gregf27
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| posted on 31/7/06 at 07:04 PM |
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atlas axle diff ratios
I'm contemplating changing the 3.75 diff ratio in my cortina atlas axle on my f27, to give faster acceleration,
can somebody advise me as to the best ratio to fit please?
axle connected to type 9 5 speed , 13" wheels fitted. engine is 2l pinto for now ( will be fitting vx 2l redtop in future )
the ratios I've seen so far are - 3.44, 3.75 , and 3.09.
what sort of speed figures would I be looking at, and what top end speed would I be losing out on?
many thanks
Greg
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big_wasa
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| posted on 31/7/06 at 07:08 PM |
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3.44 and 3.09 will give higher top end but less acceleration.
Somthing in the 4,s would do it.
I think 
try this
[Edited on 31/7/06 by big_wasa]
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tul214
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| posted on 31/7/06 at 07:18 PM |
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Try this
http://www.westfield-world.com/gtc2.html
1.6 Raw Super6 sold
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Peteff
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| posted on 31/7/06 at 07:35 PM |
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I'm sure there's a 4.1:1 standard diff in one of the Cortina models possibly an estate as they are usually lower geared.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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gregf27
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| posted on 31/7/06 at 08:00 PM |
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Just been on the gear ratio calculator,
great reading
so far on 185 70 r13's , type 9 gearbox -
4.63 diff -
at 5000 rpm 1st 20.4 mph 5th 90.9mph
3.75 diff -
at 5000 rpm 1st 25.2 mph 5th 112.2mph
3.44 diff -
at 5000rpm 1st 27.5 mph 5th 122.3mph
3.09 diff -
at 5000rpm 1st 30.6mph 5th 136mph
top speeds at 8000rpm were - 145.4mph, 179.5mph,195.7mph ,and 217.9mph!!
if only!!
so would I be right in thinking that the 3.09 diff ratio would be quicker on the acceleration front?
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tul214
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| posted on 31/7/06 at 08:29 PM |
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No, the other way round. I have just swapped a 3.75 for a 4.11 diff in my Tiger. Gives me better use of the 8000rpm limit on my 4age engine.
1.6 Raw Super6 sold
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gregf27
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| posted on 31/7/06 at 09:14 PM |
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Cheers for the replies guys,
just found one on e-bay for a 5.1 ratio!!
on abuy it now - too much dosh though!!
Is it an easy job to change them over ? or is it an axle off job?
will try to get a 4:1 or a 4:63 , I like the acceleration speed better than the top end!!
if anyone knows where I can get one from , give me a shout! ta
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lotustwincam
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| posted on 31/7/06 at 10:05 PM |
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Had a 4.63 in my MK1 Escort Twincam many, many years ago.
Acceleration was brisk, but IIRC full revs equated to about 80MPH with a 4 speed box!
Also bear in mind that with a ratio like this, from a standing start you'll suffer from a LOT of wheel spin.
On the Atlas axle the diff housing seperates from the front of the axle. So chassis clearance allowing, you'll be able to change it without
removing the axle. I seem to recall that there's some sort of pre-load to be set up when installing the new pinion.
Drew
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gazza285
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| posted on 1/8/06 at 03:18 AM |
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quote:
Originally posted by lotustwincam
On the Atlas axle the diff housing seperates from the front of the axle.
Drew
Not quiet that easy, that's the English axle. The Atlas diff is built into the axle casing.
DO NOT PUT ON KNOB OR BOLLOCKS!
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NS Dev
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| posted on 1/8/06 at 11:53 AM |
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yep, 4.1 and 4.6 are the real choices. We used a 5.1 on a mk2 escy rally car, good in forests but thats it, with a millington engine that revved to
9500 we could make 115mph!!
I used a 4.6 atlas in my RWD Pug 205 rally car and that have about 115 mph at 7000 revs iirc which is probably about what you want if you don;t do
many long journeys.
If you plan any longer trips go for the 4.1, with the extra torque of the vauxhall engine it will still be bloody quick!!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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lotustwincam
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| posted on 1/8/06 at 09:28 PM |
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quote:
Not quiet that easy, that's the English axle. The Atlas diff is built into the axle casing.
Yup Gazza, your dead right.
Realised my error this morning on the way to work. The nose comes off the English axle, but with the Atlas you have to take the back plate off and
remove the gubbins from the rear.
Still, its not all bad - less likelyhood of fouling the chassis!
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