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My 85 bronco with a 351w, c6, and lsd 3.55s will bust 34s loose. Why do people complain about 3.55s with 33s?
 

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1986 Bronco, 351w, Edelbrock aluminum top end, Holley 600, 4" BDS lift, 35" Maxxis Razr's, stuff..
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Well if you want to bust all 4 loose you need to go to 4.56! I have the same setup in mine but with 35's. It goes good. I will be upgrading to 4.10 in the near future though to get closer to the stock ratio. I had a 709 GMC with a 350 and 5.38's and it really changes how the auto feels. So much more snap.
 

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because you dont have overdrive, your engine wont bog as bad when cruising. but that also means less efficiency and higher rpms. its a trade off.

now if you had a 302 with an AOD, which has a 0.66 OD ratio its another story. you have an engine with less power, and a trans that trades 1/3 of your torque for lower rpms. thats why i recommend alot more gear for them

with an E4OD, the OD ratio is not as severe at only 0.71 and it has wide ratio gearset so 1st and 2nd are lower. but you are still trading a good amount of torque for lower rpms

when you do the math, you can use overdrive to allow alot more axle ratio while still keeping highway rpms lower than a C6
164534


we will see your C6 with 33s and 3.55 ratio makes 2350 rpm at 65mph on the chart. but because its a non-lockup torque converter, the converter will add a couple hundred rpm of slippage so we will say 2400-2500 rpm at 65mph

with an AOD with 33s and we will go crazy and say 5.13 gears which is considered WAY too high for 33s. the chart would show 3396. it does have a lockup converter so no slippage and the OD ratio of 0.66 means it would be at 2241 rpm at 65mph. still decent amount lower than the C6 but now the engine and trans have alot less load on them because more of it is at the axle. it also means that 1st to 3rd gear would be very low so acceleration would be crazy.

now a E4OD with 33s and 3.55 would be at 1668 due to its 0.71 OD ratio. so if we did 4.56 gears, its at 2143. well within a good rpm rangebut still gaining a good percentage of torque

broncos were pretty much designed for a 29" tire. so if it came with 3.55 gears, you can see what rpm range it was originally designed for. around 2800 rpm with C6 but around 1900 with E4OD. these engines were designed to be able to handle long periords of rpm around 3k rpm cruising the highway.

to answer your question, 33s with 4.56 at 65mph is 3019. divide that number by 65 and multiply it by 80 gives us 3715 rpm. add couple hundred rpm of converter slip ontop and yeahhh pretty high number
 

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for referance:

Spd * (5280/60) * gear ratio / (tire circumferance in ft (which is diameter in inches * Pi / 12)) * transmission ratio = RPM

or:

Spd * rear axle ratio * transmission ratio / tire diameter * (336.3)
 

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Premium 4 Lyfe - Way Back Staff
'95 XLT: 5.8, MAF, E4OD, 4.56's, 6" on 33's
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E4OD, 351w on 33's w/4.56 here and lots of highway miles. Very comfortable to me and pulls hard when I want/need it too. I don't really spin my tires much anymore though... on dry pavement anyway.
 

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Yo Eyhan,
Member B-man wrote, "
I am in the process of doing this right now. Fortunately. I have a 90 Bronco that was the donor, and everything that was on the 90. I have put onto my 88. All wiring from the engine compartment to the rear of the chassis.

Rescue Bronc, I believe has done this swap as well. For me, and the way I am doing it. It hasn't been easy. Course, I am doing an engine build as well. LOL, I am going to be doomed with problems. :banghead

The main parts you will need is the engine wiring harness, ECU and the E40D together. I was informed that you can splice in the O/D button, so , you wouldn't need the chassis wiring. And deal with the behind the dash wiring. I said screw it, I have all of it, I am using it.

You wil have to drill new holes on the chassis for the E40D's crossmember. Driveshafts that went with the E40D.

I am sure I am missing something, maybe someone else will chime in.

Best bet is to get the whole vehicle that you are getting the tranny from if possible IMO."
 

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1995 Ford Bronco
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I'm running 33s and I just put 4.10s in my bronco and I am happy with them. My plans are to go to 37s at some point in time so obviously the gears will be changed again at that point but I got a smoking deal on the front third member and rear gears/limited slip used and I needed something to take up some time during quarantine. I didn't hate the 3.55 and probably would have never done the 4.10s if I wasn't so bored.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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My econoline could definitely feel the difference between 29s and 33s. Has 3.73 gears, turned by a 215hp v6 through a 4r70w. Im running heavy superswamper 31s on steel wheels now and its still a bit more sluggy than with the 29" highway tires but not like the 33s. I was getting 14 mpg with the 29s. Filling up today after work to check milage with the new swampers.
 

