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Discussion in 'Driveline' started by combatstang, Dec 21, 2004.
you also have ot remember when u go to a bigger tire, u reduce the gearing also
Yes, the “more” gear you have (higher numerical ratio), the more torque multiplication and hence, the larger the force applied by the tire to the pavement. However, the larger the diameter (and radius) of the tire, the lower the force applied, i.e., F = TQ*GR/Rtire. And of course, the higher the force, the higher the acceleration. Does that help?
when people run 28" tires, its for traction purposes. the 28" tire has more sidewall to take up the shock to the drivetrain when u drop the clutch, and they also have a lot more rollout for more tire on the asphalt.
Very interesting. I have never thought about how this stuff works. I have been adding power and I think I am where I need to be. It runs great as a daily driver and wants to go fast on the track. This winter I am working on the suspension and thinking about what gear would be best at 600 rwhp in the 1/4. I have the level 5 DSS so I am trying to stay with the IRS since it is mainly a street car. Next month I am putting in a 8 point roll bar so will be ready by the time spring hits Illinois.
another thing i never understood...there was a thread awhile back talking about gears/gearing and how they have never really seemed to help on our cars(i wish i could find it)but basically everyone that runs really good times (above average drivers and E.T.'s) are still using the stock gears and....quite of few of those people have tried going to a steeper gear and have slowed down(E.T wise , not trap) They were sayin that with our cars having so much torque throughout the RPM range that you didnt need any type of lower gearing, and that the engine does better letting it stay (and pull) through each gear longer, like somehow it accelerates better that way then if you had to constantly bang the next gear because the gear ratio is so short. Almost what Bob C was saying with the old N/A cobras: not much torque so you need the gear, but with a lot of torque and a lot of gear you're not giving the engine chance to pull through each gear.
Now when i was reading this thread i DIDNT really agree with it, simply because anytime you change the gearing for the better it seems it would always have to help you. Even when "calculated" on paper it would almost HAVE to help....but....these people have been at the track and somehow (or maybe not) proved different. Like i said some of them have seemed to be above average drivers so they know you have to get traction to reap the benefits of the steeper gearing or else you'll slow down (E.T.'s) so how is this true?? Their "facts" are right there in black and white (timeslips)
if someone could find the thread i guess it would help.
whats "above" average? maybe we can make a list of cars and gearing
Good point, (although of course, I was assuming traction was not a limitation/problem. I was addressing the tradeoff of using a taller tire to overcome the problem of going through the traps and having to shift out of 4th when using the shorter gears.)
If you change the gear and lose traction, then that can end up hurting the ET just as you said, sure. It would be good to know what tires they were running.
Damn, now I'm wondering again.
haha... i know STEVEN(projectzero) is on stock F1's and still getting 2.0 60fts.... so traction is only an issue for me when its really cold out, and tires are cold.. in the day with the ground warm, i get full traction in 1st gear with my nittos
o and my 1st gear with traction, is really scary.. my girlfriend loves it, the 1st time she felt it after the gear install she said wow, what did u do to ur car, it feels like a roller coaster
This is confusing
it should only be confusing if you have 600rwhp and want 4.10s, becasue then you have to get a tall enough tire so u dont run out of gear in 4th.. but for you its simple 3.90s to 520rwhp your good!!
Gears are the best seat of the pants mod ever envented.
However, that is where they make the biggest difference.
I know I shouldn't post into this thread, because it will get into a long dawn out discussion of torque vs. horsepower.
Gears do little to make your car faster because while they add peak rear wheel torque, they do not add any power. What gets you car down the track is the amount of power it has.
Torque in an of itself is a meaningless number, without knowing the RPM. I can generate 1,000,000 lb ft of torque, just give me a long enough wrench...
Here is why torque matters. Not engine torque per se, but torque at the rear wheels that matters. Since horsepower is conserved, and torque is not, the best representation of torque availibilty at the rear wheels is HP, as it accounts for the various gearing vs speed multipliers.
Simply put, if you had two engines whose torque curve looked like a flat line, 330 ft lbs from idle to reline, but one redlined at 3000 RPM ad the other redlined at 6000 RPM, what engine would make the same car faster?
In order to race to the same speed, the car with "twice the redline" engine could have twice the rear gears and still make it to the desired speed. That car would have twice the torque at the rear wheels for the whole race. That would not be much of a race.
But with our cars, when you take the typical positive displacement blown Cobra, it is traction limited. When you do suspension and or switch to a solid rear things may be different. But for the typical IRS car, adding gear will give more torque than you need in 1st, and depending on boost level and blower type, maybe second or third, too. Once you have enough torque at the rear wheels to spin the tires in low gear, adding more won't help.
If a 4.10 or 3.90 car lines up with a 3.55 car, when both are in the same gear, the higher numerical gear car will have more rear wheel torqe, but will hit redline and need to shift, then the lower numerical geared car will have more rear wheel torque because he is still one gear lower. It will be a see-saw back and forth as the cars go through the gears, and shift at different points.
