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Old 27-01-2010, 08:17 PM   #1
awddynotodd
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Default 4.11 versus 3.46 Diff Gear test Results

I thought Iíd start a new thread with the results of our 3.46 versus 4.11 Diff gear test, rather than tack in onto the existing thread.

The opportunity came up this week to do a back to back test on the same car, so I went ahead and performed the tests, albeit with not as much test inputs as I wanted, but I only had limited time with the car so we went ahead with the tests.
I have tried very hard to do the test as best we could with identical tests conditions.

The car tested was a VY Commodore, standard except for a tune and a non standard exhaust, the brand of which doesnít matter as far as the test goes.
Vehicle was fitted with 235/45/17 Tyres, tyre pressures were set to 40psi.
The same fuel was used for both tests, I did the 3.46 tests on Monday 25th of Jan, and the 4.11 tests on the 27th of Jan.
I personally drove/strapped/tested/hooked up sensors to the car in both cases.
OBDII Vehicle data was logged in both cases.
I also logged Engine RPM and Injector Duty Cycle in both cases.
The test results are plotted using the SAE 1349 Standard.

The Graph below also shows OBDII Inlet Air temp and OBDII Ignition Timing. I specifically did this as there seems to be an element of people who have to quote numbers the way Ford do, so after reading an article in the latest Ford Motorsport parts catalogue on Dyno testing procedures, they quoted that any dyno testing that is done without evidence of actual OBDII Inlet Air temp and OBDII Ignition Timing is not valid, a statement I very much agree on, and is vastly more important than the correction standard used. The case in point, most dynoís have the ability to apply differing correction standards, but only a few dynoís have the ability to log OBDII data.

The Graph:



Summary of test and results:
I tested the car a total of 3 times with each diff ratio once the coolant temp was stabilised, and then using the Run Data Averaging feature in our software I averaged these 3 runs to come up with a valid before, and then a valid after test of. Without the ability to average Run data, it is very hard to truly come up with a valid before and after test, as the testing is prone to the operator choosing the best/worst results to suit their agenda.
The OBDII Inlet Air temp and Ignition are identical for equivalent parts of the test. Bear in mind the results are plotted over Road Speed , so the RPM reference numbers are valid for one run only.

The test with the 4.11ís was just marginally more, by 0.3kw. The car did not have as much power as I would of hoped, but seeing as though a person from the other thread has quoted he lost 15RWKW on a 170RWKW car, this car has more than enough power for the sake of the test.

I also tested the car in 3RD gear with the 3.46 Diff fitted, and itís power curve was in between the 4.11 and 3.46 4TH gear as far as Road Speed goes, and also made identical power.

I tested this car on a Dyno that would represent what around 80% of our users have, ie a Single Retarder 1600Nm Dyno, I do not however expect a DD user to get the same results, as I believe in some forms of their software there is a Dyno Speed compensation for Pumping Losses/Windage, so a higher reading with 3.46 would be expected IF there is considerable extra tyre loss with the 4.11ís fitted.

Applying a known Pumping Loss/Windage correction for the Dyno used, the test with 3.46ís shows a higher reading than the 4.11ís of 1.1RWKW. I also did a test with the 4.11ís fitted and used 3RD gear, in this test, I did lose about 5RWKW, purely and simply from additional tyre loss. However, this is a worse case scenario as the difference in gearing of 4Th gear to 3Rd gear is more than simply changing diff gears from 3.46 to 4.11. Going from 4th to 3rd is 1.00 to 1.30 which is a 30% Torque increase, going from 3.46 to 4.11 is only a 19% torque increase.

Looking at the OBDII vehicle speed showed this, using 3rd gear with the 4.11ís induced an extra 6kph of tyre slip at Torque peak, using 3rd gear with the 3.46ís only induced an extra 3-4kph at torque peak.

Iím sure as vehicle power increases there will be a point at which a positive gain will be made of using 3.46 gears, but the point this happens will be very much dependant on many factors, probably most of all tyre choice and vehicle strapping/tractioning technique.
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Old 27-01-2010, 08:58 PM   #2
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Im wondering what would happen if you used an rpm graph instead of road speed?

