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276, 294, 323 rear gear #2976912
10/21/21 05:08 PM
10/21/21 05:08 PM
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Northern Virginia
Moparmaniacc Offline OP
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Lets take your typical 318 mopar b body back in the day, would that typically have come with a 2.94 or 2.76? And My dads 318 Sport Fury seemed to have taller gears, was that a 276 or a 245?

Right now I have a 440 challenger with a 3.23 and its just too much for me... feels like a 373 or a 410 to me.

Would anyone in Del Mar Va like to meet me and trade their 2.94 for my 3.23?

thanks
John

Re: 276, 294, 323 rear gear [Re: Moparmaniacc] #2976917
10/21/21 05:25 PM
10/21/21 05:25 PM
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Kalispell Mt.
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Most likely 2.76. I have never seen a 2.45 before the mid 1970s

I have a 2.76 I am thinking about putting in my 93 318 2wd dakota, combined with the OD trans it should cruise real nice highway cruiser with a 1.90 final drive ratio


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 276, 294, 323 rear gear [Re: HotRodDave] #2976922
10/21/21 05:42 PM
10/21/21 05:42 PM
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massachusetts U.S.A.
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1969ronnie Offline
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Hi Mopar , I don't know what year your car is , guess it's a1970 or a 1971 ? drive Should have a 489 case Number . Do you care if the case number is a 741 or 742 , as long as it has the Ratio you want ? bump and big yoke or small yoke , your car should be a big yoke . We need more info to help you . wrench

Re: 276, 294, 323 rear gear [Re: 1969ronnie] #2976924
10/21/21 05:48 PM
10/21/21 05:48 PM
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massachusetts U.S.A.
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1969ronnie Offline
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Hi John , also what size are your rear tires ? tall like a 255-70-15 or short and fat like a 245-60-15 . Tire height changes cruise RPM . drive if you have short and wide tires , it would be WAY easier to get a new pair of taller tires and sell you old tires . Olanturn

Re: 276, 294, 323 rear gear [Re: HotRodDave] #2976941
10/21/21 06:29 PM
10/21/21 06:29 PM
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Michigan
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Originally Posted by HotRodDave
Most likely 2.76. I have never seen a 2.45 before the mid 1970s

I have a 2.76 I am thinking about putting in my 93 318 2wd dakota, combined with the OD trans it should cruise real nice highway cruiser with a 1.90 final drive ratio


My Fifth Avenue had 2.24:1 from the factory with 205-70-15 tires. It could wind out first gear to 45mph. I couldn't imagine driving a 1.9:1 ratio with truck tires.


1987 Fifth Avenue - 512/518/D60
Re: 276, 294, 323 rear gear [Re: MarkZ] #2976992
10/21/21 08:09 PM
10/21/21 08:09 PM
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Originally Posted by MarkZ
Originally Posted by HotRodDave
Most likely 2.76. I have never seen a 2.45 before the mid 1970s

I have a 2.76 I am thinking about putting in my 93 318 2wd dakota, combined with the OD trans it should cruise real nice highway cruiser with a 1.90 final drive ratio


My Fifth Avenue had 2.24:1 from the factory with 205-70-15 tires. It could wind out first gear to 45mph. I couldn't imagine driving a 1.9:1 ratio with truck tires.


And probably had a 998/999 with the 2.7 low gear on it.

Re: 276, 294, 323 rear gear [Re: Moparmaniacc] #2977060
10/21/21 10:30 PM
10/21/21 10:30 PM
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My 68 Coronet came with the 2.76 in the 741 case. I've never changed them.

Re: 276, 294, 323 rear gear [Re: Moparmaniacc] #2977283
10/22/21 02:20 PM
10/22/21 02:20 PM
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I believe they also made a 3.08 gear, for Nascar? back in the day, I have tried for over a decade to locate such gear, but have come up zero.


