bd0nalds0n

Yikes, I didn't mean to trigger a ****storm, it's like the durn Hatfields and McCoys around here.

However.

Given the amount of boosted 928s running stock internals, and having gone from, say, 320-ish crank HP and taken it up to 500+ at the rear wheels, which has to be somewhere in the vicinity of a doubling of horsepower at the crank, I think that suggesting that the stock stuff works within the stock parameters and a VERY small margin past it is a bit of a misstatement. Isn't it?

Again, I didn't mean to ruin the copper goo and shiny mating surfaces party, I was just trying to point out the merits of keeping everything civil.

6.0-928S

"Let he........... who is without sin ........cast the next stone"


Hammer (not my quote)

SwayBar

Just for you Brendan:

http://www.youtube.com/watch?v=w-WwM...elated&search=

BC

Well, I got mine from him, and mine are black, so take that for what it may or may not mean.

JEC_31

Dammit ppl don't go all danglerb & lowmiler on us.

This is a great thread. Very important stuff here. I'm researching, don't get the fookin' thread closed before I come up with some goods.





Mike, good luck on the custom studs. Everytime I see your sig (7 liters!) I remind myself to keep an eye out for your someday "it runs!" thread.

- Josh

hacker-pschorr

BC

One of them needs to be MUCH older to be Swaybar.

atb

One advantage of using the Cometics is that you can spec your gasket thickness.
The internals on my stroker got out of wack through my machining/part selection process (if I only knew then what I know now), and ultimately I had my pistons designed to accomodate a 1.5mm thick head gasket. I did this so I would have a .5mm fudge factor either way in order to keep my C/R in check. Now before you all start going off about squish, wedge, and flame front propagation, this is a street engine. I guess if the piston domes come in too deep, I could go with the oem 968 1mm or 1.4mm as an option. I just think the whole thing about running one of the gaskets inverted, cutting holes here, plugging holes there, seem like a lot of work. But, obviously it works and works well.

B.C. wrote:

It means you got screwed.
Just kidding Brendan. It probably means that I've got my colors ***-backwards. Maybe the studs I have are gunmetal grey and Garrity said that his were black, I'll have to look again at the studs. I haven't really looked at them in the last 8 months, they're just sitting on the shelf collecting dust. My point wasn't really so much to focus on the color as a tell all sign, but more that studs aren't studs. (Which you are well aware). I'll take a look at them again this weekend just to make sure I've got my facts straight.


Sterling wrote:

Here, here! The more options the better. I think the point is well taken that we can take more risk with our personal motor builds than someone in the business of engine building, especially building racing engines. That's a whole nother world compared to building a street mill for your own enjoyment.

Obviously there are people out there running cometics with good luck, as well as bad. It's good to hear both sides. Same thing with the studs. They must be working cause the vendors that do sell them don't seem to be able to keep them in stock.

atb

Sterling,

Okay, I think I can hang with you and B.C., but there is no way I belong in the same line up as Simard and his mad machining skills.

I appreciate the effort through

GregBBRD

All:

I'm not certain why threads turn to personal battles....but it sure gets old and makes me want to do other things. I'm here in this Forum to share what I know and gather whatever I can from others. I am not here to do battle....but I know that I can be "abrupt" I think my comments offend some, who think I'm here to do battle. I'm not. I like pretty much everyone. I actually have no personal issues with anyone here.

I thought the original tread was to share information about Cometic gaskets, not to share just the good things about Cometic gaskets. Sorry to offend you, Brendan. I misunderstood.

I don't feel that I'm on the trailing edge of 928 development. I think I'm fairly aggresive. Certainly, I need to deliver a product to customers that works, but that doesn't stop me from trying other things. Try and remember that I just built an '85/'86 engine (actually two of them) that can compete with the later engines, even though no one would have guessed that these engines had potential, too.

Certainly, I have questioned the reliablity of sleeved engines, but only because I have seen first hand what happens. Some people didn't like that. That's ok with me....I'm just trying to share what I have seen. This is fairly simple. Porsche had to change the material that the block was made out of when they went to free standing cylinders on the 944 GTRs, because of block cracking issues. We see block cracking in 928 engines on a routine basis. Therefore, I probably will not try this. I hope others are successful in this.

