Better Suit Diff Gears

[01txr]

Help with choosing a good street track friendly daily driver gear ratios

Car is a BA 1 XR6T originally T5 but upgraded to T56

Running Xforce 3.5 system, Nizpro Valve springs and injectors, walbro pump and custom tune

unknown made 275rwkw pre x-force exhaust being fitted at 12psi

Pedders lowered to legal height sports rider rear and extreme adjustable fronts

I am running 265x30x19n Toyo Proxy 4's

Just wondering what ratio would see me around 2400 at 100k

Also just went to test and tune and had nightmare getting car off the line 2.3 to 2.6 60fts

Had a lot of axle tramp warming tyres and first gear, had to ease off to soften axle tramping.

think tramping may have been due to the standard bump stops bottoming as only have approx

30-40mm clearance when car parked.

or unless the centre bush has let go.

Another point why times where down would probably be the fact that Iam crossing the line

outside powerband in 3rd and 4th.

To get it pushing accross line in 4th I had to short shift 2nd and 3rd.

If I used power each gear till it rolled off the powerband I would be very low in the revs

4th not pushing hard.

If I held it to 3rd it was well over its powerband and must have been very close to revlimiter

Reaction time (crap) .651 Havn't raced strip since mid 90's

60ft 2.309

330ft 6.140

660ft 9.231

MPH 79.67

KPH 128.22

1000ft 11.893

ET 14.153

MPH 99.80

KPH 160.61

Very disappointed as on the street it feels alot stronger than a standard T.

Have beaten FG F6 A on private race track from rollin start 60k to 120k but only just by approx car length.

and they are suppose to run 13.3s

I am also about to fit a 600x300x76 HDI GT Spec cooler

Plazmaman piping, Airbox & Plazmaman Plenum, Siemen Daka's.

when I fit the above gear I will only be running soft tune to protect BA bottom end till

I complete my engine build.

Might push it to approx 350rwkw if able to control boost set to 8 - 10psi

Engine maybe still 12 mths away to complete.

So will need to work out ratios to suit current, Induction upgrade and after engine build

thinking 3.9 to 4.1 ratio

Would like to keep car just below boost at 110k so dont end up accidently speeding

and having to make donations to QLD revenue office or pollies.

Another thing is Iam thinking to run some ET Streets but being a rag tyre will I beable to

run them with the radials on front (Back mid 90s it was a no at the track) or will I need to run rags on the front.

[Dirty32]

I might be wrong, but I wouldnt think your gonna make 350rwkw on those mods with only 8-10psi of boost dude...

Sorry, cant answer anything re the diff gears.

[Butto]

14.1 with 275+ rwkw?

pretty sure these things run 14.1 standard?

Yeh no help here with the diff gears either

And yeh id be guessing 310-320 max with an agressive tune

Edited 12/01/09 02:16 AM by Butto

[senna_T]

3.9s would be appropriate, having a T56 with 3.73 diff gears will give you ~21-2200rpm at 110kph in 6th. Getting a set of standard height springs will protect the the rear and give you more travel for the launch. Your launch is soft too, a 2.0 60ft will net you a 13 or so.

The other thing you have to look at is the way your car makes power. Alot people forget that generally the engine is not making any more power after 5500rpm, by shifting earlier and not letting the car rev to 6000rpm you will improve your time again.

Mickey Thompson E/T Streets are a radial tyre, so you can run these with your normal street tyres and not have any probs.

Post a pic of your dyno graph if you can.

[Guest]

You will be lucky to get 300rwkw with 8-10psi champ

I had 4.1's in my BA MkI with T56 & it sat around 2100rpm @ 100km iirc? Was a good ratio as all gears were usable in 'street' conditions ie. under 100km.

[Ralph Wiggum]

My ute (t56 converted 4 speed auto) Sits on aproc 2300rpm at 100pkh with 245/35/r19 on it. I would go 3.73's if you plan to drag race it.

4.09's make the car a weapon on the steet, but you do burn up the gears pretty quick. Im concerned that i will run out of rev's at the tope end of the 1/4 with 4.09's

Also take note that lower diff gears will make the car slightly more laggy and the decrease load on the engine mess you can build boost quite as early (you'l probably loose a couple of hundered rpm) the car want be any slower if you leave the line on boost but it will take slightly more revs to get it on boost.

[robbo T]

hey I have 03 xr6t ute, 6spd and 4.1's, I decided on 4.1's as im mainly around town, I'd certainly go 3.9's if you want to drag!!

[01txr]

I am thinking 3.9's but can you get 3.9's to fit the M86.

heard of 3.73 & 4.1's.

As for making the 350rwkw it should get close concidering it made 275rwkw @ 12psi

With only injectors, valve springs, centre muffler removed and tuned.

When I fitted the X-Force it make a huge differance and would be thinking close to 300rwkw.

it started turning the tyre's in 2nd when coming on boost with no clutching.

With the Plazmaman plenum, piping & HDI GT Series IC I would be pretty disappointed if it didnt make atleast

330rwkw at 8-10 psi and very disappointed if it didn't make atleast 350rwkw at 12 psi.

I have heard of many other cars running similar numbers and higher but using F6 engine or built engines.

Also keep in mind manuals usually make more on the dyno than a auto from what I have heard.

They just dont work as well on the strip as the auto.

The 275rwkw graph was retained by the previous owner, should of got a copy from him.

Didn't worry at time as though I would just get one when I take it to a dyno.

Just after I purchased it I took it to the RDP open day dyno.

Wasn't aware the previous owner set it back to the soft tune, you know how

cars always feel faster when you are sitting the pasenger seat.

It made 338rwhp (250rwkw) 25rwkw down.

I was disappointed and though the hot day maybe the reason.

Ended up using the flash tuner for my first time and found he had set it to the soft tune.

and the power was so much better when I changed it.

Was kicking myself after driving it on the soft tune for weeks.

Reason being is he knew the t5 would end up breaking as when he sold it to me he

said it had been rebuilt and fitted with heavy duty drive shafts etc.

Should of been more curious and looked at the receipt he showed me throughly.

Yes it had driveshafts but nothing about being heavy duty or strengthed.

Anyway run it ever since on the hi tune, had to replace the t5 but no other problems.

havn't bothered with anymore dyno's as was just waiting till I built the engine and

purchased all bolt ons as to do it all in one go.

things have changed since and my funds I had have been needed for family issue's.

Doing it slow now step by step.

So will be looking at diff next as it would be my best option to be done next.

Anyone want to swap or trade a 3.45 for 3.73 to 4.1 ratio diff.

I have numerous parts for sale in the for sale section if anyone wants to trade

for a diff.

[GreenXR6T]

I have a T56 and 4.1's. (Was originally a T5)

Very happy with the ratio, 2200rpm at 100kph in 6th, same as the T5 with 3.45's in 5th.