heinrich

Yeah I feel a surge of power coming on ... na na na na naaaaa

BC

Lets close this Deck Lag. Lets figure this out and do it. Then the problem's solved. Did you guys look into this there in WI? I know about Tim's rings, but that doesn't support the cylinders against the block walls right? Or do they? All we need is some sort of lateral link between the outside of the tower and in the inside ofthe block wall.

John..

Personally I like the engineering in the 928's engine, with the exception of the breather system. Just don't go crazy with the boost and it is fine. I've said this before, if you run a turbo or positive displacement blower, you don't have to run super high peak boost numbers to make the torque you want up the middle. The CS has that exponential boost curve and remember, you only spend a fraction of a second on the redline in the real world. European Car now has a rating system for area under the torque curve....that tells the real story of how she will perform on the road.

I still want someone to tell us how much boost the 928 CS cars make as a function of RPM. Has anybody looked at this?

Old & New

Well of course we have looked at it. We look at it every time we drive. And we have discussed it many times... Application of throttle depletes manifold vacuum in an accelerated manner and the engine goes into boost at under 3K rpm (I observe this at 8 and 10 psi boost levels, anyway). Absolute manifold pressure appears to be somewhat linear with rpm (when under load), not "exponential".

Again, looking at manifold pressure is not a reliable method of predicting the torque curve; take a look back at the graph I posted last time we had this sort of discussion. Remember? It showed your turbo torque curve plotted against the CS torque curve. They had similar torque curves at low rpm. The turbo fell off more rapidly at higher rpm, but you attributed that to the fact that it was a 16v vs. the 32v CS.

https://rennlist.com/forums/showthre...=122508&page=3

Getting back on topic, let me mention that I spent most of my time in the top third of the rpm band while putting along with that AMG, and I'm very happy that the torque curve of my engine is what it is.

Lagavulin

Everything you've said is correct. He has not learned anything over the past year, and is why I don't even bother anymore.

Amen brutha'!

This is the very thing I've written about on several occassions: where do you want the power in a racing scenario? 4000 RPM to Redline! Where is the RPM after an upshift at redline? 4000 RPM! Where are the RPM going to go from here with your foot to the floor? Redline! Where are the RPM's going to go after an upshift at Redliine? 4000 RPM! Where...

Under those circumstances, for ANY car, does the driver care what the power output is at 2000 RPM? Hell no; you hit 2000 RPM ONCE while backing out of the driveway; a lot good it will do you in a racing situation.

I do not think John has EVER raced anyone. What he'll tell you to do instead is 'stage' with the AMG so that you're turning 2500 RPM (..because you're at 'full boost' already), and at 4500 RPM shift, because that's when his turbos run out of breath, and the power curve falls of the face of the earth. Using that 'strategy', the AMG's tail lights would be barely visible on the horizon.

John..

You guys still don't get it. You compare my turbocharged 4.5 liter to your 5.0 liter CS cars. One is an apple, the other an orange. You already started with 100 more HP and a lot more torque out of the box. An extra 500 ccs of displacement and much better cams and heads. Of course it will make more power. Duh. The curve dipping off as it does has nothing to do with the turbos, but is a result of the 1981 cam profile, the worst in any 928 by far. Callaway used quite large turbines, so don't even begin to tell me about back pressure issues. Should I install better cams and open it up Lag? A good set will push my torque curve up the band, ask any of the 928 experts out there. Have you looked at the factory 4.5 liter torque curve Lag, strangely it looks very similar to mine, just a lot smaller. So, Lag, you telling me you would not welcome another 3 to 6 lbs of boost at 4000 RPM, 5000 RPM, or 5900 RPM? 3000 RPM Turbo at full boost, CS maybe 1.5 lbs. 4000 RPM, turbo at full boost, CS less than full boost. 5000 RPM, turbo at full boost, CS at less than full boost, 5900 RPM turbo at full boost, CS less than full boost. Do that math....on the same engine mind you. This is something the engineers at Porsche know as well as industry experts like Corky Bell. If you want full boost at 2000 RPM, then put Andy's kit in and enjoy the ride.

