Im putting together the pieces for a roadster using a stock '37 221 flatty. I have looked everywhere to find the basic rpm range for these engines. I know modern engines go 6500 no problem, whereas my '29 model A banger is 350-2750 approx. I dont plan on hopping up the engine but want to know whats the usable rpm range without tearing it up? I am using the stock 3-speed and 3.78 rear with 6.00-16's. Will this cruise the interstate @ 70 without winding it too high?
These are the rpm calculations I have made,sound right? 6.00-16 tire 28" 3.78 gear, 1:1 drive 50mph= 2268 60mph= 2721 70mph= 3175 80mph= 3628
Here is a calculator that will give you all the answers. http://car.race-cars.net/calculators/mph_calculator.html A safe infrequent redline for your engine will be about 4500 rpm.
My '38' engine (stock with 60thou over in the bore) loves cruising at 70MPH. Engine sounds good and she ticks over real nice.
If your asking redline I'd say 5k is probably it for most stock or mild flattys. I don't think I'd cruise at 70 with a 3:78 rear for any length of time without an overdrive. My car really liked 55 before the OD, now with the OD it doesn't mind 70.
for a stock 221 you could expect 3500...maybe 4k if you push your luck .thats a long stroke with a very conservitive cam weak springs, small carb etc. it was made to run ideally at 50 or 60 and wont lke 70mph very much
The question is ......."how high is too high". By that I mean that while the engine may (?) be able to do it, will you find the elevated rpm annoying on a long drive. You might try taking whatever daily driver you have and driving it in 3rd/4th gear (1:1) at 3100 rpms at whatever speed it happens to be and see if its comfortable or annoying. One of the biggest reasons many people don't drive their hot rods is because they geared them too low and made them annoying to drive at road speeds. Second, the flathead will not have an abundance of power and may struggle to pull at lower rpms. I'd look for articles on flatheads that tell you how much torque to expect at various rpms and adapt a 5 speed behind it.
Based on my experience with flatheads, the speed you're going is tied to coolant temp, too long above ~ 2500-2600 and the temp will climb and you'll have to slow to around 2200 or less. What that rpm is in mph is whatever your diff gears/tire size gives you. I have had one engine that would go 65 on level road in 90+ heat all day long so you might get lucky with yours but the last one would only do 55 in those conditions without getting above 190-200.
You will cruise just fine. Most *stock flatties can be made to spin 4800-5000. They will not want to run at that speed all day but they can be made to spin that tight. A thing to bear in mind about RPM/Speed calculators is that it is just an estimate. They do not take into consideration wind drag or slippage in the drive train. So the numbers can be close but no cigar. *stock being a relative term here.
I agree with this for the most part, the exception being that I believe the greater heat generated by the engine is a result of aerodynamics, not increased revs. I have a good running 255 Merc in my '51 Ford club coupe. The engine has reworked Edmunds heads, a 2G, and a Mallory dual point. It has 3.55 rear gears, no overdrive (yet), and 225/75R15 rear tires. The car seems to be quite happy cruising anywhere between 2300 and 2700 RPM. At 2700 RPM, the car will go down the highway at slightly over 70. After that, more revs become progressively noisier, and at 4000 (although it will turn higher), it's all done. It will go faster, but after 4 or 5 miles at 80 mph, the temp gauge starts creeping up. Like @RAK, I then back off. I attribute this increase in heat to trying to push a 3200 lb. brick through a bunch of increasingly denser air. I'm a firm believer in overdrive, having had it in a previous car. I have stock unit ready to install, not for increased speed, but for less noise and engine wear.
Funny, being he had an avatar of Joliet (Jake) Blues, maybe it is time the HAMB put the "banned" back together again. Oh and to stay on subject. I have a 5000 rev limiter on my flathead to be on the safe side.
Sorry guys! I'm the culprit. Had asked a question offline with no answers. One quick google search brought this thread up, and it answered my question. Sent it to a buddy to indicate the question was answered and everyone jumped on like it was a new thread. Again, apologies....let sleeping dogs lay!
No problem.......bet somebody out there wanted to know the same thing........ Seriously ? ....... Not the 5000, but you have a rev limiter on a flathead? Seriously ?
I've had it over 4000 a time or two and that was exciting, between my heart pumping and my wallet throbbing I thought I was having a stroke. The limiter chip makes my ass cheeks not pinch as tight.
I used to “power shift”(never let off the throttle) my 47 English Ford Prefect(4 dr Anglia) at 5200-5300(289 in flathead) and “missed”the 1-2 shift(glanced at tach and saw 5800-6000) but engine suffered no ill effects. 5800-6000 is the highest I have ever buzzed a Flathead 4 in stroker whether intentional or unintentional.5000-5200 was normal and car ran 14’s at 93-94 mph. Also ran a light alum Weber flywheel with bronze liner and ford 9 in clutch—-never had any slippage problems.
I've had two flathead 221 engines that loved to go 70 MPH. As mentioned, though, keep your eye on the temp gauge. My 255 Merc engine with 3:54 gears really perks up at 70, but...................
So are we doin this? I say why not. Fresh well tuned but stock 239, OG 39 trans, 3.78 gear, 7.00/16s around 30 ½" tall. Any calculations I do I come up with just around 2700 at 65. That's just 700 RPM over avg peak TQ, 1000 under peak HP. Can't say just yet but it should have enough room to roam.
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