Ketchmi

Cmon' guys, Mark is right...and the world is flat!

Everybody seems to agree except Mark. He must enjoy the back and forth or he wouldn't keep it up.

I will not be drug into this conversation again, I wasted way too much time on it last time and nothing has changed.

Enjoy...I have my popcorn.

m21sniper

Whatever mark.

Ketchmi, would you share some popcorn with a brutha?

mark kibort

we are trying to educate Msniper. heirich has already agreed as well.

dont throw gas on the education fire

if you cant grasp the 3.09 vs 2.2 concept of 1st changes and all other gears the same, you should just map it out and show yourself the light.
3.09 changes 1st to 39mph and the rest of the gears are the same. its pretty simple.

Mk

mark kibort

before you bow out, why dont you prove your point and show how much exact torque through the gears to 115mph are gained with a 3.09 vs a 2.2.

grap a hp torque curve of any 928 and make a statement. otherwise, you are just talking in circles. trust me, its the way ive explained it.

bet you cant prove your message

Mk

Ketchmi

H probably gave up like I did.

Sniper, if you ever make it out this way I'll buy some beer to go with the popcorn!

fst951

Dave.

So if the world is indeed flat, wouldn't I risk sailing off the edge if I tryed to circumnavigate it? YIKES!!!

I have to rethink my cruise ship plans for the New Year.

Louie928

One change the auto trans 928 owners should consider is to use a higher stall speed torque converter. That will allow the engine to rev higher immediately off the line. Torque multiplication will still work for you in the converter, but at higher rpm and even more torque than with the stock stall speed. Top gear cruising rpm wouldn't be affected as it would with the 3.09. I think less expensive too.

BrianG

I've messed around with the spectrum of GM stock torque converters in a previous project. I found that the higher stall-speed units made general drivability an issue. It made it feel like you were slipping the clutch (as if attempting a fast launch with a standard-tranny car) at every roll off of a stop. For racing applications it's a good idea but for general street driving it's really irritating!!

Louie928

I imagine that's the case. I've never tried it. I suppose the stall speed selection is a compromise. Seems to me that having a 1st gear that ran out of rpms quickly would be a pain to drive "normally" too. An auto that started in 2nd would probably be just fine with a 3.09 final drive. 'Course when you reached cruising speed, you'd be constantly reaching for the OD switch.

mark kibort

Gents,

Its really not that complicated . Lets not get lost in the psydo hype of those that do NOT have clear understanding of the concepts. These are not theories ive provided, but working models that can be used in any comparison of an engines hp vs the gearing the transmission and their effects on accelerative forces.

First off, lets address the several misconceptions and show the realities of the mechanical change.

1. Putting a 3.09 ring and pinion vs a stock 2.2, doesn’t make the gears closer together. It gives you an extra sub-1st gear at a ratio of 12.5:1 vs the stock ratio of 8.9:1 . the rest of the ratios after this new sub-1st gear, have the same spacing. In the 928, that spacing is .71 or 1.4 for most all gears except 5th.
2. After shifting out of this Sub-1st gear, you do not gain any stored energy. Kinetic energy is ½ mass x Velocity ^2 (in J) the stored energy after a shift out of the sub-1st gear at a speed of 39mph will have the same ‘stored energy” as a car at that speed in its stock 1st gear .
3. using more of the gears of a given transmission doesn’t relate proportionately to its efficiency of the hp available to the driven wheels. In the case of the sub-1st gear, there is a net gain of 26% to the driven wheels with this extra gear, but over a longer period of time , it becomes relatively small as far as the extra energy used over max acceleration using several or more gears. 26% increase in HP for less than one second (or 60hp on a 320hp engine,) has the effect of only about 10hp of net gain over a 13 second period.

The way to calculate the increase hp or torque to the wheels is pretty simple.