If you can't dazzle them with diamonds, don't waste your time, because nothing will
Re: 276, 294, 323 rear gear [Re: Transman] #2977299
10/22/21 02:55 PM
10/22/21 02:55 PM
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Michigan
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Originally Posted by Transman
Originally Posted by MarkZ
Originally Posted by HotRodDave
Most likely 2.76. I have never seen a 2.45 before the mid 1970s

I have a 2.76 I am thinking about putting in my 93 318 2wd dakota, combined with the OD trans it should cruise real nice highway cruiser with a 1.90 final drive ratio


My Fifth Avenue had 2.24:1 from the factory with 205-70-15 tires. It could wind out first gear to 45mph. I couldn't imagine driving a 1.9:1 ratio with truck tires.


And probably had a 998/999 with the 2.7 low gear on it.


Yes, and it was horrible. If HRD has a 518 in his truck and not the 500 then he doesn't even have the lower first gear. Just makes the problem that much worse. Then a taller tire on top of that? Ignoring city street driving, a 30" tall tire and a 1.9 final ratio puts you at like 1500 RPM on the highway. It just seems way too numerically low to me.


1987 Fifth Avenue - 512/518/D60
Re: 276, 294, 323 rear gear [Re: MarkZ] #2977305
10/22/21 03:04 PM
10/22/21 03:04 PM
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Originally Posted by MarkZ
Originally Posted by Transman
Originally Posted by MarkZ
Originally Posted by HotRodDave
Most likely 2.76. I have never seen a 2.45 before the mid 1970s

I have a 2.76 I am thinking about putting in my 93 318 2wd dakota, combined with the OD trans it should cruise real nice highway cruiser with a 1.90 final drive ratio


My Fifth Avenue had 2.24:1 from the factory with 205-70-15 tires. It could wind out first gear to 45mph. I couldn't imagine driving a 1.9:1 ratio with truck tires.


And probably had a 998/999 with the 2.7 low gear on it.


Yes, and it was horrible. If HRD has a 518 in his truck and not the 500 then he doesn't even have the lower first gear. Just makes the problem that much worse. Then a taller tire on top of that? Ignoring city street driving, a 30" tall tire and a 1.9 final ratio puts you at like 1500 RPM on the highway. It just seems way too numerically low to me.



I bet you would find yourself taking it out of OD a lot, I doubt it would handle a grade without lugging. And if a lockup, I’m betting it would drive you right out of the truck.

Last edited by Transman; 10/22/21 03:06 PM.
Re: 276, 294, 323 rear gear [Re: MarkZ] #2977307
10/22/21 03:13 PM
10/22/21 03:13 PM
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Originally Posted by MarkZ
Originally Posted by Transman
Originally Posted by MarkZ
Originally Posted by HotRodDave
Most likely 2.76. I have never seen a 2.45 before the mid 1970s

I have a 2.76 I am thinking about putting in my 93 318 2wd dakota, combined with the OD trans it should cruise real nice highway cruiser with a 1.90 final drive ratio


My Fifth Avenue had 2.24:1 from the factory with 205-70-15 tires. It could wind out first gear to 45mph. I couldn't imagine driving a 1.9:1 ratio with truck tires.


And probably had a 998/999 with the 2.7 low gear on it.


Yes, and it was horrible. If HRD has a 518 in his truck and not the 500 then he doesn't even have the lower first gear. Just makes the problem that much worse. Then a taller tire on top of that? Ignoring city street driving, a 30" tall tire and a 1.9 final ratio puts you at like 1500 RPM on the highway. It just seems way too numerically low to me.



I fixed that problem in my 87 Diplomat.

I got rid of the 318 and put in a 360, then I axed the rear axle with the 2.24 ratio and put an 8 1/4 with a 2.94 rear ratio from a cop spec M body, then I put an A833 in it.

Which is how Dodge should have built it. But they cheaped out to meet CAFE by not putting a 4 speed OD auto in and a better rear gear.

