How does a higher FDR affect 1/4 times?

[blackbombshell95]

On boosted and N/A applications?

I'm reading on the L67 GTPs running lower ET due to higher gearing such as 3.69 gearing.

I now have 3.73 gears in my transmission and how will that affect my 1/4 times on a N/A application? With a 3k stall.
Lets figure a 250whp N/A setup.

Also I understand that a higher than stock stall also cuts back on WHP huh? Interesting stuff. If someone can elaborate for me that would be great.


TIA

[Superdave]

the best i could run with my 3.94 diff was a 13.99 @ 104 MPH, switched to the stock 3.61 and ran a 13.73 @ 102.2 with room to grow.

[blackbombshell95]

What was your 60ft on both of those times?

[dohcfiend]

the diff ratio depends on where your engine makes it's best power. it also matters on your gear ratio's in your tranny.

stall has the same effect, if your engine is suited to make power up high then a 3k stall is what you need.

i think there is a book out there called automotive math. it will explain everything.

[torq455]

this will explain it:

http://www.converter.cc/tech_talk/tech_main.htm

[geoffinbc]

Man I'm glad people didn't start saying you need gears to go fast in the 1/4 mile. Thats what I like about this board. People always give educated answers.

Your goal in the 1/4 mile is to keep your engine in its power range all the time. Gears are the way to do this wether they are the final drive or the shifted kind. Your goal is to match your transmission and final drive to the power and estimated top speed in the 1/4. For example sometimes it is better to have a lower (numerical) gear in the final drive and shift one or two less gears in the transmission. This would be a typical case for a high torque motor in a light car.

If you look at Top Alcohol class Vs a Top fuel class the difference in power vs the difference in transmission. Alcohol has 3 speeds and Top fuel has one. But Top fuel has a few THOUSAND more horsepower. A similar effect trickles down the classes. Some run 2 speed glides, and lencos. Others are 3 speeds 4 speeds and there is also the 5 speed lencos of Pro Stock

So pretty much the lesson is figure out what works for your car unless rules dictate. In that case built the motor to the transmission.

[IsaacHayes]

Yup. Less shifts equals more time with power. And if you have to shift right at the end of the track, that costs you time. Now if you have a gutless motor then being able to wind it out quicker can help.

Us with torqy V6's don't have that problem so much. So extra low gears sometimes causes wheel spin at the start and not much help on the top.

When I ran my car when it was stock I held 2nd gear manually until the end of the quarter and got my best time. Otherwise the trans would shift right before the end and slowed me down.

[Superdave]

What was your 60ft on both of those times?

2.1 iirc on the 13.99 and 2.07 on the 13.73 both with drag radials.

with the 3.94 1st gear was useless, it would send the RPM's through the roof faster than i could shift to 2nd. the 3.61 is alot more tame in 1st. My RPM range is pretty limited, It really wakes up above 4000.

watch my tach in this vid.. i was being easy on it in 1st up till 4500 RPM, then i dumped it. you can see how fast it jumps.

http://media.putfile.com/Quick-Drive-in-the-3500Z

[sharkey]

If you look at Top Alcohol class Vs a Top fuel class the difference in power vs the difference in transmission. Alcohol has 3 speeds and Top fuel has one. But Top fuel has a few THOUSAND more horsepower. A similar effect trickles down the classes. Some run 2 speed glides, and lencos. Others are 3 speeds 4 speeds and there is also the 5 speed lencos of Pro Stock

actualy if you want to get technical a top fuel car runs a constant variable transmission of sorts. basicly they slip the clutch for the first 3.5 seconds of the run, but controlled. they use air timers that let the release bearing out slowly till its fully locked. the faster it comes out, the more power gets to the ground, but too much and the tires go up in smoke. an alcohol car is different, they run a 3 speed lenco, however they do still slip the clutch for the first second of the run (if that).

many cars run powerglides, why, i dont know. in any comparison ive seen in the same car, a 3 speed (be it a lencodrive, bruno, turbo 350/400, 727, ect) the 3 speed is always faster. other issues come up when running a glide and several stages of nitrous, ive seen it were 2nd gear loads the motor too hard and too much nitrous and the motor just doesnt survive.

and pro stocks run a liberty 5 speed. its a gear driving gear style instead of the planetary style that the lenco is. the liberty has less perisitic draw, making the cars faster.

