×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Gear ratio vs powerband

Gear ratio vs powerband

Gear ratio vs powerband

(OP)
All Dodge Vipers come with a 3.07 rear axle. Few if any owners who've gone to 3.45,3.55, even 3.73 gears can positively say they've seen an improvement in ET at the strip.
 Yet the SOTP feel is tremendous(!), on the street anyway.

 How can such a marked increase in SOTP fail to yield concrete ET gains ?

 Obviously there's a point of diminishing returns when gearing up for the track, but near stock Vipers are not running out of RPMs before the end of the 1/4, nor running up into an upper rpm range well beyond the powerband .

 I've noticed this on 4 stroke dirt bikes too.  Is there something about torquey engines that have them just as happy leveraging themselves forward, rather than doing it through gear multiplication?

RE: Gear ratio vs powerband

Yes, particularly in first gear. The rotational inertia of the engine is a significant proportion of the overall inertia of the vehicle, and its contribution is proportional to the overall gear ratio, squared.

On the road Joe Blow probably scares himself silly in first gear, pulls second, and appreciates the extra oomph from the higher axle ratio.

0-60 times always seem to bottom out around 3 seconds for road cars, I suspect due to a combination of engine inertia and tyres.

Cheers

Greg Locock

RE: Gear ratio vs powerband

A 3.0 second 0-60 time is slightly over 0.9g.  Tire grip is probably the limiting factor, as street cars don't generally achieve full weight transfer to the rear on acceleration on normal street pavement.  Especially in something like a Viper.  Any rear aero downforce would be minimal at best, so there's no help there.

There is one other factor in the 0-60 measurement of performance - the time it takes to shift is more than just wasted time.  In that fraction of a second, you decelerate slightly due to aerodynamic and rolling drag forces.  Gut feel, magazine test results, and a little spreadsheet simulation suggest that any stick-shift car that can 0-60 in much under 4.0 is holding first past 60 mph.

One way that you "feel" the difference between different axle gears (or transmission gearing, for that matter) is where the overall ratio puts you rpm-wise in a given gear at a given road speed.  First gear may be low enough that you'll spin the wheels anyway, but in the higher gears the better gearing will outweigh the greater rotational inertia penalty (especially from a lower midrange start, where you'd have more torque as well).

Regarding the 1/4 mile results - do any of these axle ratio changes force an ET-wasting extra upshift in the last hundred feet or so?  And with the 3.07's do they freely wheelspin off the line?  (read: the gears wouldn't be helping the 60' times any)

Norm

RE: Gear ratio vs powerband

(OP)
1st gear w/ 3.07 is good to almost 60mph.  

With a stock Viper and a 3.07 you can leave it in 3rd gear through the traps, but most Vipers are already shifting into 4th anyway.

Traction even w/ 3.07s can be dicey at the strip depending on track prep, and any stiffer gears would/could make it worse. Drag radials can drop .4sec easily. I guess 60' times would be the best judge of that.

 When shifting into the next higher gear the resultant rpm is always above 4000rpm, so after 1st gear there is a lesser duration for the benefit to make itself known. Still the gear multiplication is happening mathematically.

 The SOTP sensation in any trans gear with a stiffer gear ratio change, even just passing, is huge, yet so far, no one has been able to substantiate even .10sec at the strip with stiffer gears.

 Somehow the fantastic SOTP street difference isn't translating to better ETs.  There are enough Vipers with gear changes that someone'd be able to point a finger at it.

 I just wonder if a stiffer gear can kind of blow through the benefits of having alot of torque-wasting it so to speak as the stiffer winds thru the rpm range faster anyway.

