[DeTomaso] Pantera Si

Fri Dec 20 10:48:20 EST 2013

same people, that doesn't want to drive a bone stock standard Pantera.

From: Mikael 
Sent: Thursday, December 19, 2013 9:10 PM
To: MikeLDrew at aol.com ; timepiecepr2 at yahoo.com ; thomas at hax.se 
Cc: detomaso at poca.com ; jderyke at aol.com 
Subject: Re: [DeTomaso] Pantera Si

" that it just drives beautifully, like a completely modern car compared to a standard Pantera", who wants that?! J

Mvh/Regards

Mikael

Hass Consult ApS

+45 31770747

mikael_hass at mail.tele.dk

Fra: MikeLDrew at aol.com [mailto:MikeLDrew at aol.com] 
Sendt: 19. december 2013 19:37
Til: timepiecepr2 at yahoo.com; thomas at hax.se
Cc: detomaso at poca.com; jderyke at aol.com
Emne: Re: [DeTomaso] Pantera Si

In a message dated 12/19/13 8 38 2, timepiecepr2 at yahoo.com writes:

Can you summarize the upgrades that made the car so much more modern and civilized. I am just curious.

>>>The entire suspension system was redesigned in keeping with modern practice.  The standard Pantera was state-of-the-art at the time, but then again, a horse and buggy was state of the art in ITS time too.  The early Pantera uses control arms that are extremely short by modern standards, and wheels with a negative offset (and in the case of the GT5, an extremely negative offset).  This means that for a given amount of wheel travel in the vertical plane, there is a relatively large amount of angular change in the suspension arm.

Consider a standard 12-inch ruler.  Hold it horizontally, then move one end of it up and down six inches.  Now consider a 36-inch yardstick.  If you do the same thing, six inches of vertical movement at one end results in much less angular difference.

The same holds true with auto suspension design.  The Pantera Si uses control arms that are substantially longer, which spaces the hubs much further away from the centerline of the car.  If you bolted standard Pantera wheels on, the tires would stick out about a week.  So instead, it has wheels with fairly pronounced positive offset--the vertical surface of the wheel is relatively flat (particularly in front) and the rim extends inwards and envelops the hubs/brakes.

If you look at a normal Pantera suspension and compare the kingpin centerline (the imaginary line between the upper and lower ball joint, where the steering spindle rotates) and the centerline of the tire contact patch, where both touch the ground, you'll see that there is a pronounced difference, with the contact patch centerline being several inches outboard of the kingpin centerline.  The difference between where these two lines touch the ground is called the scrub radius.  The Pantera has a fairly large scrub radius, which raises steering effort and magnifies road shock, as an impact to one wheel has a leverage effect.  That's why when you hit a bump with your right tire, for instance, the steering wheel tugs to the right and you have to correct it.

(Replacing the stock 7-inch front wheels with 8-inch wheels helps correct this, as doing so reduces the scrub radius a half inch because the extra wheel width is all inboard of the wheel centerline).

The Pantera Si with its longer A-arms has much less scrub radius, so the suspension is much more immune to unwanted feedback transmitted by bumps.  I don't know for a fact, but I suspect the steering axis inclination (SAI) figures are better as well.  SAI is the angle between the kingpin line and the imaginary vertical line of the center of the contact patch.  Angling the SAI inwards causes the spindle to rise and fall as the wheels are turned one direction or the other, which in turn raises the suspension slightly. This causes the suspension to attempt to seek its low (center) position naturally, which allows the design to rely less on positive caster to keep directional stability.  Positive caster delivers stability at the expense of higher steering effort; achieving stability through more SAI and less caster allows the same stability with less steering effort.

What this all means from behind the wheel of the Pantera Si is that it just drives beautifully, like a completely modern car compared to a standard Pantera.  Driving a regular Pantera on a bumpy road requires a degree of concentration, because even with the bump steer optimized by shimming the rack downwards (which De Tomaso/Ford did starting in late '72-early '73), the bump steer curve is still there, and the scrub radius means the steering wheel is tugging at your hands constantly.  By contrast, a Pantera Si just glides across those same road imperfections, with the suspension moving up and down to absorb bumps, and delivering only wanted feedback through to the wheel.  Steering effort is probably about the same as a regular Pantera, or perhaps a bit less.

Another terrific Si improvement is the brakes.  It wears the same Brembo brakes as the Ferrari F40, and they are simply leagues ahead of the stock Pantera brakes, or even most aftermarket systems that I've tried, in terms of power and feedback.  There is NO power assist (no brake booster at all), yet due to changed brake pedal geometry, pedal effort is about the same as with a normal Pantera, but ultimate power and feedback and control are much greater.  The pedal feels nice and firm, very mechanical.

The cabin is beautifully trimmed, and things like wind noise are controlled a bit better as well.  Overall the car is much quieter going down the road, due in no small part to the engine which is as weak as a kitten, and the EU-compliant exhaust system which mutes it even further.

Most of us know the feeling after driving a Pantera for many hours at a stretch.  You get out of the car and you are pretty tired.  I'm confident the same would not be true after making that same drive in a Pantera Si.

FWIW I've heard that Pat Mical has developed a bolt-on suspension package that does away with all the stock control arms, hubs and spindles and emulates the Si design; it necessarily requires new wheels as well.  Obviously that is not a conversion for the faint of wallet, but I imagine it would improve the car's handling and driving characteristics immensely.  I don't know if any cars have been modified other than the single example that he did for himself when he converted a stock Pantera into an Si clone, which is a MUCH larger undertaking than you would imagine!

Mike

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