cpbeasley

While I may act like a kid in a candy store when it comes to these things, I'm no dummy. I may not be able to understand the physics or mechanics on a deeper level, Im not below listening to a "constructive conversation on a technical level". My patients, friends, and family may no nothing of the anatomy, microbiology, pathology, physiology, mechanical engineering, et al. behind the Dentistry I diagnose and treat, I still do my best to explain it to them

I'll bet my money that lowering the final gear ratio will have a greater effect than that of pretending I'm in 6th gear while driving in 5th.

Psst... by the way... I'm doing this to make the car more fun to drive; not to win a NHRA championship.

Glyn M Ruck

Oh crap! again - Will remedy as I always respect your input.

MW_ATL

This conversation may well jump over my head: my only experience was playing with ratios for a 1985 Mustang GT. The stock with the 5-speed manual was a 2.73 (I believe - that's fairly close anyway, been a while). Although everyone was jumping to a 3.55 or 3.73, I stumbled upon a 3.27 cheap and used that. The 3.27 was stock with the Automatic tranny for a 1986 (just to complete the story, I swapped out the true dual exhaust from the '86 too).

With the stock T-5 ratios and the 2.73, the car wouldn't rev to the upper limits in the higher gears. Based on friends cars, the 3.55+ cars would, but ended up with a lower top speed. The 3.27, as it turned out was the sweet spot, letting the car rev fully in 5th -- and ended up being faster top end than either the 2.73 or the 3.55 cars, with the performance off the line being a big step up as well; it really woke the car up and made driving it a pleasure. Didn't care about gas mileage then, but I don't think it suffered.

My long winded point is that, in theory, the 2.73 should have given me a higher top speed, but whatever the physics/mechanics indicate at first there are other factors that may end up changing the equation. It sounds to me like stepping up might make the car a lot more fun to drive, and the cost seems pretty reasonable. If you don't like it, you can change it again.

cpbeasley

Good story. You're right, there usually is a "sweet" spot gear ratio, fitting the terms you described. Obviously virtually NO ONE here has played with changing ratios (pardon an old thread I found with a c230k that went with the 3.76), so no way to know where that sweet spot is hiding.

You're also exactly right - the are plenty of other factors at play aside from just the final ratio. In the end I'll get some more use out of the revs, without losing much mpg, have more fun, and wont miss whatever theorhetical top end i'll lose, as I don't see myself cruising at 150mph often.

I may just help pave the way for an untapped, unexpensive modification to help up the fun factor and unlock some untapped torque

splinter

If you don’t mind me asking, what is its currently attainable velocity through the top of 1st, 2nd and 3rd (at redline)? RPM at 60 in 6th?

As you’re well aware, there’s no denying the joy from increasing one’s available cut ‘n thrust torque; my .83x3.06:1 final drive ratio’s 300 km/h capability is seldom utilized. Used to spin the inside rear mercilessly upon exiting 75 mph sweepers before fitting its Quaife ATB differential though. Note the W203’s various pumpkins and axles are not necessarily interchangeable, and that they’ve proven prone to premature failure when subjected decent loading, particularly when reducing the ring and pinion’s (necessarily) available loading interface in a lowered gearing retrofit. MB/AMG rightly saw fit to increase the pumpkin’s strength when sending sufficient torque loading its way.

Nevertheless, you’ll need to correct for pending speedometer error if that’s of concern.

cpbeasley

I'll find out tomorrow. Id like to check into the math to get the supposed approx corrected #s w/ new gearing at the points you have requested as well.

What a joy it is, sir!
Thank you for the nudge to further investigate the interchange of the pumpkin in question, i didnt realise they werent all the same. Do you happen to know what qualifications I need to make sure are compatible/the same between new vs current in terms of physical make? And yes Im aware the lower the gearing, the thiner the support area of the ring gear... i was lucky to never have a problem under the influence of my driving style with the often time precarious 4.10s (not as bad as the 4.56) in the stock 10 bolt under the heads/cam ls1 car. i have no knowledge of the benz pumpkin to compare its structural integrity to the 4.10 10-bolt, but the chevy rear was also known for its ability to explode. so, i'll take my cautious chances with my back-up 2.83 punkin on deck.

EDIT: There is a 3.47 out of an 05 c230 (with 21k miles) on ebay. that perhaps has a better chance of interchanging than an 02 c240 pumpkin? Again, i dont know what to look for to make sure it can interchange, so any help to figure this out the better. thanks!

Ive got Jeremy @ OE Tuning on the case!

mleskovar

I agree and remember reading that the drive shaft RPM is monitored at the transmission final output and provides input for both speed and ESP function. Without recoding it will think the rear wheels are always breaking loose. I could be wrong and stand correction though. This takes me back to my '55 Chevy, bored to 301, dual quads, cam, etc etc with 4:56 rear end and welded spider gears....a poor man's LSD of the day.

