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XR6-T ... poorly chosen gear/diff ratios

11K views 45 replies 19 participants last post by  Venom XR Turbo 
#1 ·
I’ve just been looking over the specs for the XR6-T, in particular the manual gear ratios and final
drive. The ratios are fairly close at:

1st 2.95
2nd 1.94
3rd 1.34
4th 1.0
5th 0.73
Final drive 3.45

At 6000 rpm max speeds through the gears, according to Wheels magazine, are approx:

1st 68
2nd 104
3rd 151
4th 203
5th 230 @ 4950 rpm

Now, given the wide torque band of this engine, it seems to me a close ratio gearbox is
unnecessary. Also the diff ratio of 3.45 seems way too low for economical cruising. In 5th gear 100
kph occurs at 2150 rpm. This is above where max torque is produced and so is wasteful as far as
fuel efficiency is concerned. For max fuel economy at cruising speed you need to gear your engine
either right on peak torque or just below it so for this engine that is at 2000 rpm or just below.

The other aspect of having such a close ratio box is the change points in relation to 0-100 kph and
SS 400 metre times. Now the 0-100 bracket is OK with just the one gear change necessary but there
is an extra change needed just before the 400 metre mark is reached. This is because 3rd gear runs
out at 151 kph - the car crosses the line at 160 kph so a change up to 4th is necessary for the last 50
or 60 metres or so. So the all important SS 400 m dash is probably at least 0.25 - 0.5 secs slower
than it could be with a better choice of 3rd gear ratio.

Now consider the original T5 back in 1987 -

1st 3.5
2nd 2.14
3rd 1.39
4th 1.0
5th 0.78

...and lets choose a final drive of 2.92:

The max speed in gears becomes:

1st 67 (virtually identical so no more effort on the clutch - actually a slight bit easier)
2nd 111 (gets past the 100 kph mark nicely)
3rd 172 (gets past the 400 metre mark without the extra gear change)
4th 239 (every possibility of achieving a higher top speed if it can get to the redline in 4th)
5th 230 @ 4500 rpm

Cruising at 100 kph in 5th gives just 1950 rpm.- one would have to assume this is more economical
than 2150 rpm as the torque is virtually the same therefore the engine is not under any more load.

Seems to me therefore that the Ford engineers have miscalculated again. We have to ask “why is
this so?” Surely they are not incompetants - although their efforts of late I have also questioned
regarding the Series 3 Tickfords. Also, it is worth noting Wheels criticised the gearbox and
driveline for noise and lack of smoothness - another carry-over from AU.

I’m wondering if Ford aren’t actually making a concerted effort to force ppl out of manuals
alltogether by making them inappropriate for the use to which they have been put, and user
UNfriendly - if the customers (what few of us are left who like manuals) decide, for the reasons
I’ve stated above, to select an auto over the manual there will be huge cost benefits to the
manufacturer.

What does any one else think about my “conspiracy theory”?
 
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#3 ·
Mr Jucy said:
I think you a nut but I wouldn't be at all surprised to see a 5 speed auto & a 6 speed manual in the BA Series 2 I guess they've gotta keep something up their sleeve for next time
Good contribution to the thread. Very worth while. Nice to see you thought about the discussion before you posted. :whoaa:


Good point T3man. And well made. Good to see some comparative figures on the ratios.

Like you say, has to make you wonder what Ford are doing. It literally doesn't add up. :wtf:

Conspiracy theory might be going a bit too far though... ;)


As for a 5speed auto and 6 speed manual for BA2, great. Lets hope they get the ratios right... And put them in a decent box :dead:
 
#5 ·
O
1st 67 (virtually identical so no more effort on the clutch - actually a slight bit easier)
2nd 111 (gets past the 100 kph mark nicely)
3rd 172 (gets past the 400 metre mark without the extra gear change)
4th 239 (every possibility of achieving a higher top speed if it can get to the redline in 4th)
5th 230 @ 4500 rpm
[/B]


239Km/h is quite hard to achieve when the XR6T is speed limited to 230km/h
 
#6 ·
call me insane but maybe they geared the turbo up for acceleration to get maximum performance rather than worry about fuel economy.

therefore i think your conspiracy theory says your nuts too!!
 
#8 ·
All of the I6's have been using the gearbox with the 3.5:1 1st gear since it was introduced and the V8 gearbox has been using the one with the 2.95:1 1st gear and i'd say the reason that they are using the V8 box is that it is a fair bit stronger and can cope with the torque of the I6-T.

Guess we will have to wait and see if they get the 6 speeder in series 2 that Borg Warner is currently working on.
 
