TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > Transmission & Drivetrain
  New Posts New Posts RSS Feed - Diff ratio - compare revs 3:15 v 3:54
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Diff ratio - compare revs 3:15 v 3:54

 Post Reply Post Reply Page  <1 34567>
Author
Message
jpnjim View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Nov/25/2007
Location: New England
Status: Offline
Points: 2752
Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Nov/06/2018 at 12:55pm
Originally posted by AMXRWB AMXRWB wrote:

Yes if it is ohc.3500 all day is nothing.Smaller pistons are made to run faster.

Yeah it's a tiny DOHC 1.6L,
but its actually an oversquare engine, with a stroke longer than the bore is wide (3.1" bore 3.2" stroke),
but will still run like the engine in your leaf blower, wide open without a care in the world.

It makes plenty of power at 2500 to push the little jelly bean along at 80+,
the larger Ford Escape with the same engine turns less RPM on the highway than that,
but the Escape has an automatic transmission to eliminate the driver lugging the engine.

With a 6 speed manual the same engine in an 800 lb lighter Fiesta is geared much lower,
only explanation that makes sense to me is concern that operator error of lugging it along in high gear under 2000 rpm will lead to bad things fast.
71 P-code 4spd Javelin/AMX
some Jeeps and some Fords
Back to Top
Ken_Parkman View Drop Down
AMC Addicted
AMC Addicted


Joined: Jun/04/2009
Location: Ontario
Status: Offline
Points: 1815
Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Nov/06/2018 at 12:59pm
Even those they are driving down the cruise rpm. My wife's Jeep has the 9 speed, and it cruises at 1800 rpm going 75 mph, in 8th gear. And that's with the 3.52 towing package effective axle ratio. It won't go into high gear unless you are on a downhill above 80 mph.
Back to Top
jpnjim View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Nov/25/2007
Location: New England
Status: Offline
Points: 2752
Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Nov/06/2018 at 1:08pm
Originally posted by Ken_Parkman Ken_Parkman wrote:

Even those they are driving down the cruise rpm. My wife's Jeep has the 9 speed, and it cruises at 1800 rpm going 75 mph, in 8th gear. And that's with the 3.52 towing package effective axle ratio. It won't go into high gear unless you are on a downhill above 80 mph.

I honestly hate the way new automatic transmissions drop 3-4 gears when you touch the gas pedal,
I completely understand all the logic behind them working that way,
but I don't always want to see 6000 RPM to pass a minivan.

Breaking in the engine on the Escape when it was brand new made me crazy Confused

Zero miles on it and its flirting with 5000 RPM's every time you look at the gas pedal sideways.

I'll stick to manual transmissions as long as I have two feet and they keep making them.
71 P-code 4spd Javelin/AMX
some Jeeps and some Fords
Back to Top
FSJunkie View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/09/2011
Location: Flagstaff, AZ
Status: Offline
Points: 4741
Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Nov/06/2018 at 2:23pm
I agree. I hate modern engines and drivetrains. 

When I blew up the engine in my Pontiac out in Kansas on vacation I rented a 2017 GMC Savanna van and a 2-wheel dolly to tow it back home to Arizona. It had a 4.8L Vortec with a 6-speed automatic. 

It wanted to cruise 65 MPH in 6th gear (1800 RPM), which was fine....downhill. It wanted 5th (2400 RPM) on a level and 4th (3200 RPM) for any little hill. A big hill it wanted 3rd (4200 RPM). It was constantly hunting gears. You'd think having tow/haul mode on would stop that, but tow/haul made it far worse. 

I found the manual shift feature that gave me a digital tachometer. I locked it into 4th gear and I left it there most of the time except when a big hill came up, then I downshifted to 3rd. It pulled the rocky mountains in 3rd. I drove it 1100 miles like that. 

Like most modern engines, it had no torque at low RPM. All the power was up at the high end. It was worthless below 3000 RPM but pulled like Babe the Blue Ox above 4000. That little 4.8L really surprised me at high RPM. What a screamer. Very smooth and quiet at high RPM. 

But I prefer big blocks and Diesels. Gear it down and chug along at 2500 RPM...meaning a 1965 Imperial Crown with a 413. I love how those drive on the highway. Just lock the cruise control in at 95 and relax behind the wheel to my Frank Sinatra collection. 
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
Back to Top
Craigie View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Sep/06/2011
Location: Bris, Australia
Status: Offline
Points: 369
Post Options Post Options   Thanks (0) Thanks(0)   Quote Craigie Quote  Post ReplyReply Direct Link To This Post Posted: Nov/07/2018 at 1:57am
Thanks guys, I am really enjoying the read and finding your knowledge very helpful.