Re: 276, 294, 323 rear gear [Re: Sniper] #2977312
10/22/21 03:23 PM
10/22/21 03:23 PM
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Kalispell Mt.
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HotRodDave Offline
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It does have the 518 now but I already have an A-500 for it, just one more thing to get around to. Also if it drops in and out of OD too much I can just wire up control of those for me to handle. The tires on the truck are brand new 235-75-15s so they will be there for a while and are not very tall. The 318 in my cuda had a low gear 904 and similar height tires and was bareable on the low end, on the highway it still wanted another gear. I am 100 miles from cities in 3 different directions where I live now, tons of driving on mostly flat ground 75 MPH.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 276, 294, 323 rear gear [Re: Moparmaniacc] #2977322
10/22/21 04:13 PM
10/22/21 04:13 PM
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360view Offline
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I find it is much, much better
to talk about MPH per 1000 rpm
instead of differential gear ratios.

If you are turning 2000 rpm at 80 mph
your ratio is 40 MPH per 1000 rpm,
etc

Doing it this way combines tire size, overdrive ratios, and differential gear ratios.

In highway driving there is considerable fuel economy improvement up to a ratio of 40 MPH per 1000 rpm,
slower improvement above 40.

Re: 276, 294, 323 rear gear [Re: 360view] #2977328
10/22/21 04:35 PM
10/22/21 04:35 PM
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Originally Posted by 360view
I find it is much, much better
to talk about MPH per 1000 rpm
instead of differential gear ratios.

If you are turning 2000 rpm at 80 mph
your ratio is 40 MPH per 1000 rpm,
etc

Doing it this way combines tire size, overdrive ratios, and differential gear ratios.

In highway driving there is considerable fuel economy improvement up to a ratio of 40 MPH per 1000 rpm,
slower improvement above 40.


I like this thought... but I like to take it another step and figure displacement per mile. Right now I am a hair over 2000@60mph. so about the same displacement per mile as if I had a 159 CID engine running 4000@60mph. if I slow it to 1500@60mph it is like the 159 running at 3000RPM at 60mph witch is close to what my neon was running in displacement per mile with tiny tires and no OD 122 CID at just over 3000 RPM, so actually I would still be slightly more displacement per mile so I don't think it is un doable, I know it is a truck but not a very big or heavy one at all by todays standards. The long term plan is to do some stuff to increase the low end TQ like zero deck the pistons and take about .030 off the heads and better spray pattern injectors... maybe a bely pan and some other aero tweaks.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 276, 294, 323 rear gear [Re: Transman] #2977370
10/22/21 07:46 PM
10/22/21 07:46 PM
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Originally Posted by Transman
I bet you would find yourself taking it out of OD a lot, I doubt it would handle a grade without lugging. And if a lockup, I’m betting it would drive you right out of the truck.

iagree
newer motors are designed to be fuel efficient at 1500-2000 RPM while developing enough power to push a brick down the road at 75-80+ MPH.
Older motors were not. One may actually find they lose MPG & drivability if they get to far out of the engines efficiency range wink

Re: 276, 294, 323 rear gear [Re: TJP] #2977389
10/22/21 08:32 PM
10/22/21 08:32 PM
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OK, so what am I missing? I have a 96 Dakota 4x4 chassis (under my 49 Dodge truck body) with a 318 OD auto (I assume its a 518, factory stock 46000 mile drivetrain) with 3:55 rear gears and 235 75 15 tires. it is not a lightweight truck. According to the factory tach, the motor is turning right at 2,000 rpm at 70 mph on the interstate in Iowa. The truck pulls a pretty consistent 18 mpg at 70-75 mph, and is pretty fun around town.

If the stated 318 is doing 2000 at 60 with an od trans and 3:23 gears, something isn't working, like maybe the OD trans. 2,000 rpm is about what my truck is pulling at 60 before it shifts into OD. Gene

Re: 276, 294, 323 rear gear [Re: HotRodDave] #2977469
10/23/21 05:49 AM
10/23/21 05:49 AM
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Displacement (and volumetric efficiency aka “breathing”)
does play a part.

If you attach a vacuum gauge and it reads less than 6 inches Hg at your flat level highway cruising speed,
your engine displacement is matched pretty close to the Horsepower need to go that MPH.
( but you cannot climb a noticeably steep hill without downshifting, or have an electric booster motor kick in)

Another factor is piston ring friction due to average linear speed up and down the bore.