#9 ·
bdave351 said:
call me insane but maybe they geared the turbo up for acceleration to get maximum performance rather than worry about fuel economy.

therefore i think your conspiracy theory says your nuts too!!
Read just half of what I wrote eh? - If you go back and read it again you might see that I was pointing out that the gearing is actually hindering maximum performance. Call me nuts but I like maximum performance WITH good fuel economy - and I've shown how it can be achieved if you look closely at what I've put.

The conspiracy theory was very tongue in cheek if you didn't gather that from the post...sorry for being too subtle with it.
 
#10 ·
Just guessing, I think that fords main goal in mind may of been to spread the gears so that the max speed would be where the cut-off is (giving you a 5 gear manual). Obviously making the arrangements to the gear box that you prescribed would of meant the final 5th gear wouldn't of really been needed if the 4th gear reaches the cut-off before the change...

I dunno...actually what are the ratio's for the auto box anyway???
 
#11 ·
Um I think you'd find my & Bdaves comment as tounge in cheek as well

Are they the same ratios as the AU had cause I wouldn't be surprised if they just left the gearing alone to save some dollars they have spent heaps on other areas & if they do in fact have new boxes only a year or so away I guess they would figure it not worth mucking around with

But I could be completely of the mark & a loony myself who knows after all i have 4.1.1s 7 a three speed in my car
 
#12 ·
NeoXplod said:
Just guessing, I think that fords main goal in mind may of been to spread the gears so that the max speed would be where the cut-off is (giving you a 5 gear manual). Obviously making the arrangements to the gear box that you prescribed would of meant the final 5th gear wouldn't of really been needed if the 4th gear reaches the cut-off before the change...

I dunno...actually what are the ratio's for the auto box anyway???
The point is they haven't spread the ratios at all - they have a close ratio box behind an engine with a huge torque band which is quite the opposite of normal practice.

It doesn't matter if you reach top speed in fourth - fifth is still required for highway economy.

This engine has so much torque you would only need to use 1st 3rd and 5th gears in normal everyday driving and still be able to blow almost everything on rice into the weeds.
 
#13 ·
T3man - I agree with most of what you say especially as far as 1/4 mile gearing is concerned. Looks like a good mod for a manual XR6-T would be a 3.08:1 diff centre to really get it rapping out 3rd thru the traps, plus an exhaust and a bit of boost of course :D
 
#14 ·
Hmmm 6 sppeder fpr BAII, I like the Idea of that. So Borg Warner is making a 6 speeder? When will it be ready? What will it be called the T6 or something? I was going to say Ford should use the Tremec 6 speed from the Hiller coupe, but if this Box is ready, I say ford should use it becasue they NEED a 6 speeder, or even an optional one.
 
#16 ·
I'm glad they geared it for acceleration! Well done Ford! T3man -changing just before the 400m line actually makes stuff all difference to your quarter mile time, I've missed gears before the line & it would be lucky to make even 1/10th of a sec difference (does knock your terminal around though). Quarter mile times are largely determined in the 1st 60ft of the track. Also, when you boost it you'll be well into 4th when crossing the line!! I think that given its a revvy engine & the sporting nature of the car they could not have geared it better, I was dreading another 2.92 ratio. Majority of buyers will not be buying the car for interstate economy runs.
 
#17 ·
Actually in keeping with my bogan status if I was buying one I would be chucking the manual ....

in goes the powerglide with a high stall convertor and trans brake with a minimum of 4.11 depending on tire size!

Maybe I should grow my mullet back since I cant adapt to all this danged new fangled whiz bang technology stuff!
 
#18 ·
slapper said:
I'm glad they geared it for acceleration! Well done Ford! T3man -changing just before the 400m line actually makes stuff all difference to your quarter mile time, I've missed gears before the line & it would be lucky to make even 1/10th of a sec difference (does knock your terminal around though). Quarter mile times are largely determined in the 1st 60ft of the track. Also, when you boost it you'll be well into 4th when crossing the line!! I think that given its a revvy engine & the sporting nature of the car they could not have geared it better, I was dreading another 2.92 ratio. Majority of buyers will not be buying the car for interstate economy runs.
Sorry slapper - I can't seem to grasp that on one hand you say an extra gearchange before the trap won't make much difference to the time but it does make a difference to your terminal?

And even 1/10 sec on paper is enough to persuade some buyers to shop the alternative - we're talking about an outright performance vehicle here, and surely nothing less than the absolute best performance time is acceptable.

Changing into 4th at 151 kph and shooting the trap at 160 kph doesn't put the car well into 4th IMO - you're using an extra gear to gain just 9 kph - any way I look at it that is not going to produce a best time.

I'm not an expert at 400m dashes but I would expect that by changing to the gearing I put forward the time should be sub 14 sec, maybe 13.9 and terminal around 165 kph.

