Best Speed/RPM for long engine life ?

[fiddlybits]

I can find a tachometer in my car.... I guess my engine is always at zero rpm.

but... since I know that I roll 91.75 inches for every turn of the tire and there are 63,360 inches in a mile, so I know my wheels go around 690.6 times per mile allowing me to quickly calculate my engine speed at any time by factoring in the rear end ration plus the gear ration that I am in, the current speed down the road (after converting to furlongs per fortnight), accounting for the wind cross angle, cloud cover and phase of the moon and ..... what was the question again?

(low tech = sweet spot at 45 indicated/ 50 actual)

[Dave in MN]

Chris Robbinson has decided to discontinue the production.
I spoke to him a few months ago and he mentioned the cranks would not be available after his stock was depleted.

Dave

Originally Posted by jkcrosson

When were the cranks discontinued. Did something happen?

[gary635g]

A friend has one he put the high compression head on and drove it 65mph to Wellton from Yuma he did not make it, it got to pounding and smoking (oil on exhaust from knocked out rear main) so bad he had shut down and got a lift home on a tilt bed truck.

[vermontboy]

I think people tend to baby them way too much. Thank about all the old AA log trucks spending an hour or two at wide open throttle in low (or low-low) with a full load uphill over the old mountain passes. The "air conditioning" was standing on the running board and steering through the window.

[SeaSlugs]

Got me thinking, there's a few engine RPM calculators out there. Heres one i used:
http://www.powerblocktv.com/resources/

I did for the AA worm drive high speed rearend (5.17:1 ratio) with the standard stock 600X20 tires(given diameter of 32.2") and also in 3rd gear (1:1 ratio for 28/29):

30mph 1619rpm
35mph 1888rpm
40mph 2158rpm
45mph 2428rpm
50mph 2698rpm
55mph 2968rpm

now if you bump it up to the also common Firestone size of 650X20 which has an overall diameter of 34.6 inches:

30mph 1506rpm
35mph 1757rpm
40mph 2009rpm
45mph 2260rpm
50mph 2511rpm
55mph 2762rpm

I think im going to get the slightly larger 650-20 tires to make it slightly less of a traffic obstacle and also what Ive heard is true: AA's are most happy at about 35-40 mph cruising.

For S&G i tried what the low speed worm (7.25:1) rear axle would do with standard 600x20 tires:

15mph 1135rpm
20mph 1513rpm
25mph 1892rpm
30mph 2270rpm
35mph 2648rpm
40mph 3027rpm

aint going anywhere fast but could climb up a tree if you wanted!

Anyone got what the ratios are for 1st and 2nd gears in the standard 3 speed tranny?

Could calculate absolute max speed or what rpm your at at a certain speed in a certain gear. (like on my modern pickup i know about every 10mph increase in speed the engine is at about 2100 rpm)

[tbirdtbird]

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Become intimate with automotive engineering. Look at the torque/HP curve, study it, and figure out what it is trying to tell you. It is plain as day.

[stouchton]

Here is an old rule of thumb - 2/3 Redline RPM or RPM of peak torque - whichever is lower.

Ok... that is for marine engines. And I've got no idea what the redline RPM is of a stock A motor, nor do I know of a dyno curve. If SeaSlugs numbers are representative of MAX rpm, then I would keep my cruising RPM at 2000.

[modelAtony]

Originally Posted by jkcrosson

When were the cranks discontinued. Did something happen?

Some of the cranks were having bad quality problems , like breaking on end. Have fun modelAtony Lafayette,LA

[tbirdtbird]

dyno curves:
http://www.modelaparts.net/dynosheets.htm/dyno1.htm

you can get anything you want on the internet

[Tom Wesenberg]

Notice where the spark advance is on the chart Tbird listed.
It's 30*, which is NOT full down.
Full down is 40* and IMHO is too much advance for most of our Model A's and especially if you have a higher compression head, which requires even less advance.

[stouchton]

Tom - do you think 2700 rpm is the redline? Wasn't sure why the dyno test stopped at this point, although it was falling off the torque curve quite quickly.

