Well because there's no gear overlap I'd say you would get a fraction of a second better time. You do release you'll break traction shifting from 1st to 2nd and maybe even 2nd to 3rd yeah? :p
I've driven in my mates manual XR too much. Can't wait till I can hear that satisfying chirp every time i shift gears

can you fit underdrives to a ef el motor?

Question of the decade!

Answer: Never seen any...

i assumed so..

hey guys, ill jump in here on the under drives, i just fitted it to my BF about a month and half ago, i got the power bond kit through tuff car parts, if you are on ff Justin sells the complete kit for $280, that includes, the balancer, plus 2 new pulleys as well as a new belt (you may as well replace all at the same time as its no extra effort). He also sells them through ebay for 300.

Just drop him an email at sales@tuffcarparts.com and say you want the - BA BF FG 6 XR6 TURBO 20% UNDERDRIVE BALANCER PULLEY KIT (tell him you want the same one Phil got)

My mech installed the kit for $100 but thats because it took 2 hours as we had to go part shopping etc so would have been cheaper (that was mates rates though) I took lots of pics of the process and put them in my build thread, page 2 or 3 i think they are on

Cheers

Phil

People should not feel free to give advice on matters about which they clearly have a less than working knowledge!

Can someone please explain how having a "locked diff or a stronger diff" prevents your big end from lunching itself?

What on earth does a set of 4.11's have to do with your idle speed? and at what speed with 4.11's are you thinking you'll be reving at 1000-1500 rpm?

"Instead of accelerating off 0.800rpm your car will accelerate until your rev hits 2500rpm." Umm... What? and......no it won't.

Shift kits are a bad idea on an unmodified tranny (IMO). They result in higher line pressures and actually put more stress on the bands (particularly 2nd gear) quite often resulting in catastrophic failure of the band. They reduce stresses on the clutch packs, but as they rarely cause a problem in NA vehicles, I wouldn't be too concerned about that. Increased stresses on the drive train brought on by shift kits etc result in increased strain on uni's, tail shaft & diff, and bushes, amongst other things. All so you can make your car more uncomfortable to drive in and get tickets from the cops when you start chirping into 2nd on dry bitumen. Awesome!!!

Underdrives are fine. But if you plan on increasing load on the electrical system from factory, ie stereo or spotlights etc, you might want to consider not fitting them.

Changing your diff gears to, for example, 4.11's will result in quicker acceleration, generally slightly better economy in urban driving (highly dependant on driving style), but higher RPM and increased fuel consumption on the hwy. Factory standard BF XR6's have an open diff, but can spin both wheels under certain circumstances (usually unlikely and generally for relatively short distances). It's not really an LS action, more just physics doing it's thing.

Thanks philaddis. How long would you say it would take for the tranny to fail with a shift kit installed and only using it on occasion not all the time? My mate has one in his EL and his tranny has been working perfectly.
I've got myself a 500watt amp and a subby with a 300watt RMS. In the future I might get speakers installed too. Would it be wise to put an underdrive pulley?
And as for changing the diff gears. Going from standard 3.45s to 3.9s will cause absolutely no other issues other than a higher full consumption when driving on the highway?

How long is a piece of string Jova? It's impossible to say really as it all depends on how healthy your transmission is in the first place, how well it get's looked after and how hard a time you give it down the road. It's up to you if you want to put one in, but really, ask yourself why you would??

That stereo shouldn't pose too much of a problem even if you're running underdrives. I have considered them for my car too, but have decided against it. Main reason being the 2.5 yrs of factory warranty left on my car. If not for that, I might have them too!!

3.9's will cause higher hwy mileage yes. Remembering that torque is multiplied by gearing, it will essentially wind up with greater torque being delivered to the wheels, so diff bushes may be under marginally more stress. Plenty of people have higher gear sets in their diffs tho without any problems. You'll need to get yourself the appropriate speedo sender to reflect the different diff gears otherwise your speedo will be out. If you drive mostly around the city and stay off the loud pedal enough you may even use less fuel!!

Would warranty/ford even notice the harmonic balancer has been changed? I couldnt see it being the cause of any problems anyways.

Dont mention it and they prolly wont notice. Unless it has PHILMAC Underdrive in big a*** letters around it they wont suspect a thing.

Nah the one i got was just black, no real brand names or obvious markings on it

I just weighed up the possibility of a void warranty v several hundred dollars of underdrives and 5rwkw and did the maths........

Each to their own, but I see little point in having to pay out for f'd alternator or regulator or worse for a piffling increase in performance!!!!

yeah and knowing Ford they would try and weasle out of it anyway they can. At least you got a T so power isnt hard to come by, us n/a boys gotta get what we can

hey efun, with the shift kit does it work in manual mode, and if so then does it change gears quickly when down gearing, because your manually selecting your gear

I am getting some underdrive pulleys soon, though hope it won't effect my Sub and Amp.

Stock XR6T have a LSD with 3.45 diff gears, I am looking at getting a XR6T LSD.