Jean

TB

To convert from flywheel numbers to wheel numbers, they use a correction factor that cancels (in theory ) the effect of overall gearing. Once gearing is corrected, the major things that cause a difference between flywheel and rear wheel HP are:

- Gearbox friction (R&P and gears)
- Axles
- Differential friction
- Other bearings (wheel etc)
- Torque tube in the case of our cars
- Tire slippage on dyno
- Accessories such as power steering etc..

And some other items...

What I was trying to get to is that according to acceleration data the following components:

- 2 Axles
- Torque tube
- Front differential

Represent about a 6% loss.

On a 2WD run on a chassis dyno, the losses between flywheel and rear wheel are "mainly" driven by:

- 2 Axles
- Rear Differential
- Gearbox friction losses
- Some accessories (SAE and DIN standard include most accessories anyway)

So you loose the impact of the torque tube friction but add gearbox friction...So would 10% seem reasonable?

Red rooster

" The 993tt AWD system uses the speed difference front to rear to determine the relative axle power transmission .
This means that if the rear tire grip or tire sizing cannot put down the correct power the front will take on the challenge !
The torque /power loading allowed on the front is fairly low , to be polite ! "

This highlights that the 993/993tt AWD system is best avoided for power tests .
Porsche , themselves , recommend running rear drive only for power testing .
I would view any 993/993tt AWD bhp numbers with great suspicion !

The previous 964 AWD system is much more robust and gives reliable numbers .


Geoff
----------------------------------------------------------------
KS400200,the oldest 964 on Rennlist,unless you know differently !

N51

How is it that a decoupled 993TT can have only a 10% loss as apposed to a 964 C2 which has a generally acknowledged 15% loss? What's the marked differences? If true, I'm in for the 5% gain. Tell me how.

Noah

shawsan

Thanks for all the feedback and input thus far. I thought today was going to be a great day as I took a 30 mile drive to the latest, state-of-the-art Dyno Dynamics Dynamometer (DDD) to establish REAR WHEEL HP and TQ for my modified 993TT. Three points before I disclose the results;

1) A distillation of MANY differing views, experience, and discussions with the Dyno Dynamics folks reduced several of my fears about putting an AWD Porsche on a DDD. The owners themselves of the DDD had a C4S and have dynoed several other C4Ss as well as AWD Audis w/o any issues. In other words, I was more than comfortable "taking a chance".

2) A distillation of several baseline dynos on stock 993TTs -- though fewer than I'd like -- suggest that stock rear wheel HP and TQ lies somewhere between 300-325. Moreover, the folks who own the DDD speculated that a stock 993TT with 400HP/TQ would probably put out around 320RW HP/TQ even though they hadn't dynoed a 993TT before.

3) Relevant to the discussions I've read about drive train loss,. They say, based on their experience, the drive train loss on an AWD Porsche is around 20-25% and up to 30% on an AWD Audi. They DON'T adjust the RWHP/TQ from their DDD runs to flywheel/crank HP/TQ, but if they did, they think a drive train loss of 20-25% on a 993TT would be on the mark.

My results on their DDD are, unfortunately, empty!! When they put my 993tt on their dyno, they first did a very slow engagement of rear wheel drive, creating some slippage, to observe engagement of the front wheels through the viscous coupler. But the front wheels didn't engage to their expectations, at least based on what they know from dynos of several C4Ss. This led them to speculate that my VC could be operating sub-optimally. A worse case scenario would be that it has been fried by hot and heavy acceleration in the past. Bottom line, they didn't feel comfortable doing the dyno until I checked out the integrity of the VC.

Needless to say, I was disappointed but did respect their professional stance and aversion to doing any damage to my car. Next step I suppose is to go back to our local Porche performance service (Wiessach) to evaluate the situation. Any views or suggestions would be appreciated.

TB993tt

Your original post was asking about "RWHP" which is REAR wheel hp it seems what you really were asking was about 4WHP or AWHP ? in which case your 300-325hp to all 4 is probably correct.

I would go with 10-15% - 15% will make you feel happier
Have you checked out the "loaded dyno thread"

shawsan

Thanks for the correction TB993tt. Yes, I wanted to refer to AWD HP/TQ (involving all wheels), not just HP/TQ at rear wheel (involving only 2 wheels). Once I get the viscous coupler checked and either a green light or new VC, I'll be making my way back to the dyno and will report results later. Cheers.

ScottMellor

I hate to keep harping on this.
If you dyno your car on a non-mechanically coupled dyno, you may fry your VC.
On my first run on a non-mechanically coupled dyno, my front wheels spun as fast as the rear.
On the second run, they did not spin at all. $700 plus labor.
NOT WORTH IT!!!!!!

Red rooster

It brings on despair when the 993/993tt VC system is run on a dyno .
As I explained before , it takes a few minutes to disconnect the VC for power testing .
Any small understanding of how the VC system works will leave you agreeing with the Porsche factory that the VC system must be disconnected for power tests.
Anyone that attempts to powertest a 993tt on a 4wd rolling road dyno should not be allowed near that car .


Geoff
----------------------------------------------------------------
KS400200,the oldest 964 on Rennlist,unless you know differently !

shawsan

Your message is getting through, so thanks for insisting and repeating your points. OK, so do the following three statements more or less reflect concensus on existing evidence and professional opinion?

1) Best practice is to disconnect the VC, as recommended by Porsche, and undertake power tests using 2 wheel rear drive only.

2) Next best practice is to use a dyno with mechanically coupled rollers. There seems to be only one available, the Mustand dyno.

3) There's no third best practice but rather a stern NO-NO to use any other AWD dyno -- including the most advanced dyno dynamics dynamometer -- because of a real possiblity of frying the VC.

