Revs with 3.9's or 4.11's.

NeishaXR8_347 · 20-02-2006, 09:02 PM

Hey just after some info on some of your cars sure some have fitted up 3.9 or 4.11's to ya AU's, i have au2 xr8 auto and would like to know what revs they do in 4th gear at 100km/h with 3.9's or pref 4.11's. Also how do u think 4.11's would go behind 180 odd rwkw's.

stiddy · 20-02-2006, 09:11 PM

4.11's will probably be a little to high for the street, well it really depends on if you do alot of highway driving aswell..
but say you rev at 2200rpm at 110km/h with 3.9's youd be at around 2600ish rpm

my car used to sit on 2200rpm at 110-115km/h now with 3.7's it revs about 150 or so rpm higher and im getting 4km/h less out of each gear.. Im wishing I went for 3.9's though.. 4.11's are a little too short in my opinion..

NeishaXR8_347 · 20-02-2006, 09:22 PM

Nah i dont do much highway driving and only sit on about 100 or so but i would sit on 90 if had too, mine does 2000 now at 100 with the stock 3.45

stiddy · 20-02-2006, 09:40 PM

4.11's would give it a good sting on take off.. but be revving faily high at 110km/h

3.9's would be a good compromise between acceleration, and crusing at higher speeds..

XR6-VCT-2000 · 20-02-2006, 10:13 PM

yep , 4.11's good for the quater mile, launches the car heaps more , rough eg.. it will get from 0rpm to 3000rpm faster than 3.9's , but from 3000rpm to redline the 4.11 is slower than the 3.9's , but as said above at like 100km/h with 4.11's the car will be reving higher than usual while cruising , this resulting in more fuel usage.....imo from results i have seen the 4.11's works nice with the ford 4 speed auto - matches it pretty well..... as if u have an auto now u notice the AU is a bit boggy down low but once the revs pick up it takes off - it sorta more balances the power out more- much more solid take off..but less topend speed.

All that worrys me if its not setup right is that the ecu/electric stuff reading your rev tacho and speedometer might think your doing 100km/h when your actually only doing like about 60km/h , Im not sure if there is some sort of switch u can flick - or if something has to be reprogramed to let the ecu know the gearing of the car .. ???

if you want fuel economy and dont mind the launch of the car as it is now then i'de personally leave it 3.9's
;)

Walkinshaw · 20-02-2006, 10:20 PM

Quote:

Originally Posted by XR6-VCT-2000

yep , 4.11's good for the quater mile, launches the car heaps more , rough eg.. it will get from 0rpm to 3000rpm faster than 3.9's , but from 3000rpm to redline the 4.11 is slower than the 3.9's , ;)

That comment defies all physics

XR6-VCT-2000 · 20-02-2006, 10:30 PM

sorry i worded that wrong , what i meant .. il try again .. is ... all around the 4.11's gearing is gonna give u a faster take of than 3.9's, and rev quicker through the gears all the way through - where as is now with the 3.9's the difference is like its slowish on take off but picks up more as u get through the middle of the rev range - where as the 4.11's will give u a more solid smooth constant rev rate ... but is all ИИИИ yeah u gonna finish a quater mile quicker with the 4.11's providing u dont hit top speed only half way down the track , as with the 4.11's u will have less of a top speed on the speedometer in top gear ... i hope that makes sence a bit more. sorry ..

XR6-VCT-2000 · 20-02-2006, 10:39 PM

i wasn't meaning/saying the 3.11's will rev faster than the 4.11 through to redline , i was just looking at it as if u look at 1 compared to the other in the way the 'pickup/rev response' is , how the 3.11 will be slower at take off but gets faster ,compared the the 4.11 will be like fast all the way faster , so its like u dont have that bogish start anymore . lol ..prolly just confusing u more now ...lmao , i know what i mean anyways ..lol - but i can see how i have worded it that it could sound wrong yes i agee sorry .

NeishaXR8_347 · 20-02-2006, 10:43 PM

Well considering i only have 3.45's at the moment 4.11's will feel like a big differance i hope, according 2 like 3 rpm and raqtio converters on the net it should only rev at about 2400rpm which is stuff all on a v8 considering my mum has a brand new 1.8litre corolla and at 100 it sits on 2400 std so if a baby 4cyl can do it then i think a worked v8 can do it all day long, whats the longest anyways at the most i would drive it constantly for 1hr or 2. so 4.11 i think r sounding better and better 2me. just my opinion

Casper · 20-02-2006, 10:46 PM

Comes down to simple maths. You want the shortest set of gears to get you down the 1/4 WITHOUT forcing you into 4th gear. That extra gear change will kill the times.

Net result, 4.11's in a Falcon auto will change to 4th at ~150kph. If you are going to only reach ~160kph on the 1/4 then the last change will kill your time.

For the general breakdown:
Gear rpm speed in 3rd
3.45 5500 179kph
3.73 5500 166kph
3.9 5500 158kph
4.11 5500 150kph

Choose the shortest ratio that will keep you from changeing into 4th gear and you are there

Dodge · 20-02-2006, 10:48 PM

4.11 for the strip, 3.0 for the freeway if u have enough torque and 3.5 for the best of both worlds, I have some 3.5 motive gear sets for sale , some are cnc lightened.

XR6-VCT-2000 · 20-02-2006, 10:52 PM

honestlly , only reason why i mention some help is because originally years ago my in my XE i had the first of the ford 4 speed autos from a new model stacked mustang in the states ( ford fiad i think it was ) - the gear ratio of the tranny is preyy much the same as now in the AU - except i originally had 3.25's , was still quick on take off , fast car too , but couldnt even use 4th till 100kmh then it like idled along - i then went and put 4.11's in and omg what a difference it made , the car literally launched - the car actually started falling apart after i put the 4.11's in , was twisting the hell out of the car - could see huge gaps around the doors etc etc when u booted the car from takeoff - layed some mean rubber to if needed

.. but guzzled heaps more fuel , but also made 4th gear more usable down low...

