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Why was the 6.3 quicker than the 6.9?

Started by raueda1, 15 June 2018, 11:50 AM

raueda1

0-60 mph is almost a full second faster, though top speed is a bit lower.   The euro 6.9 weighs about 4oo lbs more but has significantly more HP and torque.  Seems like the higher power would compensate for the weight.  Just a matter of gearing and axle ratios?  This troubles me because I want my 6.9 to be faster than any 6.3 out there.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

Off the line the 6.3 will beat the 6.9 but if you have enough road the 6.9 will catch and pass the 6.3. Ultimately there ain't no substitute for cubic inches ;)
Daniel
1977 450 SEL 6.9 - Astralsilber

orientrot

I'd imagine the 6.3 having a 4 speed transmission vs the 3 speed in the 6.9 is a big part of it.
75 450SEL
80 300SD- cancelled project
83 300D- 5-speed OM617
84 300D- AMG 5.4L N/A M113 6 speed
92 300D- 722.6 OM603 3.5
93 190E 2.6 Sportline LE x2- 6-speed M111 turbo, 3.0 M103
02 C320 Wagon
03 Sprinter 2500
06 E500 4Matic Wagon- AMG 5.4L NA M113

TJ 450

Yep, the 4-speed plus the considerable weight gain with the passive safety improvements of the W116.

Also, the 6.9 was geared towards a higher top speed rather than outright acceleration, even though it is more than respectable.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

oversize

Purely down to gear ratios and if you compare the two the reason is obvious. I think the 6.9 was also intentionally choked as a primitive form of traction control. If they'd aimed for the full potential of a M100 all they'd get is wheelspin, loss of control in inexperienced hands and a lot of high profile embarrassing collisions.

The 6.9s acceleration is also not helped by the extra weight and apparently the anti-dive, anti-squat rear suspension. Ive heard rhe primitive 6.3 setup actually helps traction!
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

TJ 450

Yes, it's all done for a reason. I'm not sure about better traction on the 6.3, one day I will compare the two. I do know that the 6.9 is practically unbreakable in comparison to the 6.3, where the rear axle is fragile at best, so an amount of wheel spin is its torque limiting device. It also squats in an extreme fashion.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

oversize

If you watch many street drag races, you'll notice a huge weight transfer to the back wheels. Something the 6.3 does well and the 6.9 does not.
I wonder how it would go with wider semi slicks & the anti-squat disconnected?
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

TJ 450

That's true, but the same physical situation applies to the 6.9 (or any car), it's just that there are compensating elements in place to keep the car reasonably level, the same forces are still present.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

TJ 450

You could fit the basic rear end from a 350 for no anti squat too.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

s class

I agree with tj, the 6.9 maintains a level stance during takeoff, but the weight transfer is still there.  The lack of squat means minimal change in rear geometry and alignment, so the rear wheels maintain near optimal contact patch, which is a contributor to the lack of wheels spin.  On a 6.3, the extreme squat changes rear camber such that contact is only on the inner shoulder, and wheels pin is highly likely.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

oversize

Sounds about right, so that rules out the anti-squat theory. Looks like it'll all be down to gear ratios. The extra weight should be offset by more torque & power...

It might've been mentioned before, but how does the 6.9 throttle diameter compared to the 6.3?
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

TJ 450

From memory the 6.3's is actually larger by a few mm, although I can get exact measurements.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

oversize

Given the 6.9 is roughly 10% larger in ccs, that makes no sense and gives more weight to my intentionally choked theory!
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

oversize

Here's the ratio comparison:

cc  1st  2nd  3rd  4th  Final

6.3 3.98 2.46 1.58 1.00 2.85

6.9 2.31 1.46 1.00 na 2.65

As you can see the 6.3 has a very different 1st gear and the final drive will also make a significant difference across all gears.  I wonder if MB decided the 6.3 was too much of a tyre-frying hot rod for their luxury image at the time?
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

rumb

'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio