dutchmeister Posted February 3, 2011 Report Share Posted February 3, 2011 Cleaned the crud off the carrier and found 4.3 stamped on it. I've been told I couldn't take the truck over 45 mph as the rods can't take the RPMs. Can I go say 50-55 mph with this gear ratio, or do I need to find a 3.9 to 1 if I want to go faster than 45? Hmmm, I'm 63 and maybe going only 45 mph will make it seem that time isn't going bye so fast. Quote Link to comment Share on other sites More sharing options...
JBNeal Posted February 3, 2011 Report Share Posted February 3, 2011 My '48 has the 4.1, and I could drive it around 55mph, but there was an odd vibration that radiated through the floorboards and not the steering wheel. So I self-governed to 45 mph, and that 218 seems to agree with that kind of loading. Quote Link to comment Share on other sites More sharing options...
Reg Evans Posted February 3, 2011 Report Share Posted February 3, 2011 Find some tall tires for the rear and then when the speedo says 45 you'll really be going 50 or more. Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 3, 2011 Report Share Posted February 3, 2011 this is a question I'd like a solid answer to as well as I have a 4.3 in my 1 ton...is 50 or 55mph gonna hurt the engine? Quote Link to comment Share on other sites More sharing options...
TodFitch Posted February 3, 2011 Report Share Posted February 3, 2011 I have the stock 4.375:1 rear end and 17-5.25 tires on my 1933 Plymouth and have run it all day at 60 MPH. The engine will be turning over much faster than modern ears are used to, but it is within the designed RPM range of the engine a bit below the 3600 RPM for max BHP. If you have an engine of unknown condition, I'd hesitate pushing it that hard. If there is any ridge at the top of the cylinders getting it to high RPMs could cause just a little more piston travel leading to breaking the top ring and potentially cascading into more severe damage. But if your engine is fresh, you should be able to run it at 60 with the stock rear end. I did touch 70MPH once last fall (as measured by a GPS in addition to the speedometer) but that is definitely over speeding the engine and neither the suspension nor brakes were designed for that speed. My passenger looked a little concerned. Quote Link to comment Share on other sites More sharing options...
dutchmeister Posted February 3, 2011 Author Report Share Posted February 3, 2011 I just rebuilt the 230 top and bottom so after break in I should be OK. Many years ago I heard an engine does better if after break in it is ran at the higher rpms along with in-town traffic. T or F? Obviously they don't mean redlining the crap out of it. Quote Link to comment Share on other sites More sharing options...
Reg Evans Posted February 3, 2011 Report Share Posted February 3, 2011 this is a question I'd like a solid answer to as well as I have a 4.3 in my 1 ton...is 50 or 55mph gonna hurt the engine? Here's what I meant about a taller tire making a difference in rpm's TIRE SIZE COMPARRISON Specification Sidewall Radius Diameter Circumference Revs/Mile Difference 205/60-16 4.8in 12.8in 25.7in 80.7in 785 0.0% 235/85-16 7.9in 15.9in 31.7in 99.7in 636 23.5% Now plug the different tire diameters into this rpm calculator below to see the difference in rpm's at any given speed. http://www.csgnetwork.com/multirpmcalc.html Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 3, 2011 Report Share Posted February 3, 2011 I have the stock 4.375:1 rear end and 17-5.25 tires on my 1933 Plymouth and have run it all day at 60 MPH. The engine will be turning over much faster than modern ears are used to, but it is within the designed RPM range of the engine a bit below the 3600 RPM for max BHP.If you have an engine of unknown condition, I'd hesitate pushing it that hard. If there is any ridge at the top of the cylinders getting it to high RPMs could cause just a little more piston travel leading to breaking the top ring and potentially cascading into more severe damage. But if your engine is fresh, you should be able to run it at 60 with the stock rear end. I did touch 70MPH once last fall (as measured by a GPS in addition to the speedometer) but that is definitely over speeding the engine and neither the suspension nor brakes were designed for that speed. My passenger looked a little concerned. I debate about putting a "pull out/hideable" tach on mine just to make sure it sin't going around too fast... So you are saying a fresh rebuild should be good! Quote Link to comment Share on other sites More sharing options...