I'll have to go to some Corvette forums and see what kind of ET results owners have had changing from say 2.73 gears to 3.42 or so.  Those cars also exhibited strong SOTP changes when I worked at the GM Proving Grounds in Milford, MI. (as any car would I guess)

RE: Gear ratio vs powerband

NormPeterson said:
Gut feel, magazine test results, and a little spreadsheet simulation suggest that any stick-shift car that can 0-60 in much under 4.0 is <B>holding first past 60 mph. </B>

CrystalClear:

Holding first gear 0-60 seems to be the case in this example, the R500.

http://www.r500.com/R500main.htm#3

The Superlight will give even the Fl a hard time on the dragstrip, until the very biggest numbers come up. It will merrily scream to 60mph in less than 3.5 seconds, and do it in the first of its six gears, because it will rev to an ear-splitting 9,000rpm- plus. It will go on to a top speed of 146mph if you can stand the windscreen-free blast in your face and, of course it has all the agility and instant responses of any 7. How's that for minimalism? R500 figures make outrageous reading. Its 0-30mph time of 1.6sec is 0.2sec quicker than the McLaren Fl. The benchmark 0-60mph run is dispatched in a meagre 3.4sec (only 0.2sec slower than the Fl), while our 0-100mph time of 8.1sec almost beggars belief.



Motorbikes tend to be faster than cars off the line, so it seems to me the limit on acceleration is power to weight ratio. If tire grip was an important factor the cars wouldn't be able to brake hard.

I think 0 - 100 MPH - 0 is about 11 seconds for the R500 Evolution and about the same for 1000cc Suzuki motorbike. But the Bike does it in about equal steps of say 5½ secs 0- 100 and 5½ secs to stop again, whereas the car is maybe more like 0-100 in 7 secs and 4 seconds to stop again.

Conclusion: The grip is there to accelerate to 100 in 4 seconds too. The bike would presumably wheelie and cannot accelerate faster. Braking hard, the bike would presumably stand on its nose, back wheel lifting up. So the wheelbase on a motorbike I guess inhibits much better than about 11 secs 0-100-0. Since the car accelerates slower, I put that down to power to weight, as the grip is there for stopping.
The car going 100 MPH to zero in about 4 seconds means to me that with a decent power to weight ratio, it could probably do the same in the opposite direction. So something like a Walley Larson ought to be able to accelerate 0-100 in 4 secs with no problem, its just not a normal production car.

These are the figures quoted on German website for the LE1

Walley Larson LE1

Fahrleistung
0-100km/h 2.2Sek
0-160km/h 3.5Sek
0-200km/h 4.3Sek
0-250km/h 5,7Sek
0-300km/h 7.6Sek
400m 8.61Sek (322km/h)

0-100 MPH would correspond to about 160 km/h, ie about 3.5 seconds. This beats the 100-Zero stopping time of R500, so I'd guess that downforce is starting to come into the figures when you have cars that actually built to go fast.

RE: Gear ratio vs powerband

The grip is there to accelerate 0-100 in 4.0 only if all four wheels are driving, as that is the case with the brakes and that 100-0 time.  That indicates that a mean average grip of 1.14 was attained considering all four tires and their different loadings.  Perhaps this is a reasonable figure for DOT "R" drag or autocross radials.  True drag or road-race slicks on a prepared dragstrip would do better.

0-100 in 7.0 is an average of 0.65g.  This is reasonable with a rear wheel drive vehicle on the above "R" tires having a static weight distribution of 50/50 and the longitudinal weight transfer associated with a 18" CG height and a 94" wheelbase.  Using that same 1.14 grip (which is likely a bit optomistic, as the rear tires are becoming much more heavily loaded relative to the fronts), I get 0.72g as a theoretical limit.

FWIW, that 1.14 is likely a little high for acceleration use for yet another reason.  Aerodynamic drag helps braking without requiring any tire grip but hurts acceleration by requiring more of it.  This effect also tends to pull that 0.72g average 0-100 acceleration potential down a little . . .

Norm

RE: Gear ratio vs powerband

I'm not too sure where this thread is going, but I'll just add in that the instantaneous coefficient of friction, of normal production tyres ( ie Fx/Fz), on normal road surfaces, while braking or accelerating, is about 1.2. I worked this out from some real data I had to hand last time it came up. This is sustained for several seconds during a "1g" stop.



Cheers

Greg Locock

RE: Gear ratio vs powerband

(OP)
I was just going to say....it's been hijacked.

RE: Gear ratio vs powerband

Much of this is over myhead, as I'm looking at it from a laymans point of view.

