RPM Ranges?

[ajsimpson]

Hey guys,

I'm still working on my conversion project, but I could use a little help.

If you guys could pay a little attention to your RPM gauges I'd appreciate it.

I'm trying to find out at what RPM your cars like to operate at? What I mean by that is, when your cruising around town, generally where is your RPM? When your cruising on the open road, where is your RPM?

Running numbers to determine where things should be is great, but the real world can be quite a different story.

I think that if I can get enough people to respond, that would provide a good overall feel or average to what's going on in the real world.

Oh, it would be real good if these numbers weren't just limited to 107's. What I mean is any of the older cars would be great as well, ex: 6.9's, etc.

Thanks, A.J.

 

[John S]

On my 450SEL 110 K’s was about 3,200 RPM, on my Calais about 1,800 RPM. The Merc's are definitely undergeared in my opinion, probably to give them sparkling performance overtaking from 90 mph on the expressways in Europe.

 

[ajsimpson]

Hey John,

Thanks for the numbers. I'm trying to gather as much info as I can between the different models. I have a sneaking suspicion that regardless of model the RPM's are going to all come in around the same range. More to the point, though, I'm trying to find out where these engines feel happiest. This information will help determine the gearing from a practical perspective.

Thanks, a bunch

A.J.

 

[ajsimpson]

Ah, I forgot to ask another important question.

What size tires are you guys running?

I'm not going to ask you to go out of your way and measure the tires, although that would be helpful.

I think that I'll be able to manage with a bit of information on the sidewall.

Correct me if I'm wrong, but for the most part, and regardless of model, wasn't the standard wheel size 14" on these older cars?

Are you guys still running with the original size wheels?

Thanks again,

A.J.

 

[Tony66_au]

Ah, I forgot to ask another important question.

What size tires are you guys running?

I'm not going to ask you to go out of your way and measure the tires, although that would be helpful.

I think that I'll be able to manage with a bit of information on the sidewall.

Correct me if I'm wrong, but for the most part, and regardless of model, wasn't the standard wheel size 14" on these older cars?

Are you guys still running with the original size wheels?

Thanks again,

A.J.

206/65/15's 4.5 450SE 2800 RPM @ 100 Kph.

 

[John S]

350SE/SEL 205/70 HR14 21.3 mph/1000 RPM
Max torque @ 4000 RPM
450SE/SEL 205/70 VR14 22.4 MPH/1000 RPM
Max torque @ 3000 RPM
450SEL 6.9 215/70 VR14 23.9 MPH/1000 RPM
Max torque @ 2500 RPM

Generally cars feel most lively from the maximum torque revs, and the gears are set to change down to that point for maximum performance. However, in the W116's the torque curve is fairly flat so the torque peak wont be as noticeable as in other cars of the era.

 

[SEL_69L]

My 6.9 does 3000 RPM at 110 km/hr.

Just as an aside, another car I have, (5 gear 3 ltr maunal):

2400 RPM 5th gear 100 km/hr.

4400 RPM (max torque) 5th gear 184 km/hr.

 

[hoddo]

79 450 slc 215/60R 15 120 kph@ 3000 rpm

seems like the begining of a powerband at 3000rpm the sound of the motor changes at the car just loves it

 

[Tony66_au]

79 450 slc 215/60R 15 120 kph@ 3000 rpm

seems like the beginning of a powerband at 3000rpm the sound of the motor changes at the car just loves it

I found (Remember this is on LPG) that 2800 RPM in top was where the grunt starts and at speeds around 110 you really have to concentrate or you very quickly find yourself doing 125/140 with very little throttle pressure.

I did overtake once or twice after the first few hundred km and the first time was so easy I felt I wasn't going fast enough to comfortably finish the manoeuvre so the second time I manually down-shifted to 2nd and gave her a bootfull and found myself well over the speed limit once I pulled back into the left so the power on LPG is most definately at and above 3000 Rpm.

