was Re: [BFix] Thinking outload gas mileage andEB....nowwhyditchthe lock up

[Quinn Dusenberry]

The idea is to get the engine most efficiently. Take a look at this gear
table and then try to argue the point that 4.10's and 37's is a good combo.
At 65 mph, your engine would be turning 1770 rpm. The only way you were
turning 2200 rpm would be when you were going 80 mph. Either that or your
"effective" diameter was much less than 37" which could be the case.

Your switch to 4.56's is much better, but still not ideal. Keep in mind that
this chart is purely a mathematical table based on the circumference of a
tire. It does not take into account the fact that with a larger
circumference also come more inertia and more weight. You should be gearing
more towards the red side of the chart the bigger your tires get to help
offset the mass and inertia parts of the larger tires.

http://www.4lo.com/calc/geartable.htm

Keep in mind that this chart is just your 1:1 ratio, you need to multiply
all values in the table by your OD ratio (0.73 in your case) to get the true
rpm at 65 mph.



-----Original Message-----
From: Brian Cooke [mailto:nvrstuk at elltel.net] 
Sent: Saturday, May 10, 2008 12:20 PM
To: Mike Bowlin; Quinn Dusenberry; mail at broncofix.com
Subject: Re: was Re: [BFix] Thinking outload gas mileage
andEB....nowwhyditchthe lock up

Not sure why a 351W turning at 2200rpm is bad gearing.  Not like it's 
lacking torque to adequately move me at 70mph except when climbing a long 5%

+ grade in OD. Not sure why I'd need to spin the engine at another couple 
hundred rpm for extended freeway trips is worth it for wear or for mileage 
IMO.  Guess that's how I got almost 185,000 miles on this engine I built 20 
years ago... I regeared to 4.56's last fall to help offset the taller tires.

If this was a dedicated trail rig or used 90% on trail that's a different 
story. Quite a few EB's are driven more miles off road than on-mine is. Even

if you tow your rig to Moab, you're usually putting more road miles on it 
than trail miles in a typical day. 10 miles to the trail head, 10 miles 
back. Trail is 5-15 miles long...whatever...just an example.

Most of you know I also run a doubler off road, so "go slow" gearing isn't 
an issue at all.

You're right, heat is a drawback of more HP. For sand, heavy wet snow and 
mud, you can't go wrong with more HP tho. Crawling over rocks is totally 
different. Just like tires, there's a different drivetrain combination that 
would be best used for almost every terrain.


BTW, ask Jack how much fun having that 408 is too!  :)

Brian

Brian @ Columbia River Broncos...20 forward gears & 4 reverse to choose 
from.