MR RICHARD T TRENK SR wrote:
>
> Tony, my original posting was worded using my best guesswork figures since
> I don't have a car on which to actually make tests and report exact
> numbers. I believe most experienced engineer would accept my remarks as
> being pretty accurate enough for the purpose intended.
> I may be mis-reading your last comment in which you seem to state that you
> "toured with the 3.89 gears and have added a OD unit to THOSE gears??? "
> This would raise the mph/rpm data to where 1000 rpm would make about 24mph.
> Carrying this data out to your "cruise speeds of 3000-3500 rpm, this means
> you cruise I-5 at 72-84 mph .
> You also mention that the car has nice low rpm response in OD !
>
> I too would like OD for highway touring use, but would want the proper gear
> ratio that OD works best at. I simply have a hard time seeing how a stock
> engine could have nice low rpm response when pulling 3.11:1 drive ratio you
> seem to now have.
>
> We all know the word "lugging" which means asking the engine to produce the
> power needed for a certain mph, at too low an rpm. Lugging is very harsh
> on bearings, rings, pistons and anything else which feels the power
> produced at too low a rpm. Oil pressure is not up to full psi and water
> circulation may also be below optimum for safe sustained running.
> In Colo. we have long mt. passes where a car may be on an upgrade for 45
> minutes or more. In such sustained strain, you would want to shift out of
> OD to let the engine "breath" and reduce bearing stress etc. etc.
> High revs DO NOT harm a normal engine, particularly small size import
> engines which can easily spin a 4000-4500 (and higher) all day long without
> any abnormal wear. These same small engines get wrecked or at least have
> early overhauls is they are continually made to work hard at lower rpm.
> I trust you will consider all this and perhaps avoid OD on hills at least.
>
> Jarrid has posted some additional remarks which I also endorse as being
> correct and appropriate to your situation.
> Dick T.
Dick, your points are appreciated and taken. I guess using your
calculations for a 4.22 rear end with O/D gives you a 3.37:1 which is
also quite low, so I guess the same rules might apply.
I am familiar with "lugging" being an ex. Brit!! and I agree that is not
a healthy condition either. I meant to say that in O/D the car will run
at quite a low rpm without lugging and be able to accelerate reasonably.
Not a practise I use but to me it indicates that the ratio setup is a
not too limiting for the car.
Tony Leeming
Series II
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