Young Ed Posted February 3, 2011 Report Share Posted February 3, 2011 Mark what size tires will you be running? That makes a big difference. My truck with 218-85r16s and a 3.90 diff goes 55 easily. And I'm sure it would handle more but it starts to feel unsafe above that. My car with 15s and a 3.73 goes 65 with ease. Once you have your tire size use the calculator and figure out what RPM you'll be running at a given speed. I personally like to keep mine at 3K or under. Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 3, 2011 Report Share Posted February 3, 2011 Ed, haven't gotten that far yet...maybe 17's.... Quote Link to comment Share on other sites More sharing options...
Young Ed Posted February 3, 2011 Report Share Posted February 3, 2011 Ed, haven't gotten that far yet...maybe 17's.... Well then I suggest using the calculator as part of your research when buying tires. The taller the better for top speed. Quote Link to comment Share on other sites More sharing options...
JBNeal Posted February 3, 2011 Report Share Posted February 3, 2011 the phrase "drive it like ya stole it" is more succinct than what I was told. Driving at varying speeds, hammering the throttle on hills, making more rpms before shifts up and downshift braking help to get the rings broke in well in the first 500-1000 miles. Dad drove my '48 after I had the engine broke in good, and he was surprised at how much more power that 218 had than when he had driven it on the same hilly roads 30 years earlier. I just rebuilt the 230 top and bottom so after break in I should be OK. Many years ago I heard an engine does better if after break in it is ran at the higher rpms along with in-town traffic. T or F? Obviously they don't mean redlining the crap out of it. Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 3, 2011 Report Share Posted February 3, 2011 well according to the calculator, even at 65mph and 16" (32") the RMP is only about 3K.... Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted February 3, 2011 Report Share Posted February 3, 2011 Be aware that back then, tire size was also used to dictate load rating. Smaller tires just couldn't handle the loads and the gear ratio was changed to be able to get the load moving. Most engines have a "comfort range" of RPM and work and live well within it. They also can run above that RPM but it reduces the engines longeveity and efficency when done for extended periods of time. I'd be surpised if the "comfortable" RPM on the this flathead was above 3200 RPM. JMO. Quote Link to comment Share on other sites More sharing options...
TodFitch Posted February 3, 2011 Report Share Posted February 3, 2011 well according to the calculator, even at 65mph and 16" (32") the RMP is only about 3K.... Be aware that back then, tire size was also used to dictate load rating. Smaller tires just couldn't handle the loads and the gear ratio was changed to be able to get the load moving. Most engines have a "comfort range" of RPM and work and live well within it. They also can run above that RPM but it reduces the engines longevity and efficiency when done for extended periods of time. I'd be surprised if the "comfortable" RPM on the this flathead was above 3200 RPM. JMO. Yep. See http://www.ply33.com/Misc/speed#calc 3200 RPM is about 60 MPH on my 1933 Plymouth. And if I'm going long distances on a freeway, thats where I keep it. Back roads at 35 to 45 MPH are a more interesting and fun though. I debate about putting a "pull out/hideable" tach on mine just to make sure it sin't going around too fast...So you are saying a fresh rebuild should be good! Why bother with a tachometer unless you are speed-shifting? On a manual transmission car the relationship between engine RPM and speed is fixed for each gear. I haven't bothered to figure out the max speed for first and second since I'm not racing, but I know that 60 MPH on my car is about 3200 RPM based on rear end ratio and mounted tire diameter. And 3200 RPM is my personal limit for sustained cruising on that engine. So I know that 60 MPH is the limit for sustained operation. I did get my speedometer calibrated and I do check it from time to time against a GPS. So I have a nice big instrument on the dash, thoughtfully provided by the factory, letting me know how fast my engine is turning over. Just in MPH rather than RPM. Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 3, 2011 Report Share Posted February 3, 2011 @TodFitch yah, I guess. It's been so long that I drove a vehicle w/o a tach I guess I just like to know where the engine is. My '00 328i was just fun to watch the tach! Now way back on the farm, the tractors had nothing, just the noise, and I guess I'm just not used to that! Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 4, 2011 Report Share Posted February 4, 2011 I just compared the two calculators posted here and they have a huge differential (no pun intended) in results.... Quote Link to comment Share on other sites More sharing options...
