Head fire rings

[Rawze]

(05-29-2022 )DVT873 Wrote:  ...
Probably a dumb question. When ratio's are being discussed I do not see trans final ratios mentioned. I have always thought that final ratio was trans ratio x rear axle ratio. If rears are 3.54 final will vary if trans is a .82 OD vs Direct. What am I missing. In calculating road speeds many times over the years I know the trans ratio has to be part of the calculation just like RPM and tire size.

Because the bulk of truck trannies are always 0.73 over in their top gear. I know that some are not.. but the general discussion is usually around that top ratio.

Also, it is due to the fact that the top gear, being 1.0 or 0.86, 0r 0.73 is mostly irrelevant when looking at engine longevity vs rear end ratios. This is because when the engine is working its hardest, like climbing hills, inclines, accelerating from traffic lights over and over, etc... it is NOT that top gear that is the concern, but all of the lower gears vs. the rear end ratio. Making the engine work harder in every single gear due to taller the rear ends is what eats the engine up the most.

Bettering the rear end ratio and letting the engine use higher rpm is the solution to a longer lasting engine no matter what tranny you have, simply because the entire gear train and engine does not have to produce as much torque to get the truck moving at the same rate. Torque is the enemy of wear. Less torque and more rpm to produce the same amount of work from the engine = longer engine life.. no matter what gear or range you are in.

I have driven trucks with directs in them and 2.27' or 3.08's and they will not get out of their own damn way when loaded compared to a truck with a set of 4.11's in it. This even when only usng the lowest gears ... because the engine has to work a whole heck of a lot harder to overcome those tall rears in every single gear and range .. not just the couple gears at the top end that are different.

[DVT873]

Interesting. My exposure was all medium duty, max gross was usually maybe 60k. By the mid 90's almost everything had gone auto, mostly Allison. Did get into some issues with wide vs close ratio. Fall on their face between 3rd and 4th with wide ratio. Taller gear as in 5.57 vs 4.56 gave better launch and stronger pulling thru the midrange. Have never quite got my head wrapped around "torque converter effect" but it is a factor. Above 30K usually is a 3000 series. 2000,3000 and 4000 all lock-up.
Thanks

[Nilao]

I have an oddball tyranny. Mine is a .72 overdrive which puts my 3.55 rears at the speed of a 3.42 with .73 final gears in the tranny...