In contrast from 800 to 2800 she almost seems lazy and sedate but once again a quick flick of the left hand and she wakes up just fine.

Tony

 

[Styria]

Hi AJ, I am not sure just what it is exactly that you are looking for. It's very easy to work out speed ratios per 1000 kms, and equally easy to determine maximum torque at various rev ranges. However, I think you're looking for something different, and that is the most comfortable "built-up" factor when cruising on the open road. I take my mind back to I think your original post talking about 5/6 speed manual transmissions and your somewhat unkind, yet CORRECT, comments regarding your 380SL.

In my experience, just about every Mercedes engine has a "best feel" range, whether that'd be a 6.9 or any of the smaller capacity engined models. Take my European 'dirty' 6.9 with the higher compression engine (8.8:1). There is no doubt that the moment the rev counter needle approaches 2500rpm, the engine becomes more "self propelled" - it's building up momentum and without having to depress the throttle any further, it will pick up 2.7, then 3.0 and will quite willingly keep on picking up speed. You reach 3000, and 120 kms/hr, and the next 500 rpm barely require the slightest touch of the accelerator pedal.

With the M117 4.5 litre, it starts to pick up momentum, but by then you are starting to exceed the speed limit of 110 km/h., but the comfort factor is acceptable. A 220 Finnie has nothing below 4000 rpm, but as long as you 'flog' it above that rev. range, torque is impressive. Drop below, and the engine is like a pricked balloon - dead.

That brings me to the 380 engine - sorry to say but very unncomfortable on the open road at the legal speed limit of 100 or 110 km/h. In top gear, at that speed, there is no momentum, no self propellation. To achieve that, you've got to get to 4000, and then it starts to sing. Unfortunately, at those revs, you are well and truly over the speed limit and you have to ease back and keep on pushing that accelerator to just stay on the legal limit. The 450 is better in that regard, the 6.9 just so superior - just rest your foot on the pedal and the engine will do everything else for you. 6.3s ? I invite comments, but in my view a fairly highly strung revver, and not torquer like the 6.9. Regards Styria

 

[Tony66_au]

True that bit about the 450's, you really have to watch your speed at 110 or you quickly find yourself in license loss territory.

Having owned and driven other marques with larger capacity engines the 4.5 really shines and it would be a very interesting ride with a higher ratio differential.

 

[SEL_69L]

The previous two comments point to one thing: R107's and 6.9's were not originally designed for Australian roads, but for autobahns. They were designed as high speed motorway burners. The 6.9 in particular was meant to transport four fat German businessmen quickly and in comfort over large distances.

Many years ago, (1971, to be exact), I drove between Lubeck and Nurnburg in a day, and the average speed was just a tad under 160km/hr. Traffic densities on autobahns would have been less than they are now. I only wish I had my 6.9 then!

I only had 1.5 litre car then, but it would have been a far more relaxed drive in the 6.9.

I had proposed the idea to my dad back in Sydney that he would get me to purchase a 6.3 on his behalf. You could buy one duty free from Stuttgart for a little over 7000 dollars then. At the time, James Sutherland in Waitara had 6.3's retailing for 22,000 dollars. He could have made a tidy profit at the time, even if he complied with RTA's requirement that he would not be able to sell it for a minimum of 3 years.

I just don't think that he could bring himself to his 25 year old son blasting around Europe willy nilly in a prestige car like that!

 

[Styria]

I'm always amused by the citations of "four large butted German "businessmen" being conveyed in comfort and speed on the Autobahn - don't worry SEL69L, I am not only referring to you as I have read it elsewhere on countless occasions.

What's wrong with a good looking chick sitting alongside you, parked on the edge of a fab look out, admiring the scenery and the lady alongside you - 6.9s stand up pretty good in that situation as well. Regards Styria

 

[Tony66_au]

LOL Motion seconded, Im Dutch but last time I vas in Germany I gave up on the large Teutonic stereotype altogether.

In fact the locals were looking decidedly Middle Eastern....................