G-Tech results: Octane difference
01-06-2003, 01:44 AM
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G-Tech results: Octane difference
Well, the bottom line is disappointing. No measurable difference between 91 and 98 octane using the G-Tech measuring horsepower or 0-60 times. The variability in the measurment is to large for the slight difference in performance. The gory details follow...
What I did:
I used the same section of highway for all tests. Slight differences in grade (uphill or downhill) make differences in the results. Results on each section (same start point) were very consistent.
For horsepower measurements I set the meter to a weight of 3200 lbs. In all cases I used a soft start (slowly engaged the clutch and once it was fully engaged, I punched the gas to start the meter). For horsepower I shifted at redline in 1st, 2nd, and 3rd. I slowed when I shifted to 4th (about 85 with my gearing). For 0-60, I used the same soft start, but slowed shortly after the shift to 3rd (redline in 2nd gear is about 63 on the speedometer).
For horsepower, I did four repeats of four test segments (16 measurements total) with 91 octane gas. I ran the same stretch of road and the same segments with the meter set for 0-60 timing and also got 16 times with 91 octane. After blending 104.5 octane gas with 91 to get about 98 octane, I ran the same four test segments four more times to get 16 more horsepower measurements. I only ran four 0-60 times with 98 octane because I didn’t believe I would be able to detect a difference (given the variability I saw with 91 octane).
The average horsepower for 91 octane was 216±25 and 0-60 was 6.8±0.3. For 98 octane, I got 208±31 and 6.8±0.6. No discernable difference.
The individual segments actually gave pretty consistent results on a given day (values ±5 for horsepower), but the different segments gave very different results (157 for one segment 251 for another).
0-60 times suck. I don’t know why and I don’t believe I’m that bad or slow at shifting. I did get consistent results on the same segment of road (usually within a few hundredths), so I know that if it’s my driving, I’m consistently bad.
I’ve got all the results in an Excel spreadsheet if anyone wants the gory details (but I suggest you wait for the tests with Steve’s chip to be added).
What I did:
I used the same section of highway for all tests. Slight differences in grade (uphill or downhill) make differences in the results. Results on each section (same start point) were very consistent.
For horsepower measurements I set the meter to a weight of 3200 lbs. In all cases I used a soft start (slowly engaged the clutch and once it was fully engaged, I punched the gas to start the meter). For horsepower I shifted at redline in 1st, 2nd, and 3rd. I slowed when I shifted to 4th (about 85 with my gearing). For 0-60, I used the same soft start, but slowed shortly after the shift to 3rd (redline in 2nd gear is about 63 on the speedometer).
For horsepower, I did four repeats of four test segments (16 measurements total) with 91 octane gas. I ran the same stretch of road and the same segments with the meter set for 0-60 timing and also got 16 times with 91 octane. After blending 104.5 octane gas with 91 to get about 98 octane, I ran the same four test segments four more times to get 16 more horsepower measurements. I only ran four 0-60 times with 98 octane because I didn’t believe I would be able to detect a difference (given the variability I saw with 91 octane).
The average horsepower for 91 octane was 216±25 and 0-60 was 6.8±0.3. For 98 octane, I got 208±31 and 6.8±0.6. No discernable difference.
The individual segments actually gave pretty consistent results on a given day (values ±5 for horsepower), but the different segments gave very different results (157 for one segment 251 for another).
0-60 times suck. I don’t know why and I don’t believe I’m that bad or slow at shifting. I did get consistent results on the same segment of road (usually within a few hundredths), so I know that if it’s my driving, I’m consistently bad.
I’ve got all the results in an Excel spreadsheet if anyone wants the gory details (but I suggest you wait for the tests with Steve’s chip to be added).
01-06-2003, 04:05 AM
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Tom,
Did you go to the local San Jose December gathering where we met at the wrong parking lot (dark blue 993 Cab)?
If that was you, I was the white '97 C4S behind you during the drive. I thought you had a fairly strong engine. When you accelerated I could keep the gap the same but not gain on you. Considering you had your wife and you don't have the Varioram, that's not too bad. I didn't have another passenger, but the C4 drivetrain equipment was about the same as another passenger. The difference in 10 HP wasn't noticeable between model years.