Say we have a launch rpm with a stock s4 with a the 3.09 rear end of 4600rpm***. Based on the old devek unmodified 928S4 hp torque curve of 266hp and 281 torque max, the launch hp would be 200hp and at 6500rpm (39mph) it would be 250hp for an average hp of 240hp (aprox with the peak hp of 266) Now the stock S4 with 2.2 would launch at 3300rpm or 180hp and get to 4600rpm at 39mph or 200hp for an aveage hp of 190hp . This loss (or gain) of HP is close to 50-60hp, or about 20-22% of max HP. After that, both cars are now in the same basic ratio of 8.9 or (8.3:1 for the 3.09 ) and they continue gear for gear until 155mph or so.
Now, YOUR GUY’S FAVOITE, want to check my work with TORQUE!!!????
3.09 at 4600rpm makes 250ftlbs of torque x 12.5:1 = 3125ft-lbs of torque (12.5:1 is new sub-1st gear ratio)
at redline of 6500rpm and 39mph, there is torque of 225ft-lbs = 2812ft-lbs of torue for an average of near 2950ft-lbs.
Now,
The 2.2 at 3000rpm makes 280ftlbs x 8.9:1=2492ft-lbs
at 4600rpm , or 39mph, it makes 250ft-lbs x 8.9 = 2225 ft-lbs or an aveage of near 2350ft-lbs

2350/2950ft-lbs is about 20%. Not near the 40% advantage that the 3.09 vs the 2.2 would lead you to believe at first glance. This is because we are dealing with a torque “curve”!!!!

THIS IS ALL JUST TO 39MPH. After that, there are subtle differences but basically both cars would have the same next gear ratio of 8.9 vs 8.3, they would shift in to exactly the same 5.9:1 and then finally a 4.2 or 4.5:1 ratio, maxing out in this gear to 115mph or so. Carry this on to the next gear, the 3.09 would be in its 5th gearr of 3.09 , while the S4 2.2 would be in its 4th of 3.2:1. (still pretty close) if you notice, every gear after the Sub 1st gear is actually a bit taller. (except the the 5.9:1 ratio )

I hope If you look at the work above, you will understand some of the basics also, keep in mind that the 20% gain is only for the duration of speed from 0-39mph. This hp effects on the total energy expended by the engine can be roughly calculated as HP x time. From my standing starts im only in 1st for a few seconds . I can only imagine how long you would stay in a sub 1st if it was to 39mph vs 55mph. Say its 2 seconds. 60hp for 2 seconds would be worth only 10hp if the duration was over 12 seconds. This is the net net of the 3.09 mod.

Verify this with your local physics instructor, college prof, highschool physics teacher, etc. you will see the logic and methodology is correct. If it isn’t, Ill pay you via pay pal $50. BUT, you have to show your contrarian theory, and I can have it validated by a mutually acceptable independent knowledge base. If you are found wrong, you own me $10. that’s 5;1 odds!!!! So, put your money where your mouth is, I you are so sure this “world” isn’t flat! Especially you Dave, 6.0 and Msniper.

I await to see you coward behind the keyboards!

MK

***Launch of 3300rpm with a 2.2 S4 gear box ,would equate to a 4600rpm launch to keep wheel speed equal with both scenarios.

John Veninger

http://www.angelfire.com/fl/procrastination/rear.html

heinrich

You guys agree. You're talking apples and oranges.

Ketchmi

Hey Mark, get some sleep. I said I wouldn't be drug into this mess again and I won't. I gave you several instances where you were wrong last time and you wouldn't admit it even then. It was always "but", "if", "or" and the creation of "Mark Math". Why bother now?

Save your money to buy some tires...

GlenL

Sometimes these threads bother me and sometimes I find them amusing.

What Mark is saying is 100% correct.

The problem is that some people really don't understand what they're attempting to talk about. The terms used, like power and ratio, have real meanings that people in the industry, like engineers, agree on.

Some people ("assclowns") try to express a vaguely help intuitive understanding of the physics of racing in these terms. They can not express themselves with any understandability to those who actually do know what they're talking about. The result is an argument with no agreement. And this, being the internet, those people too often won't change positions, try to learn something or, god forbid, admit they were wrong.

Will a 3.09 do better off the line than a 2.2? Of course.

Does it make a difference above 40mph? Possibly but it depends on the initial and end speeds. That is, what were the RPM ranges used and how many gear shifts were needed.

Now what is so hard about accepting these two conclusions? One does not invalidate the other.

heinrich

Glen, so pray tell who are the "assclowns"?