Red rooster

1. Disconnect the VC - Hurrrrrrraaayyyyyyyy !!!!!!!!!!!

2. Run on a locked AWD dyno - NO .

The VC is a silicone filled temperature activated power transmitter that relies entirely on the wheel speed difference between the front and rear , ideally with no change during a power test !

The 993 VC system was a cost saver and even had the front differential greatly
reduced in terms of power handling and size . Add in the precise rolling radius
sizes required for front/rear tires under load and you are looking at a potential disaster.For example if the rears take a break away on a roller ,the fronts will try to accept the total motor power ! NO WAY is the technical judgement !
A fried VC is the minimum penalty there.

It has always been known that the VC system is technically not one of Porsches best efforts and in terms of motor power measurement should be disconnected from the system .
I am always suprised that the 993tt had a VC AWD system but development money was scarce at that time .
It is interesting that pre 993 times Porsche were pretty critical of the technical performance of the VC sytem . The 997 has now returned to a very much updated 964 C4 arrangement with no VC in sight !

Geoff
----------------------------------------------------------------
KS400200,the oldest 964 on Rennlist,unless you know differently !

Q

shawson,

We used a Dyno Dynamics dyno when modifying my 993TT.
I have base figures, and figures for each step along the way....

FIRSTLY....forget all dyno figures you have read on this site.
Dyno Jets read 15% higher than Dyno Dynamics.
The two will never meet.
25-30% driveline loss = normal on a Dyno Dynamics.

>>>>>>>A standard 993TT makes 266HP on a Dyno Dynamics Dyno.<<<<<<<

BIG dyno sheet HERE
measurements are in kw, so multiply them by 1.3333333 to read as HP

SECONDLY....forget the difference between 2wd, and 4wd measurements.
The Dyno Dynamics dynos will give near identical reading in 2wd or 4wd.
Yes I have done both.
Yes, I also subscribe to the school of disconnecting the drive shaft connector.


THIRDLY...you may find this thread of interest:
"I finally got my programmable management installed"

I found it with the search function by typing 993 + dyno + dynamics
The dyno sheets were all missing, but I managed to find a back-up copy of my website from 2005

Cheers
[the other] Paul

shawsan

Many thanks Paul for sharing the dyno dynamics dynamometer data on your 993tt. Very helpful to know your baseline HP at the wheels was about 270HP, and that you concur with the estimated 25-30% drivetrain loss on an AWD porsche.

I’ve also read your previous thread pertaining to the modifications on your car. My take from your prior thread is that you were able to increase power gained at the wheels by 80HP, or, if adjusted for drivetrain loss, then 120HP at flywheel (or 520 HP at flywheel, overall). The mods on your car included K&N pod filter, Millie Miglia mufflers, K24s, and stock ECU with Xede programming. This is an impressive performance gain!

I’ve had feedback from two sources estimating what my HP/TQ at flywheel should be. One, a racing team in Seattle, with a modded 993tt similar to mine estimated my flywheel TQ would be about 500, with HP around 490. Another, an individual, reports his modded 993tt with almost identical mods as mine had 486TQ and 498HP at flywheel.

But I’m a bit confused. My car has some mods IN ADDITION to yours, and I’m wondering what their additional contribution to HP/TQ gain might be. The mods on my car that are similar to yours include K-24 turbos, OEM chip reprogrammed for the larger turbos, and a tuned racing exhaust system – meaning 100 cell cats with OEM mufflers. The mods on my car that are IN ADDITION to yours include high pressure waste gates, billet diverter valves, high pressure fuel pump, and lightweight flywheel. Would I expect these additional mods to bring any significant increase in HP/TQ over what you report, or are they more akin to mods that just make it easier on my car’s engine to sustain the performance gains from the turbos, ecu reprogramming, and sports exhaust?

My dyno day will come but I continue trying to education myself in the meantime. Cheers, Paul

Q

You are welcome

- K&N pod filter = yes
- Millie Miglia mufflers = yes
- ECU with Xede programming = yes
- K24s = Actually, No, they where modified K24's.
quite a lot of work was done to them to flow more, impellors were cropped,
wastegate was enlarged and hi-flowed, etc

What was not mentioned in that thread, but was mentioned in other threads at the time, were the other mods done to the car:
- new divertor valves
- 5bar fuel pressure regulator
- turbo S oil cooler
- light weight flywheel

With reference to exhaust, you have 100 cell cats, I had Millie Miglia mufflers.
Net effect was probably the same.

With the work done to my K24's, in theory, I should have made a higher peak power than your standard K24's !

It will be interesting to see your results !

Cheers
Paul

TB993tt

2 pennyworth in here..... K&N pod (cannister) type filters LOSE around 10hp on the 993tt MAF intake engine, this was proven on the engine dyno testing the Gruppe M style cone intake and a 996GT3 type cannister inatake. The stock intake with panel is best for the MAF system.
Using standard mufflers with 100 cell cats is pretty pointless, the stock mufflers will cancel out any extra flow from the cats.

shawsan

"Using standard mufflers with 100 cell cats is pretty pointless, the stock mufflers will cancel out any extra flow from the cats." Quote

If this is a generalization that's true, then I just wasted $3K installing Hyperflow cats (100 cell) on my Challenge Stradale, while leaving the OEM mufflers in place. Yet, in the case of the Challenge Stradale, two pre vs. post dynos confirm a performance gain. One set of dyno results, by Hyperflow itself, (and thus questionable), claims 28ft/lb torque gain at the wheels at 4500rpms. But then, another set of dyno results by a fellow who hates puffed up manufacturer claims and set out to disqualify Hyperflow, reports a 22 ft/lb torque gain at the wheels at 4500rpms. I thus have a tad of confidence some real performance gain is attributable to sports cats in my Ferrari. Would the exhaust system on a 9933tt be so different?