BTW, I did my own GTech runs and they were mostly in the 6's, but I finally got one below 6 (around 5.7 or 5.8 if I recall correctly and with a somewhat aggressive launch, but no clutch dump). I was pretty devastated as well on the readings, but I'm finding that there's too many variables that can cause the results to give different readings. I noticed that I had some slight clutch slipping when going from 1st to 2nd and this may have dropped a few tenths of a second off the results.
My braking was always around 117 feet to 118 feet from 60-0 with some slight ABS activation when the car was almost stopped.
Anyways, I've taken a few Mustang owners out for a ride and they all came back saying that they felt the Porsche was faster than their cars, especially at the top end. I don't think they were being polite but just stating their initial impressions. Lots of times we get used to the HP and think it's slow, but in reality it's just a matter of our own senses getting used to the car's capabilities.
*****
Did you go to the local San Jose December gathering where we met at the wrong parking lot (dark blue 993 Cab)?
If that was you, I was the white '97 C4S behind you during the drive. I thought you had a fairly strong engine. When you accelerated I could keep the gap the same but not gain on you. Considering you had your wife and you don't have the Varioram, that's not too bad. I didn't have another passenger, but the C4 drivetrain equipment was about the same as another passenger. The difference in 10 HP wasn't noticeable between model years.
BTW, I did my own GTech runs and they were mostly in the 6's, but I finally got one below 6 (around 5.7 or 5.8 if I recall correctly and with a somewhat aggressive launch, but no clutch dump). I was pretty devastated as well on the readings, but I'm finding that there's too many variables that can cause the results to give different readings. I noticed that I had some slight clutch slipping when going from 1st to 2nd and this may have dropped a few tenths of a second off the results.
My braking was always around 117 feet to 118 feet from 60-0 with some slight ABS activation when the car was almost stopped.
Anyways, I've taken a few Mustang owners out for a ride and they all came back saying that they felt the Porsche was faster than their cars, especially at the top end. I don't think they were being polite but just stating their initial impressions. Lots of times we get used to the HP and think it's slow, but in reality it's just a matter of our own senses getting used to the car's capabilities.
*****
01-06-2003, 11:54 AM
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Don't know if you guys have seen this, but a G-Tech was used for extensive 0-60 testing on the 964 board. In particular, UK owners:
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=4&t=002351" target="_blank">G-Tech Testing, UK</a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=4&t=003000" target="_blank">G-Tech Testing USA</a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=4&t=002351" target="_blank">G-Tech Testing, UK</a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=4&t=003000" target="_blank">G-Tech Testing USA</a>
01-06-2003, 12:51 PM
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Tom - launching a 993 is very difficult - particularly if you care about the car. On my 1995 C4 I was able to get one G-Tech 0-60 run at 5.6 - this was a soft but very good launch. I could feel that I got it just right as the engine pulled strong right away with no bogging. On the same day, I did a few other runs and they were all in the mid to upper 6 second range.
As far as HP, you would need to have the exact weight to be reasonably accurate. If you were off by say 100 pounds (remember cabs weigh more and after the holidays maybe you do too
) that would account for maybe 10-15 HP. If you really want to get accurate HP readings you should go the Dyno at Dyno Spot Racing in San Jose. I did this once in my 930 - it is an interesting experience.
I thought the main point of your tests was to get a baseline for checking octane differences on performance and also for checking the chip upgrade. If this is the case, then the actual numbers are no big deal - it is the delta you are concerned with.
By the way, when you were following me on 84 while I was in my 930, I was also impressed with the amount of power your car had. There were a few spots I was accelerating pretty hard and you did not drop back very much (just an FYI for other readers - my 930 has 450 HP).
As far as HP, you would need to have the exact weight to be reasonably accurate. If you were off by say 100 pounds (remember cabs weigh more and after the holidays maybe you do too
) that would account for maybe 10-15 HP. If you really want to get accurate HP readings you should go the Dyno at Dyno Spot Racing in San Jose. I did this once in my 930 - it is an interesting experience.I thought the main point of your tests was to get a baseline for checking octane differences on performance and also for checking the chip upgrade. If this is the case, then the actual numbers are no big deal - it is the delta you are concerned with.
By the way, when you were following me on 84 while I was in my 930, I was also impressed with the amount of power your car had. There were a few spots I was accelerating pretty hard and you did not drop back very much (just an FYI for other readers - my 930 has 450 HP).
