
FASTXR 



ok, from what i thought, the higher the diff ratio the quicker you get thru your gears, but top speed is lower.
ive got a manual with 3.45 gears and a big cam, so im lacking a little down low, if i wanted to get a quicker 1/4, id assume that a set of 3.9's, or 4.11s, would get me there quiker. now ive heard some people on here swear by lower gears, and some on higher gears. how would a set of 4.11's slow you down on a 1/4 mile?
_________________ 07 BF MKII XR6T 

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sam12h 



FASTXR wrote: ok, from what i thought, the higher the diff ratio the quicker you get thru your gears, but top speed is lower.
ive got a manual with 3.45 gears and a big cam, so im lacking a little down low, if i wanted to get a quicker 1/4, id assume that a set of 3.9's, or 4.11s, would get me there quiker. In a word, Yes.
_________________ Production Editor of Performance Motoring at Express Media Group 

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uglybob 



4.11's = more gear changes over the 1/4!
_________________ R.I.P. Scotty 

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FASTXR 



so with 4.11s your saying that ill be be hitting 5th?
_________________ 07 BF MKII XR6T 

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sam12h 



You already use fourth? Then I'd be looking at why you have such little low rev torque, nor the high rpm power (& revs) to justify this big cam.
_________________ Production Editor of Performance Motoring at Express Media Group 

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FASTXR 



well if i just hit fourth at the line, its still a gear change, and if it happens earlier with the 4.11s is that a bad thing?
_________________ 07 BF MKII XR6T 

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sam12h 



I take it this is for the 97 EL XR6, right? What is your current terminal speed? At what rpm do you change gears? & at what rpm are peak power & peak torque achieved?
You need to make the most of your combination & that means matching all components from the intake & exhaust, cam, head (ported or not), gears etc. You may find avoiding the change into fourth saves more time, or you may decide to go with 4.11s & make some use of that change into fourth. I still don't see why you are changing into fourth at the line instead of just holding third, especially since a big cam that has sacrificed torque would require more rpm to be effective.
_________________ Production Editor of Performance Motoring at Express Media Group 

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cjh 



I would suggest advancing the cam timing first, try 2dgs then 4dgs, to see if this helps. its easier to do this than change diff gears.
There is a formula for workin this out, as in revs & gears. RPM x total outside tyre dia in inches x 3 (this is a constant) ______________________________________________ = speed MPH Total gear ratio ( g'box ratio x diff ratio) Eg; 3,000 rpm becomes 3.000 or 2,500 rpm becomes 2.5 ok? So 2.5 (rpm) x 26" x 3 = 195 ________________________ _________ = 56.52mph ( 4th) 1 x 3.45 (diff) 3.45 56.52mph x 1.61 = 90.99 kmh Use this to sort out rpm verse tyre size and diff gears.
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falconkid 



going from 3.45 to 3.9 is putting in a lower ratio.
3.08 is higher than 3.9. higher ratio = long legs lower ratio = short but quick 

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