Obscenely high numerical gears got popular with N/A cars that had very limited low end torque, and usually a transmission that only was low 2.x to 1 first gear. In that case, high numeric gears got the car into the powerband on launch quickly.
With the positive blown cars "shelf" like torque curve and the stock suspension, there is no need for higher numericals. My car makes almost peak torque from about 2000 rpm upward. With about 500 lb ft available, the car can pretty much be on the verge of spin all through first. If I added more gear, I'd still be traction limited, but need to shift into the next gear sooner, loosing rear wheel torque vs staying in the previous gear.
You know what,that's how I felt about things,I've not yet put gears in mine because of that,When I talk to people I know who put gears in their Cobras,It seems like it "felt" 10x faster,in which I can understand,but track performance and improvement is some what minimal.I think the highst I would go is 3.7 gears,and with shorter rear tires on my car already,It will have the gearing that I need(it already showed difference with the tires on my ET),and will improve track times.
With 3.9/4.10s....I won't go down the track with nothing but 28" tall slicks or a centrifugal supercharger/turbo then a positive displacement blowers like Eaton or KB.That's why I like to find out if there's drastic improvement on Marc's car at the track with DRs,cus I could be totally wrong on this,and his car could run a heck a lot better at the track.Mainly it's all about the hook up,anything or mod you do to the car that can hurt it,no matter how fast it "felt",it really didn't mean a thing if you can't get out of the hole quicker,faster,hooking up,and pull like a bat outta hell up top.I go to 1/8 mile track a lot,gaining times on my 60 ft for not hooking up and going into 4 th at the end of the track are not options for me.
JT, werent you one of the people that posted in that old thread that i was talking about?? Anyways, what you said is basically what i was trying to explain.
JT...the majority of the facts you present are accurate and indisputable. Also, I agree that if a car is traction-limited, lower gearing can have a detrimental affect.
However, with traction (IRS or not), a car that is geared to take advantage of its powerband (ie...optimally-geared) will out ET (meaning out accelerate in the 1/4 mile) a car with less-than-optimal gearing. 3.55s and 3.73s are less than optimal for the majority of 03 Cobras - even with a redline limited to 6500 rpm.
"Optimal gearing" for the 1/4 mile typically means that you gear the car to run several hundred rpm above peak HP at the end of the run in 4th gear. A stock 03/04 Cobra makes peak power at ~6000 rpm, meaning you want to run the car pretty much to redline in 4th gear - or above that if your peak HP rises.
The idea is to maximize average HP in each gear. In 1st, 2nd, and 3rd gear, that means calculating optimum shift points, for which rear gearing has little or no effect. However, for 4th gear, it means gearing the car as described above.
Put another way, if you're going to use all 4 non-OD gears anyway (which we will all do with aftermarket gearing), you'll go quicker if you maximize torque multiplication (lower gears) in each gear. Torque is multiplied with gearing, so for best ET, gear the car so that it goes through the traps ~500 rpm above redline in 4th gear.
Again - this assumes traction. If you race on street tires or are otherwise traction-limited, then you may or may not go quicker with an optimum power gear.
Also, N/A DOHC Cobra's all came with 3.3x 1st gear ratios, not low 2.x. Most of us that actively raced these cars still used very aggressive gearing, for all the reasons mentioned above, and even more so to get the car moving smartly in 1st and 2nd gear, because you spend most of your time in that part of the track.
if you had two cobras with thee same power, same driver skills, and one had 3.55's and one had 3.90's the geared cobra will walk the other cobra.. not by much but it will.. PERIOD!!... That's the bottom line, thats why I did it...
you're right...but thats all things being equal and alot of the times traction will NOT be equal with steeper gearing so *some* times the geared cobra will lose. Lower gears will give you so much more power to the wheels that it will be real easy to lose traction off and past the starting line. Dont take it as a bash towards gears because i definitely believe in them (i have 3.73's in my solid rear axle now and i love them!) but traction is hard to come by with all that torque that these motors put out so its easy to NOT see the gains from gears, either at the track or on the street.
Marc,I think you made an awsome choice going with 3.90s,Steven loved how his car pulls,and has some what convince me.It's just until I can see him or you pull consistent 1.7-1.8 60fts and below 5 sec.330 fts(which is what I can do now,and on a crappy prepped track on Nitto DRs),I would still be worried about putting it on(this is just my concern on track only,I bet that car of yours is a monster on the street,it would probably totally kill me street light to street light)I know the car must feel completely different now.By the way,Is your idling problem fixed with the IAC completely??
This is the key to gearing (assuming you address any traction problem), and is totally consistent with what JT is talking about. If you don't have enough gear and run through the traps at an rpm below the peak power band, you won't do as well as you could have done if you have more gear.