To me, a coefficient of friction of 1 would be giving the same force sideways as one gets vertically. The force gravity applies to accerate me vertically gives me 1g vertical acceleration. Similar forces horizontally would give me 1g horizonal acceleration. So a coefficient of friction of exactly 1 would be required for a 1g stop. (Less if somebody picks me up for neglecting wind resistance; I'm grateful they did actually, but more so for the two driving .. four braking wheels remark!)
But that's from a Noddy point of view, not based on engineering.

If I try to bring things back to the original question - and although we strayed, maybe it wasn't too far - it seems acceleration is governed by power (to weight) and (grip to weight, namely) coefficient of friction.

So hasn't Viper488 answered his own question:
Obviously there's a point of diminishing returns when gearing up for the track, but near stock Vipers are not running out of RPMs before the end of the 1/4, nor running up into an upper rpm range well beyond the powerband.

So if they are not running out of power, the limiting factor is grip. Power is supposed to be Torque times RPM give or take a multiplication constant. So if the force (torque) you can put through the tires is known (from the  coefficient of friction), and a wheel's RPM cannot be changed for a given speed, then the power you can take from the engine can be calculated and is limited too.

If you change the gear ratios to have the power from a light throttle at high RPM giving a buzz to the driver, or have the same power at low RPM and a wide open throttle and better fuel economy form an engine that is closer to struggling, shouldn't matter: the power delivered would be the same.

If this latter case is what viper488 called leveraging the car forward it is presumably preferrable, not just for the better fuel economy, but due to less chance of putting too much power through the tires and getting wheel spin.

So gear ratios will only really become important when the tires are sticky enough, the vehicle had enough down-force, and wheel RPM is high enough to accept the engine power. At that point you start to need gears that can keep the engine at full power.

==================

I may try to do a calculation later in the day to estimate at what sort of speed power takes over from friction as the limiting factor in acceleration, as that would indicate when it becomes important to have the right gears to hold the enignine in its powerband.

If those speeds are towards the end of a ¼ mile I'll feel like I have understood what NormPeterson is saying, and if they are at the beginning, I'll feel like I did after his "4 wheel 2 wheel remarks", that I still haven't got some of the basics right.

RE: Gear ratio vs powerband


===========================================================
AXLE RATIOS DON'T MATTER, ITS ALL IN TIRE GRIP?
===========================================================
(Note the question mark! Its a title, not a statement!
I just wanted to establish what the post is about, as it takes a while to get there.)

I did some calculations. To be honest, I haven't got the fainest idea if they are about right, as I've tried to do them with Leibnitz's idea of Energy (½mv²) as that is what most people are used to, rather than Descartes' idea of energy.

But I believe Descartes was right. It shouldn't take 4 times as much petrol (energy) to get 0-20 as it does 0-10, in my opinion. That would mean three times the fuel usage 10-20 as required for 0-10 --- I just don't buy it.

But here goes, using Leibnitz type calculations, to keep conventional.

==

I worked out that for a car as light and powerful as the Caterham, its at around 80 miles per hour that tire grip stops being important for acceleration, and engine power takes over as the limiting factor.

Here are the assumptions, taken from the weblink given.

From http://www.r500.com/R500main.htm#3

Rear 215/50 R 13.
WEIGHT: Kerb weight 460 kg.
Max power: 230 bhp @ 8,600rpm.

==============

Calculations


(For the wheels- dimensions?)

50% of 215mm is 107.5mm
13" is 330.2mm
115.1 + 107.5
wheel radius is 222.6mm
0.2226 * 2 * pi = 1.39863702552 = wheel circumference

(How much torque can the wheels handle?)

WEIGHT: Kerb weight 460 kg
460 Kg * 9.81 m/s/s = 4512.6 Newtons
So with 1.0 coefficient of friction (for simplicity), wheel torque would be 4512.6 * 0.2226 = 1004.50476 Nm
So let's call it 1000 Nm at the wheels, is all the tires can handle.

(At what wheel RPM can we put the whole engine power through them?)

