Re: [VB] Trip Report and Gas MPG

["Thomas J. Tarka" <tommy@xxxxxxxxxxxx>]

On Tue, Jul 01, 2008 at 10:08:38AM -0700, Karl von Salzen wrote:
> Tom said:
> 
>  Oil temps stayed around 220-230 F while cruising at 50-55 mph: higher thanI'd
> like, but something that I've come to be ok with. Hopefully a shift to15" rims
> will help this by bringing down the RPMS ... go go gadget RubberGearing!
> ------------------------------
> 
> 15" rims is not going to change gearing. The diameter of the tire does. Taller
> 14" tires will slow the engine down. BUT it also slows down the cooling fan!


Yup.  The main thought with going to the 15" rims is to get a tire that has a bigger
diameter and an appropriate profile.

It's not clear cut though: I was looking at some 195r15's which - surprise! - 
had the same diameter as a 205/75r15 (27.1") as opposed to what I'd expect
from a 195r15 (27.6").  It may not sound like much of a difference, but it's 
probably a 1 mph difference @3000 rpm (when you're only talking 3 mph difference
overall).  So you have to watch out that you get what you think you're getting
as far as tire diameter goes.

As far as engine speed, a rough consensus from the archives seems to be that 
operating in the 2800-3000 rpm range (or was it 2600-2800 rpm?) was optimal 
for cooling.  This roughly mirrors my experience: if I drive ~50 mph I'm turning 
at about 3000 rpm and I run 10degF cooler than when I drive 53-55 mph 
(~3300-3400 rpm).  This is effected by ambient conditions, but all other things
equal, the relationship seems to hold.  

So, I'm hoping to get closer to that 3,000 rpm mark when cruising at 55 mph.  
Actually getting to 3000 is tough, but approaching it seems like a good idea.

But MAN!  My bus *loves* to cruise at 60-65 mph!  Lots of power, responsiveness,
etc.  I just wish the temps would stay down at that speed/rpm.  

Thoughts?

Cheers,
   Tom

---------------------------------------------------------------------
To unsubscribe, e-mail: vintagebus-unsubscribe@xxxxxxxxx
For additional commands, e-mail: vintagebus-help@xxxxxxxxx
Donations help keep the list going. http://www.type2.com/donate.html