3.73 diff with 205/65/15 tyres and rev limiter

**Stav** · 03-10-2005, 01:11 AM

With the stallie now in place it seems that the car needs some more revs to achieve a more efficient state of converter lockup. Considering the standard tyres and with a possible 3.7 diff will I hit the rev limiter on hard acceleration?

btw where is the rev limiter?5800 rpm?

JC · 03-10-2005, 01:31 AM

You shouldn't hit the limiter - the auto should shift at the same points. You might hit it in top though, though you will probably hit the speed limiter (180) first.

jonbays · 03-10-2005, 09:03 AM

Well you might hit the rev limiter but only if you correct your speedo as the ecu shifts up at the same speeds its programmed to.

With a lower (higher ratio) diff the car will be going slower for the same revs but the ecu won't know anything has changed as it only sees the input from the VSS speed sensor in the back of the gearbox sensing tailshaft not road speed.

now if you change the speedo drive gear to correct the speedo 9slow it down as it will read fast) then the car will rev harder before changing up possibly hitting the rev limiter in second before changing up.

I changed from brown to black speedo drive gears and mine changes up at 5550rpm in second well before rev limiter 58-900rpm. AUI and AUII could have different change up points though mine changes at about 123kmh in second on the speedo.

**Stav** · 03-10-2005, 10:15 AM

So please correct me if I am wrong....If I do the diff and simply change to a 3.45 ratio cog,my car may not hit the rev limiter right?

If the speedo is slightly out I dont really care .I drive like a snail in normally due to the level of unpredictability from the vast majority of other careless drivers.

Casper · 03-10-2005, 10:39 AM

Quote:

Originally Posted by useless

So please correct me if I am wrong....If I do the diff and simply change to a 3.45 ratio cog,my car may not hit the rev limiter right?

If the speedo is slightly out I dont really care .I drive like a snail in normally due to the level of unpredictability from the vast majority of other careless drivers.

If you do not change the speedo gear then you will not hit the limiter, it will change at the same rpm's it does now. Your speedo will be out though.

If you change the speedo gear then you effect the rpms the engine changes at and need to get around this some way.

jonbays · 03-10-2005, 10:54 AM

The car will change gears the same as it does now when you change the diff as the ecu can't learn about the diff ratio.

It will howver hit the speed limter of 180 on your speedo when you are really only going 156k

SpoolMan · 03-10-2005, 11:27 AM

we found after changing to 3.9's in the AU6 with an unopened engine car shifted fine in auto Mode.
Once Cam and other work was done to engine it shifted way to early in Auto mod, we have been changing at around 5600 rpm by the time it changes its at app 6000 rpm.
with the converter we use revs drop only to app 4500 rpm on the change, so the car is striaght back into its peak torque which is made at 4500 rpm...
you need to find out what revs your car is doing on the gear change...

**Stav** · 03-10-2005, 11:32 AM

Quote:

Originally Posted by jonbays

The car will change gears the same as it does now when you change the diff as the ecu can't learn about the diff ratio.

It will howver hit the speed limter of 180 on your speedo when you are really only going 156k

If I go 3.45 cog will I hit rev limiter?I am running 3.23 diif.

**Stav** · 03-10-2005, 11:35 AM

Quote:

Originally Posted by XRFPV8

we found after changing to 3.9's in the AU6 with an unopened engine car shifted fine in auto Mode.
Once Cam and other work was done to engine it shifted way to early in Auto mod, we have been changing at around 5600 rpm by the time it changes its at app 6000 rpm.
with the converter we use revs drop only to app 4500 rpm on the change, so the car is striaght back into its peak torque which is made at 4500 rpm...
you need to find out what revs your car is doing on the gear change...

I will go for a drive and note the gear changes.I believe that the rev limiter will only be an issue under wot.As for the safety concerns..my tailshaft is a steel one from an eb wagon unlike the alloy crap in the au's

**Stav** · 03-10-2005, 11:36 AM

Quote:

Originally Posted by Casper

If you do not change the speedo gear then you will not hit the limiter, it will change at the same rpm's it does now. Your speedo will be out though.

If you change the speedo gear then you effect the rpms the engine changes at and need to get around this some way.

Will the car be faster anyway?Without cog?With the 3.45 cog in the tranny maybe can get a higher speed limit without having to have difficulties with rev limit?

jonbays · 03-10-2005, 11:51 AM

useless cahnging the diff only makes NO Diffrence to the rev limiter at all.

The transmission does not know and will beahve exactly as it does now.

However you will find it easier to hit the SPEED LIMITER of 180k.

You wont be doing 180 really of course

jonbays · 03-10-2005, 11:57 AM

Changing the diff ratio to a 3.45 or 3.7 will drop the gearing so the car will be faster particularly at 100-160k speeds in third.

Most noticeable will be third gear which will feel more like second does now and it will rev out in third rather than struggle to rev out as it will be going slower and pushing less air than it was before for the same revs.

All the gears will be lowered the same amount but the difference will be felt less in first and second.

It will look spectacular on the speedo as the needle will race round the dial so it will "FEEL" much faster than it actually is as the speedo will be 7% or 15% fast depending on 3.45 or 3.72 diff.

**Stav** · 03-10-2005, 12:07 PM

O wow...!!! All this time I thought that fanging the car at full throttle with a 3.7 diff will have me bouncing off the rev limiter.!! I dissapoint myself some times. So there is no issue with the rev limiter but speed limiter.!! 3rd gear as you described it will have big benefits for me.First and second gear arent a problem since the latest mod. By changing th cog in the gearbox I can effectively raise the speed limit while avoiding rev limit with a 3.7 diff. Is the black cog for the 3.45 diff ?

jonbays · 03-10-2005, 12:56 PM

No by changing the speedo drive gear you will move the speed limiter speed back to normal but you will raise the revs at which the car changes gear

**Stav** · 03-10-2005, 01:02 PM

so by installing a 3.73 and using a grey cog I can compensate somewhat for speed correction and raise the speed limiter a few kays up..