Max power: 230 bhp @ 8,600rpm.
Convert to Kilowatts
(eg using http://nathankeogh.com/htm/cars/bhpVkw.htm)
170 KW

Find wheel revs per second from engine power and wheel torque
(http://www.roymech.co.uk/Useful_Tables/Drive/Shaft_design.html)
Power transmitted by a shaft P = 2 * pi * T * N (N = Revs /sec)
170,000 = 2 * pi * 1004.50476 * N
N= 26.9350050537875240426617095099926 revs per second

(And how fast is the car going at that wheel speed?)

circumference*revs =
37.6722953507955502371138589726543 metres per second
convert to miles per hour
(eg using http://www.crickhowell-hs.powys.sch.uk/eng/tools.htm)
84.22 miles per hour

==============================================

So for that particular car, tire grip is the limiting factor rather than engine power until the car is going pretty quick, about 84 miles per hour. (With a huge margin of error since I just guessed a coefficient of friction!)

An advantage to be gained by playing with the gear ratios etc is likely to be in reducing fuel consumption, or if one is after better performance, reducing the number of gear changes required.

==============================================

So now I can see what I'm trying to work out, maybe I could go back and try it again with numbers for a Dodge Viper. Then we would be closer to knowing whether playing with the axle ratio is a meaningfull change for off-the-line performance, or whether its like painting go-fast stripes on the side.

But I'll wait first to see whether NormPeterson or anybody else says picks me up on something I'm not seeing. If you don't play chess much, you do miss the odd knight fork, etc!

RE: Gear ratio vs powerband

For determining the maximum torque that the tires can support I think you can use somewhere between 1.15 and 1.20 for the grip.  But you still have to determine just how much weight is on the drive wheels, statically plus however much longitudinal weight transfer occurs under acceleration.  Overall, I'm pretty sure that you'll find that the maximum tractive force that can be exerted at the drive wheel contact patches for a front-engined sports car is less than 1.0 times the curb weight, even at 1.2 grip.

Without knowing the 7's specific data I'd estimate that the maximum wheel torque is in the vicinity of 460 * 0.77 * 9.81 = 3475 Nm.  That 0.77 is the combined effect of (assumed) 50/50 weight distribution, 1.2 grip, 305 mm CG height, and uses Caterham's listing for wheelbase.  Being sort of lazy today, I let Excel iterate for the solution.  There may well be more than 50% rear weight in the case of the 7, but that's balanced in part by the CG height likely being lower than 305 mm (16").

Other than that, just a couple of picky little things like powertrain efficiency and effective tire radius (which is neither the unloaded nor the loaded radius, BTW, and there's a fairly recent thread in the Suspension Engineering Forum titled "rolling circumference of tyres" that discusses this).

Norm

RE: Gear ratio vs powerband

Edit to the above - make that a 406 mm CG height.  The spreadsheet was set up in inches, the solution is OK for 16", and those 305's are only typo's.

Norm

RE: Gear ratio vs powerband

(OP)
Gee I hate to interrupt your hijacking of my thread, but this isn't about traction, It's about whether a stiffer gear somehow hurts more than helps on a torquey car/motorcycle (all the way down the strip) even if the vehicle is not running out of rpm at the finish line.

 Maybe you can just email each other or get a room..

RE: Gear ratio vs powerband

Tangential, maybe.  But not exactly a hijack.  If the gearing is short enough in the OE state such that traction is problematic up to a significant speed, even shorter gearing is going to be of dubious value (at the same venue, of course).  To quote from an early post to this thread
"Traction even w/ 3.07s can be dicey at the strip depending on track prep, and any stiffer gears would/could make it worse. Drag radials can drop .4sec easily. I guess 60' times would be the best judge of that."
And it [shorter gearing] could hurt you if it did in fact force a shift at the big end that the OE gears did not.  No reason has been given as to why some drivers with 3.07's use 4th while others don't, though that information is at least pertinent (the shorter axle ratio guys are all presumably being required to use 4th).

Crystalclear did mention crunching some Viper numbers toward the end of his longish reply/calculation that estimates how extensive the traction limitation issue might be.  That the car he used in his example was a Lotus 7 derivative is immaterial.  It's the approach that's pertinent here, not the car (though the example car's performance and low CG arguably makes it a reasonable choice for illustrating the method).