)

Walkinshaw · 20-02-2006, 11:03 PM

what panzy revs their car to 5500 on the strip?

XR6-VCT-2000 · 20-02-2006, 11:13 PM

casper ... but also with the 4.11's u'll get to 150kmh way faster than with the lower ratios , specially like with the 3.45's - would be like the car with the 3.45's would be 1/3 down the track and still in second just about to change to third, while the car with the 4.11's would be 2/3 down the track and in 4th but reaching maximum speeds ..... sorta all evens itself out ... but imo with a hard/solid engine with auto and 4.11's i think the 4.11's would win the q/mile ....just - and reving its guts out in top gear - where as the car behind would come screaming past just over the q/mile line ....

really 4.11's is for a more worked car , more made for the track ..

xr8ute · 21-02-2006, 12:49 AM

I love the 3.9's in my ute. The difference it makes to part throttle driving is great, the difference in first gear from a standing start is not so noticeable...

I am crossing the line at 97mph, only just before redline in 3rd gear. With 4.11's I reckon I would be well into 4th gear.

SIKSIX · 21-02-2006, 05:48 PM

get a 6 cyl auto with skock diff and cross the line in 2nd.. :sm_headba

SIKSIX · 21-02-2006, 05:53 PM

on a serious note..my brother has 3.73 also and i rekon for every day driving you can go one shorther, just lose out on economy on freeways. why not i rekon if you want them get them.

i got a mate with a ef 6 with 4.11 and a spool (burnout MACHINE!!!) and he rekons he should of gone 4.55's but them again he put a spool in his car so i rekon he's a bit

:

buickman · 21-02-2006, 06:12 PM

Quote:

Originally Posted by Dodge

4.11 for the strip, 3.0 for the freeway if u have enough torque and 3.5 for the best of both worlds, I have some 3.5 motive gear sets for sale , some are cnc lightened.

You hav'nt a 3.5 31 spline 9" diff centre for sale ?

OED666 · 21-02-2006, 06:25 PM

Quote:

Originally Posted by Walkinshaw

what panzy revs their car to 5500 on the strip?

exactly... 6000rpm is where you change gears...

to more accurately work out revs at 100km/h...

revs at 100km/h, divided by current diff gear, then mulitply by new gear...

eg..

1700 / 3.08 = xxx and then multiply your answer by the gears you want..

4.11's are great, but 3.9's probably are the pick for the auto...

NeishaXR8_347 · 21-02-2006, 08:07 PM

Thanks for all the reply's guys, i rang jim mock ms today and he said that if i change my diff ratio to say 3.9's or 4.11's then i have to get my speed limiter cut out cause it will cut in at like 150, and also said that i need to buy some electronic box to correct my speedo which is another $300, the diff all up is $1650 with so called strenghtened lsd and crap, bit pricey i think. He also said an alt to changing ratios he has designed a 3200rpm stall converter which would allow me to take off in my power band he said it was tested and it made quicker times then the 3.9's. What do you guys think?

Dodge · 21-02-2006, 10:09 PM

or change the gear box ratios, find a overdrive 4th cog

Dodge · 21-02-2006, 10:10 PM

buickman email sent I do have a 31 spline 3.5 punkin 4 sale

XR6-VCT-2000 · 21-02-2006, 11:31 PM

neishaxr8 . i though that would be the case if modding to 4.11's , sorry to hear .. good luck with whatever you choose anyway . ;)

Mark351 · 22-02-2006, 12:40 PM

...or drive a manual with a 5th gear.

xr8ute · 22-02-2006, 08:05 PM

I reckon that the 3000rpm converter would yeild quicker times than changing to 3.9's.

The prices seem a bit out there though...Cost me $900 (950?) to get my diff rebuilt and a new 3.91:1 ring and pinion. After installing an $10 speedo gear from Ford, my speed limiter is about 167km/h, and my speedo is 10% fast. $80 worth of Jaycar speedo corrector kits will fix it (need 2 kits @ $40 each).

If you have an edit, then you just need to get the value of the diff ratio changed, a decent tuner should do this for you for nothing.

But if 1/4 mile is your thing, go the converter over the diff. The very tall 1st gear in the auto is the reason why these things are so slow off the mark, converter will help that more than the gears.

Sylox · 22-02-2006, 08:22 PM

Same as xr8ute's comments here.
Au2 xr8 ute with 3.9's bugger all difference off the line (exact 60ft no wheel spin) Computer likes to play games when you change the diff ratio, some cop it hard like myself and others like xr8ute seem to only get minimal trouble. Its torque reduction though one of the trans parts of the eecv. (no ones tapped it yet)
3.9's are all you would want in a street car. But if your going to do it in a ute you will also need a new tailshaft (will want to come though the floor between 130-160kph) also you speed limiter will drop right down so factor that in to be removed.
I think XR8UTE finds the 3.9's better due to the more aggressive camshaft he has over my stock one. I'm just about to go bigger in cam again to the TSF1 so we'll see if that helps the gears out, as one theory was that its passing though the power/torque curve to quickly.
At a guess I think I get 50ish from 1st - 115ish from 2nd - 155ish from 3rd and my limiter is up round the 6000rpm
RPM @ 120kph bout 2800

100% back xr8ute on the Convertor will show more than the gears. Just watch out for limp home mode, and make sure the convertor matches your cam/power/torque curve.