6th gear ratio is ......... 0.693:1

 

The 6-speed will help you in the 1/4 mile, especially in 4th and 5th gears. 3rd is a little better, too, but not drastically (120rpm higher when shifting to 4th). The closer ratios of 3rd, 4th, and 5th will keep the revs from dropping as far as they do in the 5-speed.

You will need to shift to 5th only if you trap above 114mph. The 5-speed will make you shift to 5th only if you trap above 121mph or so.

 

Actually you're incorrect. What you're saying is that ideal would be to drag race starting and ending in 4th gear. I also find it hard to believe that a top fuel dragster would run one gear. By running one gear you reduce the average horsepower applied through the 1/4 mile to around half of it's peak.

For example, let's take two cars A and B:

car A details:
transmission: 1 gear with ideal ratio to cross the 1/4 mile at redline

car B details:
transmission: 2 gears with ideal ratios to cross the 1/4 mile at redline in 2nd gear

Both cars have the same engine with a perfectly flat torque curve and 200hp at redline. They also have the same weight.

We can all agree that acceleration comes down to horsepower and weight. Since both cars have the same weight then lets examine horsepower.

CarA will apply and average of 100hp through the 1/4 mile. This is because at 0 rpms the car is applying 0 hp and at the finish line it's applying 200 hp. So the average over the 1/4 is 100 hp.

CarB on the other hand will apply a larger average. the average depends on the ratios selected. For instance if 1st gear redlined at 75% of the 1/4 mile, then over the first 75% you would apply an average of 100 hp. But 2nd gear would not drop the rpms to 0...so your average for the last 25% of the 1/4 mile would be larger than 100 hp. So the average over the entire 1/4 mile would be larger than what CarA averaged.

So CarB would be quicker in the 1/4 than carA.

Now this is in an ideal world where gear changes are instantanious. Obviously for every gear change there is a time penalty when no power is being applied. This is the science of gear ratios. You want to keep the rpms as close to peak power as you can without having so many gear changes that your time is worse. It's the time between shifts that is the reason why automatics are prefered for the big dogs. Automatics are always applying power to the wheels, even during the shift.

The best transmission for a 1/4 mile would be a CVT (continuously variable transmission) that would hold the rpms at peak horsepower. Then the car would average peak horsepower thought out the 1/4 mile.

 

the 6-speed should be similar to the STi's for whoever asked about that... the 6-speeds gears are very similar to the 5-speeds ratio's with the addition of a lower first gear... so basicly you getting a 5-speed with an extra gear before your current 1st gear...

 

No, that's not how it is with the Evo. The 6-speed's 1st and 2nd are the same, but the higher gears are closer together than on the 5-speed.

 

You all are just too funny... HAHAHAHAHAAH

 

They slip the clutch for most of the 1/4mi, and yes... they only have 1 gear. It is a direct drive transmission. They are at no shortage of power, so they have no need for additional gears as it would only waste time and add complexity.

Have you actually seen a top fuel drag race before?

 

Absolutely correct. The clutch never locks up on a top fuel car. If it did, it'd just roast the tires. When you see them smoke the tires 3/4 of the way down the track, it's because one of the discs/plates of the clutch locked up and fed too much HP to the wheels. "tuning" a top fueler is just as much about the clutch as it is the motor.

 

Abusive Wombats theory is only correct if the fully disengage the clutch at 0RPM (realistically idle) and floor it. Since they launch at a much higher RPM they dont start with 0 HP. Thus the average is better becasue they stay in the fat powerband the whole time. If they had to shift then the shift itslef would add too much time plus they would drop down to a lower rpm (less power) right when the car is going fast enough to hook up and actually could put all the peak hp to the ground.

 

Ok guys I stand corrected. My post was mainly directed at our street cars. slipping the clutch is a good way to keep the horsepower up, ET down, and wallets slim but most of us don't want to be changing a clutch every weekend. So hence the science of gear ratios.

 

I think the coolest part is how the clutches get so hot that they essentially weld themselves together. They have to be replaced each and every run. Now that's some heat dissipation, or lack-there-of.

- Steve

 

Yeah, and they use 5 disc carbon clutches too.

That's what happens when you make around 6000 hp. Those things are really fun, go stand near one running rich at idle in the pits. It's a good way to suffocate. You will think there is some kind of chemical attack.

Clutches usually get changed every run, engine internals every 3-4 on a good day. Each injector drops about a gallon of fuel in the 1/4.

If you've never seen Top Fuel in person, you need to go, and you need to stand near the track. You will never be the same again

 

Here are the gear ratios for both 5 and 6 speed:

Little mis-print for the 5th gear on the 5 speed, should be .725 not .825

http://www.lancerevoclub.org/evo-history/e8specs.shtml

 

As you can see they're almost the same up until 5th gear

 

LOL .. .no your right.. We go through the traps in 4th at around 9k .. Thats why we opted for the a taller tire to reduce rpms through the top end. I dont know how the 6speed will work out ratio wise. We will soon find out as i think they are coming very shortly right ???

Mark
Turbotrix