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From: steve sage
To: alpines(at)autox.team.net
Subject: Thanks And A New Question
Date: Thursday, October 08, 1998 4:01PM
>Here's a timing question. I've got more "zip" from the car by advacing
>it. With the idle between 900-1000 RPM, it's set at about 14 degrees (as
>per the book taking 8-10 degrees and adding 4 more at 1000 RPM idle
>speed). Centrifigal and vacuum advance both work fine up from there. It
>still feels like there's more performace there and I'm going to try
>advancing the timing a bit more. 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.
For setting the optimum spark advance, I reccomend using
a chassis dyno. Short of that, buy a G-Tech II, dashboard dyno.
It costs $129 to $139, and uses an accellerometer to calculate
Velocity, position, and road horsepower.
Not the ultimate as far as accuracy goes, but excelent to discern
small changes in engine improvement.
>Final question: I've been lucky enough to find an overdrive transmission
>and all the hardware for my Alpine at a junk yard. It came from a Humber
>Sceptre sedan, of all things, but appears to be exactly the correct
>unit. 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
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