6500rpm in second..what speed au wagon?

[Stav]

Never mind the six speeds. I have found their achilles heel!! All I need is a 6000 stall converter with a 6500 limit.hehe. I think the wagon will run 12's maybe 11's with that combo.

[Stav]

T3 man..I was thinking along the same lines. 3.23 standard diff would do the job.Only problem is the lost benefit of the 4:11's opn takeoff and midrange punch. The answer is a bigger stall converter..I am getting 2.022 best 60 footer so far with a 2500 rpm unit. I really would like a 1.6 to 1.7 60 footer to get it really moving crazy. To get this however is a tradeoff in drivablity for the daily driven wagon..
I am just gonna have to find a way to get as much power with a few more mods and maybe go up to a 3000 or 4000 stally.3000 being drivable and 4000 just to intimidate more hsv's.

[big_waity]

Maybe swap to a 5 speed manual?
Closer gear ratios, less power loss through the box...

[Sox]

Originally Posted by Stav

That dam 3rd gear is too lazy!! these cars would be heaps faster down the 1/4 with a different ratio 3rd gear. 1:1 is just wrong for the job. No wonder the six speed auto boxes are thrashing us. Having a more aggressive ratio there is flogging us!! We need to be able to use the first 2 gears instead.

If 3rd is too lazy, the easy answer is to fit a shorter diff ratio. Ideally you want to be close to peak power across the finish line.

A shorter diff will get you off the start line even better too.

A 2 speed is not an option in a car with such little power and high mass.
2 speeds are very good in a big power / lightweight car, but in your gutless (comparatively speaking) tank, it wouldn't work.

Grab a 9" with 4.5 or even lower gears and you'll cross the line at the right rpm.

Rick.

[Sox]

BTW, that calc is way off......
.........Mainly because it is for a 5spd manual ratio set, no wonder the speeds are out of whack.

Your way of thinking in this is not right Stav. What you really want with a big heavy car with low power is lots of gears, not less. You see, small capacity engines in heavy cars rely on good gearing and lots of them to get going - big blocks in light cars can get away with less gears as they have wider power bands and much more of it.

If you had only 2 gears to play with in your wagon, their would be even more compromises made. The gears would either be spaced too far apart and create a big hole in power between gears, or be too close spaced and you'd have nothing off the line or run out of rpms up top (depending on diff ratio).

You NEED a lot of gears, and 3 ain't enough. What you should aim for is to reach peak power across the finish line in 3rd gear, that way you would be maximising your current stack of ratios.

Forget the 2 speed idea though, that ain't gonna work in your 6 pack. Throw on a hair dryer with 20lbs boost, and you might be in business.......

Rick.

[Stav]

Thanks Sox. I have been lookihng at 6 speed boxes but they cost too much for me at the moment.

Just for everyones benefit. With my 4:11 diff ratio..in second gear with my 6000 rpm rev limiter I hit 130 kmph.

[Stav]

To do the 1/4 mile in 2 gears I need to go back to a 3.73 ratio and raise my rev limit to 6600.This should see 155 kmph in second gear.No maths just done half the theory and found these facts.

[StealthAu]

Originally Posted by Stav

To do the 1/4 mile in 2 gears I need to go back to a 3.73 ratio and raise my rev limit to 6600.This should see 155 kmph in second gear.No maths just done half the theory and found these facts.

I think your off by more then 10kmph

EDIT, forget it, your right. Didn't see the diff in revs

[Stav]

I would see 143 in second at 6000 rpm.It depends how much faster the extra 600rpm will get me to.

[FS5]

stav, have you thought about mucking around with rim and tyre sizes to get what your after?
if it was me i'd set the limiter to 6500 and watch everyones botom jaw drop!

[Road Games]

Originally Posted by FS5

stav, have you thought about mucking around with rim and tyre sizes to get what your after?
if it was me i'd set the limiter to 6500 and watch everyones botom jaw drop!

Yeah remove your rear brakes and fit some escort 13" ones ...

[sly]

Originally Posted by Stav

3rd gear is where the converter is fullly locked and torque mutilpication dies.

3rd only locks in Econ mode. In Pwr the converter still slips.

[Stav]

Originally Posted by sly

3rd only locks in Econ mode. In Pwr the converter still slips.

Hmm that might explain why my car is faster in power mode.Sox is right..I need a ratio of 4.5 to cross the line at 5700rpm in 3rd.

[Stav]

Originally Posted by FS5

stav, have you thought about mucking around with rim and tyre sizes to get what your after?
if it was me i'd set the limiter to 6500 and watch everyones botom jaw drop!

Jake good to see you here again mate. Truth is that th revs rise very fast in 1st and 2nd. If I can ride second to 160 kmph I believe the car will be quicker if it doesnt blow up.heheh again

[russellw]

More info here:

[Road Games]

Originally Posted by russellw

More info here:

Awesome work Russ, when do you get the time to help like this ....

[Stav]

When I hit that link it goes to a blank page .Must be something wrong with my browser..:(

[Road Games]

Originally Posted by Stav

When I hit that link it goes to a blank page .Must be something wrong with my browser..:(

To calculate overall gear ratios there are a couple of things you need to know. In brief we will look at a these with some worked examples.

Tyre Diameter

It is still usual to calculate this in inches thanks to the fact that our tyre and rim sizes are still a mix and most programs that use the input are American.

The formula is deadly simple:

Tyre Diameter = Rim Diameter + twice the tyre height.

Now the tyre height is the width multiplied by the aspect ratio - in Australia we use the P-Metric system where tyres are stated as width in millimetres x aspect ratio. That is to say a 235/45 tyre is 235mm wide with an aspect ratio (or sidewall height) of 45%.

