Jarrid Gross (Yorba Linda, CA) wrote:
> ----------
> "From: steve sage
> "What's the most advance you'd all
> recommend?".........
>
> I wouldnt tread beyond 40 degrees total advance.
> You cant readilly buy gas that will run there, and the likelyhood
> for detonation is nearly assured.
>
> The din of an alpine motor makes it tough to detect detonation,
> so pay very close attention to the sound. Mind your plugs too.
>
>
> " I've been lucky enough to find an overdrive transmission
> >and all the hardware for my Alpine at a junk yard.
> In figuring out wether to stay with my current 4:22 rear end or
> >change over to a 3:89 I have available, I've been playing with the
> >RPM/Speed calculator from the Alpine web page. I currently, with the
> >stock 4 speed, run about 4300 RPM at 65 MPH and 4600 at 70. If I'm
> >figuring things correctly, keeping the 4:22 and adding my new overdrive
> >will get me (assuming .8031 4th speed overdrive gearbox ratio and a
> >3:38 final drive ratio in O.D., which I got from the "Alpine, The
> >Classic Sunbeam" book,) 2800 RPM at 65 and 3000 at 70, which would be
> >amazing and great! Am I figuring things correctly? It seems like a BIG
> >change.
>
> Ive said it before, I dont think you have a 4.22 rear end in your car.
> Even a 4.22 rear should give you 3750 RPM in 4th gear at 60 MPH.
> Me thinks (once again) that either your tach is hosed, or you are running
> a 4.55 gearset or 4.78(externally visible by verifying if the pinion is
> low in the case [hypoid], or higher in the case[spiral bevel]).
>
> Oh, the 4.55/4.78 are spiral bevel diffs.
>
> Math = as follows.
>
> Assume with normal tires and a 3.89 gear ratio, 60MPH yields 3450RPM.
>
> (4.222/3.888) * 3450 = 4.222 specific RPM (at)60MPH = ~3750
> (4.555/3.888) * 3450 = 4.555 specific RPM (at)60MPH = ~4040
> (4.78/3.888) * 3450 = 4.782 specific RPM (at)60MPH = ~4250
>
> So now you have to ask yourself, is my tach hosed, or do I have
> a hillman differential in my car?
>
> Jarrid
Jarrid:
We did measure out the differential and it does appear it is genuinely a
4:22, not higher. The tach SEEMS to be fairly accurate up to 4,000 RPM at
which point it does exaggerate a bit. I can tell, just from having driven
3:89 Alpines through the years, that this car definitely revs higher, by
quite a bit, than those 3:89s, just by "feel", if nothing else.. I do run
fairly low profile Pirelli's on the car and I wonder if this is adding to the
higher than stock RPMs for a 4:22.
In any event, I've decided to stick with the 4:22, or whatever the heck it
is, when I install the overdrive as I like the acceleration I get and I think
the OD will lower the RPMs enough for a lot more comfortable highway
cruising.
As to the distributor advance, I'll try advancing it in small stages, bearing
in mind your caution about getting too agressive.
Thanks.
Steve Sage
This archive was generated by hypermail 2b30 : Tue Sep 05 2000 - 10:19:10 CDT