Top speed in 3rd with an auto and the 1/4mile

[Stav]

Does anyone know what speed an auto can be held in without changing into 4th under wide open throttle?

I read that in economy mode the base au six can go to 175 kmph before changing.The xr range changes at 150 kmph.
In power mode the base ford au six changes into 3rd at 179kmph the xr models change at 167 kmph.
Does this mean that the base car has better shift points for the 1/4 mile stint over the xr and can run a stiffer diff ratio without problems?

[5L]

the fact the xr changes sooner, is due to the higher diff ratio. xr's actually rev out higher than base models.

[Stav]

If I ran 4.3 diff ratio what would I need to do to have t right for the 1/4 mile? Also what can we do with the edit to help?

[xr8ute]

It all depends on the gearing Stav, and how your shift patterns have been programmed (edit)....assuming they've been changed from std?

Wheres your rev limiter? At what rpm is your car shifting from 3-4 at WOT?

The reason the base AU Forte, and XR have different speeds for gear shift is because of the different diff ratios.

I am crossing the line in third, at 99-100mph, at just under 5500rpm with the 3.91's. I need to shift the gearbox manually so that it doesn't shift up too early.

[Stav]

I used to cross the line at 4700 rpm at 92.7 mph 149 kmph. Assuming a 4.3 ratio from my 3.73 it is a 15% change. I would cross the line at 5405 rpm for the same mph.The 4700 rpm is not the meat of my power in third.Power peaks at 5000 rpm.Bulk of power is at 4700 to 5400 rpm..Rev limiter is 6000rpm.
If I put the car in third for the run will it still change up to 4th or will it hold it more?

[Stav]

I might have to modify the box by reading its wiring diagrams to guarantee the box will be locked in 3rd.

[The Monty]

Im pretty sure the Fairmont (AU1) changes right on the limiter, so 179-180 in non econ mode. Thats for me anyway.

[eXi7w0unD]

my stock i6 does 150 in 3rd lolz.

i usually go to 40 in 1st then change, when i hit 70-80 i change to 3rd. im a nut.

[Stav]

Can the auto be taken past the normal change up speed by somehow holding 3rd gear across the line and hence avoiding fourth gear?

[EFFalcon]

Originally Posted by Stav

Can the auto be taken past the normal change up speed by somehow holding 3rd gear across the line and hence avoiding fourth gear?

it should hit the limiter.
work out what speed you're doing when the rev limiter kicks in.
thats what 3rd will rev to :P

[Stav]

Hmm 6000 rpm limiter with no speed limiter.So holding the gear lever in 3rd should go to the limiter then?
My rev limit is 6000 and no speed limit

[Stav]

The wagon will pull 5500 - 5800rpm across the line.It may hit the limiter at the line actually.I get it to 6100 rpm then.ehe

[Ruger]

Originally Posted by Stav

Can the auto be taken past the normal change up speed by somehow holding 3rd gear across the line and hence avoiding fourth gear?

Yep when you use the 1 2 3 D method your not holding the gear but rather locking out the next gear - i.e if you leave it in 2 your locking out 3rd and 4th but the auto will still shift normally through 1st and 2nd What you can do is put it in D start racing, then when its in second or third and you want it not to upshift just move the lever back one spot to '3' and it wont shift up again.
Just manualise the auto ;)

[stiddy]

If you leave it in third it wont shift, it will just keep going till you hit the rev limiter in that gear, which would be around the 160km/h mark maybe?

thats weird, even with a manual before I had my diff gears done I was crossing the line in 3rd at about 5500-5800 or a little more which was around 150km/h, sometimes I hit 3rd gear limiter on the line or a little before it.

[Mechan1k]

If you lave it in 3rd it will stay in it ... and not shift up to 4th ... I have tried it with it locked in 1st and in 2nd ... and it doesn't shift up ... and i leave in locked in gear.

I suggest manually shifting it when racing ... it will hold it longer in the gear than just leaving it in D in power mode.

[Stav]

This is good news.With a 4.3 or 4.11 ratio the wagon would miss the rev limiter under wot then get held in third for crossing the line where it would hit the speed limiter for a theoretic 13 second pass at 100mph. Nice.

[Mechan1k]

Just make sure you have the right speedo gear ... other wise the ECU likes to cut it out earlier ... also you can get a Limp Home Mode Defender box installed as well (I didn't realise there was one until I saw one the other day.)

Jase found out the hard way the other week ... was set to crack 13's after new axle and shorter diff in it ... went from 3.23 to a 3.89 from memory) ... hit speed limiter ... fule cut and ECu went into LHM/Guard mode and wouldn't rev over 3K RPM ... not happy.

Oh well .. next time ... he still managed a 14.2 after hitting fuel cut and coasting over the line very slowly ... so there was definitely a 13 in it.

Next time I guess.

[Stav]

The speed limit can be raised with the edit tune and so can the rev limit. Any cut outs should then be eliminated.Dont you think?

[Mechan1k]

True ... true.
That's the next thing he has to do (as he is still running factory tune)

[Stav]

He will do well and it should also help my wagon to do a bit better.

[Mechan1k]

Especially if power is still being made at redline ... if you can extended the relatively short redline it will help ... how much did you get your shift-points altered with the tune??? Or just get line-pressure increased with it???

He needs to save up a bit of rego now ... all in good time I guess ... and there's a set of MT's he is going to run with next time as well ... and increased redline (as he still making power/torque at rev-limit as is now).

[Stav]

I dont know? i did install black speedo gear for the 3.73 I am running. Still the speed was out by 5 odd percent. I drove the car in first today to check my redline and its confused me a bit. Tacho show 6400 rpm and a second tacho showed 6150 rpm in first.So I geuss it may be at 6150? i am getting this checked soon to be sure.

[xr8ute]

Originally Posted by Stav

Tacho show 6400 rpm and a second tacho showed 6150 rpm in first.So I geuss it may be at 6150? i am getting this checked soon to be sure.

the std tach in the dash is pretty innacurate in my experience as well.

it shows 5800rpm when it hits the limiter, while datalogs from the "clean tacho output" pin on the EEC show 5500rpm as the limit.

[Mechan1k]

Run the dash diagnostic ... the digital readout for the speedo and tacho seems more accurate than the analog gauges (I have been doing testing recently myself with it) ... the digital speed readout matches my GPS reading on the highway ... analog is about 2 kays out.

[Ruger]

26" tall tyre 3.7's in the bum and 3rd gear in the auto (1.00) youll be doing well over 100mph.

If you hit the limiter in third somethings odd (or youve put a hairdryer under the bonnet :P)

EDIT: Stav - Before you outlay some money there is a program called gearcalc. google for it and itll answer all your questions better than any of us can.

[eXi7w0unD]

any 1 can drive auto but to drive stick in an auto.. thats takes skillz

[Casper]

about 5750, rpm cutout

[Stav]

Thats awesome.That is such a big help mate..Top stuff!!! : . A slightly raised rev limit will see our cars across the line with limiter not kicking in.

[Casper]

Originally Posted by Stav

Thats awesome.That is such a big help mate..Top stuff!!! : . A slightly raised rev limit will see our cars across the line with limiter not kicking in.

unless you are looking to run 101mph with 4.11 diff gears the limiter in 3rd is not going to even be close to an issue. I'm not even close to touching it and cant see it being a problem for NA I6 AU's.

[Ruger]

Stav what size tyre you running mate?

245/45/17 5750rpm with a 3.7 gearset in the bum, math tells me its good for 120mph @5750rpm 4.33:1 = 103mph @saidrpm