Perhaps what is really needed is an instrumented test sequence of a Viper, first with the OE 3.07's and repeated for the same car with any of the other ratios.  One that includes data acquisition of both half-shaft torques in addition to times to speed/distance.  But nobody has asked for that (yet).

Norm

RE: Gear ratio vs powerband

Hi NormPeterson,
seems like I did my usual trick of ignoring number of wheels (this time for weight distribution), but I think when you calculated 3475 Nm you ignored wheels size, so my figure might be closer anyway. You mentioned effective radius, but I think it comes into torque calculations and speed calculations the way I did things, effectively canceling itself out later. I'm going to calculate differently with the Dodge Viper numbers, so that wheel size is left out of it.

Let's get some figures from here:-

http://www.thecarconnection.com/index.asp?n=157,184&sid=184&article=4853

2003 Dodge Viper
Base price: $75,000 (est.)
Engine: 8.3-liter V-10, 500 hp
Transmission: six speed manual, rear-wheel drive
Length x width x height: 175.5 X 84.8 x 47.6 in
Wheelbase: 98.8 in
Curb weight : 3357 lb
EPA City/Hwy: N/A
Safety equipment: dual front airbags, security alarm, pretensioning seatbelts
Major standard equipment: keyless entry, tilt steering wheel, six-disc in-dash CD changer
Warranty: N/A

And a 0-60 time from here
http://www.modernracer.com/features/dodgevipervsf162.html

The Dodge Viper first began production in 1992, with more than 14,000 sold to date.
The 2003 SRT-10 is a two-seat convertible with 505-cubic inch all-aluminum V-10 engine
producing no less than 500 horsepower and 500 pound-feet of torque.
The 2003 Dodge Viper goes on sale in the Fall of 2002.
The Dodge Viper Competition Coupe is a single-seat racing version of the SRT-10 convertible,
but wrapped in fully enclosed coupe bodywork and designed exclusively for GT-class racing.
Viper Competition Coupe performance estimates: 0-60 mph in 3.8 sec.;
0-100 mph in 9.2 sec.; 60-0 in 90 ft.; 100-0 mph in 260 ft. and top speed of 193 mph.


============

(Convert units to metric)

Engine: 8.3-liter V-10, 500 hp
Curb weight : 3357 lb


Curb weight : 3357 lb
use http://www.choicelogistics.com/html/links_pkc.htm
= 1525.91 Kg

500 HP
Convert to Kilowatts
(eg using http://nathankeogh.com/htm/cars/bhpVkw.htm)
= 369 KWatts


60 MPH
http://www.crickhowell-hs.powys.sch.uk/eng/tools.htm
26.8385 m/s

==============

(A note on the weight)

Caterham .... With 230bhp on tap, the R500 is easily the most powerful, with an incredible power-to-weight ratio of 500bhp per tonne.

The Dodge Viper has 500 HP and weighs about a tonne and a half. So the Viper's poorer power to weight would explain its lower performance once the tires grip.


=================

(Work out 0-60 MPH time at 1g acceleration)

v = a * t
t = v/a = v/g

60 MPH = 26.8385 m/s

v/g = 26.8385/9.81 = 2.7358 secs

=============

(Work out how many g the cars are making - method)

The combined effect of weight transfer (j say) and friction (c) determines possible G force the tires can take
under acceleration and we can see what the figures look like from the 0-60 times.

f = m * a
v = a * t

fx = fz * c (coefficient of friction)
fz = mj * g (j=amount of weight transferred to driving wheels, eg 0.75 if 3/4 is transferred)

Combine the above and rearrange them.
so v/t = a = f/m = fx/m = fz * c / m = (m*g)*j * c / m = g*(j*c)

60 MPH = 26.8385 m/s

v/t=g*(j*c)
so
j*c = v/g/t           [or (v/t)/g = a/t ie how many time the force of gravity the car is accelerating]

(Work out how many G the Viper is making)

Dodge Viper (v/g)/t = 2.7358 secs/3.8 secs = 0.71995

(Work out how many G the Caterham is making)

Caterham 2.7358 secs / 3.5 secs = 0.7816

========================

(How long can the engine power sustain 1g acceleration? - method)

Power = force * velocity
p = f * v

Force = mass * acceleration
f = m*a

so p = m*a*v

v = p/m/a

if acceleration = 1g

v = p/m/g

(For the Viper)

369,000/1525.91/9.81=24.65 m/s

55.108 miles per hour

(Caterham)

power 170,000 watts
Weight 460 kg (and its so low better add 100Kg for a driver! 560Kg)

v = p/m/g
30.945 m/s
= 69.181 MPH

===============

(How long can the engine power sustain the sort of real world acceleration we are seeing from the weight and tires?)

