dfwx

I was hoping to change the final drive ratio on my W215 CL65 to 3.05 or, if not possible, 2.86, particularly since his has 20 inch wheels and I don't plan to drive 211 mph.
Was told there was nothing that could be done with a Renntech LSD and that basically there is nothing available at all except possibly for astronomical costs - and then maybe not. However, Renntech told me someone did put a 3.05 in a CL65 7-8 years ago.
Anyone know of any option info on changing the final drive ratio but not using the OEM differential?

Welwynnick

The CL65 is already appallingly under-geared as it is. Hard to imagine the need for even lower gearing?

Nick

dfwx

The redline top speed on my CL65 with the final tire/wheel combination it will have is 211 mph.

When I would do so even with the 187 mph speed limitation removed is exactly never. Therefore, the 2.65 final drive makes absolutely no sense and exists only to add 1-2 mpg, which I don't care about. If I cared about gas mileage I would not have a CL65 anyway.

The performance dominance of the CL65 is in the 1 kilometer run, which has no relevancy t me, nor do I have any goal of quarter mile drag racing. My goal is to maximize it's 50 to 100/110 acceleration. In that regards, a lower final drive is essentially free horsepower at no additional load on the motor. With 305s it would essentially increase accelerate once their is total tires hook up to turn my 680ish and 850ish TQ rate of acceleration to around 780hp/960TQ just by the ratio change.

If that is combined with low ratio street but sticky 305/25/20 rear tires it would take some effort not to have at least a high 10 second car, although that is not my goal.

That certainly wouldn't over rev the motor at Interstate speeds and there are other model AMGs running a 3.05 final drive.

But I'm not really pondering why, I'm pondering how and is it even possible in my year and model AMG? Choices become very limited for 65 series Mercs.

How often do you drive 200 mph? Me? Never have. Never will. So why would I want gearing for it? My "quest" is maximum acceleration ability from 50 to 100/110 ish. That would be the usable performance range for it.

Dr Matt

Heck if gears were available I'd swap to a 3.23 or even a 3.50 in my CL. I only drive a few highway miles a day so lower gears would be great for me considering I will be drag racing. Can only imagine how a CL65 would pull from 0-150 with a 3.50 ring & pinion.

Grip Grip

I did a 3.07 to 3.27 swap in my Crossfire thanks to Rudy Compart. You might want to PM him and see if he can help you out. His username is "Rcompart".

TwinTurboTim

That may not benefit what you want because then your first gear will run out shorter so instead of your car shifting down to first gear its not going to and it will lug in second. A lower final drive will mostly benefit in first gear if you can handle the added acceleration. I could be wrong but it may be something you want to think about. Plus I think the tuning would be a bigger obstacle but maybe some people can figure it out.

dfwx

The CL65 gearing is basically a 1980s luxury car extremely long geared 4 speed auto (a bit faster shifting) with overdrive.
The CL63/600 (I can't remember which it is) in OEM form is actually 1/10th faster in the quarter mile than a CL65 because of their 7 speed transmission.

MB deliberately downtuned the CL65 and (in my opinion) made the so they can not accept enough tire width to safeguard the transmission from torque damage - and has such a long final drive for the same reason. MB doesn't really want the rear tires to hook up to the ground well. They want them to give to save the tranny from warranty claims.

This reminds me of the 80s Porsche 928 - one of the 3 iconic symbols of financial success (the other being the Lambo Contact and Ferrari Testerossa). The 928 for its era was a fantastic GT2+2 BUT was clearly designed by Porsche to not be built up. The had semi skirt structure over the rear wheels to prevent wide tires. They used cast pistons despite it being astronomically expensive for its time. And basically a 1 wheel drive differential.

Why? The transmission would obliterate once you took it much past 600, and would go at 500 if super sticky tires and a true posi-type LSD was installed.

The gorgeous 3.5 twin turbo Lotus Esprite was built as a 500 hp motor, but downtuned by the factory to 350 because that is all the Renault tranny could take.

While people look at motors and horsepower to evaluate a car, engineers look at torque and the transmission/drivetrain. All car manufacturers knew how to make 600+ hp production car motors by the late 60s. Motor design is simplistic compared to transmission design and tooling for a new one. Massive torque is being put into relatively tiny gears - and all of that torque in that tranny to have to hold together in an aluminum case and transferred by relatively small plates.