I know some ppl have programs that can do these calcs so can anyone do this and let us know please?
 
#19 ·
T3man - without going into the physics of it all, have you ever drag raced yourself or been to the drags? A simple example is where you see a door-slammer shut the engine down after the 1st 200 meters, yet it will still run a flat 10 at about 60mph. Drag racing is all in the first 60ft of track. Your gearing proposal would produce slower times, why do you think racers like bdave351 stick 4.11 diff ratios in their cars?, because it increases the torque to the rear wheels hence gives quicker acceleration hence quicker quarter mile times (albeit more gear changes). In my VLT, I changed from a 3.45 to a 3.77 diff ratio & dropped my times by .3 sec. PS I was referring to the car being well into 4th when boosted (ie 18-20psi + mods ie something running about 125mph).
 
#20 ·
Slapper, drag cars and street cars are very different in how they get off the line.

Look at the AUIII XR8 and the SS. The AU gets of the line quicker than the SS, but the SS catches it in top speed. Why? Gearing. (And the Gen III loves a rev)

T3Man, I know you are getting on. Act your age mate, buy a Auto. :1poke:
 
#21 ·
Ken - yes, drag cars & street cars are different but they are equally affected by the same factors ie weight transfer, traction, gearing etc. I agree gearing is part of the equation but I think you'll find the major contributing factor in your example between the XR8 & the SS would be the SS has a better power to weight ratio & more importantly, a stack more torque.
 
G
#22 ·
Ok put the XR6T into a program and ran it down the 1/4 with the 2 different gear setups.

Actual Ford gearing for the Ford Falcon BA XR6T 2002 Manual
Gears
2.95
1.94
1.34
1.0
.73

Final 3.45

Km/h
0-40 1.7
0-60 2.6
0-80 4.4
0-100 5.9
0-120 8.5
0-140 10.9
0-160 13.8
0-180 18.4

0-100m 6.1
0-400m 14.2 @ 160Km/h
0-100m 25.8 @ 208.1 Km/h

Terminal Speed of 259.5 (if no limiter of course)
Time taken to reach top speed 173.21 sec
Distance Covererd to get to top speed ~11.5km


Proposed gearing for the Ford Falcon BA XR6T 2002 Manual
Gears
3.5
2.14
1.39
1.0
.78

Final 2.92

Km/h
0-40 1.7
0-60 2.6
0-80 4.5
0-100 6.0
0-120 8.5
0-140 11.2
0-160 14.1
0-180 17.8

0-100m 6.1
0-400m 14.2 @ 161.1Km/h
0-100m 25.9 @ 204.4 Km/h

Terminal Speed of 250.9 (if no limiter of course)
Time taken to reach top speed 106.7 sec
Distance Covererd to get to top speed ~6.5km

All other factors were left the same in the test, only the ratio's were changed. Also The program can not emulate traction control so there is wheel spin taken into account above.

{Edited} added fuel consumption details.

The program also estimated fuel consumption (not very well)
Fords gearing produces
19.8/100 City
13.0/100 Highway
16.7/100 Combined

Proposed gearing produces
18.3/100 City
11.6/100 Highway
15.3/100 Combined

So although the figures are obviously WAY out, they can possibly be use to decide relative fuel consumption. So the proposed gearing is possibly more fuel economical.
 
#23 ·
Interesting stuff, but curious re 3.45 ratio as the program calculates a 0-160 at 13.8 sec yet 0-400m is 14.2 sec (but still at a terminal of 160)? Shouldn't these times be the same or am I missing something? Why is time & distance to reach top speed have such a massive difference between the 2 set-ups? What program did you use to crunch these numbers?
 
G
#24 ·
The program I am using is:
CarTest - Car Acceleration Simulation, Version 4.5
Copyright (c) 1992-98 Patrick Glenn, All Rights Reserved

The reason for the 0-160 13.8 and the ET of 14.2 is the fact that 160km/h is 6000rpm in 3rd gear. So there is no acceleration due to the gear change between reaching 160km/h and hitting the 400m mark.

During a gear change because 0 power is being put to the ground and there is a large amount of air resistance (friction) the car starts to slow down until 4th gear is engaged and the power re-applied.

The reason for the massive difference in that the last few km/h take such a long time to reach. The 2 different setups reach 250km/h at 3950m and 3635m for the Proposed and Ford setups respectivly.
 
#26 ·
Mighty Highlig > Yes, thanks for that - I knew someone out there had a program to test the figures on - makes it all very interesting and looks like I'm not too far away with my reckoning.

When I get my XR6-T it'll probably be an auto ... sigh ... never before willingly purchased an auto if a manual was available.
 
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