Hammy360
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| posted on 18/4/11 at 08:22 PM |
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Diff ratio choices
what sort of ratio should I be looking for ? I have an MT75 mated to a 2.0 blacktop. Iwant the best acceleration and top speed doesnt need to be more
than 125mph, although I still want it to be a smooth drivable car in traffic. Im gonna be running on 15" wheels with 195/50 tyres. So whats the
best compromise?
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flak monkey
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| posted on 18/4/11 at 08:23 PM |
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3.91 will be fine and the most common ratio with push in shafts...
Sera
http://www.motosera.com
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Xtreme Kermit
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| posted on 18/4/11 at 08:43 PM |
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Yep, I agree with the 3.9. Works well with my 2.1 pinto/anchor
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Hammy360
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| posted on 18/4/11 at 08:59 PM |
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I was told that the 3.9 would render 1st gear almost unusable............
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mcerd1
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| posted on 18/4/11 at 09:54 PM |
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quote:
Originally posted by Hammy360
I was told that the 3.9 would render 1st gear almost unusable............
in that case try a 3.62 
or swap to a type 9 box with a modified 1st gear (I don't think you get mods for an MT75)
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Chippy
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| posted on 18/4/11 at 10:23 PM |
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I personaly think that whether you go 3.9 or 3.6 first gear is just a decoration. IMHO Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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snapper
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| posted on 19/4/11 at 05:13 AM |
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I said a 3.9 would be unusable with an MT75, I have done extensive research with gear ratios and the MT75 whilst a stronger box has lower 1st and
second gears than a Type 9, the Cosworth used this box and had a 3.6 diff because it had the power to pull through the longer diff ratio and better
aerodynamics than a 7 so it can pull higher top speeds.
If you have a higher rev limit you can to some extent hide the low first and second.
I am running a 3.9 diff on a V6 type 9, 35 to 40 mph in 1st at 7750 rpm with a 3.36 ist gear, the second gear, 1.81 was the gear that allowed the V6
Sierra to go over 60mph in second, key to the 0 to 60 times.
Do yourself a favour, get one of the readily available gear ratio calculators and have a play with diff ratios, gear ratios and tyre sizes, this soon
highlights the conundrum of gear ratios in a standard Ford box, to short in the low gears to long in the high gears.
If you get a decent first and second gear, 5th gives speeds over 160mph.
THIS IS WHY WE ALL WANT CLOSE RATIO GEARBOXES
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Hammy360
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| posted on 19/4/11 at 06:14 AM |
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quote:
Originally posted by daviep
quote:
Originally posted by Hammy360
I was told that the 3.9 would render 1st gear almost unusable............
Why are you asking a question to which you already know the answer? Is this some kind of test? Did we pass? Do you know what happened to JKFK? what
about Elvis?
I dont know the answer thats why Im on here
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daviep
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| posted on 19/4/11 at 07:25 AM |
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quote:
Originally posted by Hammy360
quote:
Originally posted by daviep
quote:
Originally posted by Hammy360
I was told that the 3.9 would render 1st gear almost unusable............
Why are you asking a question to which you already know the answer? Is this some kind of test? Did we pass? Do you know what happened to JKFK? what
about Elvis?
I dont know the answer thats why Im on here
Yeah sorry deleted due to alcohol induced ignorance.
Sorry
Davie
“A truly great library contains something in it to offend everyone.”
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mcerd1
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| posted on 19/4/11 at 07:47 AM |
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try this calc: http://locost7.info/gearcalc.php
(just bear in mind calculators like these don't take account of the power needed to pull the top speeds ithey come up with...)
there are a couple of different ratios for the MT75 - what car / engine did your g/box come from ? (sierra / granada / scorpio ? )
most have a 3.61:1 1st gear as far as I can tell...
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