Redline

[meadowbrook]

Hey guys I am wondering what is the redline of the 230 engine? Is it really 3600 RPM? What happens if you exceed it? Is it valve float territory? Would the engine scatter? What is the weak link? What would be the maximum sustained RPM you would recommend?

[greg g]

3600 is where the peak HP is achieved, not the readline.  However, the 230 had nearly a 5 inch stroke, long stroke engines by design make their torque pertty low in the rpm range and their peak HP about about 3x that number. Some have suggested 5000 as peak rpm for an unmodified engine, but twisting it that high seems bad for their health and doesn't seem to make a lot of difference in acceleration or speed.  Most reports here from folks with tachs  to center on 4200 to 4500 as max for street work.

[TodFitch]

The standard for Chrysler engineering back in that day was for the engine designs to be able to survive a 50 hour test under load at wide open throttle at 3600 RPM with no evidence of damage. So the redline value is going to be higher than 3600 RPM.

 

I've only seen one factory torque and horsepower curve for the L-6 engine and the engine in question was a Canadian one which is more like a Chrysler or DeSoto engine than a Plymouth or Dodge. That chart went to, if I recall correctly, 4200 RPM. So I'd put maybe 4000 as a reasonable redline.

 

For everyday driving, especially for cruising longer distances on the highway, I use 3200 RPM which with my 4.375 rear end works out to just over 60 MPH. You guys with new (1940s) cars with 4.11 rear ends ought to be in the 65 to maybe 70 MPH range for long distance cruising.

 

My impression is that Chrysler did a fairly balanced job of engineering: The suspension and brakes get pretty scary when you exceed the speed the original drivetrain was designed for. So if you are "upgrading" the engine, transmission or rear end for higher speed you really ought to be looking at the brakes too.

[Plymouthy Adams]

one of the things I do not like is the shocks at higher speed..the stock configuaration leaves a lot to be desired and car seems just to much of a floating boat at about 75+ I have yet to do my shock relocation..thought I would hold off till the time I also need to do brakes and do the disc at the same time...but for everyone I know and the cars I have driven with the relocation...it is by far as much a safety item as it is anything else...

[james curl]

I was told no to exceed 85% of the rated horsepower RPM for extended periods of time.  I have run mine at 75 MPH which is the speed limit on most of the rural roads here in Texas to keep up with traffic and not make every one mad by being a rolling road block.  That is cruising at close to 3600 RPM with my 3.55:1 Dakota rear end, I have done this hours on end with no difficulties so far in 20,000 miles

[Plymouthy Adams]

this is a tough question to answer..I do not recall any real specifics on redline anywhere...but given that most are based on piston speed and that is considered about 4000 on stock engines and even higher on race or well built performance engines to the tune of 7000 piston speed...one can do the math of the stroke x rpm/number of cylinders...so lets say 4.375 stroke times 4800 rpm divided by six slugs gives you a piston speed of 3500  well below the 4000

 

I believe the valves as they are pure mechanical can handle this and the bottom end if within specs and good oil pressure...you could be safe..but then...this is just posting the rule of thumb as most use for a reference...I also would not recommend this unless you know that there is no ring ridge at the top of the cylinder..common sense has a lot to do with making this determination...you need to know your internals of the engine.....

 

most folks also consider the better shift point some 500 above the peak HP rpm so that would say 4100...again..only you know how much to push your engine...your engine will talk to you if you listen closely...again..most lal this is mute unless you have a good tach to measure you rpm...

 

this is just information as gleaned from reading many articles on the subject...

 

 

NOTE...as a side note here for whoever may be interested..I did the above math formula on one of my engines here....not sure of the actual readline but the factory shift point is set at 6200 RPM in any gear if you hold the pedal to the metal..( say any gear as I have never ran to this RPM in third..got in enough hot water with the law just running out second gear....anyway..... math on that is 3.19 x 6200 / 6 = 3296.33 piston speed...

Edited June 26, 2014 by Plymouthy Adams

[Lumpy]

Adams is right...! An engine's redline is generally related to piston speed. And that value is usually used when stroking engines. Oil delivery is another one, sometimes depending on the engine, oil won't go down side galleries, won't make sharp turns over a certain RPM, so some bearings will starve for oil. I know that with small block Chrysler V8's, you have to do some modification to the oil system and galleries to safely run at higher RPM than 5500. (and exceed that by quite a bit)

 

Generally speaking, flatheads red line around 4000-4500 RPM. My flathead Harley's factory redline is 4400, not much different than a Dodge 230. I believe that with the motorcycle engine, it is piston speed, as just about everything in the engine is on roller bearings, which does not require a lot of pressurized oil. In fact they have been known to run for over 100 miles with no oil pressure. (and the pre-1936 engines had NO oil pressure, period, just splashed-oiled like a Briggs&Stratton)

 

Flatheads are generally long stroke engines, which of course reach unacceptable piston speeds faster than a short stroke engine.

 

With OHV engines, how long the push rods will hold up and not bend is a factor, and of course spring pressure limits RPM in either a OHV or a flathead. Flatheads don't have pushrods to bend (underhead cam!) but the valves will still float.

 

Then there's my BMW motorcycle's engine, which runs best at 4250rpm, I mean it's loafing, which always amazes me to think that at that RPM, the '37 bike or Lumpy would be very unhappy. They'd be talking to me! But the BMW redlines at only around 7500rpm, which is way under what many newer motorbikes redline at.

 

So yeah, 4000-4500rpm would be the normal redline for our flatheads. And of course with any engine, it's not going to like being held at redline, whatever it is...really you would only go there for short periods of time, seconds, such as running through the gears aggressively or something like that...maybe if you were running for your life!

 

k.

Edited June 26, 2014 by Lumpy