500HP quarter mile times

[Paul Workman]

432 hp @ the wheels /.85=508 crank
378 ish torque at the wheels
70ºF, 650 amsl
121-122 mph

Now for the bad news...(the driver!)

60' = 2.1s on street tires
reaction time 0.5 typical
12.4s best (so far)

I'm a neophyte at the quarter mile game, so take it for what it is worth, far as ET goes. The car is capable of better ETs, with drag radials and a skilled driver aboard, I'm sure!

[Paul Workman]

Originally Posted by Bob Eyres

Don't worry about e.t.?..........Huh?

Low E.T. means you got there first, you win. There is no bigger thrill at the drag strip than to beat a car that cuts a better trap speed. That means you won the race with less power.

Yeah, winning is winning, BUT! What really hikes up the ol' grin factor (for me) is a come from behind...which is sort of a trademark with our Zs, from what I've observed.

I agree w/ Bob G that our Zs would probably be better served in the quarter with something closer to a 4.10:1 gear. However, if this 1/2 mile shootout game is going to be a regular "thing" in Chicago, then one might consider a compromise between a 3.45 rear and?? OR, do as Pete has the resources to do, and change the diff ratio depending on the race in question.

[Dean Nelson]

I have stock 3.45 rear end and I am in 3ed at the end of the 1/4 and right at 6800, about 20 to 30 feet after the end if I keep my foot in it, it hits the rev limiter.

in the 1/2 mile runs we did, I am in 4th at the end at 6500.

the 1/4 is 12.3xxx and 12.2xxx at 120.xx and 121.xx
the 1/2 mile run was 146.54

all on street tires 18 psi for 1/4 and 35 psi for the 1/2 runs.

I need more seat time for the 1/4 runs as my 60 foot was 2.04 to 2.15

I left the line at 1500 to 2000 and that worked with small bog and go. I tried 3000 and as other have said.......I went up in wheel spin and went no place!

Dean Nelson

[Paul Workman]

Originally Posted by Dean Nelson

I have stock 3.45 rear end and I am in 3ed at the end of the 1/4 and right at 6800, about 20 to 30 feet after the end if I keep my foot in it, it hits the rev limiter.

in the 1/2 mile runs we did, I am in 4th at the end at 6500.

the 1/4 is 12.3xxx and 12.2xxx at 120.xx and 121.xx
the 1/2 mile run was 146.54

all on street tires 18 psi for 1/4 and 35 psi for the 1/2 runs.

I need more seat time for the 1/4 runs as my 60 foot was 2.04 to 2.15

I left the line at 1500 to 2000 and that worked with small bog and go. I tried 3000 and as other have said.......I went up in wheel spin and went no place!

Dean Nelson

Thanks for the data, Dean. I was wondering about the lag in the analog tach reading for the quarter vs. the half; guessing it would be less in the half as the rpm change rate in 4th gear is less than 3rd (in this case).

From Haibeck Automotive Engineering, this chart:



Checking your tach vs. speed (oh, oh...Dom. It's one of those proportional "ratio questions" again!)

3rd gear: (7000rpm/119.2mph* : X/121mph) ≈ 7105 rpm

Tach reading in the quarter @ 121 = 6800 rpm observed vs. 7105 rpm actual = 96 (95.71)% of actual


4th gear: (6500rpm/143.9mph* : X/146mph) ≈ 6595 rpm

Tach reading in the half @ 146mph = 6500rpm observed vs. 6595 rpm actual = 99 (98.55)% of actual

*(on "std" 315x17x35 tires)

Observations:

First, it appears your tach calibration is quite close (w/in about 1.4 % in 4th in the half mile. Was it ever adjusted?)

Second, it would appear there is ≈ 4% variance between observed and actual in the quarter mile vs. ≈ 1% variance the half mile.

