How low can You go?

[Iron Duke NCRS #22045]

Yeah, I figure the "real" engineers use it, but...

When I was at GM in the late sixties, I was a production engineer, so my "engineering tools" consisted of the proverbial BFH (usually with a rubber head) and "big rubber crowbars" that were used on the assembly line to get the hoods to fit on steel bodied cars.

Duke

[John W.]

Re: How low can You go? *TL*

Andy,

Please check your e-mail address. I keep getting bounced messages from the e-mail notification of responses checkbox.

To everyone else: Please check that YOUR e-mail address is correct if you have the e-mail notification box checked. If you visit the board often and don't really need to be notified uncheck that box and save some system resources. You would not believe how many bounced messages land in my e-mail box each day.

Give me a break.

John

[Dave #24235]

Sorry I got it backwards, Dave......ntx

The 2.54:1 low gear with groove on the input shaft is the kind I have three of - wide ratio (wr). I have a lot of trouble with names. What is yours? - Dave

[Dave #24235]

Yeah mine are wr, the other way around!

I got the ratio (2.54:1 low) right and the name wrong. The 2.54:1 low gear with groove on the input shaft is the kind I have three of - wide ratio (wr). I have a lot of trouble with names. What is yours? - Dave... and I never met a 5 liter that I didn't eat, or a Porche either, but some of those old goats (GTOs) give me grief. I can still power shift with the best of them.

[Dave #24235]

Thanks for the good advice. No more notify.

[Iron Duke NCRS #22045]

Re: Yeah mine are wr, the other way around!

'63 SHP, CR four-speed, 3.08 posi - all factory installed. Speed in gears - 75, 105, 130, rotate and liftoff. Back in the old days I never ran from a light, but sucked 'em out to an open road with little traffic. Some big block muscle cars got me on the rolling start, but their lifters pumped up about the time I shifted into top gear.

Duke

[Martin M.]

Re: Yeah mine are wr, the other way around!

Hi Duke:

Some may not buy your speeds in the lower gears, but I will back you up. We have a '64 fuelie tanker with 3:08's, and it's a dog from a stop, but my how it pulls once you get on the torque curve. Have seen 100 in second many times.

Marty

[Iron Duke NCRS #22045]

Speed in gears

Hi Marty - Until I joined the Board I thought I was the only guy in the world with a SHP or FI with a CR and a 3.08. So you've got one too, huh, and a Tanker to boot. I think Dino Lano's '64 SHP has the same setup. The speed in gears are easy to calculate with 6.70x15 or equivalent rev/mile tires.

First - 6500/(760x3.08)x60/2.2 = 75.7 MPH

Second - same/1.64 = 101.6 MPH

Third - same/1.31 = 127.2 MPH

Fourth - drag limited, about 152/154 MPH at 5900/6000

This same "formula" can be used to calculate the speed in gears using your tires' revs/mile figure, axle ratio, and gearbox ratios, and if you plot the the data on a x/y graph and draw lines from the top speed to the origin for each gear, you have a "gear chart", which I find very useful.

Guess I fudged a little on the second and third maximum speeds. I took the car to a drag strip a few times in the mid-sixties. At the time I had 6.70-15 Michelin X radials (4.5 inch tread width) and exhaust cut outs. Any attempt to launch the car with a clutch drop or clutch slippage just resulted in uncontrollable wheelspin, so I ended up just driving it out of the hole like a normal street start. I drove halfway down and shifted to second gear - going through the lights right at around 6500. My best ET was 14.42, and I almost always broke 100 MPH in the speed trap with a best of a little over 102.

Duke

[Iron Duke NCRS #22045]

My name is Duke. What's yours?

Sorry, Dave. Just having some fun. I've got a '63 SHP with a CR and a 3.08 - all factory installed. There's more detailed info in my response to Marty's post higher up in the thread.

Duke

[motorman]

Re: I gotta believe some GM engineers used..

my wife also saves everything, she even has a box labled "string to short to save"

[Martin M.]

Re: Speed in gears

Hi Duke There is a legend that came with my car that says A.J. Foyt drove this in '64 in Texas at 158+. There is paperwork I have that is supposed to document this as fact, but to me it looks like a simulation run on the old GE time share system. In any event, it's a nice story. If you have old Vette Vues around, the car is on the cover, with a 5 page story. Car is still mint with only 50K.

Marty

[Martin M.]

Oops

The vette vues issue was April, 1977 Vol 5 #10 Marty

[Wayne M.]

Re: Speed in gears

Duke & Marty (Hi Marty -- tankers rule !) Duke: My very first car ever was a '65 L79 with close ratio and 3.08 gears (still have carbon copy of P-O-P on dealer work orders). Al Grenning suggests it may be a COPO, as it wasn't a combo listed for the 350hp, even though OK with the solid lifter 327's.

Tires: Is it possible that, before radials, there were several "sizes" of (say) 7.75 x 15's ? I have 2 original non-DOT tires that have a different rolling circumferences; both have about 80% tread left. Uniroyal Super Low Profile, 4-ply rating, 2 ply @ 85.0" (745.1 revs/mile), and a BF Goodrich Long Miler 4 ply Nylon @ 88.2" (718.5 rev/mi). This is 3.7% difference. The BFG is so tall that it gets stuck in my spare tire carrier, which defeats the reason I bought it.

[Iron Duke NCRS #22045]

Re: Speed in gears

Wayne - The 760 rev/mile spec is the standard figure for a 6.70-15 from the fifties and sixties. It is the value published in Corvette News and the AMA specs for those vintage Corvettes. Now you remember our revs per mile discussion from a few months back. You cannot derive it from the static OD, because of tire distortion, and I found from modern radial tire data that the actual quoted rev/mile data is about two to three percent less than what you compute from the inflated OD ("rigid body") figure. Can't really tell you the difference with bias ply tires, I don't have enough data, but I have noticed that the various 6.70-15s listed in Coker's catalog vary in OD by about one inch, which is a lot. It could be that the Tire and Rim Association standards were not as tight 40 years ago, or the repro molds are not in conformance with standards.

The actual tire revs per mile data is measured with the tire loaded, but I'm not sure what percent of max load and pressure they use, but it might be 100 percent. At a given pressure, more load will cause more distortion and fewer revs per mile. Remember my "regression analysis". It showed that tires for a specific manufacturer's model lay on a straight line when plotting OD versus revs/mile, but the various lines, depending on the manufacturer were two or three percent below the "rigid body" rev/mile calculation from pi OD squared over 4.

Another interesting point is that the old bias tires expanded with speed, sometimes by several percent, but radials, with their very stiff belts had very little measureable expansion. Pirelli and Michelin used "accurate odometer readings" in their advertising copy back then, and radials were popular among the time-speed-distance rallyists, both professional and amateur for this reason.

Duke