Rear Wheel HP vs. Flywheel
#16
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I would have to agree to the incorrect dyno reading theory.
Two months ago I made several major modifications. SFR Stage II bb turbo, maf, test pipe, tial wastgate, Arc II. I then put the 951 onto a dyno. With 13psi of boost and 75k miles on the odometer, print out showed a SAE corrected reading of 275 rwhp.
Last week end here in Nor Cal, I attended a dyno day at a different shop. We were getting readings that I felt were high. A stock 944 S2 with 110 mi. got 220 rwhp. So being curious as I am, I put up the $100us and did 2 pulls. This time the print out showed 245 rwhp!
In the two months that had passed, I have done absolutly no changes on the car with the exception of adding 500 miles to the odometer. I keep my tire pressures religously at 36 psi and neither shop bothered to ask the weight of my vehicle.
I have the print outs to back this story up.
The funny thing about it, my air/fuel curve is exactly the same on both sheets.
The part that burns me....how could a stock 944 S2 put down 220 rwhp first off. And then 2 hours later my modified 951 only put down 245 which is a drop of 30 rwhp from my prior dyno reading?
I left that session feeling embarrased by my readings and ripped off for five minutes of dyno time that cost $100. At least at the previous dyno shop, I got an hour on the rack with many pulls/adjustments...and checked my speedometer accuracy.
Two months ago I made several major modifications. SFR Stage II bb turbo, maf, test pipe, tial wastgate, Arc II. I then put the 951 onto a dyno. With 13psi of boost and 75k miles on the odometer, print out showed a SAE corrected reading of 275 rwhp.
Last week end here in Nor Cal, I attended a dyno day at a different shop. We were getting readings that I felt were high. A stock 944 S2 with 110 mi. got 220 rwhp. So being curious as I am, I put up the $100us and did 2 pulls. This time the print out showed 245 rwhp!
In the two months that had passed, I have done absolutly no changes on the car with the exception of adding 500 miles to the odometer. I keep my tire pressures religously at 36 psi and neither shop bothered to ask the weight of my vehicle.
I have the print outs to back this story up.
The funny thing about it, my air/fuel curve is exactly the same on both sheets.
The part that burns me....how could a stock 944 S2 put down 220 rwhp first off. And then 2 hours later my modified 951 only put down 245 which is a drop of 30 rwhp from my prior dyno reading?
I left that session feeling embarrased by my readings and ripped off for five minutes of dyno time that cost $100. At least at the previous dyno shop, I got an hour on the rack with many pulls/adjustments...and checked my speedometer accuracy.
#17
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Bill,
I might be wrong, but I think the S2 had 188hp. Granted your's was low. I didn't know you had a 275 reading from before.
As far as the turbo cars go, we didn't get a good boost reading on several of the cars. I know I set my AVC-r to 1.3 bar and only peaked at 1.2 on the dyno.
Here's a link to the readings I got from the videos.
<a href="http://members.rennlist.org/dan10101/dyno_day_in_nor_cal.htm" target="_blank">Nor-cal dyno day</a>
If we do this again, we'll need to clarify that we can climb in the car and make adjustments on the fly. Could make a real difference, rather than just moving cars in and out. The operator seemed ok with us making changes. (even liked it)
I might be wrong, but I think the S2 had 188hp. Granted your's was low. I didn't know you had a 275 reading from before.
As far as the turbo cars go, we didn't get a good boost reading on several of the cars. I know I set my AVC-r to 1.3 bar and only peaked at 1.2 on the dyno.
Here's a link to the readings I got from the videos.
<a href="http://members.rennlist.org/dan10101/dyno_day_in_nor_cal.htm" target="_blank">Nor-cal dyno day</a>
If we do this again, we'll need to clarify that we can climb in the car and make adjustments on the fly. Could make a real difference, rather than just moving cars in and out. The operator seemed ok with us making changes. (even liked it)
#19
Race Car
[quote]Originally posted by Bill:
<strong>I would have to agree to the incorrect dyno reading theory.
The part that burns me....how could a stock 944 S2 put down 220 rwhp first off. And then 2 hours later my modified 951 only put down 245 which is a drop of 30 rwhp from my prior dyno reading.</strong><hr></blockquote>
That's inaccurate. Karl's S2 put down 187 RWHP which is perfect for that car, and Jeff's 968 put down 199 RWHP, again perfect for that car. When I dynoed my 968 last March down at the Dyno Shop in Santee the car pulled 198 RWHP before tuning, 205 RWHP after, so the dyno is pretty darn accurate. A stock S2 puts out 208 horsepower at the flywheel and a stock 968 is rated at 236.