HP = torque x rpm/5252..

Could the results for hp and tq end up almost the same?
Arent you lowering the rpm value by using road speed with the lower diff gears?

Last edited by nugget378; 27-01-2010 at 09:07 PM.
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Old 27-01-2010, 09:13 PM   #3
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Thanks for posting the results Todd, great work.
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Old 27-01-2010, 09:16 PM   #4
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Thinking on this some more, I guess you would see a tractive effort difference, due to the greater acceleration of the car with the lower gear installed.

But possibly it might "show less" on the dyno using an rpm graph instead of road speed?
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Old 27-01-2010, 10:53 PM   #5
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Quote:
Originally Posted by nugget378
Thinking on this some more, I guess you would see a tractive effort difference, due to the greater acceleration of the car with the lower gear installed.

But possibly it might "show less" on the dyno using an rpm graph instead of road speed?
The peak HP values are the same if plotted over RPM instead of speed, the way the data is captured is by whatever RPM value is present at each road speed point.
The 4.11 curve is shifted slightly to the right with about a 5kw offset when viewed over RPM, this is due to the extra tyre loss with the 4.11's and the faster acceleration rate of the ENGINE when 4.11's are fitted.

Each test I revved the engine to very similar RPM points.
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Old 08-02-2010, 10:02 PM   #6
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Very thorough. Interesting reading and much appreciated.
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Old 29-05-2010, 11:54 AM   #7
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Fantastic - this is a true measure of a change. It also confirms what i was saying in the thread about how Tex should not have lost 15rwkw with a diff change.
The next interesting bit would have been to have a before and after measurement of 400m drag times and speeds.
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Old 29-05-2010, 10:47 PM   #8
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Quote:
Originally Posted by GTP owner
Fantastic - this is a true measure of a change. It also confirms what i was saying in the thread about how Tex should not have lost 15rwkw with a diff change.
The next interesting bit would have been to have a before and after measurement of 400m drag times and speeds.
I wouldnt say conclusive results, alot of variables as usual with dynos.
Re quoting last thing he mentions.

"Iím sure as vehicle power increases there will be a point at which a positive gain will be made of using 3.46 gears, but the point this happens will be very much dependant on many factors, probably most of all tyre choice and vehicle strapping/tractioning technique."

But as you mentioned the real only way to see is at the strip.
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Old 30-05-2010, 02:44 PM   #9
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Quote:
Originally Posted by Quadcams
I wouldnt say conclusive results, alot of variables as usual with dynos.
Re quoting last thing he mentions.

"Iím sure as vehicle power increases there will be a point at which a positive gain will be made of using 3.46 gears, but the point this happens will be very much dependant on many factors, probably most of all tyre choice and vehicle strapping/tractioning technique."

But as you mentioned the real only way to see is at the strip.
Not conclusive, no, but certainly a stronger form of evidence than because the tuner said so.
It seems that you still cannot come to terms with the fact that rwkw does not change, whether it be in a high hp car or low. If you dispute the findings, then do your own testing - then post your before and after results. I will be happy to ammend my conclusions based upon the evidence
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Old 06-06-2010, 09:55 PM   #10
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Quote:
Originally Posted by GTP owner
Not conclusive, no, but certainly a stronger form of evidence than because the tuner said so.
It seems that you still cannot come to terms with the fact that rwkw does not change, whether it be in a high hp car or low. If you dispute the findings, then do your own testing - then post your before and after results. I will be happy to ammend my conclusions based upon the evidence
What i can come to terms with is a dyno is a tuning tool, definately not a very accurate way of measuring power, way too many variables, maybe thats something your having trouble coming to terms with lol.
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Old 08-11-2011, 06:53 PM   #11
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Default Re: 4.11 versus 3.46 Diff Gear test Results

Quote:
Originally Posted by Quadcams
What i can come to terms with is a dyno is a tuning tool, definately not a very accurate way of measuring power, way too many variables, maybe thats something your having trouble coming to terms with lol.
i second that
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