all but one 993TT motor I have torn down was fitted with standard steel studs. The same steel stud you would use on a 2.4 motor. I also have torn down many 94 3.6 motors and at least two of them were fitted with standard steel studs from the factory. Both were virgin motors. At one of the tech sessions I was speaking at with Bruce Anderson we chatted about this and he also confirmed my findings. It has since been my recommendation that if you are staying under the 400HP mark the steel studs are the better way to go. I have seen every example before hand with the exception of ARP, RW and the steels break.

Nothing wrong with a stock motor. The motors should be built for the owner and not the dyno. In fact I am rebuilding my 76 motor and it is painfully STOCK. I keep itching to do something, but I want to preserve what it was and will be.

irover

Thanks! That sorted out some things...

Generally you can say Porche is a pretty popular car in the US. I had one before this turbo, a 2.7 1974. When i bought that i had lots of people telling me i should steer away from it (because of it's weak magnesium engine) But the car was so nice and ran like a dream. I was of course interested by what i had been told, and started digging around on the net for information on the 2.7 engine. I found most points given on this 2.7 originated from the US. The 2.7 1974 for instance had in the US version the heat reactors fitted, restrictive exhaust and sometimes an AC. Also generally we drive cars differently in Europe than in the states, especially in those days when these cars were new. (we have speed limits now and cameras in every corner) But the conclusion is that faults that would be common in US would not necessarily be a problem here. Like different climates also affects the cars. If you go to northern Europe, UK and scandinavia, the cars have generally rust problems but are kept tidy and well maintained by their owners. Southern europe have more accidents, bad service, but never any rust. (The French particlarly are very careless drivers, not the Italians as one may think, my opinion)

The Dilavar studs break when they corrode, and i could imagine that it would be rather common in the NewYork area, whereas in Arizona this would not be a problem. Like cars driven in London would break studs more often than in Rome. Does this make sense?

Peter

m42racer

Putting a taper on th Cylinder Tops sounds like agood idea in order to put a point of contact. But in reality, it gives you a very limited seal. A true flat concentric surface is always the best if no sealing system is used. I also recommend the sealing system by PD. Its been proved by many to really work.

Good luck on your build.