LG · 03-10-2005, 01:13 PM

You'll need a white cog for 3.73s. I think.

**ebxr8240** · 03-10-2005, 01:26 PM

Actually the alloy drive shafts are stronger and better at hi rpm due to less weight...They are used in commercial [most] vehicles and XR"s for this reason...
Go to Jaycar and get a speedo corrector, should fix all your auto issues...
http://www.jaycar.com.au/productResu...p?FORM=KEYWORD

Type in speedo corrector in search box...

jonbays · 03-10-2005, 05:00 PM

Useless mate I have a a brown and a grey speedo drive you can have to play with and see what happens to the change up speeds. 5 min to swap them over just better to do it on a cold engine as the exhaust is close enough to give you the s burning yourself.

You don't need to change the diff ratio to try them as the ecu doesnt know about the diff ratio remember.

**Stav** · 03-10-2005, 06:00 PM

ok..this way I can see if I will hit the rev limiter without changing the diff!!

**Stav** · 03-10-2005, 06:03 PM

Quote:

Originally Posted by LG

You'll need a white cog for 3.73s. I think.

You are dead right on that mate.I have seen one of your posts before ..they are available from usa

sfr rob · 03-10-2005, 06:35 PM

i didnt know that the AU had a rev limiter, does it?
when does it kick in?

hey useless, can you list waht mods you have done that have REALLY made a HUGE difference, and what i should be looking at?

so far i have the K&N panel filter, tickford intake, 2.5' mandrel exhaust, no extractors YET.

what should i do next?

cheers mate
Good luck with the modding, sounds like your getting into it in a BIG time!

**Stav** · 03-10-2005, 07:06 PM

Rob ...it depends what you want out of the car? A 0-100 killer or 1/4 mile killer.? The best mod I did was the Jim Mock race series extractors and a 2.5 inch straight through lukey exhaust. 0-100 best time 7.2 seconds

Next I installed a dev 4 cam only.It did nothing for my 0-100 times at all.However when on Croydons dyno here put out 141 -147 rwkws.So while nothing changed on the street the power did increase up top.A standard car with just exhaust wont be putting out 141-147 on any consistent dyno here in Sydney. 0-100 time 7.2 seconds (gtech)

Then the unichip was a great mod.0-100 best in 6.53 seconds flat!!

Lastly the stallie has not been tested yet but I have a feeling fuel economy will be bad .I havent tested times yet but it seriously doesnt feel that much better .It feels less responsive at normal speeds.

yobboford · 03-10-2005, 08:19 PM

will be interesting to see how you go at wsid, if you can get a before diff gear time and then again after you do the swap.

we need to see some more quick wagons out there

.

**Stav** · 03-10-2005, 08:41 PM

Quote:

Originally Posted by yobboford

will be interesting to see how you go at wsid, if you can get a before diff gear time and then again after you do the swap.

we need to see some more quick wagons out there

.

Mate I dont have a clue what I will really run?The plugs are fouled by running too rich at the moment so it needs to be rectified.Then when I run it on my only ever run to be 5th november it will be spot on.I would like to see what the car will run.I like to think I had done it once and done it well.I could be dissapointed but could be surprised. Thanks Yobboford ...

ps Either way a 17 or 14 sec pass...I am having a crap load of fun. I wont be crying if it does not perform as I had hoped it would.

**Stav** · 04-10-2005, 12:58 AM

Well after much thought I have decided that the best diff for me is a 3.45 lsd (or not).My peak power is at 165 kmph .A 14 % change will see peak power at 142 kmph with a 3.73.Then power will die. A 3.45 diff on the other hand will give a 6.7%difference bringing peak power to 153 kmph in 3rdfor me is perfect. Sure a 3.73 will give me more revs quicker but that is no good for my 1/4 mile run next month.
If anyone has a convincing idea that the 3.7 is better then let me know. Of course the 3.7 is the max to go to and should no speedocorrection be made a top speed of 156 kmph is where it will all end.
Technically by the dof ratio ..the more revs does mean fatter power curve lower.So it artificially creates a bigger average power which will also show on a dyno as big numbers early.

Casper · 04-10-2005, 06:52 AM

I have 3.45's in mine.... I'd rather have 3.9's. For the 1/4 they are ideal for the auto I6.. crossing the line in 3rd at over 5000rpms rather in 3rd at about 4100rpms..

I dont have to worry about a speed limiter or auto change points vs speedo correction though so that helps

:

**Stav** · 04-10-2005, 08:37 AM

I think that if peak power is at 4500 rpm then going to 5000 may be a waste of time.Unless of course you use peak power and hold it.Either way the car wont be making more power witha 23.7 or3.9.It will just rev its ring out and not be accelerating anymore. But then again 3.7 will be great for street.Thats where I live ..the street.Dam I am swaying back again.1/4 mile 3.45 diff...street 3.7

SpoolMan · 04-10-2005, 09:32 AM

Quote:

Originally Posted by jonbays

useless cahnging the diff only makes NO Diffrence to the rev limiter at all.

The transmission does not know and will beahve exactly as it does now.

However you will find it easier to hit the SPEED LIMITER of 180k.

You wont be doing 180 really of course

Good point Hamo's AU was hitting the speed limiter before it hit the line, speedo reads wrong after the diff change car thinks its going quicker than it is...thats where the chiptorque j3 comes in to play..