(BTW. I have several 944 GTR engines in my shop. You should see the head bolts on those babies!)

My experience comes from many areas of Porsche performance, not just the limited knowledge of the 928 world. Porsche uses the multilayer gaskets in all of the water cooled race engines. I've built many of these. They work very well. They don't use sealants and the surfaces are not polished, but are actually fairly rough. They look the same as Cometics, to me. They don't seem to work the same, nor do they seem to need the "dance" that Cometics seem to need to seal.

I frankly don't care if someone wants to install their heads with clay and drywall screws. If it works for them, I'm happy for them. However, I may not want to try it on my own.

gb

Mike Simard

More stud babble-
It's refreshing to hear about others that have experience with aftermarket studs and have gone back to OEM ones. I used to line up with the other sheep, buy the ARP studs from Summit or Jegs and wonder to myself during assembly why these studs are a fat stick with the smallest diameter being the thread root, doesn't that screw up pre-load stretching? Well you ask others including profesional builders and many never consider studs beyond just using the 'high end good stuff'. We're all like the cows in a Larson cartoon eating grass when one of them suddenly realizes "hey! we've been eating grass!". A stud needs to have a reasonable length dedicated to stretching, not just the remaining thread minor diameter that's not within the block or nut. I've built engines with speed shop ARP studs, after some street miles they still have the same torque level on the studs but then I go to the track and have detonation problems and notice that the studs have lost 'torque'. So what happened? Someting moved, either the stuff in between the nut and stud bottom(block, head, gasket) got shorter or the stud got longer. What I suspect happens in these cases is that the stud is a certain stretching amount away from deformation and this happens during detonation hammering. Also likely with aftermarket full body studs is that the block where the main and head studs anchor is being hammered by the full shock of detonation. I've seen other engines where a chunk of block is ripped out and suspect that a proper stud would have allowed the head to lift off of the block momentarily and returned to it's original condition and clamping force, same thing applies to main bearings IMHO.

If anyone wants custom studs, ARP can make custom studs and should be able to make them with undercut bodies per your (our) drawing. They quoted me something like 1000 bucks or so for a set of head and mains which is a good deal although it will presumebly be higher for reduced body designs. Well I'm ASSuming anyway, feel free to call them and ask, they do customs all the time. No non-production fastener companies should be making studs, mine included. I'm just being the machinist equivalant of the guy who has all the screw slots pointing in the same direction for a concours show, actually worse than that, I do all this work, nobody ever sees it and those that hear about it on a forum think I'm a hack working with a Shopsmith lathe in my garage. That's understandable because a typical machine shop would probably not even know where to buy the material necessary for studs as well as the heat treatment and importance of rolled threads after heat treating.

stuartph

Guys


So would you use the standard torque settings with the cometic gaskets.

And if i got thicker gaskets to lower the comp, could i lower it alot and would they be safe with 12 plus psi

SwayBar

Yes.
That's never really an ideal way to lower the compression in that fashion as you disrupt the factory-engineered squish/quench area of the engine. One of the jobs of the squish is to create turbulence on compression to homogenize the mixture, thus minimizing detonation due to lean pockets in the mixture which can flash.

On the other hand, Tim is currently running 13 psi on virgin S4 engine internals, including head gaskets, with an automatic putting down 510 rwhp. The car was extensively SharkTuned on the dyno, and records no knocks after the tuning session. He drove that car to and from SITM, and is running perfectly.

Based upon that, a properly tuned blown engine with stock thickness head gaskets should not be a problem at 12 psi.

Vilhuer

All this stud tall made it simple for me to decide to use original bolts. They are under 200 euros for set including washers. If truly working custom studs cost 5 times that much I rather change bolts and gaskets few times for same money. Since Cometic gaskets work together with stock stuff when properly installed and really do not cost more than stock 968 parts which need to be modified I think I'm willing to take risk with them.

BC

I think one of the links that I posted mentioned that the thickness of the "rubber" (its more than rubber, but the description works for now) coating is what allows for the roughness of the machined surfaces, and certain brands have certain thicknesses. One poster mentioned (not here) that the "Fel pro" brand of "MLS" gaskets had the rubber "Membrane" much thicker.