So, I'm running an early-model 59AB flathead, T-5 (.72), 28.03" tall tires, 8.8 rear with 2.73 gears and 180 degree thermostats. When the ambient temp gets above 80, I've seen the temp climb to 206-210 at sustained highway speeds. When I slow down, the temp drops back under 200. In lower ambient temps and/or lower speeds, it never climbs above 200. With the T-5 O/D and rear gear ratio I'm running, at 74 MPH, it's turning less than 1,800 RPMs. At 64 in 4th (1:1), it's turning a hair under 2,200 RPM. I had Jim Linder (Bubba's) test my Pertronix install, and adjust as necessary prior to initial engine assembly. Correct me if I'm wrong, but I believe these crabs are set to not reach full advance until about 2,200 RPM, and that's about what it looks like when I hook up a timing light. I have read that retarded timing can contribute to overheating. So, when I'm cruising at 1,800 RPMs, the timing is not fully advanced, and I'm wondering if that's contributing to the overheating at higher ambient temps? Is there a way to adjust the advance to bring it all in by 1,700 RPMs or so? If so, what would that do to overall driveability?
I’ve seen this happen before with OD. It’s sounds like advancing the distributor to meet your cruising speed rpm will effect your performance at a lower gear ratio. I’d suggest installing a 4 pound cap and also a pressure regulator on your overflow tube to at least prevent coolant loss at high speed. Lowering your rear end ratio may work but it’ll effect your OD for sure.
Put in some 3.00 gears? Gives you a little more umph from the stop signs, and cures the top speed RPM problem. My flathead likes to go down the interstate at 2,600 best. It's weird how it just likes that RPM better than any higher or lower.
Rear gears are wrong for an OD IMO. Especially for the low hp flatty. 3.50ish ratio would work pretty good. Like said above, my flatty in my F-1 likes about 2500 rpm cruise.
Coincidentally I was driving my flatty down the highway yesterday watching the temp gauge and going between 4th and 5th, but not long enough to see a difference. I have 4:10s. Running about the same temps. I have my own issues with cooling, limited radiator capacity, grill, fan space.. Anyway adjusting the vacuum brake on the crab might make a difference. I would guess you would would want it loose for full advance, but I've never really figured out how that confounded thing works.
There’s a basic irony about these engines we love. American engines, especially of this period are low RPM engines. Low RPM engines that were designed for and function best at the higher end of their RPM band. Present day engines are high RPM engines ironically designed to function at a lower RPM due to fuel efficiently and other factors. A modern driver will assume what’s good for the late models must be better still for the old models. This is not really true. The setup you have now would pretty much be like a “Lakes” car in 1950. Just playing around with the numbers from the Spicer RPM calculator. In 5th gear at 3800 rpm (3811) exactly, your car would be at 147 MPH! Like I said.....a Lakes Car. 3800 RPM is based on 1950 specs for R and B series flatheads. Earlier engines are similar with 3500-3600 for 85 hp engines. Let’s look at torque.... Stock torque is reached at 2000 rpm. At 75 mph in high you not even at stock torque peak. Look at this! Think about it...... Top HP (3800 rpm) for a stocker puts you at 150 mph theoretically. At 75 in high your not even into the peak torque for a stock engine(2000) rpm. Again, Lakes car speeds and you don’t have a push truck. Now let’s look how cars were set up in the period per gear ratios...... Standard shift 3 speed......3.73 common 3 speed Overdrive.............4.11 common Automatic...............,..........3.55* common *automatics could have higher ratios especially past 1956. It takes more Rpm and power to run an auto... thus higher gears function better. An old bootlegger trick was to put an automatic rear into a manual shift OD blockader car. 90 mph in 2nd Overdrive! This is not getting into ignition curves and all those rabbit trails. This is based on basic spec data. In closing, these engine are designed to function effectively at a higher rpm. You state your car does fine going through the gears. When going through the lower gears you are closer to the RPMs it likes. In layman’s terms......you are lugging it. That car with a 3.55, 3.73 or even a 4.ll would be a different car living where it wants to, and was designed to live.....At higher rpm than we are used to today.
Another thought that fits right in. When I was running a stock Flathead in my ‘50 Coupe the oil gauge was like a tachometer. Cold after crank up....it would shoot up. After it warmed the pressure would reflect rpm. Idle....pressure would creep down....at speed.....it was right back up there where it was supposed to be. I mention this because at a lower rpm on theses old engines, not only is the timing curve off but there’s oil and water flow.
I'm so sorry. I thought that information may be of some benefit. I know it's basic stuff and I have a tendency to be long winded. If I was condescending, that was not my intent. Speaking of basic stuff...... Sometimes these old cars are missing panels. My '50 F1 and my '50 Coupe were both missing the air panel below the radiator core to the crossmember,to about the axle on the f1. The panels were commonly taken off and never put back on. If missing, this could cause cooling trouble at speed. Again, so sorry.
Don't be sorry. You are just trying to help. If they can't handle the message or the delivery, then that is on them. I agree that the rear end needs lower gears (higher numerically) so that the engine and its cooling system can work more effectively. I use this gear calculator to compare different combos side by side to see how the numbers look. You can change a gear ratio, a tire size, or a transmission ratio and see how it affects RPM and speed. http://www.grimmjeeper.com/gears.html
No reason to apologize F-ONE! You're right, I was thinking current school of engine RPM. I've got a lot to learn about this engine yet. This is a fairly fresh build, so I'm still dialing it in. The rear axle was from a salvage, so plan was to initially run it as-is, but after gaining more knowledge about the flathead, I understand I need to change the gears so the engine is more in it's design RPM range. My plan is to do that over the coming winter. I was just wondering if there was a timing adjustment I could make in the interim. Not a big deal if I can't as I know how to deal with it in it's current configuration. Thanks again!
Absolutely not meant to be facetious F1. I am totally serious. Your sharing teaches us a lot. You just keep on rambling young man and I’ll keep on learning. Thanks again for taking time to explain your thoughts. PJ MKubakak. I never disrespect someone who shares their wisdom and experience.
Thanks. That calculator is better than the one I've been using. Yes, I intend to change the gears. 3.73 might be the best compromise. Sent from my SM-G930V using The H.A.M.B. mobile app
Holy crap I have a 51 merc flatty 3spd od 4.27 rear gear she runs at 185 degrees at 65 mph but she has a gigantic radiator in it. The original all recored.
Ritzy, you’re a cool dude. I am and old fart in NC enjoying a new 40 Ford. I like your questions and your logic.
My current fix is keeping it between 1,600 (65 MPH) and 1,700 (70 MPH) RPM when it's hot out. That seems to keep it below 200 degrees even when air temp is 95. I'm also interested in adding an A/F gauge to verify jetting and to make sure it's not running lean.
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