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16v Power Band / Rear Diff
Topic Started: Wed Aug 5, 2009 6:51 pm (1,816 Views)
The Gorilla
Part of things
[ *  * ]
Hi,

I acquired a 2.3 16v a few months ago,
well used, OK issh body work, and appears
to have been quite well maintained.

Been to the moon and back a couple of times
etc, you get the picture.

This car is not for my project car.

After now having a nice S/S tube for it
to breath through, many thanks Phil,
and a few routine jobs, Valve shims,
filtres etc, the car is so overgeared,
that unless doing well past the national
limit + 30 in forth, you really have to
work hard to keep the engine in the
power band.

I was even changing down to third
on the Motorway to keep the engine
up on the cams.

So, the question is who
has changed the CW/p for at least
a 3.46 if doing lots of motorway
driving or 3.69 if wanting a
far more responsive car that
comes into the power band
much earlier through the
gearbox ?

The best mod you can do to a
E46 M3/CSL is change the
standard rear diff from the 3.6
CW/p to a 3.91 or 4.1 CW/p.

The standard car is so overgeared
its almost like BMW had sole rights
to all the CW/p.

The car is so different to drive
and so more involving and alive,
you would swear that it had been tuned.

So I am at a loss as to understanding
why more of you 16v owners have not
done this mod ?

I'll bet that with a 3.69 rear CW/p
a good exhaust, 65mm min single or
better still twin 55mm tubes, your
2.3 16v will be like somebody has
given your car some serious tuning mods.

I'll even wager that the 30 or so BHP that
the std EVO 11 has, did very little for
its through the gears performance, most
of the gains will have been due to it running
a 3.45 rear diff.

Why ?

Engine Torque moves the car, BHP makes
it go faster.
The Torque figures for the Standard Evo 11
do not differ greatly from your 16v.

Regards,

The Gorilla.




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feoffle
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Part of things
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Changing the final drive in Integra Type-Rs is a very popular mod too.

The 96-98 JDM models had a 4.4, whereas UK and 98+ JDM models got a 4.785. Many people go for a 4.92 as an aftermarket option. Very cheap way to give the car a bit more *zing* when you're low on torque.
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The Gorilla
Part of things
[ *  * ]
Hi,

Feoffle- thats what I mean, just seems
very strange to me that more, maybe
some are not letting on ? have not
changed their 16v Diff ratio, in that
its not a great expense for what it delivers
to a car that has a 4 pot lacking in Torque ?

Most E30 M3 [S14] Owners even those running
quite standard Cars switch the std 3.25
for a 3.45 or 3.64 LSD.

Regards,

The Gorilla.

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Johnboy Mac
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More than part of things
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Gorilla you mentioned this before when you gave me a contact for rebuilding my own diff which is still not done. I must look into this. But a couple of question if you don't mind?

Would 1st & 2nd for a road car & daily driver not be too low coming from a 3:07 diff. And how much top speed would I lose?

I know Merc fitted the 2.5 with the higher diff for MPG gains, so that might be something else for me to consider as I do big mileage.
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jeremy
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Too Far Gone To Help
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I've been saying this for a year and a half now , it's almost like free bhp ....... all I get back is .." yeah but you get worse petrol consumption !"


Jeremy
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bri957
More than part of things
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I went the other direction with my 2.6, from 3.92 ASD to 3.07 ASD.

Has made the car far more enjoyable to drive, although slightly highly geared (geared maximum of 180mph now :lol: )

Before, first was too low, almost unusable.
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The Gorilla
Part of things
[ *  * ]
Hi,

Johnboy IRL- If you do mainly Motorway
mileage I would say a 3.45 would be
a good compromise.

No Car pulls full revs in top, so
you do not loose top speed you
just take more Revs to make it.

Bri 957- I do not know the gearbox
ratios of a 2.6, so I can not know
what your pulling.

There is a spread sheet on here somewhere
where Johan.c or Mikale did the rev drop
for using different CW/p.

Based on 255 x 35 x 18 at 635 Diam
and at 7750 rpm in each gear you have this-

Diff Ratio - 3.07 3.27 3.46

1st 4.08 46.00 43.00 40.00
2nd 2.52 74.00 69.9 66.0
3rd 1.77 106.1 99.6 94.0
4th 1.26 149.0 139.9 132.00
5th 1.0 187.0 176.0 166.0

I rounded up some of the numbers, but you get the
overall idea of how changing the diff ratio can bring
the engine power band into a much better spread
for a 16v.

For a car that does proper Track time, then 3.46
would transform a standard car, without doubt.

But as with all things in life there is no free lunch
and more revs means higher fuel consumption.

