RPM Question

[MurphyJ]

Where can I find information on what RPM's my engine is running at different speeds and in different gears? What is the max (Red Line) for
a Model A engine. Torque curve too? So far I have been unable to locate a previous thread that addresses my question. Thanks again.

[Richard in Anaheim CA]

A stock Model A engines torque is maximum at 1000 rpm and the max horse power is at 2200 rpm. If you engine is in good shape you should be safe to run between these two speeds all day long.

Many won't drive their A over 45 mph yet many more drive 55 mph which is over 2200 rpm.

You need to find your cars "sweet spot". You may get vibration at 40 mph but it will be smooth at 47 mph or 50 mph. If you are getting severe vibration at less than 45 mph that won't go away at higher speeds you need to find out why it is vibrating and fix it. Henry Ford bragged that all Model A's would go 65 mph right off the assembly line. I don't think anyone would feel comfortable driving that speed for any length of time.

If your speed falls off going up hill and you engine sounds strained, you need to back shift to 2nd gear.

Don't worry too much about your speed. Our speedometers read all over the place. When you are going 45, my speedometer may read 50 mph and your friends, 40 mph.

Richard
Anaheim CA

[Richard in NC]

I used to have a little tachomoter designed for any engine 1 cylinder on up. It had a wire about 3 feet long that you fished through a hole in the firewall and wrapped around a spark plug wire(strip) several times. It would read rpm and doubled as an hourmeter. I don't know where you can get them because mine came from work and was used when i got it but I was told they are inexpensive.

[johnbuckley]

e-bay is a place to look for simple tachometers- I bought mine for the quivalent of about $15, don't look right in a 1930s car as they are digital and plastic , but comparing it with an optical tachometer ( also ebay!) and an old Gunson analogue one it proved to be surprisingly accurate.

2600rpm with ratio 3.70 with 21 inch wheels=58.1 mph, with 3.54 ratio=60.7 mph.( and about 2 mph less for 19 inch wheeels) - You'd have to be hammering a stock A to get 65 mph and the ones that have passsd through my hands sit comfortably at 40 -45 mph most of them if you take over that you feel it's thrashing them

[steve s]

Does this help? One of the real mechanics on this board posted dynamometer data like this a while back. I hope that Mr. Piranio doesn't mind me reposting.



Steve

[Chris in CT]

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Hi Murphy, All good answers above, assuming you know what your rear end ratio is. With that information you can calculate just about anything. You can raise your "red line" by a good 1000 rpm by adding a good counterbalanced crankshaft to the mix, whether this would be with added weights, or one of the two available new forged cranks. Adding the counterslung crank would necessitate removing 20 lbs from the flywheel and becoming more active with accurately adjusting your timing while driving. Happy Motoring!

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www.burlingtoncrankshaft.com

[MurphyJ]

Once again guys I can't thank you enough for your response and information, amazing! This is the best forum that I have ever seen. Many thanks again.
Murphy J.

[MrTube]

What does "corrected horsepower" mean?

I get the same HP as the non-corrected by doing torque x rpm / 5252 which as far as I knew was the standard formula.

[Sparky]

Originally Posted by MrTube

What does "corrected horsepower" mean?

I get the same HP as the non-corrected by doing torque x rpm / 5252 which as far as I knew was the standard formula.

Lots of info here:

http://www.land-and-sea.com/dyno-tec...horsepower.htm