Posted by RDavis on Sunday, February 24, 2002 at 9:43AM :
In Reply to: Am I ready for Diesel????? posted by Doug Higgins on Saturday, February 23, 2002 at 10:53PM :
There are two problems to be overcome when adding higher speeds and 5:83 gearing.
first is to reduce the engine and drivetrain rpms.Anything over say 45mph raises the noise level greatly and is not really good for the engine or drivetrain due to excessive rpms. The fuel mpg efficency is reduced also. So first you should consider the method by which you plan to reduce the rpms, ring & pinion gearsets, taller tires, or overdrive unit, or a working combination of any two. No mater what engine you repower to, it will run at less efficient rpms with the lower gearing and higher speeds.Some will argue different but we all know, the lower the rpms of a drive train to accomplish the same result, is better for everything involved.
Next you will find that with a 230 and even a 251 you will be underpowered so as to take efficient advantage of the regearing as a daiy driver on the streets and hiwy. You may now reach a higher topend speed but it will take longer to reach that higher speed due to being underpowered so, now you must repower to whatever will handle the taller gearing but not put too much hp and torque into the driveline,over powering can harm drivetrain parts. A hemi or other big block mopar is really too much for these old PWs in my opinion,they don't need that much hp and torque.If one could control the urge to use the spurs on those big blocks, it would become only a matter of fitting that monster under the hood. I believe a small block V-8 mopar or diesel should be sufficient to handle the taller gearing.
OD units are expensive by the average guys standards but so would two new installed ring&pinion gearsets, as well as a good set of 38"-40" tires. I'd try to stay away from using excessive tire size to regear with as it puts stress on the clutch,axle shafts and steering components. A comination of 4:89 gears + 38" tires would be good or a OD unit as a stand alone.
These are just my opinions based on my limited knowledge of actual hands-on doing. I have read and watched over the years all the many ideas and experiences of others plus my own experiences.And while its not rocket science,you can never give anything too much thought before you make your decision.