S6 vs. S8 preformance Part II -- Gearing thickens the plot! (longish because I'm obsessed).
11-06-2002, 10:39 AM
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S6 vs. S8 preformance Part II -- Gearing thickens the plot! (longish because I'm obsessed).
If there is little or no 'real world' difference between the S8 and S6 engines, the question has come up about differences in favour of the slightly heavier S8 in most real world testing. So, as a follow-up to my original post, Finman's G-tech times, etc. some bright light (Auto Union Jack) on the S8 forum suggested I check the S8 specs on AW -- duh!
Aside from quoted HP and torque (at exactly the same rpm), as well as slightly better quoted perfomance numbers, the ONLY difference in the quoted specs for the engine and transmission is in the FINAL DRIVE: 3.73/1 (S8) vs 2.727/1 (S6).
Now, you have to adjust for the only other quoted difference in the drivetrain -- the bigger tires and wheels on the S8, which are 678 mm in diameter vs. 636 mm for the S6. This works out to a negative adjustment to 3.5/1 for the S8, but still leaves the S6 with a 22% taller final drive.
Now, any drag racer could tell you that you should get a noticeable difference in 0-60 and 1/4 mile times by shortening your final drive from 2.7 to 3.5.
So, what can we conclude today?
1) There may be real differences in S8 vs S6 hp and torque (depending on which engine you test on what day). However, I submit that they are minor -- largely due to small differences in intake and exhaust tuning.
2) The real difference in the performance is due to the significantly shorter final drive on the S8.
3) The S8, therefore, is the best North American expressway performance car -- big and quick.
4) The S6, with the longer legs and more compact dimensions, should be the better flat-out autobahn stormer.
Thus endeth today's sermon ;^)
Aside from quoted HP and torque (at exactly the same rpm), as well as slightly better quoted perfomance numbers, the ONLY difference in the quoted specs for the engine and transmission is in the FINAL DRIVE: 3.73/1 (S8) vs 2.727/1 (S6).
Now, you have to adjust for the only other quoted difference in the drivetrain -- the bigger tires and wheels on the S8, which are 678 mm in diameter vs. 636 mm for the S6. This works out to a negative adjustment to 3.5/1 for the S8, but still leaves the S6 with a 22% taller final drive.
Now, any drag racer could tell you that you should get a noticeable difference in 0-60 and 1/4 mile times by shortening your final drive from 2.7 to 3.5.
So, what can we conclude today?
1) There may be real differences in S8 vs S6 hp and torque (depending on which engine you test on what day). However, I submit that they are minor -- largely due to small differences in intake and exhaust tuning.
2) The real difference in the performance is due to the significantly shorter final drive on the S8.
3) The S8, therefore, is the best North American expressway performance car -- big and quick.
4) The S6, with the longer legs and more compact dimensions, should be the better flat-out autobahn stormer.
Thus endeth today's sermon ;^)
11-06-2002, 11:23 AM
#2
The *US*-spec S6 has much lower gearing than 2.73:1...
...it was specifically one of the changes made for the delayed 2002 release of the S6 to the US. I believe the gearing is in the neighborhood of 3.42:1, but not quite as low as the S8's 3.73:1. I've been in an S6 that redlines near 70mph in 2nd, and can close in on 100mph in 3rd. If the S6 had 2.73:1 (like the A6 4.2), it would do something like 86mph in 2nd. And per the magazines, the S8 tops in 2nd at something like 61mph (far shy of 70mph).
11-06-2002, 12:48 PM
#4
Last I checked, the M5 had optimal gearing for 0-60 times...
...in that it redlined in second gear at about 62mph. Any taller of a final drive, and it accelerates slower. Any shorter of a final drive and it has to waste a couple tenths of a second shifting to third gear before hitting 60mph. I doubt that helped 0-60 times any.
11-06-2002, 01:51 PM
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OK, OK, I give up :^(
I just back calculated from the indicated speed /rpm on Finman's run, and checked it against my own experience and...
...that engine rpm vs. wheel circumference requires either:
a) a 3.5/1 final drive ratio (more likely), or
b) a direct 1/1 ratio in fifth with a final drive of 2.8/1 (less likely).
to achieve the indicated speed.
Heh, but isn't some idle speculation what most of these forums are about?
...that engine rpm vs. wheel circumference requires either:
a) a 3.5/1 final drive ratio (more likely), or
b) a direct 1/1 ratio in fifth with a final drive of 2.8/1 (less likely).
to achieve the indicated speed.
Heh, but isn't some idle speculation what most of these forums are about?
11-06-2002, 02:08 PM
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Re: Point #4, taller gear ration doesn't neccesarily mean the S6 has longer legs
its not like the S8 will run out the rpm to reach its 155mph speed limit and if my calculation is correct it could reach over 170mph when reaching its red line. Short gearing also allows for short rpm fall off between gear change that would allow the S8 to stay in the higher power zone more so than S6; therefore, there are no supporting theory why a taller gear ratio would benifit anything lower or higher speed acceleration; but it does improve in most case fuel economy which didn't work to well with the S6 anyways....
Do you have any idea on the extra wind resistance of the wagon body with roof rack into consideration when constructing your theories; you should consider every possible variance if you truely want to be objective.
Do you have any idea on the extra wind resistance of the wagon body with roof rack into consideration when constructing your theories; you should consider every possible variance if you truely want to be objective.
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11-06-2002, 02:17 PM
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check the article Lance
0-60 in 4.1 vs 4.7
redline 7300 vs 7000
shorter final drive (3.45:1 versus 2.81:1).<ul><li><a href="http://www.caranddriver.com/xp/Caranddriver/features/2002/november/0211_specialtyfile_dinan.xml?keywords=Dinan">dinan m5</a></li></ul>
redline 7300 vs 7000
shorter final drive (3.45:1 versus 2.81:1).<ul><li><a href="http://www.caranddriver.com/xp/Caranddriver/features/2002/november/0211_specialtyfile_dinan.xml?keywords=Dinan">dinan m5</a></li></ul>
11-06-2002, 04:47 PM
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Cornelius, I just added a couple 3 or 4 threads to you're original post; not noticing you'd started
anew. Just a little feedback on my MTM efforts and communications. I will post all the dyno specs for my S6, but I was theoretically waiting until the last of my mods are finished (which better be soon) before rolling it onto the 4-wheel for some graphs.