Should I build this twin turbo 928 S4? Let me count the reasons...

Now, I have asked this before and I will ask again....Where are those performance specs? Andy has put his numbers up, where are your's Lag. You are fast to tell us how quick your car is after you point to a dyno sheet. As the saying goes, the proof is in the pudding and I haven't even seen the Jello yet. Send me your address and I will let you use my G-Tech.

Old & New

John,

Why do you always need to step in and start a pissing match? Last time I checked, this thread had nothing to do with turbocharged 928's.

Aside from that, I don't think it really matters what rpm the torque curve lives at. How about that huge F350 turbo diesel truck that turns 11.4 at 118? It is just important to balance the curve with the proper gearing and breathing characteristics of the motor. <the hair on my neck standing up, realizing that I have opened yet another topic> If you read my last post more carefully, you will see that I only stated that the torque curves were similar, and I spoke nothing about the numbers.

Your car is designed properly, setting the curve lower for a 16v motor cammed as it is. My car is also designed properly; with better breathing and hotter cams, it deserves a higher power curve.

Personally, John, I think you are a gifted individual who ought to spend less time making pointless arguements on the forum, and spend more time building an incredible TT 928S4 (with an automatic, of course) so that you can run with the big dogs.

John Welch

Heinrich,

Please don't fall into the trap that I have seen so often here. The concept that just because we haven't seen/heard of something, then it doesn't exist or couldn't possibly work. I couldn't believe that some of the initial 928 S/C 'tuners' were blowing head gaskets because they didn't seem to understand A/F ratios. Over on the 951 side, we have covered that topic more than a few times.

I'm amazed at the 'We're different than anyone' attitude that precludes the reuse of technological solutions. I mean, I like inventing wheels as much as anyone else, but...

There have been several discussions of deck plates in the 951 forum.

One discussion about deck plates: https://rennlist.com/forums/showthre...ght=deck+plate

From that discussion, Danno states:

I suspect that cylinder flex is responsible for a large portion of the blown headgaskets on 951s out there. Under high combustion pressures when the engine knocks, I'm sure the fretting between the head, gasket and cylinder tops creates miniscule gaps to develop that allows the intense heat in the chamber to sneak past and burn the headgasket. As can be seen in the later 3.0l engines, Porsche made these modifications themselves. The cylinders are shorter and are also siamesed together for addtional strength. This obviously makes a differnce as can be seen from the numerous 3.0l Turbo cars running around using 18psi of boost and 9.0:1 compression with fewer headgasket problems than a stock 951.


----

I can't say this is truly the cause of head gasket failures, but I wouldn't be too quick to rule it out.

Just some more info,

heinrich

JohnW thanks, yes there is a lot of speculation along those linesl however there are IMHO several other, far greater culprits for things like head gasket failure, not the least of which being gasket design. Remember Porsche designed many engines with *no* head gaskets, and in the 924GTR's case, welded the head right onto the block.

I do not rule cylinder shake out as a gasket cause, but truly I have seen absolutely ZERO evidence that an open deck design is or could be responsible even slightly, for head gasket failure. Even for a 951. Again, I point you in the direction of Porsche's several other racing boosted applications. Lagavullin pointed out correctly that the aircooled cylinder heads are actually affixed and supported differently, however again, there is .... still .... no .... evidence.

Personally I would direct my attention to the obvious, namely:

1) overboost versus head gasket design and
2) o-ring absence.

To me it is very simple, and of course ...I may be wrong, I may be right ...."Hey, but it just may be a lunatic you're looking for .... Remember how I found you there, alone in your electric chair, I told you dirty jokes until you smiled .... I was only having fun, wasn't hurting anyone ... and we all enjoyed the weekend for a change ... "