[Tom Wesenberg]

2700 would be my redline. I'm not sure who or how the red line is determined, but going past the peak horsepower is more harm than good to the long life of an engine IMHO. These are long stroke engines and give good torque at lower RPM, than most of today's short stroke engines.

[stouchton]

Originally Posted by Tom Wesenberg

2700 would be my redline. I'm not sure who or how the red line is determined, but going past the peak horsepower is more harm than good to the long life of an engine IMHO. These are long stroke engines and give good torque at lower RPM, than most of today's short stroke engines.

Thats a good point - if the hydrocarbon burn is not being put to work as mechanical energy, it is toasting the motor.

With that in mind, 45 mph seems like a conservative "cruising" based on the HP curve and the 2/3 marine rule of thumb (assuming 3.78:1 rear and 4.75/5.00x19 tires).

50 mph would put it right at the end of the peak HP curve.

[fiddlybits]

I make 690.57 revolutions of the tire per mile and with a 3.78 rear end that should give me:

30mph - 1305rpm
40mph - 1740rpm
45mph - 1957rpm
50mph - 2175rpm
55mph - 2392rpm

It has a "warm fuzzy" feeling at 27mph, 40mph and 53mph (gps speeds, not indicated)

As for a redline, here's my take.

First, for most stock engines you do not want your piston speed to exceed 3500 ft/minute and piston speed is simply calculated by the stroke times the rpm divided by 6.

So: at 3000rpm our pistons speed would be 2125 ft/minute, which is still a 30% margin.

How about 55mph...or 2392rpm? well, that comes out to 1694 ft/min piston speed, or about half of what would be considered red line.

So, what's my redline? Frankly I'm not going to worry about it. I'm going to drive my car sensibly and enjoy it knowing that the car basically will limit itself.

[Gunmetal blue2]

Does any body make the counter balance weights to weld to the crank or have a drawing and measurements of one [so that you can make them].

[CarlG]

Originally Posted by Gunmetal blue2

Does any body make the counter balance weights to weld to the crank or have a drawing and measurements of one [so that you can make them].

Berts has them: A-6216 Counterweight for crankshaft $8.00
http://parts.modelastore.com/show_Product.asp?ID=3541

[tbirdtbird]

what, exactly, is to be accomplished after 2200 in a stock motor? Your HP is past peak. Your torque is long past peak. Your dynamic compression ratio has turned to crap. (dynamic ratio is always less than static ratio and gets worse with revs.) You have a non-counter weighted crank. You have a center main that is undersized for the job. You have a long stroke motor with a very high piston speed. Think about it.....

And Tom, I agree with your timing advance observation....30 is plenty for a stock A. In fact the FSI electronic dizzy maxes out at 26-28 degrees. A stock long stroke motor will not do well with a lot of advance...not enough 'burn' left in the chamber after the piston swings past TDC...you will actually lose some torque and risk knock

[Brother Hesekiel]

Which makes me wonder . . . how to advance properly on a flat road?
I start fully retarded, and then go pretty much to the 9 o'clock position. How many degrees would that be? Should I retard a bit when idling at a red light? When should I advance more, and where would the 30 degree point be?

[Tom Wesenberg]

Originally Posted by Brother Hesekiel

Which makes me wonder . . . how to advance properly on a flat road?
I start fully retarded, and then go pretty much to the 9 o'clock position. How many degrees would that be? Should I retard a bit when idling at a red light? When should I advance more, and where would the 30 degree point be?

A lot depends on the compression your engine has.
I have a stock head on a worn engine and have 50 lbs. compression.
I start the engine at full UP, which is 0*. As soon as it starts I pull the lever half way down, which is 20*, then leave it here for all around slow driving. When I'm driving about 30 MPH or faster I pull the spark lever down to 2/3, which is about 28*.

With a higher compression head I would need less advance. With a Snyder 5.5 head I might not have to go past half way down on the spark, and maybe 1/3 down for idle. If you pull the lever down and feel no increase in engine speed or power, then you might be advancing it too far.