A Die Hard Ford guy told me that a Model A would run on Interstate, without overheating. I told him I have seen too many overheat running 65 to 70MPH on Expressways. His smart answer to me was: Then Da** well wasn't put together right. He got real loud and obnocious, because I have seen too many overheat on Interstate. According to him, he is the only one right. They are not geared for interstate, w,ith a stock Model A Engine. If you build a Race car with a 4:56 gear in it with 350 Tranny, it will overheat running 70 & 75 MPH. It makes the Engine work harder. A 700-R4 is a little better.
I don't know if he's right or wrong, but having owned a few stock Model A's none I ever had could do 70-75 down hill, let alone sustained on a freeway. Guess I never got one of the good ones!
All I know is that they do well in Parades, because of going slow. I don't think this guy was listening too close, because he is the only one that knows anything! LOL I know a guy that tried to run with us on Interstates, he had two, and they both overheated, when he tried to keep up with us. He sold one and got himself a nice '37 ford, Street Rodded, and no problems. I raised my son witha wrench in his hand, and today, he Manages a Big shop near Cinn. I told him some of the stuff he said, and he said I have to listen to that kind of stuff all the time.
Are you arguing both sides of this debate, or are you making a distinction between the cooling effectiveness of stock Model As and your modified Model A?
Since stock Model A's do not have thermostats, coolant flow through the entire cooling system varies greatly with 1) temperature of coolant going in to the radiator and 2) coolant pump speed. I believe the overheating issue was because at 65-70 mph (doubt Model A's can do that stock...) the engine rpm and pump shaft speed is so high that the pump is pushing coolant through the radiator faster than the rad can cool the coolant. The end result is ever increasing coolant temp and eventually overheating. A neat experiment would be to install a temp gauge on the radiator inlet and outlet... run the car at speed & monitor the difference in coolant temp.
Stock, I know of many people that say he thinks he is God, and just ignore him. This guy is a Antique Guy.
Rogi, you are exactly right, he says the Engine wasn't built right ! don't get me wrong, I like Stock Engine Cars, but they came out with over drive for a purpose.
I have a stock '31 RDPU with 3.54 gears. I used to routinely go up grades like the Grapevine in Califorrnia at 55 (the speed at which it was comfortable). Many newer cars would be parked at the side of the road with their hoods up overheated. Charlie Stephens
I like Modle A's too but the cooling comes from Radiator, and the Water Pump. They were designed to run at 50 MPH, and they run fine that way. Remember, they didn't have Interstates back then.
I have two banger powered Model A's, one is inserted from H&H, the other is counterbalanced. Neither will run 75, they both have 3:78 rear gears and are 50-55 mph cars. A good A won't overheat if it is driven at a reasonable speed. This means not overbored, good radiator, timed right, running a thermostat and they won't cause problems.
After cleaning the mouse nest out of the radiator my A never over heats. It runs 60 65 very well. My top speed on gps is 73 I don't hold it long but it gets me out of the way when need be. Some day I will put the 5 speed in it and see how she does with over drive.
That theory doesn't hold up to physics. The more coolant you get through the radiator, the cooler the engine will run. Likewise, the more air you get through the radiator, the cooler the engine will run. What could happen is that there might be a dead spot where airflow through the radiator is limited due to bad aerodynamic effects at a certain speed. That might cause a car to run hot. I think that the timing and fuel tune are important, but keeping the engine RPM down would be a better idea in general...
If your car is totally stock with 4:11's 50 is reasonable and safe for the RPM range. Time it right, keep the advance in it and a clean radiator and it'll run cool. But for fun here is a solid formula tried and true: 7:50 -16s on the rear or the 19-21's with tires equaling 31" with 3:54 gears in the Banjo. Doesn't matter if you have an A box or V8 as they are both 1:1 out the tailshaft. 2500-2800 RPM and 70 is an easy cruise and 75 is completely doable. I prefer the 16" wheels because they have less shake and I like the spokes better. Have fun and enjoy the car. Tim
This is only partially correct. The coolant has to hang out in the radiator long enough to exchange heat with the air passing through. If you run too much coolant through (velocity) it will not have enough time to exchange heat before it returns back to the engine. This is part of the reason we run thermostats. They help keep the coolant in the right range by limiting or increasing flow rate of coolant. Now, of course "more coolant", meaning a bigger radiator (more volume of coolant and a larger area to dissipate heat) will cool better compared to stock, but as a general rule, you need the fluid to sit in the radiator for a certain amount of time in order for the radiator to do it's job. The more efficient the rad, the less time the fluid has to sit in it.
