Flat spot @ 3500 RPM

slide · May 31st, 2006, 10:33 PM

Hi

Just got my new Cayman S - loving it. I wonder if I am not used to the drive by wire throtle or if there is generally a bit of a flat spot in the torque curve as you pass through 3500 or 4000 rpm. Any comments appreciated.

slide

baxter · June 1st, 2006, 04:05 AM

My 987S does this at 3000 RPM. I can't explain it, just confirming that it occurs................

baxter · June 1st, 2006, 06:43 PM

I am very surprised that no one else has chimed in on this subject. Are we (Slide and me) the only people to have this occur? I had thought about mentioning it here before, but just never thought about it at the right time. Surely someone has some imput...................i hope.

Tom M · June 1st, 2006, 07:39 PM

What RPM does the vario cam kick in?

arenared · June 2nd, 2006, 12:28 PM

Quote:

Originally Posted by slide

Hi

Just got my new Cayman S - loving it. I wonder if I am not used to the drive by wire throtle or if there is generally a bit of a flat spot in the torque curve as you pass through 3500 or 4000 rpm. Any comments appreciated.

slide

You mean this dip?

It's in the manual. Are you in the SF Bay area?

Dr. Zoom · June 2nd, 2006, 02:13 PM

Well, that chart certainly indicates that it's a real thing. However when looking at the OM I didn't see any explanation of what causes it. Anybody know for sure?

slide · June 2nd, 2006, 06:37 PM

Quote:

Originally Posted by arenared

You mean this dip?

It's in the manual. Are you in the SF Bay area?

No, I'm in Santa Barbara, I will look in the manual. Thanks, slide

slide · June 8th, 2006, 09:49 PM

Well I looked at the power/torque vs RPM curve and it does have a dip in torque at the RPM at which we feel a flat spot. However, there is no dip in the power curve, Since power is simply a calculated value (the product of torque and RPM divided by a constant) this seems odd. FYI for english units the constant is 5252, so torque in ft-lbs times RPM divided by 5252 yields horse power. Keep in mind that dynos measure torque, horsepower is calculated.

Now the torque value at the bottom of the dip in the referenced curve is 300 Nm at 3500 RPM. Converting to english units this equates to 221 lb-ft times 3500 RPM divided by 5252 = 147 HP or 109 Kw. This values is in synch with the curve in the manual.

Something stills seems odd, I will work on this. BTW, torque and power should be equal at 5252 RPM but the curve indicates cross-over at 5500 RPM. Could be a metric thing? slide

arenared · June 9th, 2006, 05:01 PM

That graph is using different numbered axis as well as kW and Nm. The dip is most likely caused by the timing of the resonance valves. If you were local, I'd show you a temporary hack to check. I've talked to a few tuners to include that in a custom ECU tune, but no such luck yet. Maybe one day...

mtom78632 · July 4th, 2021, 06:59 AM

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May 31st, 2006, 10:33 PM	#1
slide Junior Member Join Date: Apr 2006 Posts: 7	Flat spot @ 3500 RPM Hi Just got my new Cayman S - loving it. I wonder if I am not used to the drive by wire throtle or if there is generally a bit of a flat spot in the torque curve as you pass through 3500 or 4000 rpm. Any comments appreciated. slide

June 1st, 2006, 04:05 AM	#2
baxter Senior Member Join Date: Nov 2005 Location: Branson Posts: 602	My 987S does this at 3000 RPM. I can't explain it, just confirming that it occurs................ __________________ 2005 987 S. Artic Silver/Stone Grey

June 1st, 2006, 06:43 PM	#3
baxter Senior Member Join Date: Nov 2005 Location: Branson Posts: 602	I am very surprised that no one else has chimed in on this subject. Are we (Slide and me) the only people to have this occur? I had thought about mentioning it here before, but just never thought about it at the right time. Surely someone has some imput...................i hope. __________________ 2005 987 S. Artic Silver/Stone Grey

June 1st, 2006, 07:39 PM	#4
Tom M Site Founder Join Date: Dec 2003 Location: Westfield, IN Posts: 2,635	What RPM does the vario cam kick in? __________________ Tom M (Westfield, IN) '04 996 C4S MBM/GG (gone) '00 986 S MBK/NBL/BLK (gone) '11 958 Cayenne S

June 8th, 2006, 09:49 PM	#8
slide Junior Member Join Date: Apr 2006 Posts: 7	Well I looked at the power/torque vs RPM curve and it does have a dip in torque at the RPM at which we feel a flat spot. However, there is no dip in the power curve, Since power is simply a calculated value (the product of torque and RPM divided by a constant) this seems odd. FYI for english units the constant is 5252, so torque in ft-lbs times RPM divided by 5252 yields horse power. Keep in mind that dynos measure torque, horsepower is calculated. Now the torque value at the bottom of the dip in the referenced curve is 300 Nm at 3500 RPM. Converting to english units this equates to 221 lb-ft times 3500 RPM divided by 5252 = 147 HP or 109 Kw. This values is in synch with the curve in the manual. Something stills seems odd, I will work on this. BTW, torque and power should be equal at 5252 RPM but the curve indicates cross-over at 5500 RPM. Could be a metric thing? slide __________________ slide

June 2nd, 2006, 02:13 PM	#6
Dr. Zoom Senior Member Join Date: Feb 2005 Posts: 169	Well, that chart certainly indicates that it's a real thing. However when looking at the OM I didn't see any explanation of what causes it. Anybody know for sure?

June 9th, 2006, 05:01 PM	#9
arenared Senior Member Join Date: Sep 2005 Posts: 131	That graph is using different numbered axis as well as kW and Nm. The dip is most likely caused by the timing of the resonance valves. If you were local, I'd show you a temporary hack to check. I've talked to a few tuners to include that in a custom ECU tune, but no such luck yet. Maybe one day...

July 4th, 2021, 06:59 AM	#10
mtom78632 Senior Member Join Date: Jun 2021 Location: chicago Posts: 549	sam A growing blog on how to make money online. With the ways to make money online, making money online couldnt be so much easier. 휴게텔 ================================================== ===== I really like what you have acquired here, certainly like what you are stating and the way in which you say it. 먹튀검증

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