Regards,

The Gorilla.
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Martrider
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Longest build time in history?
So the big question is, where to find these ratios. Please forgive my ignorance, but where which model are we looking to steal one from, and how do you fit them to an LSD?
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matsalleh76
Matsalleh76. RIP. Gone But Never Forgotten.
[ *  * ]
Going to a higher numerical ratio makes sense for a track car where you do not want to use 1st gear for anything but a standing start, but for a road car the standard 3.07/3.27 diff ratios are fine. After all you have five genuine - not overdrive - gears to play with.

We went from 3.27 to 3.07 which made the car more pleasant to drive with increased flexibility in the lower three gears. First and second will still tear you head off but are much more useful. Third takes care of most city traffic speeds. Fourth and fifth are fine for higher speed cruising/speeding. We have effortlessly and strongly pulled 255 on the clock in 5th. That's fast enough.

However, after saying that, the EVO-2 was supplied with a diff 3.46 ratio but it was after all a different car with different power characteristics. The DTM cars had ratios all the way up to the mid 5.XX's but they are another story all together.

The normal small housing 201 diff was available with ratios up to 3.9X in some of the less exciting/less powerful models (ie the 1.8), but the small housing diff is just that: small and not very strong.

The 16V used a larger body diff from the 124's and was the only car sold with LSD. The 16V's and later 2.6's were later available with ASD (the 16Vusing the same large diff housing. The standard ASD 201's and 2.6's used a smaller housing) but without LSD, although the ASD diff when ASD was not engaged did give a ~30% LSD effect....when new.

The highest available ratio in a 124 with the larger housing that I know of was 3.29 in the 4-Matic with ASD.

In summery, from what I know, looking for a large body Merc factory high numerical diff for a track 201 may be a futile exercise. The local fellows who track their cars here have modified their sub-frames, prop & drive shafts and sacrificed ABS by fitted 4.4 diffs from a Supra.

If there is a lower numerical compatible Merc diff out there, please let me know..........the above comments are based on info I have collected and experience sorting through mounds of diff's in breaker's yards.

I have my own mound of six diff's in back of the me workshop.

Regards,
bobf.

Edited by matsalleh76, Thu Aug 6, 2009 3:54 am.
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stwat
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Many thanks, bobf for that brilliant and informative post :) That certainly answered a lot of questions i have been pondering about the 16v ASD diffs.


Stu
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RobertE
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Serial victim...
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I'd not seen this thread - brilliant info, thanks to all! When I was messing about with Astons there used to be a favourite conversion which involved using the (Salisbury) crown wheel & pinion from a Daimler DR Limousine or, better still, a hearse, which were not put together to do more than 70-80 mph. You could even graft a Powr-lok (Sp?) LSD diff onto this ratio, which transformed the indirect gear performance of a standard DB4/5/6. The key, I suppose, is that the diff. housings were all the same size. Noisy as F, of course - but given that the 'quickest' option for the DB4 was (IIRC) a 4.09:1 and you could achieve more than 5:1 doing this trick, then nobody cared. Natch, most people neglected to change the speedo cable, so you never knew where you were.

Someone posted up a spreadsheet before on available rear end ratios for the 201 but I'm damned if I can find it...
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jeremy
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Too Far Gone To Help
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RobertE
Thu Aug 6, 2009 4:58 am
Natch, most people neglected to change the speedo cable, so you never knew where you were.


Today you can use your sat-nav or Road Angel to give you an even more accurate readout .


Jeremy :evo2: :driver:
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bri957
More than part of things
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matsalleh76
Thu Aug 6, 2009 3:41 am
The highest available ratio in a 124 with the larger housing that I know of was 3.29 in the 4-Matic with ASD.
Bob

The post '92 manual 2.6 W201 was fitted with a 3.92 rear differential, mine was the ASD equipped one. I think this higher ratio was to compensate for the reduced power with a catalyst.

I found it far to highly geared, 1st being all but unusable and 5th was not an overdrive, so motorways were slightly busy. With the 3.07 fitted, first has become far more 'normal' a gear to use around town, while 4th has ended up at the same ratio as the old 5th - with 5th now a bit intergalactic....

I'm fitting a 3.0 shortly, which will hopefully even things out slightly.
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The Gorilla
Part of things
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Hi,

Guys at the end of the day its all about
what you want from your Car.

I personally however would change the 3.07 rear
diff in any 16v for at least a 3.27 or better still a
3.46.

I think Matsalleh gave a very good account of
things in general but I would disagree with
his comments regarding the 3.46 on the Evo
11.
To get the engine power band best suited to the
Getrag Ratios, a 3.46 was used, and as the Evo 11 Torque
figures are not way above a 16v then a 16v would also
gain with a 3.46, but to a slightly lesser degree.

BHP makes a car go faster, its the Torque that makes
the power.
High revving 4 pots are not known for their Torque
so its important to keep the engines power band
well suited to the gearbox ratios.

