107 high revs at 70mph

[43722]

Don't know if it is normal but at 70mph my 280sl is at 3500-4000 rpm, it is a 4 speed box, the manual says it should start in first however I only ever count 3 gears? has anyone else found their SL low geared? other question how do I get my name and details to show up as at the moment

 

[sjg]

High Revs

I think this is a standard problem. The 280SL is high revving (max. torque well over 4000rpm etc) so MB seem - in those days - to have fitted an auto box that gives only 20mph per 1000 rpm in top. So at 70mph mine is belting along along at 3500 (rather than the 3,000 rpm you'd expect on a modern box). The engine is very smooth at 3-4000 rpm but the fuel consumption horrible. I'd love to find a cheap way to solve this - but replacing rear axle etc or fitting a newer auto box (even if possible) would not be cheap...

 

[mlc]

I have a 1972 350SL with a four speed manual. This is geared to about 20mph per 1000 revs and I understand that the auto should be similarish. You have to remember that these cars were designed for a US market where fuel costs were (and still are really ) negligible, not 2005 UK at £4 per gallon. The plus point is that the cars have lively acceleration even though they weigh so much.

Mark.

 

[SLinKyjoe]

I have a 1972 350SL with a four speed manual. This is geared to about 20mph per 1000 revs and I understand that the auto should be similarish. You have to remember that these cars were designed for a US market where fuel costs were (and still are really ) negligible, not 2005 UK at £4 per gallon. The plus point is that the cars have lively acceleration even though they weigh so much.

Mark.

The SLK does 3000rpm and 75mph with the 5 speed auto. Just for your reference.


I did laugh when I was in the US last year. They are really up in arms about the fuel costs increase they have had to bear lately. A whole us gallon cost a whole $2.08. so with my really bad calculation that works out at todays exchange rate of 29p a litre for us. or £1.30 a gallon. in my case £20.30p($37.80) to fill my tank rather than the £56.70 it would cost in real terms today. which is $106.03. And they moan.

Tell you more. My car cost $64,982.50 and the i could have got one over there for $53,000. Mind you it is Yank spec and left hooker. plus import costs.

ps. I spent ages calculating the gallons to litres bit as their yank gallon is 3.79litres.....and todays rate is $1,87 to the £1...cant be bothered with the Euro conversion. corrections by the more mathematically astute accepted.

and if someone says it is actually 3.7852 i shall burst.

all figures approx. No liabilty etc

 

[mlc]

Uncle Slinky - we know all about your SLK! but we are talking about real MB sports lightweights here, from a time when men were men and women were greatful, when getting around the next corner was a matter of skill rather than electronic control, when 200 miles between top ups on a 20 gallon tank was a success and CAT's were not part of the MOT

Before you get too carried away with the 2004 model 171 and how advanced it is consider how advanced the 107 was at its launch. The entry level 350 was around 200bhp, the US safety rules for convertibles were rewritten to ensure that all future cars were as strong as the 107 SL. The car had electronic injection and an on board computerised management system, which has the added advantage that since it is all transistors it acts as additional heating to the passenger compartment. What it didnt have is any pretence of economy, but the early 70's were a different time.

On the cat front the early 107's were different for the California market, having a device in the upper front pipe of each bank that attempted to burn any remaining fuel - we would call such a device a CAT - MB called them after burners, they only lasted a couple of years before things moved on, but I quite fancy the idea of a car with after burners.

Mark.

 

[SLinKyjoe]

wasnt meaning to cause an issue. Just mentioning that if my was in 4th it probably wouldn't be far off the revs mentioned in the thread. so even tho it may well be 30 years on you can bet the insides are similar. And i am not sure i was gloating? far from it.

I would have something like you have it if wasnt wasted on my mechanical skills. I can open the door but thats about it. Best leave it to those who can i say. at least they get proper looking after. and long may they live.

But i think that the revs mentioned above are not that high when you consider it. It is probably that we have become more used to higher gearing.

still hope that clarifys things before I get booted off the forum for being a pain.

 

[mlc]

Slinky, your not a pain, I think you're the most fun guy on here at the moment

I suspect your right, in round figures 4th will be similar in both cars but the new model has another gear left. The problem is that for economy you would want to be able to cruise at nearer 30mph per 1000 revs, which I supose why many cars are moving to 6 and 7 speed boxes to give them the best of both worlds.

Keep up the good work, it gives me something to do whilst taking a break from pressure washing the decking.

Mark.

 

[SLinKyjoe]

missed a bit over there look~~~~~~~~~~~~~~>

 

[SLinKyjoe]

and at the risk of coming over all daft.

washed the slinkymobile today, well it is sunday, and took it for a drive...at 70mph it is doing 3400 rpm in 4th and 2850 in 5th.

bear in mind i didnt check the accuracy of the speedo so it could be 3500 at 70 and so on.

i realise it is a different car but it points out that the original posting probably is right.