01-07-2003, 12:36 AM
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To reduce variability, you might consider something as simple as timing the car from 3000 rpm to redline in 2nd or 3rd gear. This would at least tell you if there was going to be an overall difference.
If you want to get more information, use Bowling's highway dynamometer program at:
<a href="http://bgsoflex.com/auto.html" target="_blank">Interactive Highway Dyno Calculator By Bowling & Grippo</a>
Choose the "Roadway Vehicle Dynamometer" from the left side frame.
Chip
If you want to get more information, use Bowling's highway dynamometer program at:
<a href="http://bgsoflex.com/auto.html" target="_blank">Interactive Highway Dyno Calculator By Bowling & Grippo</a>
Choose the "Roadway Vehicle Dynamometer" from the left side frame.
Chip
01-07-2003, 01:14 AM
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Boris: LOL. No, not a tip, your basic 6 speed - with the RS LWF and a gearbox that has shorter gearing (5th became 6th with 2-5 replaced).
*****: Yep, that was me.
Bill: I know you warned me about the 0-60 times, but it's still hard to stomach the numbers. Yes, this was baseline data and to be used for comparison. I was a bit surprised that there was no discernable difference in the numbers for 91 vs 98 octane. The car sure feels stronger.
I put in Steve's chip on Sunday late afternoon and went out for my first run to get it set (Steve says 2-3 cold starts before full effect). i did a quick 0-60 run at the start of a 30 minute cruise down Highway 1 (6.29) and back (6.04). There may be some hope yet. Both numbers are better than the stock chip and the number after the 30 minute drive better by a wide margin.
Thanks for the comments about the car on the drive - I was going slow because of Stephanie's complaints about getting thrown around
. I'm really starting to look forward to my first DE in March at Thunderhill.
The car goes in for the wiring harness replacement tomorrow. If they don't break it, I'll do the timings with Steve's chip this weekend and post the results.
*****: Yep, that was me.
Bill: I know you warned me about the 0-60 times, but it's still hard to stomach the numbers. Yes, this was baseline data and to be used for comparison. I was a bit surprised that there was no discernable difference in the numbers for 91 vs 98 octane. The car sure feels stronger.
I put in Steve's chip on Sunday late afternoon and went out for my first run to get it set (Steve says 2-3 cold starts before full effect). i did a quick 0-60 run at the start of a 30 minute cruise down Highway 1 (6.29) and back (6.04). There may be some hope yet. Both numbers are better than the stock chip and the number after the 30 minute drive better by a wide margin.
Thanks for the comments about the car on the drive - I was going slow because of Stephanie's complaints about getting thrown around
. I'm really starting to look forward to my first DE in March at Thunderhill.The car goes in for the wiring harness replacement tomorrow. If they don't break it, I'll do the timings with Steve's chip this weekend and post the results.
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01-07-2003, 07:01 AM
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At last...my post...
Tom
the root of your poor times are your start technique - letting the clutch fully engage & then flooring the throttle. Your engine is trying to wind up from low revs under full load. Remember, at low revs the torque output of the engine will be VERY low.
You need to get into a rev band with high torque output, say 4000 - 5000 rpm and feed this torque to the wheels, allowing a little controlled wheelspin. As long as your not stupid about it (ie dropping the clutch at 6000 rpm will give you ridiculous wheel spin & fry your clutch) your clutch will be fine and, most importantly, you will slash those 0-60 times.
But what do I know - I drive a tiptronic!!!
BTW, my 964 tip does less than 6 seconds on the G-Tec AND my 1st & 2nd gear ratios are like 2nd & 3rd in your car!! Go figure!
Tom
the root of your poor times are your start technique - letting the clutch fully engage & then flooring the throttle. Your engine is trying to wind up from low revs under full load. Remember, at low revs the torque output of the engine will be VERY low.
You need to get into a rev band with high torque output, say 4000 - 5000 rpm and feed this torque to the wheels, allowing a little controlled wheelspin. As long as your not stupid about it (ie dropping the clutch at 6000 rpm will give you ridiculous wheel spin & fry your clutch) your clutch will be fine and, most importantly, you will slash those 0-60 times.
But what do I know - I drive a tiptronic!!!
BTW, my 964 tip does less than 6 seconds on the G-Tec AND my 1st & 2nd gear ratios are like 2nd & 3rd in your car!! Go figure!