If you examine performance cars' power to weight ratio (other than mega costly supercars), there actually has been very little change over the last 5 decades. Rather, it has been in tire quality, suspension, fuel economy, clean exhaust and transmissions.

Trying to turn low production, super costly imports into drag racers is both astronomically expensive and with very little options. To the opposite, if you have a Chevy you can buy virtually anything off the shelf and just bolt it on or plug it in. If you want to drag race fast - easiest and cheapest - buy a Camero or Vette. Its been that way for decades.

In short, there are many reasons there are huge challenges and limitations trying to build up Mercedes and particularly CL65s - and beyond their limited production numbers and therefore lack of aftermarket companies interest in them. Mercedes deliberately designed them to be limited to protect themselves on warranty claims and potential bad reputation from blown transmissions, drive shafts, and the other destructive forces of massive torque combined with posi-traction hooking to 2 super sticky 12 inch tires.

If these CL65s and 63s has Merc's 7 speed transmission and the SLS rear gearing the CL65 would be a very different performance machine. But the 7 speed couldn't and can't take it from a warranty standpoint nor could the old 5 speed take all that the 6.0 biturbo can really put out in terms of torque, nor can their body control/traction control computers handle it.

Yes, 12 inch super sticky tires on the back with a true posi of a reprogrammed CL65 and a few other mods running 3.5 rear gears would be a high 9 second car. Astonishing for what it otherwise is - a luxurious GT2+2 full sized cruising coupe.

It is designed to prevent you from making it that way by MB for many reasons. And given the low production numbers plus the even smaller percentage of owners who have any interest in modifications, there is little aftermarket companies interested.

dfwx

Some years ago I read some interesting material of how the manufacturers basically negotiate power-to-weight and performance capabilities between them. I also had an uncle who was a fairly high up engineer for Ford and Pontiac, whose job was to design cars to die. For example, he designed the nylon timing gear - which absolutely would fail between 105K to 120K miles, taking out the push rods and possible popping the top of a piston. The public reason given was "they are quieter" - as if noisy timing gears were a problem. They designed a/c units to fail in the same mileage range (failure based on vibration fatigue). And, of course, interiors were designed to last about the same amount of time.

Difficult engineering because if they got it wrong there would be a million warranty claims. Extensive testing to assure certain parts lifespans within the desired range. As car financing became longer, they had to extend how long a car will likely last. Semi-tractors (trucks) are designed to last a million miles - and they are worked vastly harder than a car engine. But who would buy a semi truck tractor that lasted only 200,000 miles? Back in the 60s, 70s, 80s, not 1% of cars were still on the road with 200K miles on them because they are designed that way. My auto engineer uncle used to talk about that quite a bit.

My first new car was a 73 Firebird 400. He told me to take it to a certain dealership that he had talked to the lead mechanic, with specific instructions of what to change. It was an very different (better) running and performing car after that, nor ever had a mechanical problem with it.

On the American side, it was MOPAR that first started listening to the insurance industry asking themselves of the ethics of putting 500 horsepower motors into 2 door taxi cab quality chassis, suspension and brake designs on nylon bias-ply ballon tires and selling them to teenagers.

But it was GM that actually joined the insurance industry in the drive to stop the insanity (in their view). Ford was prepared to take the 429 to nearly 700 CID and Chrysler the same with their hemi. Porsche, Ferrari and Lambo all understood it merely took adding turbos to their big motors to drop weight to power ratios down to 5-1 by the early 80s.

For GM, Mercedes etc to turn their lesser costly cars into 0-60 in 2 seconds, 9 second quarter mile cars with a top speed of over 200 mph would merely be to tell their designers to build it. More boost. More cubic inches. Bigger injectors. Big tires. Lots of gears. The manufacturing costs increase would be trivial after initial tooling/design costs. GM, Ford and Chrysler could be turning out 1000 horsepower pony cars within 60 days if they wanted to. They don't.

I suspect some of the computer junk on cars (you really don't need computers to operate lights, windows etc) is they want these cars to die in terms of affordability as high mileage used cars. Limiting super cars to only people spending $100,000, $200,000, $500,000 etc mostly keeps them out of the hands of teenagers and working class folks who can't afford new tires and brake pads for their 200 mph old super car.

Porsche 928 motors were 300,000k motors. But anyone who knows them knows their computers and electrical problems now are so endless they aren't worth their dirt cheap used prices. Does ANYONE have a 250,000 CL65? Will there ever be one? I seriously doubt it and I seriously believe this is not accidental.

