S38B36 - Maximum Continuous RPM? - The Unofficial BMW M5 Messageboard (m5board.com)

Northwester · 19th June 2007, 20:33

A simple question.

What is the maximum continuous RPM one can operate the S38B36 engine at? This is assuming that all of the engine systems such as lubrication and cooling are working as designed and the engine is delivering the correct fuel/air mixture to the cylinders.

Is it 4500, 5500, 6500......................?

Mmm-Five · 19th June 2007, 20:46

I've driven at a more or less constant 4000rpm for about 100 miles before now - if I'm cruising then anything above that is a bit jarring.

I suppose in the Vaterland it would be possibly to keep 5-6000rpm up for a good while - although I don't know how long you'd be able to stay at the exact same revs with traffic.

miles · 19th June 2007, 21:03

Criusing with wife 160-190 Km/h (Noise from passenger begins to be more than the wind & motor together ).

Alone 180-220 Km/h conditions allowing .

My 3.6 only gets used on the Autobahn. & I dont run less than 4000rpm after it warms up . I dont thrash it but I run the rpm spectrum. 3rd gear is always a delight.

My motorcycles get used the same way 1975 Triumph T160 & 1977 Rickman Kawasaki , & to date I have never killed an engine.

MM

farrell · 19th June 2007, 21:31

Just a view point.
I generally consider maxmum rpm that you can run the engine at, as those quoted by the manufacturer in the owners handbook.
Assuming that you do not have the handbook, maximum safe rpm = up to 7,250 in each gear.
Thats nothing to do with peak power which occurs @ 6900 rpm as quoted.
It should be noted that the E34 M5 & many other production saloon cars are limited to 250 kph.
Many will exceed this speed when delimited including the E34 M5.

That does not automatically mean that the cooling system & the engines physical construction will remain stable at wide open throttle @ 270 kph for long periods even if the car is capable of reaching this speed.
I think a test centre environment or a very long deserted stretch of Autobahn ( rare these days !) @ 270kph with an adverse ambient temp would bring a cooling related failure in not many kms.

I do think that you could keep the E34 M5 at 250 kph in top gear all day long though.
This would have been part of the high speed durability sign off & cooling calibration would have been designed to meet this.
Assuming the vehicle is well maintained, this would still be the case.
The S38 B38 will reach close to 270 kph, the B36 a little less.

Farrell

Northwester · 20th June 2007, 00:03

Thanks for the feedback.

I was working on the notion that just because the reciprocating/rotating parts and the valve train are rated to turn a certain maximum RPM, it does not necessarily follow an engine will stand up to continuous use at or near that maximum RPM for lots of reasons. That notion is mainly borrowed from marine applications where most engines have a continuous duty rated RPM that is somewhat less than the maximum or intermittent duty RPM.

I also asked the question out of curiosity mainly because I recall reading somewhere that some and maybe all M30 engines (without modification) have a propensity to pool oil in the valve train as a result of it not draining back into the sump quickly enough when run continuously at high RPM.

In any event, all things being equal, it sounds like it is open to me to run around at 5000-6000 RPM all day long if I really want to, provided that the radiator gets enough airflow to properly dispose of the heat and that the engine oil temperature remains below 130C.

Long live the S38!

nixter · 20th June 2007, 10:43

how are you enjoying the car so far?

unesential · 20th June 2007, 14:17

There is a difference between operating parameters of marine and auto engines in that a typical marine engine life is rated full power hours. When running at speed they are power output is relatively constant at a set RPM. Auto engines athough running at a constant speed must have continuos variation to compensate for different road conditions. So although running high in the curve you will not be high in the power output. Downhill : uphill, level cruising.

This is why service indicators are different in air/marine powerplants as opposed to motorcar. Engine hours vs mileage. A hard driven motorcar is not accounted for in this.

John

Northwester · 20th June 2007, 18:39

Quote:

Originally Posted by nixter

how are you enjoying the car so far?

Now that I'm getting to know the car, I'm enjoying it more than ever. I never ever believed that driving an automobile could be so much fun until now.

Don't tell my wife that I'm now looking for an E24 M635 or M6 to go with it!

It's going in for a service next week to get a leaking oil pan gasket replaced. While we are at it I'll have an oil and filter change done along with new plugs, rotor, distributor cap, air filter and oxygen sensor.

Are you going to the German Car Festival Nikolai? If you are which of your automobiles will be coming with you? Or will you bring both? I will be catching the 0630 ferry and meeting the group at Tim Hortons on Marine Drive.

de Witt · 20th June 2007, 18:55

Hmm maybe Ill see you on the roads in early July, if you are down near Sidney. I have a boat at Canoe Cove.

Northwester · 20th June 2007, 19:08

Quote:

Originally Posted by de Witt

Hmm maybe Ill see you on the roads in early July, if you are down near Sidney. I have a boat at Canoe Cove.

Canoe Cove is a very nice spot to keep a boat moored. Power or Sail if I may inquire? I live in Nanaimo and don't often go to Sidney but I could be persuaded to give away some of my secret techniques for catching salmon with the right inducement.