Go Back   The Ford Barn > General Discussion > Early V8 (1932-53)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 06-14-2016, 07:02 AM   #1
JonC
Senior Member
 
Join Date: Oct 2011
Location: Central NY
Posts: 629
Default Proper gearing question

I have started to drive the 40 pickup quite a bite lately and am wondering about gearing. As some of you know I have built a stout motor (I think) with a L100 cam and shaved flywheel. it is a 48 engine with a .060 over bore and sharp heads running 3 holley 94's and runs very strong. I have a quick change in the rear and have been running a set of gears that give me a 3:48 or 4:11 final drive. I live in upstate NY so it is hilly but when running the 3:48's the truck pulls wonderfully. I put a tach in it with a 12V system but I get tach bounce. it ranges fron 2500 to 3500 going down the road at 55 (or so I think) so I really have no idea how fast the motor is turning. It sounds fine and is quiet but I don't know what gearing I should run, does this sound right or would you try a different set?
JonC is offline   Reply With Quote
Old 06-14-2016, 07:31 AM   #2
Ol' Ron
Senior Member
 
Ol' Ron's Avatar
 
Join Date: May 2010
Location: Chester Vt
Posts: 8,842
Default Re: Proper gearing question

Having run many L-100 cams,I find the "sweet spot to be around 24-2600 RPM. With the proper ignition timing this will give the best economy. There are a number of programs on the internet that can calculate your engine rpms to MPH. I run a 3.73 rear with 38& OD which comes out to 2.8 (I thinK). I live in VT, we have a few hills too, but i'm running a stock cam in a 280 engine.
Ol' Ron is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 06-14-2016, 07:40 AM   #3
JSeery
Member Emeritus
 
JSeery's Avatar
 
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
Default Re: Proper gearing question

As O'Ron points out it is easy to calculate the engine RPM to see where your at. I have found that some of the online calculators do not provide the correct results, I would do the calculations by hand, it is not difficult math at all.
JSeery is offline   Reply With Quote
Old 06-14-2016, 11:08 AM   #4
JonC
Senior Member
 
Join Date: Oct 2011
Location: Central NY
Posts: 629
Default Re: Proper gearing question

Thanks guys I will do the math and base the gearing on that. Jon
JonC is offline   Reply With Quote
Old 06-14-2016, 11:28 AM   #5
JonC
Senior Member
 
Join Date: Oct 2011
Location: Central NY
Posts: 629
Default Re: Proper gearing question

OK so if I did this right ?????? with my 28 inch rear tires (235/70R 15) and 3:48 ratio I am coming up with 2297 RPM at 55 MPH, sound right? Now I would like to find out why the tach is not steady, is that a problem because of the dual points? I am taking the signal from the negative side of the coil with a negative ground 12V system.
JonC is offline   Reply With Quote
Old 06-14-2016, 01:40 PM   #6
JSeery
Member Emeritus
 
JSeery's Avatar
 
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
Default Re: Proper gearing question

Sponsored Links (Register now to hide all advertisements)
I wouldn't think the dual points would matter, one set opens the circuit and the other closes it.
JSeery is offline   Reply With Quote
Old 06-14-2016, 06:38 PM   #7
rotorwrench
Senior Member
 
rotorwrench's Avatar
 
Join Date: Jun 2010
Location: San Antonio, Texas
Posts: 16,369
Default Re: Proper gearing question

If it is a modified ignition from FoMoCo stock, the dual point set up could have an effect. Does it have a stock distributor or is it an early aftermarket type?
rotorwrench is offline   Reply With Quote
Old 06-15-2016, 04:44 AM   #8
JonC
Senior Member
 
Join Date: Oct 2011
Location: Central NY
Posts: 629
Default Re: Proper gearing question

Stock distributor crab style with a pertronix coil.
JonC is offline   Reply With Quote
Old 06-15-2016, 07:22 AM   #9
JSeery
Member Emeritus
 
JSeery's Avatar
 
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
Default Re: Proper gearing question

Does it have the proper resistance for that coil?
JSeery is offline   Reply With Quote
Old 06-15-2016, 08:58 AM   #10
rotorwrench
Senior Member
 
rotorwrench's Avatar
 
Join Date: Jun 2010
Location: San Antonio, Texas
Posts: 16,369
Default Re: Proper gearing question

An older tachometer design might not be compatible with a hall effect solid state breaker system.
rotorwrench is offline   Reply With Quote
Old 06-15-2016, 10:56 AM   #11
JonC
Senior Member
 
Join Date: Oct 2011
Location: Central NY
Posts: 629
Default Re: Proper gearing question

Quote:
Originally Posted by JSeery View Post
Does it have the proper resistance for that coil?

Yes I believe it does, I have an internal resistance in the coil 1.5 ohm plus a ceramic resistor on the firewall.
JonC is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 05:20 PM.