What would a 250,000 CL65 with bad paint, ragged interior, a/c dead and bad tires sell for used? $10,000? $8000? $6000? Then filled up with 17 year olds on meth and booze racing thru the city and down the highway in a 5000 pound bullet with 15 year old dry rotted cheap H rated tires? I truly believe they want these super performance cars to die before they are too cheap on the used car market.

These topics became serious discussions between manufacturers, the insurance industry, liability lawyers, and the governments starting back in the late 1960s and continue to this day.

dfwx

And that was my soapbox speech for the month.

TwinTurboTim

After I read this I quit reading. The long gearing puts more load on the transmission not less! Think about it. What is harder to turn? What is easier to push 2.70 gears or 4.10.

Also put in a drag calculator some variables and you will see that a CL65 will no where be a 9 second car if you change the gear to 3.5

Needless to say I am sorry but I quit reading your rant.

dfwx

All I would agree with is that you didn't read to. I wrote the following qualifiers beyond being a bone stock CL65:

Factoring in TQ, it calculates to 9.88 in the quarter mile with the variables I presented, which factoring in the higher TQ compared to typical horsepower to TQ ratios. True solf racing tires pre-race heated up could knock another 0.1 to o.3 off that. Long life low ratio streets would add time and could add quite a bit of time. A 9.88 car could be a 10.5 car on street tires - or even worse.

As to low gears hammering the transmission, the lower the ratio the more working load per revolution. You're writing about how hard it is to turn the crank on the gears. Lower gears are easier on the motor and harder on the drive train.

It would be interesting if you went to a drag strip and explained to drivers if they want to win they should start out in 5th gear for the best gear ratio - but warning if the pop the clutch from a start in 5th gear it'll probably blow their transmission.

The benefits in lower and tighter gear ratios for drag racing for street weight cars has only been understood for a century. For muscle cars manufacturers called low ratio options "drag packs." Why do you think that is?

What you REALLY should do is send Mercedes a letter explaining what fools they are in their SLS design to have a 6th (final) gear ratio of 0.72 and a final drive of 3.56 - and REALLY they should have a final drive ratio of 2.65 like the CL65 - telling them your calculations of how much faster that LOOONG 2.65 would make the SLS accelerate.

2014 SLS
Trans Type 7 Trans Description Cont. Auto-Shift Manual w/OD First Gear Ratio (:1) 3.40 Second Gear Ratio (:1) 2.19 Third Gear Ratio (:1) 1.63 Fourth Gear Ratio (:1) 1.29 Fifth Gear Ratio (:1) 1.03 Sixth Gear Ratio (:1) 0.84 Reverse Ratio (:1) 2.79 Clutch Size N/A in Final Drive Axle Ratio (:1) 3.67 Seventh Gear Ratio (:1) 0.72.

Speaking to RENNtech, who know something of these cars, I was told they only set up one CL65 with 3.05 rear ratio about 8 years ago, and that to do so is very costly. I guess their "special customer' decided he wanted to make his CL65 slower and hoping to blow his transmission while making it this way?

Fact: IF the tires can hook up to the pavement, lowering the final drive ratio will cause it to accelerate faster within redline limitations. Then again, that is the ENTIRE principle of a transmission having multiple gears to begin with, isn't it?

Welwynnick

Its good to see other people getting really interested in their cars, but you seem to think that you can get something for nothing with different gearing. Maybe it works a little bit with some cars, but heavily blown turbo cars dont.

If you look at the power and torque curves for the 600 & 65 engines, you'll see a relatively flat power curve, and this is becoming more common. People used to talk about how a flat torque curve is ideal, or a good indication of flexibility, but that's misguided. A flat power curve is what allows you to use wide ratios, or avoid changing gear to keep the engine on the boil.

With a flat power curve, when you accelerate throught the gears, and have the revs drop to a lower speed, the power won't be much lower. The benefit is that the area under the power curve is large - specifically the area straddling the rev range used during acceleration. In other words (notwithstanding the peak power) the average power is high, and that's what gives our cars such good acceleration (better than the power to weight ratio would predict).

And a car with a flat power curve is much more tolerant of wide gear ratios. And that's the real reason why short gearing is used to imporve acceleration - because the transmission spends more time in the higher gears, where the ratio gaps are smaller. Its a small effect, and I'd say vanishing small for our cars. First gear is virtually redundant in our cars, so the extra torque multiplication is wasted.

