Cayman S on Dyno

[ralphmusic]

I joined the Dorset and 944 groups today at West Tuning near Thruxton race circuit for a dyno session.

I believe my Cayman was the most powerful on the day with 239hp on only 50% power per Ray West, (so really 478hp ho ho) courtesy of Porsche electronics that cut power if the front wheels are not going fast enough for the rears!

I had expected the electronics might interfere as the Handbook (I had actually read it) does discuss wheel speed mismatching causing the safety systems to kick in, so several warning lights came on and (a benefit?) the auto stop/start is turned off. Anyway to reset the electronics just drive off, stop after 10 miles, ignition off, key out for a minute or so, repeat once and all is back to normal.

I'll connect the Durametric tomorrow to see if any error codes were logged or remain open.

 

[Nick_USA]

ORIGINAL: ralphmusic I joined the Dorset and 944 groups today at West Tuning near Thruxton race circuit for a dyno session. I believe my Cayman was the most powerful on the day with 239hp on only 50% power per Ray West, (so really 478hp ho ho) courtesy of Porsche electronics that cut power if the front wheels are not going fast enough for the rears! I had expected the electronics might interfere as the Handbook (I had actually read it) does discuss wheel speed mismatching causing the safety systems to kick in, so several warning lights came on and (a benefit?) the auto stop/start is turned off. Anyway to reset the electronics just drive off, stop after 10 miles, ignition off, key out for a minute or so, repeat once and all is back to normal. I'll connect the Durametric tomorrow to see if any error codes were logged or remain open.

You may find this of interest: http://www.planet-9.com/987-cayman-boxster-modifications/63184-how-dyno-cayman.html

 

[ralphmusic]

I had seen these which pointed me at the handbook, thanks. Aside from a day with some new (to me) Porsche owners I went hoping to find confirmation or otherwise of the odd torque curve for the Cayman 981S from the Porsche US site as below:

- I do not understand the relationship between the plot and the Y axis either - just look at the plot... Note the torque between 2,500 to 4,500 revs, then see the graph for the 991 Carrera 3.4 below:

So why the fall in torque in the 981s? Does it need more power or better mid-range torque? How best to drive it?

 

[CarreraRSR]

Cayman's linear plot

 

[Nick_USA]

The torque curve for the 981 is very similar to that of the 987 ie there is a dip. Porsche engineered it is way to give more torque at lower revs. From 987 tech info (similar for 981 although rev ranges slightly different): "The new engines are equipped with a new intake system featuring a double flow distribution pipe. With this new system, the distribution pipe flap in the intermediate pipe connecting the two intake air distributors is closed in the low rpm range. The distribution pipe is designed with a partition wall running along its length (between the electronic throttle and the distribution pipe flap in the intermediate pipe), as a result of which the 6-cylinder engine behaves like two 3 cylinder engines running in parallel in the low rpm range (when the distribution pipe flap is closed), leading to an improved torque characteristic in the low rpm range." Boxster S (987) – The distribution pipe flap is opened in the two rpm ranges from 3500 to 4700 rpm and from 5400 to 7200 rpm. and Tuning Flap The resonance intake system on the new engines is again designed with a switchable tuning flap in the perpendicular resonance pipe between the intake distributors. This resonance intake system can be used to adjust the air oscillations in the intake system to the respective engine speeds to ensure high torques even at low rpms, an even torque curve and high maximum output. The tuning flap is closed in the low rpm range. Boxster (987) – The tuning flap is closed at full throttle between 5000 and 7200 rpm. Boxster S (987) – The tuning flap is closed at full throttle between 4700 and 7200 rpm. I'll dig out the 981 and the one for the 991.

 

[ralphmusic]

ORIGINAL: Nick_USA The torque curve for the 981 is very similar to that of the 987 ie there is a dip. Porsche engineered it is way to give more torque at lower revs. I'll dig out the 981 and the one for the 991.

That will be very interesting but why would anyone profile the torque in the way they have, it seems an odd thing to do.

 

[Motorhead]

Yes Ralph, the Cayman scales are rubbish. It looks to me as though they might have superimposed the 3.4 S curves on the scales for the 2.7l car. Some time back I found a reference on P-9 which compared part numbers for the 991 and 981 engines and found that they share the same crankshaft, connecting rods, pistons, cylinder heads, camshafts, valves, injectors and intake distributor. However, the throttle body and plenum are different. It seems that the 991 uses an 82mm throttle body and the 981 a 74mm version. Certainly, the 981 does have a very strange looking torque curve - difficult to interpret why but variable valve timing and lift, the variable intake and engine tune will also play their part. The 3.4l is quite a torquey engine and I can't say that I've ever really noticed the dip in torque between 2,500 and 4,000rpm on my 987.2. How best to drive it? I think it depends upon your driving style but, for me, there's plenty of low and mid-range torque in the higher gears for everyday driving....and more than sufficient power on tap if I choose to extend the engine a bit in the lower gears too..! Jeff

 

[ralphmusic]

Yes that was my understanding but absent the parts list it seems to include some guess work. It will be interesting to see the 981 GTS version power/torque plots. The difference between the 997.2 S and GTS/Powerpack was mostly top end but built on pretty good base torque

 

[Motorhead]

If you got a torque curve from your (part) dyno run, did it display the same basic characteristics as the published curve? Jeff

 

[ralphmusic]

Jeff, I did not get a print since the run was invalidated by the electronics intervention. TPC in the US do a kit with larger throttle body etc http://www.tpcracing.net/981-atmo355-powerpak.html and I have to say 355hp if indeed that is what it delivers, sounds good but I have difficulty seeing that on their dyno plot. Their kit seems also to deal with inputs but retains stock exhaust. I am sure there is more "low hanging fruit" performance with driver skills but I am intrigued by the odd profile.