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I currently have 3.55s with 35s and I could notice the difference between 3.55s with 33s and going to the 35s. My engine is pretty well built and can still break the 35s loose easily but I still lost acceleration with bigger tires and plan to swap to 4.56s in the future. My current fuel mileage is about 10 mixed driving and 13 highway at 65 mph.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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I currently have 3.55s with 35s and I could notice the difference between 3.55s with 33s and going to the 35s. My engine is pretty well built and can still break the 35s loose easily but I still lost acceleration with bigger tires and plan to swap to 4.56s in the future. My current fuel mileage is about 10 mixed driving and 13 highway at 65 mph.
I have a healthy 300 in front of a 4spd manual. 37s and 4.56s and get about 12 mpg.

With my 94 With a healthy 351w , I got better milage with 4.88s and 37s than 3.55s and 37s or 35s. Again, about 12 mpg.
 

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I have a healthy 300 in front of a 4spd manual. 37s and 4.56s and get about 12 mpg.

With my 94 With a healthy 351w , I got better milage with 4.88s and 37s than 3.55s and 37s or 35s. Again, about 12 mpg.
Makes sense you got better mileage w
ith lower gears. Engine is working less at lower speeds. Must override the higher rpm at highway speeds. My mpg for just city driving is generally pretty bad, 8 or so usually. I bet 4.56s would help alot, I have to give some throttle especially on hills to get the heavy 35s i have moving. I have a 4 speed manual as well.

I also destroyed my driveshaft a few months ago. Probably has something to do with the 3.55s, 35s and hopped up 347...
 

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Premium 4 Lyfe - Way Back Staff
'95 XLT: 5.8, MAF, E4OD, 4.56's, 6" on 33's
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When I pushed my old '89/5.8 from 33's to 35's w/3.55's... it wasn't long before I started poppin' u-joints. The loss of power was noticeable enough to me, that I pushed the pedal down more to make up for it... which didn't help. Instead of upgrading u-joints, I went to 4.10's from an old member and was much happier and the difference was absolutely notable to me with that AOD. My last '90/5.0 came from the PO with 4.56 and I ran 31's & 33's on it and was so pleasantly surprised, I wished I had gone there with the '89. I honestly don't think I'd have put up with the 5.0 as long as I did without 'em but I tow often enough and live in a mountain area. My current '95 was mentioned previously.
 

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1989 Eddie Bauer 5.8, C6, True Trac diffs, 4.56 gears, 4" C&T lift, 130A 3G Alt, 35" Grabber AT2s
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89 5.8 C6 35s 4.56 gears. Whatever you do, avoid any situation where any speed over 65 is needed. Speed limit on the highways is 75 here, and my truck pushes 3,800 rpms at that speed. Garmin GPS for speed accuracy, using factory in dash tachymeter.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Makes sense you got better mileage w
ith lower gears. Engine is working less at lower speeds. Must override the higher rpm at highway speeds. My mpg for just city driving is generally pretty bad, 8 or so usually. I bet 4.56s would help alot, I have to give some throttle especially on hills to get the heavy 35s i have moving. I have a 4 speed manual as well.

I also destroyed my driveshaft a few months ago. Probably has something to do with the 3.55s, 35s and hopped up 347...
The main reason for increased milage is a tremendous change in throttle input. With the throttle barely open, it uses much less fuel. 50% throttle at 2200 is probably gonna suck more fuel than 20% at 3000 rpms. This is very relevant to the six cylinder crowd for good economy.
 
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89 5.8 C6 35s 4.56 gears. Whatever you do, avoid any situation where any speed over 65 is needed. Speed limit on the highways is 75 here, and my truck pushes 3,800 rpms at that speed. Garmin GPS for speed accuracy, using factory in dash tachymeter.
sounds like you have alot of converter slippage or something wrong.. using chart above, 35 and 4.56 would be 2847 at 65mph. divide that by 65 and multiply it by 75 and its 3285. if its a C6 without lockup converter, add a couple hundred rpm but should not be adding 600rpm


theres alot of factors that go into fuel efficiency. as Blue said, an engine at 3k rpm at 50% load it more efficient than a engine at 2k rpm at 100% load. also torque curve of the engine will determine which rpm it likes best and the more you are over that range the better and more efficient. so you can build a bigger engine with a higher rpm range and still be more efficient than a small engine at a lower rpm range if you plan your vehicle build out good. higher rpm does not necessarily mean less mpg. of course there is also more drag on components at higher rpm so you cant expect an engine/vehicle built for 6k rpm to be as efficiency as one built for 2k rpm. its all about maximizing efficiency while still making decent power and using that power at the proper times. its gonig to take X ammount of force to move a vehicle. so the more efficiently you can create X ammount of force is whats going to give you mpg.

also like pepe was getting at, you want to keep all the stress in the drivetrain pretty evened out. put big tires on and now you add more stress to everything cause now you stewed the drive ratio. some components handle it better than others, his weak link was u-joints. some poeples weak links are transmissions, some axles. this is where if you change axle ratio to better match the tire size, you shift the load before the axle to be less but now the axle has to carry more burden. generally it can handle it fine but of cource there are limitationsand the bigger the tire the more stress till you eventually need to get bigger axles.
 
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