The Ford Barn

MII · 03-18-2018, 11:58 AM

I am kind of new at this, but here goes
my 49 Fi really revs up at 55 mph, and the ratio is 4: 27
what is the best solution to drive at 65 and reduce rpms

HDowse · 03-18-2018, 12:20 PM

Others with more experience than I have will chime in on possible solutions. A few choices come to mind: you can change the ring and pinion in the rear end, buy an overdrive unit or even something simple as larger diameter tires. Here's a website that you can play with to see what rpm you are turning at 55 once you measure your tire diameter. BTW, 55 is pretty fast for the design of the truck back then. I'd guess 45 was 'top' speed back then.
http://www.advanced-ev.com/Calculators/TireSize/

MII · 03-18-2018, 01:51 PM

rpm is 2770 at 55 wonder if a complete rear assembly can be adapted that will give a ratio that do 22 2300 at 55

JSeery · 03-18-2018, 01:54 PM

Sure, if that is the route you want to go. What diameter tires are you currently running?

MII · 03-18-2018, 01:57 PM

28.75 od 600.16

19Fordy · 03-18-2018, 01:58 PM

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Overdrive transmission is the best way to go. Most 49-51 Merc cars with 4:27 came with OD. Mercs with automatic came with a 3:31 rear but may be harder to find. Standard transmission Mercs also came with 3:91, 4:27 and 4:55. Or, consider installing a more modern rear.

MII · 03-18-2018, 02:02 PM

thanks Fordy, that will keep me out of mischief for a while
Walt built the engine and it is very good--just started driving it

JSeery · 03-18-2018, 03:38 PM

Yep, looks like the rear tires are already fairly large.

MII · 03-18-2018, 04:20 PM

I will keep it off the interstate til I find an overdrive transmission
is there one that is a floor shift I really don't know how they shift

George/Maine · 03-18-2018, 04:21 PM

Best thing to get a Ford 9"1957 to 72 or s10 4x4 rear-end or explorer.

19Fordy · 03-18-2018, 05:30 PM

MII: Measure the wheel mounting surface to wheel mounting surface of your present rear to find what other rear matches. For instance, the stock WMS to WMS of 49-51 Mercs is 64 1/4 in. 1970-73 Mustang 9 in. is also the same distance. Keep in mind that the wider your tires are, this distance may have to be altered. Rim width and offset also changes what may be needed for adequate fender tire clearance.

03-18-2018, 11:58 AM	#1
MII Junior Member Join Date: Aug 2011 Location: Veazie, Maine Posts: 29	gear ratio I am kind of new at this, but here goes my 49 Fi really revs up at 55 mph, and the ratio is 4: 27 what is the best solution to drive at 65 and reduce rpms

03-18-2018, 12:20 PM	#2
HDowse Senior Member Join Date: May 2010 Location: Hancock, New Hampshire Posts: 375	Re: gear ratio Others with more experience than I have will chime in on possible solutions. A few choices come to mind: you can change the ring and pinion in the rear end, buy an overdrive unit or even something simple as larger diameter tires. Here's a website that you can play with to see what rpm you are turning at 55 once you measure your tire diameter. BTW, 55 is pretty fast for the design of the truck back then. I'd guess 45 was 'top' speed back then. http://www.advanced-ev.com/Calculators/TireSize/

03-18-2018, 01:51 PM	#3
MII Junior Member Join Date: Aug 2011 Location: Veazie, Maine Posts: 29	Re: gear ratio rpm is 2770 at 55 wonder if a complete rear assembly can be adapted that will give a ratio that do 22 2300 at 55

03-18-2018, 01:54 PM	#4
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: gear ratio Sure, if that is the route you want to go. What diameter tires are you currently running?

03-18-2018, 01:57 PM	#5
MII Junior Member Join Date: Aug 2011 Location: Veazie, Maine Posts: 29	Re: gear ratio 28.75 od 600.16

03-18-2018, 01:58 PM	#6
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,944	Re: gear ratio Sponsored Links (Register now to hide all advertisements) Overdrive transmission is the best way to go. Most 49-51 Merc cars with 4:27 came with OD. Mercs with automatic came with a 3:31 rear but may be harder to find. Standard transmission Mercs also came with 3:91, 4:27 and 4:55. Or, consider installing a more modern rear.

03-18-2018, 02:02 PM	#7
MII Junior Member Join Date: Aug 2011 Location: Veazie, Maine Posts: 29	Re: gear ratio thanks Fordy, that will keep me out of mischief for a while Walt built the engine and it is very good--just started driving it

03-18-2018, 03:38 PM	#8
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: gear ratio Yep, looks like the rear tires are already fairly large.

03-18-2018, 04:20 PM	#9
MII Junior Member Join Date: Aug 2011 Location: Veazie, Maine Posts: 29	Re: gear ratio I will keep it off the interstate til I find an overdrive transmission is there one that is a floor shift I really don't know how they shift

03-18-2018, 04:21 PM	#10
George/Maine Senior Member Join Date: May 2010 Location: Mid coast Maine Posts: 1,878	Re: gear ratio Best thing to get a Ford 9"1957 to 72 or s10 4x4 rear-end or explorer.

03-18-2018, 05:30 PM	#11
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,944	Re: gear ratio MII: Measure the wheel mounting surface to wheel mounting surface of your present rear to find what other rear matches. For instance, the stock WMS to WMS of 49-51 Mercs is 64 1/4 in. 1970-73 Mustang 9 in. is also the same distance. Keep in mind that the wider your tires are, this distance may have to be altered. Rim width and offset also changes what may be needed for adequate fender tire clearance.