TodFitch Posted February 4, 2011 Report Share Posted February 4, 2011 I just compared the two calculators posted here and they have a huge differential (no pun intended) in results.... Between http://www.csgnetwork.com/multirpmcalc.html and http://www.ply33.com/Misc/speed#calc ? When I plug in my rear end ratio and mounted tire diameter, the http://www.csgnetwork.com/multirpmcalc.html calculator says 62MPH is 3242RPM for a manual transmission. When I plug 3242RPM into http://www.ply33.com/Misc/speed#calc it returns 62 MPH. Seems like a small differential to me. I am a bit confused by the various outputs at http://www.csgnetwork.com/multirpmcalc.html for "Auto", "AOD", "Manual" and "5 Speed". I am guessing that AOD is "auto with overdrive". I am also guessing that some slippage is assumed for the two auto outputs. And I am assuming that they picked a fixed reduction rate for the overdrive and "5 Speed". All that seems to match up with the explanatory paragraph at the top but I don't see what overdrive reduction or final drive reduction is for the 5 speed is assumed. Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted February 5, 2011 Report Share Posted February 5, 2011 OD's have different final ratios varying from about .68 to .75 or there about depending on which one you have. Quote Link to comment Share on other sites More sharing options...
Kensoldtruck Posted February 5, 2011 Report Share Posted February 5, 2011 I have a 1949 1/2 ton with the 4;10 gear. I also had a 48 with the same gear. I changed the 48 to 12volt so that I could put a tach on the truck. 48 to 52 mph was about all the truck wanted to handle. I met a guy who had a 39 Plymouth. He swapped the rear end out for an Aerostar 3:45 gear. He said that he can get over 70 mph and the car handles it well. I asked him about how the car stops from higher speeds. He said that thus far he has been able to get by without any panic stop situations. Scarebird has a kit that will allow disc brakes to be installed on the front to bring the truck to a stop. Going fast is good, but being able to stop is "priceless". Quote Link to comment Share on other sites More sharing options...
grey beard Posted February 5, 2011 Report Share Posted February 5, 2011 Mu '48 Pilothouse half ton used to have a 4:56 rear and would only do 50 mph down hill with a tail wind. Now I have a 3:56 differential center section from a '48 Windsor. That swap made all the difference in the world, and now I can stay with local traffic on interstate roads. My tires are tall - 215-86x16's on stock truck rims with no tubes, and are about 29 inches tall. I couldn't be more pleased with the end result of the rear end swap. If anyone attempts this gear swap, you must also use the axles from the donor vehicle that fit the side gears. My origihal axles would not go in. Also, I had to keep the same pinion shaft yoke. I put a new seal in before I installed the new lump, and thought I could use my original yoke, but had to change back to the one that came from the donor to keep everytging happy and get the drive shaft to go back into place. Believe me, the difference in top speed was worth all the work. I'm happy! 1 Quote Link to comment Share on other sites More sharing options...
ggdad1951 Posted February 5, 2011 Report Share Posted February 5, 2011 (edited) Between http://www.csgnetwork.com/multirpmcalc.html and http://www.ply33.com/Misc/speed#calc ?When I plug in my rear end ratio and mounted tire diameter, the http://www.csgnetwork.com/multirpmcalc.html calculator says 62MPH is 3242RPM for a manual transmission. When I plug 3242RPM into http://www.ply33.com/Misc/speed#calc it returns 62 MPH. Seems like a small differential to me. I am a bit confused by the various outputs at http://www.csgnetwork.com/multirpmcalc.html for "Auto", "AOD", "Manual" and "5 Speed". I am guessing that AOD is "auto with overdrive". I am also guessing that some slippage is assumed for the two auto outputs. And I am assuming that they picked a fixed reduction rate for the overdrive and "5 Speed". All that seems to match up with the explanatory paragraph at the top but I don't see what overdrive reduction or final drive reduction is for the 5 speed is assumed. yah when I was playing with it was a big difference, like 10mph...maybe I was just being dumb somehow... just redit it all...I was being dumb! D-oH! Edited February 7, 2011 by ggdad1951 Quote Link to comment Share on other sites More sharing options...
MarkAubuchon Posted February 6, 2011 Report Share Posted February 6, 2011 anything over 55 with 4.30 gears, 1 ton or bigger and biased ply tires you will do it ONCE. the sound of that little flatty rapping out to 3,000 plus RPMS, no sound deading material, body sway etc. It will be fun, but probably not something you will want to do for a couple of hundred miles:eek: Quote Link to comment Share on other sites More sharing options...
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