Viper 55.108/0.71995 = 76.54 miles per hour

RE: Gear ratio vs powerband

So if I get back to Viper488's question about gear ratios and trying to make a Viper quick off the line, I'd be thinking about the following g forces from the 0-60 times.

Dodge Viper  0.71995
Caterham     0.7816

Both cars have the power to pull 1g acceleration, to about 55 MPH for the Viper and nearly 70 MPH for the Caterham. I would try to get some sticky rubber for the Dodge Viper and put some weight in the back to try to get the wheels to stick better.

The Viper has the power to sustain the acceleration we are seeing in practice up to about 77 (55/0.72) miles per hour. So I'd be thinking of having a gear ratio that red lined AROUND 77 MPH, to make sure the power was available as long as the rubber could take it.

In the hope that I could get better tire grip and need the whole engine power sooner, or if I added weight at the back to try to improve the grip - to give an effect like the driver sitting almost over the back wheels in the lightweight Caterham - I'd probably make it red line a little sooner. Then, even pulling the extra weight and handling the extra tire grip, I should have all the power the tires can take and maximum acceleration up to around 70 MPH.

The thing to avoid would be gearing things so that a gear change caused RPM to drop and power to be lost, just at the point where the tires are starting to grip well enough to take most of the engine's power.

Speed gained early on during acceleration is carried for longer and so makes a bigger difference to times, eg a mistake at a chicanne might cost an F1 driver 0.1secs, whereas a mistake going on to a long straight might cost him 0.5 secs as the lower speed stays with him longer.

So if the first real chance gearing has of affecting the Viper's acceleration (apart from any time lost with unnecessary shifts at low speeds - remember the Caterham does its 0-60 all in first) is making sure the engine power is available when it first becomes needed at what I estimate to be around 60-75 MPH. Being in as low a gear as possible (in the {1,2,3,4,5,6} sense) at around 60-75 would mean the gears could then be placed closely together to keep the engine near to peak power when accelerating further with adequate grip.

All that, is as I see, it. Don't take it as the gospel truth! What I say is a bit more open to debate than what Greg or Norm says (meaning I make more mistakes, and not that they are less flexible!)


RE: Gear ratio vs powerband

I have a program which calculates 1/4 mile times etc. I looked up the 03 viper specs, found someone's dyno printout, and saw what it gave me. I obviously have to make some unknown tire and driver reaction assumptions, but the changes are what's important.

Baseline w/3.07:
0-60: 3.9
0-100: 8.6
60': 1.8
1/4: 11.7@117 mph

3.45 gears:
0-60: 4.4
0-100: 9.1
60': 1.9
1/4: 12.2@117 mph

3.73 gears:
0-60: 4.5
0-100: 9.3
60': 2.0
1/4: 12.3@117 mph

This obviously depends a lot on exactly how you drive, but the trend is interesting.

I think the main factor contributing here is how well you can use first gear. 1st is difficult to use, but apparently manageable with 3.07's according to this program. It looks completely useless with 3.45's or higher. You basically have to shift to second right away, and then you're gearing is messed up.

Just for fun, the acceleration at 80 mph (SOTP feel) is 0.39, 0.41, 0.42 g respectively for each of the above axle ratios in the optimal gear (2,3,3). When casually playing around, you're probably not in the optimal gear, which would usually make the SOTP feel of the aftermarket gears even better.

RE: Gear ratio vs powerband

(OP)
Well your software results kind of throws out the long standing practice of putting stiffer gears in your car for the strip... If the ET's just going to drop.

 But that's not usually what happens at the strip unless you're running out of rpm before the finish line.

 I'm not buying the 'not in the optimal gear' theory either. You're saying if one is in the wrong trans gear he's going to feel stronger Gs but still be slower somehow?