01-07-2003, 01:17 PM
#12
Tom,
I’ve noticed a lot of variability when I do these tests as well. What I do is try to eliminate myself from the equation. I trigger the unit to start at say 30 MPH and finish at 60 MPH. This is entirely within second gear so I don’t have to shift in the middle of the run. I shift to second around 25 MPH and put my foot to the floor. As you can see, the entire run is done at max throttle with no shifting. I just sit there, holding the wheel straight and have my foot on the floor. Hope this helps.
Tom
’95 993
I’ve noticed a lot of variability when I do these tests as well. What I do is try to eliminate myself from the equation. I trigger the unit to start at say 30 MPH and finish at 60 MPH. This is entirely within second gear so I don’t have to shift in the middle of the run. I shift to second around 25 MPH and put my foot to the floor. As you can see, the entire run is done at max throttle with no shifting. I just sit there, holding the wheel straight and have my foot on the floor. Hope this helps.
Tom
’95 993
01-07-2003, 02:02 PM
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Tom: The 30-60 scenario is what I really wanted to do. I was hoping to do a bunch of all 2nd gear measurements because that's what really matters in autocross (and I have no desire to try and simulate Laguna Seca on a public highway).
Unfortubately, the G-Tech/Pro that I borrowed doesn't support this type of testing. It's strictly 0-60 or 1/4 mile results (I downloaded the directions off the web to make sure I knew how to use it). If Bill had just spent more money to get a fancier meter it would be no problem! <img border="0" title="" alt="[Wink]" src="wink.gif" /> But, as my mother always told me, beggars can't be choosers.
John: I certainly suspected that it was my launch technique, but I'm not interested in doing a bunch of hard launches that will add a lot of wear to my nearly new RS clutch. Since the main purpose is comparison between test conditions, I figured it was good enough (although slower than hoped or expected). I've probably done about 40 of these runs/measurements in the last two weeks. Even dumping the clutch at 3-4k rpm (I think) would be a lot of wear when you do it this many times.
Unfortubately, the G-Tech/Pro that I borrowed doesn't support this type of testing. It's strictly 0-60 or 1/4 mile results (I downloaded the directions off the web to make sure I knew how to use it). If Bill had just spent more money to get a fancier meter it would be no problem! <img border="0" title="" alt="[Wink]" src="wink.gif" /> But, as my mother always told me, beggars can't be choosers.
John: I certainly suspected that it was my launch technique, but I'm not interested in doing a bunch of hard launches that will add a lot of wear to my nearly new RS clutch. Since the main purpose is comparison between test conditions, I figured it was good enough (although slower than hoped or expected). I've probably done about 40 of these runs/measurements in the last two weeks. Even dumping the clutch at 3-4k rpm (I think) would be a lot of wear when you do it this many times.
01-07-2003, 04:13 PM
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Bill,
Does Dyno Spot Racing in San Jose have the capabilities to Dyno an AWD car like the C4S?
I've been toying with this idea just to see what the engine is capable of but I've read that unless the place has the correct equipment for all 4 wheels, it could damage the drive train during the pull.
Any thoughts on this?
Thanks,
*****
Does Dyno Spot Racing in San Jose have the capabilities to Dyno an AWD car like the C4S?
I've been toying with this idea just to see what the engine is capable of but I've read that unless the place has the correct equipment for all 4 wheels, it could damage the drive train during the pull.
Any thoughts on this?
Thanks,
*****
01-07-2003, 05:33 PM
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Tom - how about doing street starts - basically letting the car roll to about 5 MPH and then pushing your foot to the floor. If you start slowly the G-Tech will not be triggered. If you need someone to sit in the car to time other tests, let me know and I can help. The new G-Tech Pro (or whatever it is called) was not available when I bought this or I would have gone for that one.
***** - Dyno Spot did not have an AWD dyno. In order to test a C4 you would have to disconnect the front drive shaft. Believe it or not there is even a mention of this in the Porsche manual. I wonder if The Racers Group up by Sears Point has a 4WD dyno?
***** - Dyno Spot did not have an AWD dyno. In order to test a C4 you would have to disconnect the front drive shaft. Believe it or not there is even a mention of this in the Porsche manual. I wonder if The Racers Group up by Sears Point has a 4WD dyno?