Nick

dfwx

Thank you for your comment.

Nothing is "free." Lowering the gear ratios (also bringing them therefore closer together) reduces top redline potential speed, more wear on the motor, and generally worst gas mileage.

As a comparison, Mercs that cost much less and not boosted weighing as much will slightly best a CL65 in the quarter mile because they have 7 speed transmissions for which all then are operating at a relatively lower and closer gear ratios. A CL65 would not be faster if 2nd and 4th gear eliminated from it.

It is the high level of torque across a long flat range that makes it impressive, although much of that flat-line is largely due to computer TQ limiting. So if it is reprogrammed to give you the 850ish TQ, you lose much of that flat line, meaning there is a TQ increase but not as great at would seem as it unlikely there is the same flat line at 850 TQ.

It also depends upon the goal of the specific owner. Mine is very specific. To maximize acceleration from 40ish to 110 mph. At best I can add an inch of tire and some stickiness to the rear tires, so below that speed there isn't anything more power will do. I don't care what performance is past 110.

While I was planning to throw a pile of money at my CL65 for that specific goal, the more research I do on options and limitations the more I feel like really I'm just throwing myself against deliberate design limitation walls. In a sense, it seems I'm trying to figure how to build up a 2005 version in this era of a 1971 500 cid Cadillac Eldorado in the 1970s era.

The CL65 is an impressive full sized luxury GT2+2 coupe with a lot of pickup and go for a full sized luxury GT2+2 coupe. But that also is largely it's ceiling too. MB only had a primitive 5 speed auto to put in it incapable of really taking the motor AMG built - so they limited it by computer, by an odd wheel offset, in general limiting tire width, nearly a 1-wheel drive differential (correctable by a differential swap) and a very long final drive ratio. Although lightened half a ton by models before and after it, it still is a heavy car.

While there is the ability to significantly increase horsepower - as that can be done to any motor regardless of brand - from the motor back its a dead end. Other than such as a Quaife differential, there are exactly no choices to even pick from. I could add 1 inch to the inner rear wheels by having them custom modified due to some rear fender modification I had done - and that all there is.

This is not unique to 65 series or Mercedes. I came up against this with my XRK coupe for which I got rid of it. Way back when I finally accepted the manufactured-in limitations by Porsche on a 928 that was modified with a turbo charger, 8 coil blocks, hot exhaust and more. However, other than a Quaife style differential, there were no options from motor back - for which I gave it up. Because such cars are all limited production numbers and only a small percentage of owners interested in modifications anyway, there is no aftermarket manufacturers interest.

The blame is mine. I didn't do my homework before buying. It is what is it, and that is an exquisite, heavy luxury grand touring full sized sport 2+2 coupe. I am coming to the conclusion that it is not a performance car no matter how much money I threw at it. It does not have a potential to meet today's standards for my personal interest areas due to inherent limitations.

Time has passed it by. I could throw $20K more at it, plus shave off 250 pounds and add an inch more of rear sticky tires - and any merely ECU tuned ZO6 with a performance exhaust would spank the CL65's *** between 40 to 110. It is irrelevant to me that the CL65 might catch up and pass the Z06 at 175. When I would drive it 175 or even 150 is exactly never.

Could a 4600 pound car beat a 3200 lb car? Sure. It's all by the numbers. Horsepower/TQ factoring in weight, tire traction and a tad for weight transfer, shifting speeds, aerodynamics, and - of course - gearing. With the 65 series running 21.8 psi boost - which is huge compared to most turbocharged street cars - definitely possible. But if added to that is lesser tire and long, long gears far, far apart in what is basically a 4 speed transmission with an extra overdrive gear? That becomes a huge mountain to try to climb as it is gear for 220 and I don't need any of it past 110. In that speed range of up to 110 with it's gearing? It has a 3 speed transmission running a 2.56 rear end.

That's my growing sense of it today anyway. Continually coming up against "it's can't be done" and having to accept inferiorities on this CL65 is getting to me. All I could deal with or one way or another except no-gearing options. "Difficult and costly" is one thing. "Can't be done" is something entirely different.

However, this likely does not apply to anyone else as everyone has their own wants, needs and goals. Just my thing. It will make a great special occasions weekend travel car for us. So my inclination is to shift my focus about it that direction. It is still well suited in that regards. That approach certainly is easier and costs less. Just keep it maintained and clean.

Thank you for your comments.