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 Post subject: What axle ratio?
PostPosted: June 13, 2020, 10:54 pm 
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Joined: June 21, 2010, 9:02 pm
Posts: 56
Location: Spencer WV
My unusual 4x4 build will have larger diameter tires than is "traditional"

I have my engine and transmission and am planning a junkyard trip for next weekend. Hoping to pick up some Explorer front and rear differentials, uprights, and halfshafts so I can get width measurements.

So I'm using a T5 out of a ~2000 v6 Mustang. That would have come with a Ford 3.8.

I'm mating it to a na GM 3800 (L36) out of a ~2000 Regal/LeSaber/Park Avenue/GP/Bonneville/etc.

The Mustang came with a 2.73 final drive and 205/65r15 tires.

I'm planning on using 215/85r16 tires to get ground clearance and they should have a bit of old-school skinny tire look on 6" rims.

Mustang tire diameter was 80". Mine will be 95.4"

So I did a little math assuming the Mustang had my tires on it, what would the final ratio be to keep the revolutions the same.

Result was 3.89

Explorers come with 3.55, 3.73 and 4.10 although the 4.10s are generally hard to find.

My Locost is probably going to be on the heavier side considering the iron v6, the 4x4 drivetrain and larger tube diameter to accommodate the front drivetrain torque and rougher roads I'll be using it on, but it still should be at least (hopefully) 1000lbs lighter than a Mustang (Mustang weighed 3000-3500lbs). I also plan on a little more body than is traditional although it will be fiberglass. Guessing 2500# with overengineering.

The Mustang had 190hp@5250rpm and 225ft-lbs@2800rpm

3800 should have 200hp@5200rpm and 225ft-lbs@4000rpm

What's your opinion? I'm leaning towards the 3.73 but would a 3.55 be a better choice? I can always regear, but it gets pricey with two differentials. Would like to get as close as possible the first time (and some differentials require a new carrier too to change gears).

I'll have a transfer case with 4wd low for rougher terrain. In 2wd and 4wd hi there is no reduction for general and highway use. We have 70mph speed limits commonly in WV but I can't see me going much over 85 in my old age.

The goal is to have all the gears usable but I'd rather have 1st be right and seldom use 5th. Most of my driving is under 55 on curvy pavement or gravel/dirt backroads below 25.

Trans ratios should be: '99-04 V6 T5 ... 1st: 3.35:1, 2nd: 1.99:1, 3rd: 1.33:1, 4th: 1.00:1, 5th: 0.68:1

Thoughts?


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 Post subject: Re: What axle ratio?
PostPosted: June 13, 2020, 11:59 pm 
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Joined: March 19, 2011, 10:22 am
Posts: 1692
Location: Holden, Alberta, Canada
As for tire size comparison, here's a tool that pretty handy.
https://tiresize.com/calculator/
As for your other ratio questions, I'll leave that to the guys here that know that stuff.

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Perry

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 Post subject: Re: What axle ratio?
PostPosted: June 14, 2020, 4:22 am 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
chrisser wrote:
The Mustang came with a 2.73 final drive...
I thought it was 3.27, which would skew your numbers to an even shorter (numerically higher) equivalency. I'd probably lean towards the 3.73's.

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 Post subject: Re: What axle ratio?
PostPosted: June 14, 2020, 10:18 pm 
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Joined: June 21, 2010, 9:02 pm
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Location: Spencer WV
Is dyslexic typing a thing?

3.27 is correct and it's what I used in the math. Somehow I typed the wrong thing multiple times.


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 Post subject: Re: What axle ratio?
PostPosted: June 15, 2020, 10:51 am 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
I have that with phone numbers!

Running it through my gearing spreadsheet yields these results for top speed in each gear (stock 6000rpm rev limit) and rpm in 5th at speed:

Axle.....1st.....2nd.....3rd.....4th....5th.....@60.....@70
3.55.....44......75.....112.....148.....218.....1650....1925
3.73.....42......71.....106.....141.....208.....1735....2025
4.10.....38......65.....97......129.....189.....1900....2225

I'd be looking at the 4.10 if I could get them, or the 3.73 if not...The 3.55 wouldn't even enter the equation for me.

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Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Last edited by Driven5 on June 15, 2020, 12:36 pm, edited 1 time in total.

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 Post subject: Re: What axle ratio?
PostPosted: June 15, 2020, 12:19 pm 
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Joined: June 21, 2010, 9:02 pm
Posts: 56
Location: Spencer WV
Driven5 wrote:
I have that with phone numbers!

Running it through my suspension spreadsheet yields these results for top speed in each gear (stock 6000rpm rev limit) and rpm in 5th at speed:

Axle.....1st.....2nd.....3rd.....4th....5th.....@60.....@70
3.55.....44......75.....112.....148.....218.....1650....1925
3.73.....42......71.....106.....141.....208.....1735....2025
4.10.....38......65.....97......129.....189.....1900....2225

I'd be looking at the 4.10 if I could get them, or the 3.73 if not...The 3.55 wouldn't even enter the equation for me.



Thanks for that.

I've noticed front 4.10 axles are pretty plentiful on ebay but rears demand a premium over 3.73. My suspicion is the Explorer IRS is similar enough to other vehicles (Mustang?) that those are finding their way into swaps. Just a guess. Plus I hear that the aluminum 8.8 weighs about the same as an iron 7.5, so that's a possible avenue for the apparent demand.

Might even luck out and find one with limited slip. Junkyard is always a craps shoot.

One thing that works in my favor is the 2002-ish Explorers have the halfshafts going through the frame. Great for interior packaging. Sucks for owners who want to do a lift as the axles will contact the hole in the frame if you try. So that generation generally doesn't get molested like the earlier ones.


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 Post subject: Re: What axle ratio?
PostPosted: June 18, 2020, 8:59 pm 
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Joined: June 21, 2010, 9:02 pm
Posts: 56
Location: Spencer WV
Heading to the junkyard tomorrow.

There are four Cherokees there and I'm hoping to pick up a 242 xfer case.

Plenty of Explorers so I should be able to find some uprights, halfshafts and hopefully differentials. Also looking for a few 3800 parts (the 2004+ FWD intake is aluminum and swaps with the early plastic one with slight modification. And I need a block that's tied to a VIN in case the state of WV wants that for the eventual inspection. Last time I inquired they are a whole lot less uptight about it than when I discussed it with OH when I lived there, but if anything is going to require a VIN, it will be the engine.

Plus a list of odds'n'ends if time allows. The Locost stuff is actually secondary to parts for the other vehicles in the stable, but since I'm there...


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