<strong>I would have to agree to the incorrect dyno reading theory.
The part that burns me....how could a stock 944 S2 put down 220 rwhp first off. And then 2 hours later my modified 951 only put down 245 which is a drop of 30 rwhp from my prior dyno reading.</strong><hr></blockquote>
That's inaccurate. Karl's S2 put down 187 RWHP which is perfect for that car, and Jeff's 968 put down 199 RWHP, again perfect for that car. When I dynoed my 968 last March down at the Dyno Shop in Santee the car pulled 198 RWHP before tuning, 205 RWHP after, so the dyno is pretty darn accurate. A stock S2 puts out 208 horsepower at the flywheel and a stock 968 is rated at 236.
#20
Race Director
"And then 2 hours later my modified 951 only put down 245 which is a drop of 30 rwhp from my prior dyno reading?"
Bill, sorry you had a bad experience. We'll talk to the dyno shop into giving you a little extra attention the next time. BTW, which chips where you using this last time around? And which ones did you have the last time?
Bill, sorry you had a bad experience. We'll talk to the dyno shop into giving you a little extra attention the next time. BTW, which chips where you using this last time around? And which ones did you have the last time?
#21
There's really only one way to get relevence from a dyno session described above.
Always test on the same dyno and pay attention to atmospheric conditions,tire pressures,etc.
i believe that any particular dyno's accuracy is fairly irrelevent as long as the dyno's repeatability is there...
I have always used the same dyno religiously for this reason...dont know if it's accurate and dont really care,but i "think" it's repeatable.
This allows me to accurately gauge various improvements (or detractions!) i've made to the car and THAT'S what i care about.
"Did this camshaft hurt me or help me?"
"Which one of this fist full of chips has the best power band?"
Bottom line..."dyno days" are just an excuse,and a good one, for car guys to congregate,bench race and have a good time...that's ALL.
Always test on the same dyno and pay attention to atmospheric conditions,tire pressures,etc.
i believe that any particular dyno's accuracy is fairly irrelevent as long as the dyno's repeatability is there...
I have always used the same dyno religiously for this reason...dont know if it's accurate and dont really care,but i "think" it's repeatable.
This allows me to accurately gauge various improvements (or detractions!) i've made to the car and THAT'S what i care about.
"Did this camshaft hurt me or help me?"
"Which one of this fist full of chips has the best power band?"
Bottom line..."dyno days" are just an excuse,and a good one, for car guys to congregate,bench race and have a good time...that's ALL.
#22
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"Always test on the same dyno and pay attention to atmospheric conditions,tire pressures,etc"
Well said QUICK'44. I couldn't agree more! There are so many factors that come into play when dynoing a car that it's not surprising some results aren't what you'd expect.
Thanks for all the input guys!
Well said QUICK'44. I couldn't agree more! There are so many factors that come into play when dynoing a car that it's not surprising some results aren't what you'd expect.
Thanks for all the input guys!
#23
It would be nice if all the magazine's would test ALL of the cars on the same dynojet. But different altitude's/temp's/dyno's would probably give different results. Shoot, if I put Viper sized tires on my 944, I am sure the rolling resistance would detract from the numbers.
So I can't see the concern for flywheel HP figures? for comparing before/after mods on a dynojet, YEAH!
IMHO, whether I use 10% or 30% to figure my flywheel HP, the HP to the road is the same. I will go conservative when I dyno my 944. (10%)
Jon
So I can't see the concern for flywheel HP figures? for comparing before/after mods on a dynojet, YEAH!
IMHO, whether I use 10% or 30% to figure my flywheel HP, the HP to the road is the same. I will go conservative when I dyno my 944. (10%)
Jon
#24
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[quote]Originally posted by PorscheG96:
<strong>
...Karl's S2 put down 187 RWHP which is perfect for that car, and Jeff's 968 put down 199 RWHP...</strong><hr></blockquote>
Trevor is correct. I pulled 187 RWHP which implies 220 BHP at the crank (assuming 15% loss).
Here's a parrallel thread on the subject:
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=011134" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=011134</a>
Karl.
<strong>
...Karl's S2 put down 187 RWHP which is perfect for that car, and Jeff's 968 put down 199 RWHP...</strong><hr></blockquote>
Trevor is correct. I pulled 187 RWHP which implies 220 BHP at the crank (assuming 15% loss).
Here's a parrallel thread on the subject:
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=011134" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=011134</a>
Karl.