[Will'sFiero]

And the tires on a Fuel car grow SIGNIFICANTLY as speed increases, effectively transitioning from short ratio to tall ratio continuously and seamlessly.

[Will'sFiero]

the best i could run with my 3.94 diff was a 13.99 @ 104 MPH, switched to the stock 3.61 and ran a 13.73 @ 102.2 with room to grow.

2.1 iirc on the 13.99 and 2.07 on the 13.73 both with drag radials.

with the 3.94 1st gear was useless, it would send the RPM's through the roof faster than i could shift to 2nd. the 3.61 is alot more tame in 1st. My RPM range is pretty limited, It really wakes up above 4000.

watch my tach in this vid.. i was being easy on it in 1st up till 4500 RPM, then i dumped it. you can see how fast it jumps.

http://media.putfile.com/Quick-Drive-in-the-3500Z

The 3.94 isn't entirely useless... I'm sure you've noticed that your trapped higher with it, even with a longer ET. It definitely gives you better top end... it just had other compromises at the same time.

It would probably be great with a 2.50/1.85 first/second combo, but nothing that nice is available for the 282. You just need some more traction.

With the 3.94 FD and 2.19 second, I might be able to launch in second gear and get rid of that useless first gear time... The V6 trans has 2.05 * 3.61 = 7.4 overall second; a hybrid box could drop that to 2.19 * 3.94 = 8.6, which is getting down to the same range as first gear in a T56 car with factory rear gears.

[Superdave]

I'm planning on swapping the 3.61 FDR into my W41 tranny which will give me the better 4th and 5th gears. Should work out pretty good once i get some slicks on the front.

Even launching the 3.61 in 1st is hard, damn FWD cars.

[geoffinbc]

actualy if you want to get technical a top fuel car runs a constant variable transmission of sorts. basicly they slip the clutch for the first 3.5 seconds of the run, but controlled. they use air timers that let the release bearing out slowly till its fully locked. the faster it comes out, the more power gets to the ground, but too much and the tires go up in smoke. an alcohol car is different, they run a 3 speed lenco, however they do still slip the clutch for the first second of the run (if that).

Yes that is true but slipping clutches and timers didn't have anything to do with the kind of cars we drive so I left it out. Clutch timing in top fuel is an entire art in itself. The clutch in top fuel is more like a power metering system rather than a transmission. It wont multiply torque it just doesn't send it all to the ground off the line.

[treeZ24]

I'm planning on swapping the 3.61 FDR into my W41 tranny which will give me the better 4th and 5th gears. Should work out pretty good once i get some slicks on the front.

Even launching the 3.61 in 1st is hard, damn FWD cars.

keep the 3.94, its better suited for your engine anyways. just get slicks. i dont get 1.8 second 60' s for nothin perhaps the tranny is better suited for my engine because i only rev to 6700 rpms but when i always drop a gear it ends up just before peak torque....

and swapping 5th gear was enough for me on the highway, so its a little higher rpms then with the 3.61 it cruises along nicely matched to the cam.

[Superdave]

keep the 3.94, its better suited for your engine anyways. just get slicks. i dont get 1.8 second 60' s for nothin perhaps the tranny is better suited for my engine because i only rev to 6700 rpms but when i always drop a gear it ends up just before peak torque....

and swapping 5th gear was enough for me on the highway, so its a little higher rpms then with the 3.61 it cruises along nicely matched to the cam.

You just want me to go slower..