 

[davidv111]

When I saw that in the manual i thought it could be to make the car feel like it kicks or gets a second wind, could that work ?

 

[Motorhead]

Yes Ralph, I'm aware of TPC Racing - they do some interesting stuff, including 986 and 987 intercooled and non-intercooled turbo kits which give significant power increases compared with N/A tuning options. Re the torque "bump", maybe - as Nick says - Porsche have engineered it that way to boost torque at low revs (2,000 - 3,000 revs/min) at the expense of a more linear torque curve like that of the 991. As to the reason for it, you'd have to ask the development 981 engineers. Maybe they just preferred the feel of the car that way or perhaps they saw some incremental emission and/or fuel consumption benefits. Jeff

 

[chrisH]

Ralph, That's the trouble with dyno testing, you are now on the slippery slope of modifying! If so i would be interested in seeing what the larger Throttle body and intake gives on the dyno, as I would expect these two mods. to give similar power to the 991 3.4 version. The ECU tweak may not be essential. You've then got yourself Cayman R 981 performance without the wait, what a track weapon! Chris

 

[ralphmusic]

Chris, Well I think the S is a bit lardy with amongst other things motors for the seats, steering column, mirrors but I am doing my bit having lost 3 kilos since semi-retiring - fewer hotel breakfasts! I think the modification route would be a big decision as I take comfort in newer cars and warranties. Basically I do not enjoy the majority of road driving what with traffic density, idiots, random cameras etc so going on a track gets me back some enjoyment. If I really wanted a track oriented car I would start somewhere else but I have room for only so many cars and enjoy my comforts driving back and forth to circuits.

 

[Motorhead]

Ralph, I know where you're coming from on those points. Also, that PDK lump is making your 981 S even more lardy - an extra 30kg or so hanging out the back where you don't want it.! I often wonder how may basic Cayman Rs are out there - despite the lightweight doors and wheels, by the time you add essential creature comfort items like aircon, radio/PCM and then PDK, much of the weight-saving over a manual S will have been negated. Jeff

 

[chrisH]

Jeff & Ralph, Yes, indeed all extra weight factors to dull the car's performance. My point was about engine power, with these simple mods the power must be getting very close to the 991 3.4, infact it would be interesting to find out what engine parts are different on the upcoming GTS to give +15 bhp. Its' a fair bet these are the throttle body and intake from the 991 with a suitably detuned map to keep the 991 marketing folks happy. Chris

 

[flat6]

ORIGINAL: ralphmusic I had seen these which pointed me at the handbook, thanks. Aside from a day with some new (to me) Porsche owners I went hoping to find confirmation or otherwise of the odd torque curve for the Cayman 981S from the Porsche US site as below:

- I do not understand the relationship between the plot and the Y axis either - just look at the plot... Note the torque between 2,500 to 4,500 revs, then see the graph for the 991 Carrera 3.4 below:

So why the fall in torque in the 981s? Does it need more power or better mid-range torque? How best to drive it?

Aha, 981 Cayman S on dyno[] Interesting - hadn't even realised that the safety systems would invoke based on front wheel speed. Along with the dip in torque, would be interesting to know why the peak torque is flat over a rev range, like a turbo?

 

[ralphmusic]

I went yesterday to Regal in Southampton who were able to access the Dyno test set up in the ECU via their Autologic tester, thus were able to run the car on their Mustang MD-500-AWD Chassis Dynometer without the 'nanny' cutting power. The people there are very helpful and organised (appointment at 11.00 tests run 11:20, feed back and out by 12:00). Anyway as Porsche made it (no mods) and with premium fuel, it recorded 323.9hp and 271.5 lb/ft v spec 325 and 272 after transmission loss adjustment so I have now satisfied my curiosity. The image below shows an overlay of the two runs showing a nice torque curve and linear hp line, albeit from 2800 rpm.

 

[Motorhead]

Interesting, Ralph. Nice smooth power and torque curves with no "bumps" cf the Porsche curves, which is rather a surprise(?). The Porsche curves would have been obtained on an engine dyno, whereas Regal's curves you say were wheel horsepower/torque "corrected" for transmission losses. Did they indicate to you how they arrived at the figures for these losses - are they Porsche-specific or generic? Jeff

 

[ralphmusic]

Is is calculated by the Dyno and as I understand it is derived from the 'slow down' phase. The routine being to build revs steadily to max then foot off gas and during this slow down phase to idle the flywheel is calculated from the road wheel readings. You can see a lower line which is the road wheel power and apparently typical transmission loss is circa 15% but the Dyno loss and gross results are specific to the vehicle and particular run.