 One Viper owner posted that after installing 3.55 gears he routinely dusts-off Vipers with the 3.07 gears who've added bolt ons, even headers, with ease, and recommended the 3.55s as one of the first things to do to the car to someone else.

 His car was since Vorteched to over 900rwhp, so he's beating just about everyone now...

 I'll be sure and do a good comparison with the 3.07s and 3.45s later making sure the gear is the only change and see what happens.. The 3.45s are good to almost 140mph, so I shouldn't be running out of rpms in 4th. :)

RE: Gear ratio vs powerband

You're the one who said the higher gears don't work at the strip. If I put in really sticky tires in the program, then higher gears do improve ET's. Another thing is that if the car is launched very softly -- just feather the clutch off idle -- then higher gears improve your times also (but being agressive lowers the times further still).

Its only when tire slip comes in that the benefits go away. I think that this is intuitively reasonable.

By the way, I frequent corvette forums, and they usually get the same results. Higher gears don't do much for ET's on street tires, but feel much better. Practically any car with lots of power will have the same effect. I'll guess that its more true with manual transmissions than autos, although I have no data to back that up.

I never said that being in the wrong gear gives better acceleration. That's wrong by definition! I meant that if you're cruising along as opposed to seriously racing, you're usually going to be in a higher gear than the optimal one. Say you're on the highway in 5th. With the stock gears, you're best off in 2nd, but with the other two, you're best in 3rd. So on top of the expected torque multiplication, you'll tend to be closer to the optimal rpm's in casual situations. The higher revs associated with the aftermarket gears will certainly improve throttle response, which is realistically more important than WOT.

RE: Gear ratio vs powerband

has anyone put in  a 2.8 ish rear gear and run through third skipping the last shift?
In my car (not a viper) i get out of first at 4500 to 4700 putting me in second starting at just over 3000 (my powerbad begins here due to the computer) and run the rest of the gears up to 6800 because first is so low that the motor won't spin up fast enough for the top end of first to accelerate faster than the bottom of second.
one other thing when switching to a lower rear gear if your not double clutching your shifts then your shift times would be longer due to the higher inertia for the synchro's to overcome in the gearbox.
basicly there has to be a point of dimenishing returns and dodge's engineers might have already pushed the viper there.

RE: Gear ratio vs powerband

Before I put 4.10 gears in my 1996 LT4 Corvette I plotted rear wheel torque vs mph for both the stock 3.45 and 4.10 gears based on actual dyno curve.

In essence the big gain in rear wheel torque occurs only in first gear up to the shift point(mph) with the 4.10 gears.

After this mph it flops back and forth as to whether you have more torque with the 4.10's or the 3.45's.

So to really benefit from the 4.10's you need to have traction in order to use increased torque.

Wish I could furnish before/after track data, but with street tires the after data was lots of tire spin at the track.

no_stray_voltage@yahoo.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

eBook - Integrating the Engineering Ecosystem
Aras Innovator provides multiple options for integrating data between systems, depending on the scenario. Utilizing the right approach to meet specific business requirements is vital. These needs range from authoring tools, federating data from various and dissimilar databases, and triggering processes and workflows. Download Now
Research Report - Simulation-Driven Design for SOLIDWORKS Users
In this engineering.com research report, we discuss the rising role of simulation and the paradigm shift commonly called the democratization of simulation. In particular, we focus on how SOLIDWORKS users can take advantage of simulation-driven design through two analysis tools: SOLIDWORKS Simulation and 3DEXPERIENCE WORKS. Download Now
White Paper - Industry 4.0 and the Future of Engineering Education
With industries becoming more automated, more tech-driven and more complex, engineers need to keep their skills and knowledge up to date in order to stay on top of this wave—and to be prepared for the Industry 4.0 future. The University of Cincinnati offers two online Master of Engineering degree programs designed specifically for practicing engineers. Download Now
eBook - The Design Gridlock Manifesto
In this eBook, you’ll learn 6 ways old CAD technology slows your company down and hear how design teams have put those problems to rest. “The Design Gridlock Manifesto” shares first-hand modern CAD experiences from 15 companies around the world. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close