I need help analying a dyno chart...
09-05-2008, 10:59 PM
#16
Rennlist Member
Thread Starter
Problem Solved....
As it turns out, my small vacuum leak (in the ac unit in the the dash) was the culprit even though it seemd very minor (the valve would open and close but would not hold vaccum once the engine was turned off). I wen back to the dyno shop today to do a true apples to apples comparisom (old car vs new car). So to prepare I did a little homework this week:
1) Confirmed compression and leakdown numbers were good
2) Fixed vacuum leak
3) Talked to the previous dyno operator and confirmed he ran the previous test in 3rd gear (right or wrong)
4) Reinstalled stock exhaust
Reran the dyno test again and the numbers matched (within 1%) the old car (5 years ago). Ill post teh results of the DACH changes in a separte post but sufice it to say the results were even better....
219hp & 205ft-lb tq. This is on a mustang, so forget the absulute number, the point is to match a known baseline....
Moral of the story, as posted here numerous time... CHECK THOSE VACUUM LINES..... very important on these motors...
As it turns out, my small vacuum leak (in the ac unit in the the dash) was the culprit even though it seemd very minor (the valve would open and close but would not hold vaccum once the engine was turned off). I wen back to the dyno shop today to do a true apples to apples comparisom (old car vs new car). So to prepare I did a little homework this week:
1) Confirmed compression and leakdown numbers were good
2) Fixed vacuum leak
3) Talked to the previous dyno operator and confirmed he ran the previous test in 3rd gear (right or wrong)
4) Reinstalled stock exhaust
Reran the dyno test again and the numbers matched (within 1%) the old car (5 years ago). Ill post teh results of the DACH changes in a separte post but sufice it to say the results were even better....
219hp & 205ft-lb tq. This is on a mustang, so forget the absulute number, the point is to match a known baseline....
Moral of the story, as posted here numerous time... CHECK THOSE VACUUM LINES..... very important on these motors...
Last edited by jscott82; 09-05-2008 at 11:43 PM.
09-06-2008, 01:27 AM
#17
RL Technical Advisor
Hi Jeff,
Glad to hear that you found the problem and fixed it!
This is a good reminder for people to never overlook the smallest things before assuming anything major is wrong, given the complexity of these cars.
As they say, "The devil is in the details".
Glad to hear that you found the problem and fixed it!
This is a good reminder for people to never overlook the smallest things before assuming anything major is wrong, given the complexity of these cars.
As they say, "The devil is in the details".
09-06-2008, 10:06 AM
#19
Rennlist Member
Thread Starter
As far as the effect of the vacuum leak, it wasn’t necessarily the extra air introduced (at least in my case), the leak was very, very minor. Rather it was the weak vacuum signal created. It did not allow the computer to accurately control the resonance valve. If you remember, the in intake resonance valve was one of the tricks Porsche used to improve volumetric efficiency (ability to “breath”). The key here was the motor was running rich (too much fuel) not lean.
The other factor which played into this a bit was dyno operator inexperience. The 173 HP in 4th gear was a red herring. The real problem was torque, that was down from 210 to 184. I’m not exactly sure what happened, but apparently something was not setup right for those pulls, you could hear the car lugging like there was just too much resistance being applied. I don’t think it ever got to full redline on those runs.
09-06-2008, 01:26 PM
#20
Rennlist Member
Yeah, it does sound like there was some dyno operator error. The resonance flap doesn't make a huge difference, like 10-20 hp (not 60 hp), and only above 5200 rpm.