Yes AMXDREAMER, as Sonic Silver has mentioned, running 14 inch rims with 235 x 60 on the front and 245 x 60 x 14's on the rear. I am getting the front tyres rubbing the fender now, but maybe an option to run something slightly larger on the rear in conjunction with some gearing change to the diff ? Maybe I should look around for a pair of 15 inch rally rims to put on the rear for the extra long Highway runs ?

I have just spent plenty rebuilding motor and tranny, so won't be looking to swap the tranny out anytime soon.
Craigie.........

1968 Dodge Charger "Bullitt" tribute
1971 SC/360 Hornet
1973 "Levi" Gremlin
Back to Top
Craigie View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Sep/06/2011
Location: Bris, Australia
Status: Offline
Points: 369
Post Options Post Options   Thanks (0) Thanks(0)   Quote Craigie Quote  Post ReplyReply Direct Link To This Post Posted: Nov/07/2018 at 2:03am
do have some space in the rear for a bigger rim or tyre


Craigie.........

1968 Dodge Charger "Bullitt" tribute
1971 SC/360 Hornet
1973 "Levi" Gremlin
Back to Top
farna View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar
Moderator Lost Dealership Project

Joined: Jul/08/2007
Location: South Carolina
Status: Offline
Points: 19611
Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Nov/07/2018 at 6:06am
I use the tire size and gear calculators at www.4l0.com... only because it's so easy to remember! Ignore the "LT"  in front of tire size. Stands for "light truck", and the only difference between a light truck and car tire is the tread design (and maybe more plies/tougher), sizes are the same. Use "1" for the transfer case ratio (1:1). Get the diameter of the tire size you want, then plug that into the gear calc. Leave whatever you want it to calculate blank. It will calculate needed tire diameter, then you can find a tire size that's close. Hard to find some diameters, and there can be a +/- 0.25" between manufacturers (only 25-50 rpm).

If you want a 3.08 axle Jeep XJs used 3.08 with the 4.0L/5 speed combos. It might be easy enough to find, and the D35 is tough enough for a mid range 360 on street tires. It will be fine for an occasional trip down the strip on heater slicks, but regular drag racing would accelerate wear. Don't think you'd break anything without warning, it should start making warning noises first. 5-6 passes with cheater slicks 2-3 times a year shouldn't faze it. That many every month will likely wear it out in a year or two.

The XJ axle will fit a Hornet, but you'll need to cut the shock mounts off and weld in new spring saddles. It's a bit wider, but fits perfect with the deep Jeep wheels or deeper aftermarket wheels. Save on the rear axle, but make up for it in wheels. You can get new 3.08 gears, but not 3.15 that I could find. Goes from 3.08 to 3.31. 


Edited by farna - Nov/07/2018 at 6:10am
Frank Swygert
Back to Top
WesternRed View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Aug/03/2010
Location: Australia
Status: Online
Points: 5787
Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Nov/07/2018 at 6:10am
You would probably need to have 14" rally wheels re-rimmed to 15", the chances of finding some in Australia is next to zero and you might have noticed the command pretty high prices stateside. 

Taller tires will help with the gearing, maybe even if you just bolt them on for longer road trips.

Given that is is a genuine SC360, I'd imagine you probably want to keep the drive line original.

Here are some 15 x 8 rally wheels I whipped up earlier:



PS: If you can get something like a 29" tall tire under there (it's 25.6" at the moment), say 255/70/15, then that would have a similar effect to going from 3.54 to 3.15 with the gears.


Edited by WesternRed - Nov/07/2018 at 6:17am
I've finally given up drinking for good...........now I only drink for evil.
Back to Top
Craigie View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Sep/06/2011
Location: Bris, Australia
Status: Offline
Points: 369
Post Options Post Options   Thanks (0) Thanks(0)   Quote Craigie Quote  Post ReplyReply Direct Link To This Post Posted: Nov/08/2018 at 2:00am
lol............... you teasing me with the pic of the Rims

Yes, a couple of those will be on my future shopping list.

Even though it's not the original motor and Tranny, they are period correct for the car so really can't see me changing them out at any stage.
The 3:15 or 3:08 diff gear will also be part of the shopping list after I try the rear tyre/rim option ............. I suspect the combination would be the ducks nuts !!
Craigie.........

1968 Dodge Charger "Bullitt" tribute
1971 SC/360 Hornet
1973 "Levi" Gremlin
Back to Top
WesternRed View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Aug/03/2010
Location: Australia
Status: Online
Points: 5787
Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Nov/08/2018 at 2:37am
You might be able to throw a pair of Jeep XJ wheels on the back just to see how it runs with taller tires, they have the same stud pattern.
I've finally given up drinking for good...........now I only drink for evil.
Back to Top
 Post Reply Post Reply Page  <1 34567>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 3.328 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or