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06-14-2016, 07:02 AM | #1 |
Senior Member
Join Date: Oct 2011
Location: Central NY
Posts: 629
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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?
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06-14-2016, 07:31 AM | #2 |
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Join Date: May 2010
Location: Chester Vt
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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.
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06-14-2016, 07:40 AM | #3 |
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Join Date: Nov 2012
Location: Wichita KS
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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.
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06-14-2016, 11:08 AM | #4 |
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Location: Central NY
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Re: Proper gearing question
Thanks guys I will do the math and base the gearing on that. Jon
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06-14-2016, 11:28 AM | #5 |
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Location: Central NY
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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.
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06-14-2016, 01:40 PM | #6 |
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Re: Proper gearing question
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06-14-2016, 06:38 PM | #7 |
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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?
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06-15-2016, 04:44 AM | #8 |
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Location: Central NY
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Re: Proper gearing question
Stock distributor crab style with a pertronix coil.
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06-15-2016, 07:22 AM | #9 |
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Re: Proper gearing question
Does it have the proper resistance for that coil?
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06-15-2016, 08:58 AM | #10 |
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Location: San Antonio, Texas
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Re: Proper gearing question
An older tachometer design might not be compatible with a hall effect solid state breaker system.
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06-15-2016, 10:56 AM | #11 |
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Location: Central NY
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Re: Proper gearing question
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