Stay below an average ring speed of 1200 feet per minute,
unless you have super hard and slickly polished bore walls (plasma sprayed on or a hi tech liner)
or extremely thin high tech rings.

New tech may have pushed optimum ring speed up
maybe 1500 feet per minute.

MDS as done by Chrysler on Hemi V8s proves that their engine to drivetrain matching for highway cruise is off by 50% or more.

Or...
on these 10 speed automatic transmissions
the top 6th, 7th, 8th, 9th, and 10th gears should be progressively lower overdrive ratios.

Scientific knowledge of many car buyers is so low
that they think a vehicle that shifts to climb hills is “weak”
and CVT is “weird”
hence MDS.

You do not see MDS on big truck diesels,
but you have seen truck diesels that can idle on 1 or 2 cylinders
although APU’s to stop idling are now the norm thanks to CA.

Re: 276, 294, 323 rear gear [Re: 1969ronnie] #2977986
10/24/21 07:26 PM
10/24/21 07:26 PM
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Northern Virginia
Moparmaniacc Offline OP
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I do have short 245-60-15 BF Goodrich rear tires, Ronnie. Come to think of it, the car does sit pretty low. So which taller tires would do the job and still look relatively good on my 70 Challenger R/T, for the rear? And would you get a different size for the front? (It would make my manual steering easier thats for sure).

Another approach would be to keep these tires and use the 2.76 sure grip I have. Or expensive option is to replace my 833 with a 5 speed...

And finally, see the attachment on full size Dodges in 1970. Cars usually got 2.76 or 3.23

thanks...

DODGE__1970_AXLE RATIO_ENGINE_P63 1970 D Code List.jpg
Last edited by Moparmaniacc; 10/25/21 07:17 PM.
Re: 276, 294, 323 rear gear [Re: Moparmaniacc] #2978656
10/26/21 03:52 PM
10/26/21 03:52 PM
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massachusetts U.S.A.
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1969ronnie Offline
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Hi John , there was a Moparts tire post about a month ago , I hope someone can find it and bump it back up . I think post was named 255-70-15 tires ? drive Anyway , the moparts members like the 255-70-15 on the back of E Bodys and B Bodys . I just installed a pair of 255 - 70 -15 cooper cobras and I love them . Didn't hook up a Tach yet , but engine sounds like it's spinning 500 or 750 RPM , LESS easy ! I love it on the highway and just drove to the Lebanon Valley Mopar show which is Over 2 or 2 1/2 HOURS on the highway going 70 MPH for me depending on traffic . Cheapest and BEST $300 bucks Ive spent on that car . WAY cheaper than changing a 8.75 dropout , or going to a 5 speed . yellow ronnie

Re: 276, 294, 323 rear gear [Re: HotRodDave] #2978757
10/26/21 08:59 PM
10/26/21 08:59 PM
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Originally Posted by HotRodDave
Originally Posted by 360view
I find it is much, much better
to talk about MPH per 1000 rpm
instead of differential gear ratios.

If you are turning 2000 rpm at 80 mph
your ratio is 40 MPH per 1000 rpm,
etc

Doing it this way combines tire size, overdrive ratios, and differential gear ratios.

In highway driving there is considerable fuel economy improvement up to a ratio of 40 MPH per 1000 rpm,
slower improvement above 40.


I like this thought... but I like to take it another step and figure displacement per mile. Right now I am a hair over 2000@60mph. so about the same displacement per mile as if I had a 159 CID engine running 4000@60mph. if I slow it to 1500@60mph it is like the 159 running at 3000RPM at 60mph witch is close to what my neon was running in displacement per mile with tiny tires and no OD 122 CID at just over 3000 RPM, so actually I would still be slightly more displacement per mile so I don't think it is un doable, I know it is a truck but not a very big or heavy one at all by todays standards. The long term plan is to do some stuff to increase the low end TQ like zero deck the pistons and take about .030 off the heads and better spray pattern injectors... maybe a bely pan and some other aero tweaks.




I had a 93 Dakota with 5.2 518 combo. Picked up nearly 1mpg average on interstate driving just by adding a tonneau cover.to the bed.

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