For our calculation above we need to convert that to inches and we do this as follows:

Width in Millimetres multiplied by 0.03937

In our 235 mm example therefore we end up with 235x0.03937 = 9.25195.

To use this in our formula above (in red) we now have:

Tyre Diameter = 17" (rim dia) + 2 x (9.25195 (tyre width in inches) x 45%)

thus: Tyre Diameter = 17" + 2 x (9.25195 x 0.45)
= 17" + 2 x (4.1634)
= 17" + 8.2638
= 25.3268

It's usual to apply a small discount to this to allow for tyre wear - I usually allow 3% as do most of the actual calculators so we would end up using a figure of 24.567 (25.3268 x 0.97). This is pretty close to the 24.6 that my copy of RacePro comes up with so our math is ok.

Rolling Circumference

This is the main input used for the calculations below - it is calculated by taking the diameter calculated above and multiplying it by pi.

Rolling Circumference = Tyre Diameter x pi (3.1605)

Thus our example above yields:

24.567 x 3.1605 = 77.644 inches this is then converted to feet by dividing the result by 12 - 77.644 divided by 12 = 6.47 feet.

Ok that's our first basic input done. The usual thing done with this information is to calculate either engine RPM at a given speed or speed at a given RPM. The math for both is related (obviouusly) so let us look at a couple of worked examples.

Calculating MPH from engine RPM

To perform this calculation we need two more inputs which can generally be obtained from your vehicle owner manual - the rear axle ratio and the gear ratios in each gear. For the purpose of this exercise we are going to assume a direct drive top gear (fairly rare these days - most 5 speeds have a direct or even slightly overdriven 4th) but this will simplify the math and we will use a 3.23 rear axle ratio which is fairly common in the Ford world.

MPH = (RPM x Circumference) divided by (Gear ratio x Final drive ratio x 88)


So for our example above the inputs are as follows:


Circumference = 6.47 feet
Gear Ratio = 1
Final Drive = 3.45
RPM = 5400 (about what a Windsor should pull in direct drive).


thus:


MPH = (5400 x 6.47) divided by (1 x 3.45 x 88)
MPH = (34,938) divided by (303.6)
MPH = 115.08


If you want to convert this to km/h simply multiply that result by 1.609.
(In the example above 115.08 x 1.609 = 185.16).


Calculating RPM from MPH

This simply turns the formula around:


RPM = (MPH x Gear ratio x Final Drive x 88) divided by circumference


Using the following inputs:


MPH = 100
Gear Ratio = 1:1
Rear Axle Ratio = 3.45


RPM = (100 x 1 x 3.45 x 88) divided by 6.47
RPM = (30,360) divided by 6.47
RPM = 4,692


Looking at more worked examples


Let's look at the difference changing the rear axle ratio would make if we went from the 3.45 used above to both the 3.23 option or the Territory 3.80 ratio.For this exercise we'll still assume a direct gearbox ratio but we'll change the tyre size to the 245 x 35 x 18 option.


Tyre Diameter = Rim Diameter + twice the tyre height

First we will calculate the tyre width in inches:

245 x 0.03937 = 9.6456

TD = 18" + 2 (9.6456 x 0.35)
TD = 18" + 2 (3.3759)
TD = 18" + 6.7518
TD = 24.7518

Allowing our 3% wear we end up with -

TD = 24.7518 x 0.97 = 24.009

Next we calculate the rolling circumference

Rolling Circumference = Tyre Diameter x pi (3.1605)

RC = 24.009 x 3.1605
RC = 75.880 inches
RC = 75.880 divided by 12 = 6.323 feet

That gives us our basic data to do the rest.

Next we will look at the difference in RPM at 65 mph for our three chosen rear axle ratios.

RPM = (MPH x Gear ratio x Final Drive x 88) divided by circumference.
Our input data is thus:

MPH = 65
Gear Ratio = 1:1
Final Drive = 3.45 or 3.23 or 3.80

For 3.45 -

RPM = (65 x 1 x 3.45 x 88) / 6.323
RPM = 19,734 / 6.323
RPM = 3,121

For 3.23 - RPM = (65 x 1 x 3.23 x 88) / 6.323 RPM = 18,475.6 / 6.323
RPM = 2,922

For 3.80 - RPM = (65 x 1 x 3.80 x 88) / 6.323 RPM = 21,736 / 6.323
RPM = 3,438

As you can see at a steady 65 mph (close enough to 110 km/h) there is a 516 rpm difference from the highest to lowest rear axle ratio - significant when it represents almost 10% of the available rpm range.

Next we will turn these calcs around to see what difference in SPEED we get at a fixed RPM.

MPH = (RPM x Circumference) divided by (Gear ratio x Final drive ratio x 88)

Input data:

RPM = 5,600
Circumference = 6.323
Gear Ratio = 1:1
Final Drive = 3.45 or 3.23 or 3.80

For 3.23 -

MPH = (5400 x 6.323) / (1 x 3.23 x 88)
MPH = (34,144.2) / (284.24)
MPH = 120.12 x 1.609 = 193.28 km/h

For 3.45 -

MPH = (5400 x 6.323) / (1 x 3.45 x 88)
MPH = (34,144.2) / (303.6)
MPH = 112.46 x 1.609 = 180.95 km/h
For 3.80 -

MPH = (5400 x 6.323) / (1 x 3.80 x 88)
MPH = (34,144.2) / (334.4)
MPH = 102.10 x 1.609 = 164.29 km/h

Almost a 30 km/h drop in top end speed but that gearing change will also make a difference in the 400 m and 0-100 km/h times due to the lower overall (numerically higher) gearing but that's a topic for another article.

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