Bass993

My experience with the stock k 16's and the same setup with an FVD ECU reprogram compared with stock sport K24's and FVD 1997 ECU reprogram is like night and day. By 3700 RPM the car pulls hard and is light years ahead of the K16's. No question that good tuning and a well matched combination contributes to this result. Now if I can get the bypasses and 100 cell cats, things will only get better.

TB993tt

If you could get hold of a GPS device (Driftbox, Performance box. AX22) you could make the above meaningful and run some 50mph-75mph times in the different gears and ascertain whether what you say above is actually true

Here is the data for Porsche K16 and K24
K16 K24
3rd gear 3650rpm - 5470rpm 2.8s 3.2s
4th gear 2820rpm-4235rpm 4.1s 4.3s
5th gear 2380rpm-3570rpm 6.2s 6.6s
6th gear 1760rpm-2640rpm 8.6s 10.4s

Essexmetal

Appreciate the effort everyone has put into the graphs and technical info. Great information.

Hard numbers aside, the driveability of my K24’s completely changed the car’s personality. With the K16’s acceleration was fairly linear to the throttle application and early in the rpm range. The K24’s respond differently depending on how fast the pedal moved. If you have quick but even throttle application the car will go through the 3700 rpm range quickly and continue to pull. “Stomp” the pedal and it revs up the same until it hits 3700 and the power hits in the way everyone has been describing.

For those of you who are contemplating a change to K24’s and reading this thread with all its data and wondering what does it translate into in real world driving? I can say that after a slight modification in driving stile you will find your car exponentially more fun to drive. The “lag” is minimal and in street use may never be an issue. On the track I tend to like the power moved up the rpm range a bit to offer a little more throttle control before the majority of the power hits. Guess I am just posting some defense for the “perceived” bad rap the K24’s sometimes get. Personally I think they make the car a two-headed monster with a bit more controlled drivability down low and a very hard pulling car when you need it. As Jean’s graph shows it does not take long for the K16 & K24 lines to cross over. No looking back after that point.

Besides a LWF, 5 bar fuel reg. my motor is stock. The exhaust post cat has been bumped up to 2.5” for 2.25”, 100 cell cats, two resonators and then out the back. Not too loud and a bit of a drone at constant 3K rpm. Maybe not for everyone but it certainly has open flow. A non-data based observation, made a huge difference in how the K24’s spool up , but again the extra noise may not be for everyone.

Rick

Kevin

For the under/ sub500HP 993TT the K16 hybrid with modded turbine section when mounted with the very same K24 compressor wheel will outperform the K24's.. If you take TB's factory graph and raise the boost to the threshold of 1bar or equal the same output the lines will rise higher and sooner vs the K24's..

Felix

What ECU are you running with your K24s?

Essexmetal

Fleix,

Evo Motorsports / GIAC ECU. Not sure what stage for sure. We think it is a stage II.

Felix

If you can get your hands on a datalogger to generate some more numbers to add to TB993tt's table that would be great.

KPG

I should have mine back soon and he is welcome to it since we live in the same town....

TB993tt

OK, not that it means very much but always of interest in building a data base I got the DB out and ran some 80-120kph runs.

I did about 3 runs in each gear and these are the average.
Temp 14DegC running weight ~1545kg (4WD, full tank, new HD battery )
My turbos are 996tt 2006 RSK24/26 car is 3.8litre higher CR than stock
Ran off a couple of 60-130s around 7.8s.


K16 K24 UMW stage2 TB993tt
3rd gear 3650rpm - 5470rpm 2.8s 3.2s 2.13s 1.60s
4th gear 2820rpm-4235rpm 4.1s 4.3s 3.49s 2.63s
5th gear 2380rpm-3570rpm 6.2s 6.6s 5.62s 4.32s
6th gear 1760rpm-2640rpm 8.6s 10.4s 8.51s 8.16s

Amazing is how lethargic the 6th run was - I thought it was going to rattle the big ends loose Absolutely amazed to see that it is similar time to stock - jeez those stock cars are slowwww

Edit: My WOT engine dyno boost curve at the low end is:
2540rpm - 0.45bar
3050rpm - 0.93bar
3490rpm - 1.11bar
this may have been slightly helpful to explain the above, I noticed in 6th there was virtually zero positive boost (on the gauge) during the run

Bill S.

Here's an 80 to 120 km/h run in my Ruf Turbo R in 6th. HEIGHT VARIATIONS MAKE A HUGE DIFFERENCE! I saw runs vary from the 8 to 11 second range. This one is the flatest I could do.

BTW, I'm not sure how meaningful this data is besides maybe 3rd and 4th gear, since you wouldn't normally drive your car like this. There would be no reason for the engineers to focus on this.

TB993tt

Bill -below is one of the 6th gear runs I did -slightly uphill...

It is quite interesting to compare the 3rd,4th,5th and 6th gear runs since for cars with the same gearing like ours (and with known weight) one can get a feel for what the lag is like and how fast the car is in daily driving. Yours is interesting since it appears that the cams possibly move the on set of boostslightly up the rev range ? It would be great to see your 3rd.4th and 5th numbers

Bill S.

Now it's getting interesting. Here's my 3rd gear run...

Jean

TB993TT, your numbers are mind boggling... For a car that has so much top-end, this is very serious performance.

The main benefit of higher compression is exactly what you are seeing here, better performance at the low end (think about it as early boost), this is where experienced engine building and tuning make the difference, by finding the absolute best balance of compression/boost levels/performance, to keep overall intake temps in check while performing like a N/A at the low end and a race car at the top end . I would simply say that your car serves spot-on the purpose that you wanted.

From all the above, 6th gear seems to be the only meaningful measure of lag, other gears are directly impacted by tuning levels more than turbo size. Great thread!

Bill S.

For these cars, the 6th gear runs are primarily based on displacement and compression. That is, most of the time the car is off-boost.

I think these tests may be a little miss-leading because they don't include throttle response (i.e., when you release the throttle and step on it again, how long does the turbo take to spool up?). The bypass valve helps a little here because it allows the turbo to maintain its speed when you let up on the throttle momentarily. The other delay is when you first press the throttle when the turbo is not already spooled up.

How about running tests in 1st gear from a 5 mph roll to right before the 2nd gear shift point? That's where you'll see a huge difference in the 993 vs. the 997. This test will include throttle response... that is, the time it takes the turbo to spool-up after you press the accelerator.

Jean

Bill

What you are saying makes perfect sense if boost was nowehere present during the run in 6th, but it is not really the case, some boost has built by then before the end of the run.

If you look at the run in 6th gear, and taking TB's data, he starts at 1.7K RPMs and has 0.45Bar of boost 100 RPMs before the 120kph mark, meaning you are really measuring his boost onset, as it could have been not there at all.

In his 5th gear run, he is only 100 RPMs without boost, and then it is almost full boost before he has finished his run, you are therefore measuring boost onset only for 100 RPMs, the rest has to do with tuning state. Anything lower than 5th gear you are only measuring the tuning as boost is there throughout the RPMs.

I agree with you that this test is really meaningful to measure "lag" only if the 2 993TTs have similar displacement and compression.

I have zero consideration for lag as I simply don't believe it means much if anything, unless the turbos or tuning are really unsuitable, the 6th gear test is meaningless from a practical, however the only one that really shows boost onset threshold and it's impact, which is the subject of this thread.

None of us would be accelerating from 2k RPMs in 6th gear if he was looking for performance anyway. So this is only interesting as far as data is concerned.