Sumarizing:

Insufficient data to draw a conclusion, but if speed in the quarter is the actual trap speed, it seems reasonable to assume your tach calibration is quite close, if the rpm were to be static. Therefore, if tach lag of your car is at the apex of the statistical "bell curve" for 500 hp Zs, "6800 rpm" (for those w/o a shift light) is about what the tach should read in the quarter for Z with a stock differential ratio and tire size. (Again...assuming your tach lag is typical of all our tachs - unknown, but perhaps likely)

There appears to be an increase in the analog tach lag** in direct proportion with rpm change rate. That being the case, it would suggest lag would be less for a stock Z in the quarter (or half), and more for higher HP Zs. (Keeping in mind, one datum does not a trend make, i.e., error linearity vs. rpm change rate = undetermined)

** expected characteristic of the (analog) D'Arsonval meter movement used in the Zs analog tach

The data does not however suggest that IF the tach reads 6800 rpm in the quarter, you have a 500 hp LT5...SORRY!

[Dynomite]

Just some more details (Items 4 & 5) from Tech Info - ZR1 Differential Gearing and Vehicle Speed Calculations

4. Vehicle Speed at 7,000rpm 3rd Gear (Fly Wheel RPM).
Vehicle Speed in Miles Per Hour (mph) = (Tire Circumference in ft x Tire revolutions/hour)/5,280 ft/mile

(7,000rpm/1.29/3.45) = Wheel rpm =1572.85rpm = 1572.85rpm x 60 = 94,371 revolutions/hour
80.64/12 = wheel circumference in ft = 6.72ft
94,371 revolutions/hour x 6.72ft/revolution/ 5,280 ft/mile = 120.11 miles/hour

OR
One Mile = 5,280ft
(1572.85rpm x 6.72ft x 60 min/hr)/ 5,280ft = 120.11 mph

5. Vehicle speed with tire loaded deflection of 1/4 inch at Engine rpm (7,000 rpm).
Assuming third gear (Transmission 1.29 gears and Differential 3.45 gears).

Stock 315x17x35 Tires. 25.68 tire diameter x 3.14 = 80.64inch circumference.
Deflected Tire Diameter 25.68in - .5in = 25.18 inch tire effective deflected tire diameter.
New wheel circumference in ft = 6.59
Vehicle Speed at engine speed of 7,000rpm = (1572.85rpm x 6.59ft x 60 min/hr)/ 5,280 ft = 117.78mph

Now that we got 500 hp and 120 mph in the quarter....lets talk brakes

ZR-1 (90' and 91') Wilwood Rotors and C4 to C5-Z06 Conversion

[Dean Nelson]

You guys!.......my head can't take it!

now that you have done all the math, and it was neat to read that it worked out so close, when I looked at the rpm at the ends of the runs it was a fast look down, at the point that I think is the end, and it is the number I think I saw. I would say it was my best guess at what it said.

Paul, the tach has never been adjusted same as the day GM made it.

Dean Nelson

[LGAFF]

My tach was off by about 400 RPM, they stopped it at 6800 the first time on the dyno

[Bob Eyres]

Running the quarter mile with stock gears and street tires is fun, but it isn't the optimum setup for the track. I would not sink $10K or more in engine work, then only use 3 gears at the track. It just won't give the best results.

On Paul's gear chart, look at the 4.10 gear. In fourth at 7K (which is where you want to be in the traps), you're at 130mph. You need way more than 500 crank hp to do that. That tells me, ideally 4.10 gears are STILL a little too tall to be the optimum for the Qtr. Maybe a little more tire, say 255X50X16" and a 4.56 gear might just be the ticket.
Of course nobody, even Pete, has done that. But once you start bolting slicks and skinnies on the car, why not?

[Meanmyz]

Thanks to everyone who posted. There are a lot of good thoughts and information here.

[Kevin]

Originally Posted by Bob Eyres

Running the quarter mile with stock gears and street tires is fun, but it isn't the optimum setup for the track. I would not sink $10K or more in engine work, then only use 3 gears at the track. It just won't give the best results.

On Paul's gear chart, look at the 4.10 gear. In fourth at 7K (which is where you want to be in the traps), you're at 130mph. You need way more than 500 crank hp to do that. That tells me, ideally 4.10 gears are STILL a little too tall to be the optimum for the Qtr. Maybe a little more tire, say 255X50X16" and a 4.56 gear might just be the ticket.
Of course nobody, even Pete, has done that. But once you start bolting slicks and skinnies on the car, why not?

if I was going to pick a car to drag race it wouldn't be a zr-1