Glyn M Ruck

You are correct Mark.

cpbeasley

Splinter:

1st: 35 mph
2nd: 65
3rd: 110
60 mph in 6th: 1950 rpm

e1000

Your calculations are wrong.

TemjinX2

i know the s2k guys go from low 14's to high 13's just from upgrading there fd from a 4.10 to a 4.4 like the type S. So i can see how you would be interested in doing this to improve your 1/4 time.

I would be more worried if your car will throw a code and put you into limp mode from the new gear.

cpbeasley

Excuse me? Rude often?

Those are my current mph and rpm, as splinter had asked for.

Go take a happy pill.

Unless you feel like including me in on any of your "construcive" thoughts, leave me be to my proposed ratio swap.

cpbeasley

Yes sir I am interested in that!

I dont have to worry about any tranny module with the 6 spd, but Im working with Karo on getting the proper steps to make the adjustment via Star. Others who have done this w/ 6 spd (one with an 03 c230 in mind) had to make no ECU changes oddly enough.

e1000

I've provided nothing but accurate information in your thread.

No, those aren't your current mph at max revs.

You should take some of your own advice. I'm perfectly happy over here.

e1000

There's a very good reason why a shorter (numerically higher) final drive would slightly increase performance in a car like the S2000. Even in that instance however, tradeoffs are made that do not necessarily present themselves in a 1/4 mile ET.

cpbeasley

Are you effing kidding me? You are really going to sit there and tell me this? I drove the car last night, gingerly let it rev up so I could see the needle a moment before it bounced off the rev limiter.

Since I apparently cannot read my own speedometer, would you like to tell me what the correct readings are? I suppose my reading of the RPM in 6th at 60 is a wrong "calculation" as well too?

If you're going to tell me that 1st is 37 instead of 35, then Id agree with you bc I was approximating a couple marks.

I cant believe Im responding to the sentiment that my own mph readings at max revs are incorrect. You are full of crap in that accusation sir.

I cannot believe the snobbery from some people on this board on occasion.

If you want to give me something constructive, then tell me what physical difference between w203 rear differentials exist.

e1000

Go take a happy pill.

cpbeasley

Splinter:
My current readings as is,
1st: 35 mph
2nd: 65
3rd: 110
60 mph in 6th: 1950 rpm

MW_ATL

Ok, I am puzzled. If those are his "observed" readings, and your argument is that they are not matching the "theoretical" limits then there has to something that is not being accounted for.

Defend your assertion that they are not the mph for the gears. I'm curious.

P.S. No happy pill needed here.

cpbeasley

+1 to that question

LILBENZ230

Yes, what are the correct figures, E?

W203E35

I'm interested as well, to compare it to the 7speed. The 1st in the 7speed goes higher and 7th gear (which people say is overdrive) cruising at 75mph is close to 2k rpm (around there).

cpbeasley

If you're interested, look at the numbers I posted above to compare. These were taken from my speedo and tach. I dont understand why he's questioning my ability to observe my own guages lol.

splinter

It’s seldom my intent to get in the middle of a pissing match. :nix:

The gearbox ratios in yours manifest results remarkably similar to mine:

1st: 38 (3.59)
2nd: 64 (2.19)
3rd: 101 (1.41)
4th: 142 (1.00)
5th: 179 (.80)
~2225 rpm at 60 mph.

Aforementioned GPS-verified figures obtained with a 3.06:1 R&P ratio, ~24.9-inch rear tire height, 6200 rpm upshifts and account for the 722.6’s PWM torque converter slippage.
Note those beyond the legal speed limit were recorded exclusively during sanctioned off-highway, closed course events.
Seems MB may have used the extra cog in its 6MT to help cheat CAFE requirements.

To your other thread - my early differential required 220 350 20 45 output flanges when swapping in later hardware. Its 002 980 17 02 bearings and 025 997 27 47 seals were replaced concurrently as a matter of course. Your installation may indeed go off without a hitch.
Trust, but verify is always a sound policy. Regret that I can’t be more forthcoming.

cpbeasley

No pissing match here anymore, no worries.

Yes they are quite close. I was most definitely off a few marks using only my guages. It would be nice to have access to GPS for greater accuracy. Hopefully come time for the swap I'll be able to do so.

I'll look over the pumpkin with the shop before the install. Hopefully the flanges at most can be swapped for the retrofit and go without a hitch as you said. I'll inquire about the bearings and seals (thank you for the PNs!) to see if I need to get them myself as Im not sure if the indy shop included them in the over-the-phone quote I was provided for the install.

Unless I can locate a 3.67 in outstanding condition by tomorrow, Im sourcing a 3.46 w/ 20k miles out of an 05. Without an LSD at the time, I wont mind the slightly taller ratio.