I think what you are saying is true on a micro scale, but not at the scales we are talking about. If you split the coolant into little 1 cubic inch chunks (I know, silly, but imagine it) ... Now imagine that the radiator can hold 100 ci of coolant. You could push 100 ci of coolant through the radiator, and each 1-ci chunk would spend 1 minute in there. Or you could push 200 ci of coolant through it, and each 1-ci chunk would spend 30 seconds in there. If you rush a whole bunch of these chunks through the radiator, each chunk will have less time to transfer heat to the radiator tubes, then to the fins, then to the passing air. So less heat will be shed by each cubic inch of coolant. I agree so far. But if you push twice as many chunks through, they will make up in volume what they give up in time. In an ideal world, I think both options should shed an equal amount of heat at the radiator end. But that ignores how much heat they are picking up at the engine end. The difference in temperature between the engine and the coolant is probably going to be higher than the difference between the coolant and the air, so potentially, more heat will enter the coolant in 1 second than leaves it in 1 second. For that reason, I think you would want a much longer coolant dwell time in the radiator than in the engine, or the engine might be able to "overpower" the radiator. So you would want to size the radiator so it can shed heat at the maximum rate that the engine is likely to generate it ... and all that has to take place on a hot summer day. Then you throttle the coolant flow down with a thermostat, like you said, to avoid overcooling the engine. Consider that a partially closed thermostat decreases the volume flow rate, and automatically increases the dwell time that the coolant spends in the radiator. Yet the partially closed thermostat keeps the engine warmer. In this case, longer dwell time means less heat shed and more heat retained. I believe that is because the heat differential at the engine end is much higher than the heat differential at the radiator end. When the engine starts to heat up, the only way to cool it is for the thermostat to open and increase the flow rate (and the speed) of the coolant, which reduces the coolant's dwell time in the radiator. The only situation I can imagine in which a short dwell time in the radiator would lead to an engine overheating would be in the case of a radiator that was just undersized to begin with. And in that situation, slowing the coolant flow down won't help.
Thats' right, no amount of coolant velocity will cure a radiator that is not sized correctly to begin with. Too much dwell time in the radiator is bad, just like not enough dwell time is bad. That's why thermostats or restrictor plates (some racers don't want to risk a thermostat sticking and costing laps or performance) exist. It's really rare in the real world to run into too much velocity of the coolant, but in something like an A, given the constraints on radiator surface area/efficiency to extract heat, I could see it as a possible cause.
If you do some searches on heat exchanger efficiency/fluid thermal transfer coefficients/dwell time/flow rates and thermal loading you'll find that Rogi is correct. For a fixed/limited heat exchanger size there are thermal loading limits, however, there is a 'sweet spot' where thermal loading and heat transfer are balanced out and that is accomplished by optimizing coolant dwell time in the tubes.....and typically controlled by your thermostat. Your particle theory has some validity in that "particles" conduct a thermal load to the tube/fin then to air but you forget that the only particles conducting heat to the tubes are ones in contact with the tubes....the "particles" near the center of the tube ID need to conduct heat to the particles next to them then to the ones against the tube wall then to the outside....and that takes time....dwell time.
the guy who said his overheats above 50, did not have his timing right and or his carb adjusted too lean. although every A i have seen run for long periods of time over 50 mph started knocking.
Most is over thinking something that has worked for over 80 years. Like said above (Timing and a Clean Radiator) The A radiator is a huge radiator for the size of the engine. The bad part is the tubes get fill with grease from the water pump and water can pass. If that happen to half the tubes then you are only running a radiator 1/2 the size. Timing is every think with the little banger. To little and it has no balls to much you put a hole in you piston (don't ask) I run the balls out of my car from a 25 deg day to over 100 deg. And it is always cool. Last summer I went 7 straight weeks of driving nothing but my A I get pissy if I don't drive it at least 2 times a week to work. I love passing slower cars To help with less stress on the engine I am running 750-16s out back a mild cam valve spring spacers poring 6.5 to 1 head Single 94 and a header most of the time open. All this talk about over heating.... just for fun ask about the brakes And yes I to love the HAMB
Sorry but he's right. If the water goes through the radiator too fast, it does not cool properly. Guys used to put a flat washer in the water neck to slow down the water flow long enough to cool it. Now all you need is a thermostat. This is fact - not theory! As far as the reason why a can Model A overheats is because the cooling system lacks all the things we have learned about keeping engines cool. Zero pressure radiator, no recovery system. dinky fan, small water pump, pig iron motor. Don't get me wrong. "A's" can run cool all day long. Push 'em and they will heat up.
So how much of timing is trial and error and how much is science. It sounds like I am set up similar to you, and am running right at TDC. Runs good with no known issues. If I decide to play around with it, what kind of advice would you give. Oh, and I love the hamb too.
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