3.54 vs 3.89

Langlia · Post by **Langlia** » Sat Mar 10, 2018 9:59 am

Looking at new differential ratios.

Did a online calculator based on wheel size.

As far as a car that will be mostly city driving with occasional highway,

How much would dropping to a 3.54 affect my acceleration vs the current 4.12.

I see it's a 500 RPM difference doing 100km/h, do plan on going on the highway just don't want it to be unbearable (wife)

Thanks guys

enfoprefect · Post by **enfoprefect** » Sun Mar 11, 2018 9:14 am

Just making some assumptions here but... From 4.12 to 3.54 is a 14 percent drop, about like being in overdrive all the time and it would also be a 14 percent drop in observable torque. If your town driving is all right with the 4.12 then it probably would not be too bad normal taking off in 1st gear with the 3.54. But I suspect you would do a lot more down shifting and driving around town in a lower gear than before.

enfoprefect · Post by **enfoprefect** » Sun Mar 11, 2018 9:15 am

Just making some assumptions here but... From 4.12 to 3.54 is a 14 percent drop, about like being in overdrive all the time and it would also be a 14 percent drop in observable torque and acceleration. If your town driving is all right with the 4.12 then it probably would not be too bad normal taking off in 1st gear with the 3.54. But I suspect you would do a lot more down shifting and driving around town in a lower gear than before.

Langlia · Post by **Langlia** » Sun Mar 11, 2018 12:11 pm

Good point. Was out looking at brake parts yesterday and happened upon a 3.89 what a coincidence

Brett Wilkie · Post by **Brett Wilkie** » Sun Mar 11, 2018 1:58 pm

Langlia wrote:Good point. Was out looking at brake parts yesterday and happened upon a 3.89 what a coincidence

What did that diff come out of, I think it is an unusual Ford ratio to find here?? The 3.9:1 is the most common I have found with a 39-10 tooth count, if you have yours apart count the teeth as I am curious to know.
I have had a lot of diffs over the years and all my 105e diffs were 4.1:1 and the regular Cortina's were 3.9:1, my Locort was a 3.77:1 though.

Langlia · Post by **Langlia** » Mon Mar 12, 2018 12:54 pm

Most likely is 3.9 and I'm mistaken Brett. Came from another Anglia

Brett Wilkie · Post by **Brett Wilkie** » Mon Mar 12, 2018 2:46 pm

I did over the years find two 105e axles with 3.9s in, they were likely donated from Cortina's? The 3.89 Is a proper Ford diff, I think from the Escort series?? Yours still could be one of those with a 35 x 9 tooth count, I keep reading about them but have never seen one in the flesh.

Langlia · Post by **Langlia** » Mon Mar 12, 2018 9:08 pm

I will count and get back to you

JAN · Post by **JAN** » Tue Mar 13, 2018 1:19 am

It should actually be stamped into the rim of the crownwheel, e.g. 8 : 33 = 4.125.

mark · Post by **mark** » Tue Mar 13, 2018 2:40 pm

I don't intend to hijack this topic, but I wonder too....
How would the 3.54 do with the 2.3 Pinto engine. The engine is begging for another gear at 50 mph with the 4.1 and I can start off in 2nd gear easily.
I too ran the calculations with the online tools, and I see only a few mph difference with the 3.9 gearing, I don't think this will be enough.
I assume there are not any 3.54 diffs in the US and it would have to come from England? what do you guys think?

Brett Wilkie · Post by **Brett Wilkie** » Tue Mar 13, 2018 10:40 pm

mark wrote:I don't intend to hijack this topic, but I wonder too....
How would the 3.54 do with the 2.3 Pinto engine. The engine is begging for another gear at 50 mph with the 4.1 and I can start off in 2nd gear easily.
I too ran the calculations with the online tools, and I see only a few mph difference with the 3.9 gearing, I don't think this will be enough.
I assume there are not any 3.54 diffs in the US and it would have to come from England? what do you guys think?

I remember my Mk2 Cortina with a 2 litre Pinto engine, I had a 3.9 diff with my 13 inch wheels and it was great around town and slightly busy on the freeway but tolerable. Do you do a lot of freeway driving? I know Burton's sells them but it is not inexpensive. It might be more cost effective to narrow a Pinto or Mustang II diff, maybe one from an automatic???
http://www.burtonpower.com/crown-wheel- ... cwe35.html

mark · Post by **mark** » Thu Mar 15, 2018 2:34 pm

thanks Brett, You are right, its great around town. I am 2 miles off of the interstate but never use it...the speeds are 70-80 and it is just safer to use the back roads although it takes a lot longer to go anywhere. Being somewhat rural, it is about 10-20 miles to anywhere by the interstate. I don't care to go 70-75 mph but would like to do 60-65 at a lower RPM and I could use the interstate then.
I have seen those gears on Ebay.UK. During the build, I looked at the Pinto and Toyota but overall the best fit seemed to be the 105E...no messing with brake bias and brake cables worked out too. I have thought about 14" or even 15" wheels might help some but prefer to stay 13".

Langlia · Post by **Langlia** » Thu Mar 15, 2018 5:59 pm

Could throw a 5 speed in there.

If you're looking for a CWP to stick in at 3.54 you could always post in the wanted of Turbosport.co.uk , lots of stuff for sale over there.

What type of car is it?

mark · Post by **mark** » Fri Mar 16, 2018 7:52 am

Langlia....lol...that is with OD !! yes I have been considering the new gears from the UK, have not looked at Turbosport but will. I have been wondering would it be the right ratio for the 2.3 and would i be happy with it. Gears, bearing, shipping, and set up can get $$$. I need to have some certainty I would be happy with it and if pulling out in first gear would be good.
Its in a 300E, stock pinto 2.3, Merkur 5 speed, 13" tires. I think the Pinto it came out of had 3.2 ratio and 13" tires and no OD.

Langlia · Post by **Langlia** » Fri Mar 16, 2018 10:07 am

It's a 39-10 Brett