4.10 gears...not what I expected.

[XfireZ51]

Using 19s and 3.55s, the stock trans speedo gear puts me at about 3mph low on the speedo when running 70mph. Something along the lines of 3-4% off which is acceptable to me.

[Pete]

They must've installed it wrong.
Have DD in the 441 auto Z for about 10 years works great no issues.

Pete

[Hog]

Originally Posted by Bob Eyres

Except for one thing, E.T. is the only relevant factor.
Except for the factor of who leaves first, who gets the jump.
That's the essence of bracket racing, which programs the tree to hold back the the quicker car to make the race even. Then, whoever responds to the light quicker theoretically wins.
In a "heads up" race, both drivers respond to the same light sequence. If both cars run the same e.t., then whoever leaves first wins.

This puts driver skill into the equation. Shifting quicker also allows you to minimize the rpm drop between gears.

That was my point, there are ways for a slightly slower car to win a drag race against a quicker car.

Yes in bracket racing, if both cars run their dial in, the car that crosses the finish line first gets the win, so long as you dont "breakout" and run a lower ET than your "dial-in".
I remember being in a money class for eliminations. There were cars that sat on the line for many seconds before they got to launch. I see them launch wheels up in my rearview mirror and then charge by me at the finsh line. The guy was choked that he lost though.


Using the Pro tree in "heads up" drag racing whichever car gets to the finish line without "red-lighting" wins. The ET you run in this type of drag racing doesnt matter. ET is meaningless in heads up because the timers for your own lane dont start until your vehicle moves, and end when your car breaks the beams at the finish line.

On the quicker shifting. Having quick shifts on a manual trans increases the amount of time that the drive wheels are putting power to the ground. The only way rpm drop during an upshift would increase appreciably is if shifted VERY slowly. Slow enough that the car actually loses speed during the shift, otherwise rpm in a manual trans car is pretty constant. This is where an automatic has an advantage, power is always being transmitted to the rear drive wheels during upshifts. But thats a different discussion.

[Hog]

Originally Posted by XfireZ51

Using 19s and 3.55s, the stock trans speedo gear puts me at about 3mph low on the speedo when running 70mph. Something along the lines of 3-4% off which is acceptable to me.

I see you mentioning 19" rims often, but what is your tire height? Curious.
Thanks.

[Paul Workman]

Originally Posted by Hog

I see you mentioning 19" rims often, but what is your tire height? Curious.
Thanks.

OR, better yet, is what is the center wheel to pavement height - allowing for some "squish" factor?

[USAZR1]

Originally Posted by Hog

I see you mentioning 19" rims often, but what is your tire height? Curious.
Thanks.

Fronts are 275/35/19 (26.6")
Rears are 335/30/19 (26.8")

[Bob Eyres]

Originally Posted by Hog

ET is meaningless in heads up because the timers for your own lane dont start until your vehicle moves, and end when your car breaks the beams at the finish line.

On the quicker shifting. Having quick shifts on a manual trans increases the amount of time that the drive wheels are putting power to the ground. The only way rpm drop during an upshift would increase appreciably is if shifted VERY slowly. Slow enough that the car actually loses speed during the shift, otherwise rpm in a manual trans car is pretty constant. This is where an automatic has an advantage, power is always being transmitted to the rear drive wheels during upshifts. But thats a different discussion.

I know what you're saying, but I don't think e.t. is meaningless in a heads-up race. I think what you mean is that e.t. isn't the only factor, and that the quicker car can still lose if his reaction time is slower, giving the slower car an advantage.

On the quicker shifting issue, I think about it in terms of inertia. The difference between a power shift, and a granny shift, is that in a power shift the gas pedal is on the floor throughout the shift. When the clutch is disengaged, the rpms shoot up, the shift is made while this is happening, and when the clutch re-engages, the power is higher than before, therefore helping the engine rpm stay up higher in it's power band.
In the granny shifted car, shifted at the same rpm, as the clutch disengages the driver lets off the gas until the clutch is re-engaged. As it re-engages the rpms are lower than before, and pulled down further by the next gear. This loses inertia. The engine has to climb that rpm mountain again, three times during the race, (twice in a three speed car). It goes with out saying that when you are letting off the gas three times during the race, even for milliseconds, that is slowing you down.

Wear and tear on the gearbox is obviously the downside to power shifting. I've been through 3 transmissions doing this. So, now that I'm a Grandpa, I shift like Granny tells me to.

[Hog]

Originally Posted by Bob Eyres

I know what you're saying, but I don't think e.t. is meaningless in a heads-up race. I think what you mean is that e.t. isn't the only factor, and that the quicker car can still lose if his reaction time is slower, giving the slower car an advantage.

On the quicker shifting issue, I think about it in terms of inertia. The difference between a power shift, and a granny shift, is that in a power shift the gas pedal is on the floor throughout the shift. When the clutch is disengaged, the rpms shoot up, the shift is made while this is happening, and when the clutch re-engages, the power is higher than before, therefore helping the engine rpm stay up higher in it's power band.
In the granny shifted car, shifted at the same rpm, as the clutch disengages the driver lets off the gas until the clutch is re-engaged. As it re-engages the rpms are lower than before, and pulled down further by the next gear. This loses inertia. The engine has to climb that rpm mountain again, three times during the race, (twice in a three speed car). It goes with out saying that when you are letting off the gas three times during the race, even for milliseconds, that is slowing you down.

Wear and tear on the gearbox is obviously the downside to power shifting. I've been through 3 transmissions doing this. So, now that I'm a Grandpa, I shift like Granny tells me to.

Semantics, quickest car, with the best reaction time wins.

I agree 100% with you during a proper "powershift". Including the factors that you describe, which are 100% correct, there is also the slight torque multiplication that occurs as the friction materials slip as they come together as the clutch is released. This multiplicarton is only apparent while the clutch disc and the flywheel are turing at different rates. Once the rates are equalized, only gearing supplies the multiplication.

I apologize for the "granny" shifting term. No matter anyones age, they deserve the same respect (perhaps more) that someone of another age.



USA ZR-1 thanks for the specs.

[Bob Eyres]

Semantics are important if you want your meaning to be clear.

I've never understood the semantics of the term "torque multiplication". I've seen it used, mostly, to describe the advantage the automatic transmission has, at launch, in the quarter mile. The torque converter allows enough slippage to let the engine come higher into it's power band before the car starts moving. So that you have more power available at launch. The automatic has other advantages, and disadvantages, but I don't see how torque is literally "multiplied" in any way. Semantics

[XfireZ51]

Originally Posted by Hog

I see you mentioning 19" rims often, but what is your tire height? Curious.
Thanks.

I have 19s on the back. The fronts are 18s. Just measured the rears sitting there w ~ 35psi, they stand at 26.25". Size is 325/30/19. These are the Nitto Invos which I like quite a bit. Good wet, fairly quiet, and grab pretty well on hard shifts.