A std 2.3 16v is 'on' the cams from around 4500 rpm,
so you would have to be doing over 100mph in forth
to keep the engine on the cams.
when then dropping down to say third, as the rev drops
from say 5000 rpm to 3500, on the down change,
most cars drop 1500/2000rpm, the engine comes
off the cams until you have built back up to around
4500 rpm.
Higher lift cams push this window further up the
Rev band.

With a 3.46 rear CW/p 100 mph in forth would be say be nearer
6000 rpm so when you change down to third your engine
is only just off cam, and picks up much quicker.

The above numbers are guesstimates to try and
explain why the rear diff ratio is so importatant.

Even more so on engines where Torque is at a premium.

Regards,

The Gorilla.











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Johnboy Mac
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More than part of things
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Thanks for the info Gorilla & Matsalleh.

I'll give the diff change some more consideration in due course as I've said my car is daily and I like the idea of getting up to 32mpg (not often enough), averaging out at about 27-28mpg.
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matsalleh76
Matsalleh76. RIP. Gone But Never Forgotten.
[ *  * ]
Bri,

That is good info.

I have a 3.92 diff listed for the 2.6 but assumed it was an open (small housing) diff. As yours was ASD then the housing should be the larger 124 housing. To confirm this, if it is still available, measure the distance from half shaft drive flange to half shaft drive flange. Here are the flange to flange dimensions of the various diffs we have played with:

201 open diff: 22.5cm
201 (16V) LSD: 24cm
201 ASD : 28.5cm
124 open diff : 24cm
124 ASD : 28.5cm

They all used different length half shafts, the shortest being the 201 ASD shafts. Anyone considering changing a diff would be wise to source the diff and matching half shafts as a set.

Where did your 3.07 replacement diff come from? Is it ASD or open?

---If the replacement is ASD and bolted right into your 2.6 using the original 3.92 half shafts, then your old 3.92 was a large housing diff and would be an attractive option for someone building a track car.

---If the replacement is open (not ASD) and you installed the diff together with the half shafts and rear prop shaft section from the doner car, then the replacement is a small housing 201 diff. That's fine because it indicates that the original 3.92 diff was large housing.


Now I want to ask a question that has been bothering me for years:

Some 201 diffs have "pie plate" drive flanges. The plates are large & thick and appear to have some sort of inertia damping purpose. Some 201 diffs have a pie plate on each side while others have the thing on one side only. Some have no pie plates at all. 124's do not use any pie plates.

Does anyone know the actual purpose of the pie plates on the 201 diffs?

The pie pates are another example of mystifying Merc voodoo engineering. The other is that useless propshaft damper that does nothing except randomly disintegrate making a huge noise and scaring people. Everyone removes them; usually after they disintegrate, and find that removal has no negative effect whatsoever.

Cheers,
bobf.
Edited by matsalleh76, Thu Aug 6, 2009 11:37 am.
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RobertE
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Serial victim...
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Excellent, Bob! I shall now trawl - I rather agree with the primate that these cars are a bit overgeared...
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Johnboy Mac
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matsalleh76
Thu Aug 6, 2009 11:30 am
Where did your 3.07 replacement diff come from? Is it ASD or open?



Bob, that's ratio for the ASD diff in a 2.5-16.
Edited by Johnboy Mac, Thu Aug 6, 2009 12:02 pm.
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bri957
More than part of things
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Bob

I bought a complete 2.5-16v rear end, subframe - the lot.

I only used the differential, it bolted straight up to mine no problems. I still have the 3.92 ASD in my shed, I'll have a look at the part number on it. I have seen a W124 3.92 ASD differential for sale on German ebay, but only the one in three years of looking.
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feoffle
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After switching from one car with a lower ratio, to a car that's the same but with a higher ratio final drive, you'd be amazed exactly how much of a difference it makes.

I realise this is for a seperate car, but the theory is still the same. This is a table someone made that graphically shows the difference a final drive makes as a torque multiplier, through the gears.

Posted Image

You can see how it lowers the power band in each gear, and how much extra acceleration force it provides.

Gearing isn't where I have a great deal of knowledge, so I can't really explain too well. Hope it makes sense.
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Johnboy Mac
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I presume the top graph is 1st gear and moving on down to 2nd,3rd,4th and 5th at the bottom?
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feoffle
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Correct sir.
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Johnboy Mac
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Ok, feoffle. I'll study the graph again now. Thanks.
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feoffle
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In case anyone is wondering, the "hump" in the lines is when VTEC kicks in y0!
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Martrider
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Longest build time in history?
:lol: Do people still say that? :lol:
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Neil
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Martrider
Thu Aug 6, 2009 4:47 pm
:lol: Do people still say that? :lol:
No, there's a new phrase on the street...

Posted Image
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feoffle
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Martrider
Thu Aug 6, 2009 4:47 pm
:lol: Do people still say that? :lol:
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