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The only remaining way to move increase low end torque with the current system is basically installing various intake manifold spacers to reduce the first, flappy closed resonance peak rpm.
can you expand on this? are there are variety of spacer choices?
I see, thanks for the clarification.
With a torque plateau as wide as 3K rpm and holding up beyond 6k rpm, this is in my opinion excellent and may be hard to be improved.
What are the flappy switch points?
Flappy switch points are stock at this point. They haven’t been particularly tuned at this point. There may be something there at the margin, but it’ll be the last thing to do.
The main thing that’s left to improve spool is space the intake manifold plenum more to move the first torque peak to lower rpms. Then, I believe that if the LH and EZK column is placed at the optimal flappy switch point, one can give the engine much more ignition timing at that column and smooth out that torque dip.
Wiring the flappy valve in a different way may help the torque curve a little bit with high powered cars. I believe that it would be slightly better to have the flappy open at low rpms, then temporarily close for the first torque peak, and stay open after that. It may be a little harder to tune and drive in the street, because there’s a flappy switch point at the low power cruise rpms, so probably not worth it for a pure daily driver. I think PorKen experimented with this idea.
The sudden jump in torque on the 2019/08/02 graph at about 3600 rpm more than likely corresponds to the factory-set 3585 rpm opening point of the flappy.
It would be interesting to see the difference when opening the flappy earlier, depending on when the turbos begin to build boost.
The sudden jump in torque on the 2019/08/02 graph at about 3600 rpm more than likely corresponds to the factory-set 3585 rpm opening point of the flappy.
It would be interesting to see the difference when opening the flappy earlier, depending on when the turbos begin to build boost.
more likely related to boost control algorithm, but when the smoke has cleared it will be easy to run the whole dyno run rpm range flappy closed and then flappy open.
i have a "gently used" SPEC 5 clutch doing nuthin' if you'd like it. It'd be cheaper than a new one. Worked good for me up to about 900 HP, then it started to slip and I went to a Tilton triple-disk. Its in very good condition, lots of material left. I can get you pictures if your are interested.
i have a "gently used" SPEC 5 clutch doing nuthin' if you'd like it. It'd be cheaper than a new one. Worked good for me up to about 900 HP, then it started to slip and I went to a Tilton triple-disk. Its in very good condition, lots of material left. I can get you pictures if your are interested.
Thanks, already ordered and received the Spec 5 disc.
What torque level did the clutch slip, as power is irrelevant given the torque? With a clean stock flywheel and correct installation, we are finding that these Spec clutches hold up at minimum their rated torque. Spec 3+ went over the rated torque of 770 lbf-ft. Similarly, the expectation is that correctly installed Spec 5 clutch will hold 888 lbf-ft against a clean stock flywheel. Aftermarket flywheels may be another story...
Did your Spec 5 disc slip against the stock flywheel or some aftermarket flywheel?
That matches my experience too - that the SPEC clutches hold what they are advertised to hold and usually a tad more. I first noticed the clutch slip at 930 ft lbs of torque with the SPEC 5 clutch. It would hold up to about 5300 rpm for me, then let go as output went higher. It was very predictable.
I think you will find the Spec 5 clutch too be too "severe" for street use. And any of Tilton's race clutches are on/off switches.
I've still got one brand new carbon/carbon clutch left, which will easily hold your torque...and whatever additional torque you can develop.
After running these clutches for the past...not exactly sure, but about 5 years, I decided that even though they COULD be driven on the street without much chatter (Jim and Sue Corenman drove one for 35,000 miles in their street car), they do require very careful releasing, and are too "severe" for most people. The carbon/carbon "grabs" itself very hard and has a very narrow range of "engagement slip"...which in part, is due to the design of the diaphragm. (There are long release diaphragm/pressure plate designs and short release diaphragm/pressure plate designs.)
All of my "prior" clutch designs (still have a flywheel for a Tilton 5.5" clutch, too) required moving the bell housing back to be able to get the flywheel/clutch assembly installed (like a 928 automatic requires to get the flywheel off.). They also required removing the stock starter bracket, finding an early lower bell housing, and machining it for clearance (and usually repairing various threaded holes.)
Since I'm constantly "on the search" for a smooth clutch that can hold the increased torque of higher torque engines, plus looking for a good solution for replacement stock clutches (the parts are getting very hard to find and very expensive....most have to come from Porsche, directly), none of the "solutions" I had come up with were truly "street" clutches.
I "started over" and am now a few weeks from the pieces being finished (new flywheel, trigger ring, starter ring gear, input shaft, hydraulic T/O bearing, etc.) for a brand new clutch assembly that was designed for pure street use, which will easily hold your torque.
[Hint: Look at Tilton's brand new ST-246 street clutch. Their cerametallic version (not going to be as "butter" smooth as their organic version) will hold 1250 ft.lbs. The diaphragm/pressure plate design is a "long release" style....reducing the "on/off switch" of any of the racing clutches.]
My goals for this clutch are to build a super smooth clutch/flywheel assembly that would hold any torque the 928 world could throw at it, plus be able to install the clutch up into the bell housing (like a stock clutch and flywheel), and to be able to use the stock starter bracket.
The Spec 5 clutch is probably not the right solution for parallel parking in Boston, but it should do well for the next couple of dyno experiments that produce more torque than the eventually detuned version of the engine.
The Spec 5 clutch is probably not the right solution for parallel parking in Boston, but it should do well for the next couple of dyno experiments that produce more torque than the eventually detuned version of the engine.
can you expand on this? are there are variety of spacer choices?
This is just theory and simulation at this point, but there are three spacers that one can install in the S4 intake: Right plenum, left plenum, and a plate that extends the up-chimney and intake ports. Increasing the plenum volume will _theoretically_ reduce the rpm at which the torque curve first peaks in the flappy-closed mode, and the plenum spacers increase plenum volume. A plate between the heads and the throttle body on the bottom and the intake manifold main casting on the top would increase the rpm at which the torque curve first peaks in both the flappy closed and flappy open modes, again based on theory. So increasing the plenum volume, increasing the primary runner length, and increasing the zip-tube (i.e., up chimney) length all THEORETICALLY move the torque curve peak to a lower rpm. If so, then it might be useful in getting the turbo to spool earlier. That's one of the experiments I want to try out this winter.
One thing to note. Even with the massive 3.5 inch down pipes and correspondingly large wastegate dump pipes, the clutch can be replaced without removing the exhaust.
09-04-2019, 08:51 AM
