Tom,
1. I see what you mean thanks. But isn't loaded radius the height of the
axle above the pavement? If that's the case it seems to me that radius is what
governs the effective circumfrence of the loaded tire. Dividing that
circumfenece into a mile gives revs per mile. My quarter mile simulation
program shows 22.3" diameter for a 205x50-15; 22.4" for a 195x60-14; 22.4" for a
185x70-13; 22.6" for a 165x80-13; and 21.7 for a 5.90-13.
The revs per mile (respectively) are 906, 900, 901, 893, and 931. Not a lot of
difference; only about 25 revs per mile for the 205 versus the 5.90 (about 3%).
That would only effectvely change a 2.88 to a 2.97; not enough to notice
probably.
2. Gotcha, you meant the specifcs of the Boss 302. I agree, for a road
racer, with close ratio gears most of the driving would be up in the higher
RPM's. Quite unsuitable for the street.
At any rate I've decided to go with a wider ratio top-loader 4-speed
transmission (2.78 low) and leave the rear end alone at 2.88.
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From: "Tom Ballou"
Sent: Wednesday, May 29, 1996 6:25 AM
To: 76276,1555
Subject: re:
1. The rolling radius (loaded radius doesn't matter - think about it) of a
205/50x15 is dead stock for a Tiger (941 revs/mile) (165x13 = 185/70x13 =
195/60x14). BFG has published a neat little guide which shows both radii and
revs/mile.
2. The Boss 302 cam requires special lifters because it has a different
radius on the lobes and lifters. But that doesn't really matter as long as
you match them, the real problem is that the Boss 302 cam ( and the rest of
the set up) was tuned to produce high rpm power for Trans-Am racing. The
engine idles poorly and actually produces less power than a 289 "k" engine
below about 3400 rpm; however, it is a powerhouse from there all the way to
7400. I think the cam has a similar grind to the "Le Mans" cam which had a
similar power band (and equally bad idle and bottom end). There are much
better cams for street cars, and actually there are much better cams for
racers today (remember, this cam design is almost 30 years old), the roller
hydraulic cams, for example, which can package significantly more effective
opening with shorter duration and much less overlap than the cams of the
60's. Ain't technology great?
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