Chrysler V8 recommended max rpm

[Thomas591]

First I have to mention that I am living in Germany were there is no speed limit on some stretches of the autobahn. I would like to use my 411 S5 for some long distance traveling and I wonder what is the recommended maximum rpm for continuous operation. If I am talking about continuous I mean which would be the maximum save rpm to use for a duration of 30 minutes. Would it be 3000, 3500 or even 4000 rpm?


Regards

Thomas

[David C]

I will be interested to see what others think but with modern oils I can't see why 4000 RPM for 30 minutes at a time would do much harm, but I wouldn't want to pay for the fuel. If you plan to do that sort of sustained speed I suggest you consider fitting an overdrive transmission such as the A518.

[Thomas591]

I am afraid that the heat generated on the piston top can not be dissipated. Due to the absence of a piston cooling system ( spraying engine oil to the piston underside) I fear that after a certain time the piston might melt.

Yes, I’d like to fit a A518 but I think that it needs substantial changes to the transmission and driveshaft tunnel. This would also requires to fit different seating to the car. Nevertheless I would be happy if someone could show me a solution.

[David C]

Unless the 411/5 has a significantly different tunnel arrangement to the 410 there would be no need to alter the seating.
One of the forum members has a 410 with an A518 and I have just fitted an A500 to my 410. This has the same overdrive casing as the A518. We both have the original seats fitted. It's not the simplest of jobs to fit the overdrive 'box but I am very pleased with the result.
It would be interesting to know more about the factory conversions of 411s. I think they probably had replacement 360 cu in engines but I'm not sure. There is now an Ultra -bell adaptor which simplifies fitment to big block Chrysler engines.

It is my understanding that the oil sprayed under the piston on a standard engine will keep the heat down to a manageable temperature but I'm no expert. Big block V8s have done very well in endurance races such as Le Mans, working much, much harder than you are considering for 24 hours continuously. It isn't just the RPM but the load on the engine at that speed that generates the heat.

[David C]

Here's a link to the fitting of an Ultra-bell adapter to a 518

https://board.moparts.org/ubbthreads...ics/35994.html

[Barrie]

To my way of thinking the idea of piston melt is theoretical. I have never heard of a case on road engines. What would concern me more is that, over a period of time, oil may not return fully to the sump and build up in the upper part of the engine eventually starving the sump and causing bearing failure. A warning of this would come by falling oil pressure. On long fast runs on my 440 engine the oil pressure falls but then stabilises. I rely on the oil pressure gauge.
3000 rpm on the Torqflite gearbox is 3 x 26.5mph per thousand rpm so, say, 80 mph. I would have thought that’s easily achievable as would 4000 rpm (110 mph) the difficulty is finding roads open enough to do that continuously even in Germany.

[AndrewA]

Great to see someone's interested in very high speed touring in their Bristol - well done.
The factory claimed a top speed of 140 mph so perhaps if you leave some margin that'd be kinder to the car.
I can't see why there should be a problem using any of the rev ranges you suggest - either for half an hour or longer.
Usual caveats apply about engine in good condition etc.

[Thomas591]

I think the top speed is higher than 140 mph in my car. While checking the Air/Fuel ratio at wide open throttle my engine guy and me reached 136 mph “by mistake”. I can tell you there was quite a bit of “slack” in the accelerator pedal.
If you ask me how it felt… I am not so keen to do it again! The car behaved quite well, but I was too scared to press on. The engine guy was shocked, as he normally does engines for american classic cars. Normally they never go faster that 90 mph on those. He claims that this was the fasted drive he ever had in a car with an US V8…and couldn’t stop giggling for some time.

[AndrewA]

What a flying machine, that's brilliant!
I guess you could ask your chap if he thinks it'd cope with a gentle cruise at 120 mph for a few hours - I suspect he'd say of course!
I've got an old magazine article from the 70's where a chap was on an autobahn in a series 5 411, hunting down 450 SEL 6.9's and the like with great success - will try and dig it out.
Let us know how you get on - perhaps a few early morning runs to see how she behaves when well into three figures?
Cheers
Andrew

[Sam410]

Originally Posted by Thomas591

Would it be 3000, 3500 or even 4000 rpm?

My rev meter is not completely accurate, but I feel I have routinely driven at 3000 rpm (an indicated 4000rpm in my car, but I know it over reads) for long periods (2-3 hours and then you run out of petrol!) on a motorway in my 410 with no problems.