Rear gear recommendation for highway.....

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73SlantSwinger

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67 valiant post with built 318 and 8 3/4 3:91 sure grip, 727 tranny. I recently bought the car and would like to be able to take this thing on the interstate sometimes and cruise at 65-70 without the rpms being crazy high. Recommendation for a higher gear for this combo? As it sits right now if i even do 55-60mph its pushing 3K and higher......
 
How built is the 318?

If the cam and converter allow I loved the 2.94 gear I had in my dart. If you want a little more then go 3.23. Of course you may give up a little at the track though.
 
How built is the 318?

If the cam and converter allow I loved the 2.94 gear I had in my dart. If you want a little more then go 3.23. Of course you may give up a little at the track though.
How tall are your rear tires it will help calculate rpm?
 
I like my 2.76's. I turn just under 2100 rpm's at 55 mph.
 
I turn 2k on the nose at 90mph, but I can still blow smoke on command around town. :D
Yea, I'm flaunting it. LOL
 
I like sub 2000 rpm so 2000/3000 x 3.91 =2.61s
Add 15% to go plus 15% faster equals 2.22s
Thats what you need 2.22s
These will run at 2.22/3.91 = 56.8% of your current rpm so .568 x 3000 =1703 at 55/60 which at 75 would be 75/57.5 x 1703 =2222, unless your TC slips down there, or your gauges lie.

I like 1600@65, but that's just not doable without an overdrive.That would be 2200@90.........lol

Put a vacuum gauge on that teener, and rev it up slowly. When the vacuum peaks, that is the minimum recommended cruising rpm.This is the rpm at which the engine first becomes efficient. Cruising on either side of it will cost fuel. The higher side usually costs more. If it has a long slow vacuum curve like a stock teener, then almost any hi-way gear will work.
If you have a nasty cam that won't vacuum-peak until 2800 rpm,buy a Neon. Or earplugs
If you have a 3000TC that slips 10%,buy a Neon.Or stock in an oil company.
Good luck finding 2.22s
On the flipside 2.22s would destroy the teener performance. First gear would be good to over 75 mph, but the car is basically gonna be a turd, cuz it will feel like it's starting in second gear.More like 2nd and a half compared to those 3.91s. The engine won't even wake up until 50ish in first.
So what to do?
Well everybody has there own experiences. If the teener is making a lotta cylinder pressure, then 2.76s are the old standby.
But if the built teener failed to get hi-compression pistons, then 3.55s are the standby gear.
In-between is in-between.
140psi will pull 2.76s off the line, but it won't be particularly quick with a stock-type stall.
140psi will pull 3.23s pretty good, off the line.and
140 will be peppy with 3.55s.
If the built teener can't muster at least 130, it needs to be re-"built".
If it cranks 165, hallelujah, you got yourself an engine.Put 2.76s in and a 2400TC. With 28 inch tires,this will get you around 2500@75. The 2400TC at 165psi, will get you off the line reasonably well, especially with shorter tires like about 25s. That would be equivalent to a gear change from 2.76 to 3.09s
If the teener only makes 130psi, it needs those 3.91s to be peppy, so you will really really miss them when they are gone.
 
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What rear gears do you run? Trans?

2.73's with a 42RH overdrive and converter lockup.
26" 15 inch tires.
Also pressure switching from the governor port for fully automatic shifting for OD and lockup.
It's going to get an 8.25 locker with lower gears before long, hopefully this winter but it's a freeway runner and 25 miles to the gallon with a 350hp Magnum naturally aspirated.
 
What rear gears do you run? Trans?

2.73 gears with a 42RH overdrive with converter lockup.
15 inch tires at 26 inches tall.
It's set up with governor pressure switching for fully automatic OD and lockup and gets 25mpg at 90mph and 2k on the tach.
This winter I hope to get the 8.25 locker with lower gears, but it's a freeway killer for sure.:D
8 miles to the gallon better than the 318 and 904 but now has a 350+hp naturally aspirated Magnum in it.

It's also a lot quieter inside the car so it's easy to let it get over the speed limit.
 
2.73 gears with a 42RH overdrive with converter lockup.
15 inch tires at 26 inches tall.
It's set up with governor pressure switching for fully automatic OD and lockup and gets 25mpg at 90mph and 2k on the tach.
This winter I hope to get the 8.25 locker with lower gears, but it's a freeway killer for sure.:D
8 miles to the gallon better than the 318 and 904 but now has a 350+hp naturally aspirated Magnum in it.

It's also a lot quieter inside the car so it's easy to let it get over the speed limit.
The
 
Wow you've spent a fortune on your setup. I'm learning on my 72 dart 340 .391 rear and 4 speed overdrive. I don't think the overdrive trans is going to work pops out of third and makes whining noise. Thought I'd buy a four speed rebuilt from Brewer's they've helped me a lot. I'd be neat to have it done by someone you trust. Think I asked them once and they told me $1300 +freight. Then I was thinking of a 3.23 center in my 8 3/4 to cruise. Switch over to go draggin.
 
Wow you've spent a fortune on your setup. I'm learning on my 72 dart 340 .391 rear and 4 speed overdrive. I don't think the overdrive trans is going to work pops out of third and makes whining noise. Thought I'd buy a four speed rebuilt from Brewer's they've helped me a lot. I'd be neat to have it done by someone you trust. Think I asked them once and they told me $1300 +freight. Then I was thinking of a 3.23 center in my 8 3/4 to cruise. Switch over to go draggin.

Well, I do all the work myself so the entire trans, converter, shift kit, shift switching, driveline shortening and all ran me about $350-400.
Some people don't like to talk about how much they spent or whatever, but I like people to know it can be done for a lot less than buying everything out of a catalogue and paying someone to mess it, ops I meant do the work.:D

The rest of the car is fairly unique with a lot of "one of a kind" solutions.
It's been fun. :D

Sorry if I hijacked the gears post.

SANY0030.JPG
 
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Well, I do all the work myself so the entire trans, converter, shift kit, shift switching, driveline shortening and all ran me about $350-400.
Some people don't like to talk about how much they spent or whatever, but I like people to know it can be done for a lot less than buying everything out of a catalogue and paying someone to mess it, ops I meant do the work.:D
 
Thanks for the advice. You are very knowledgable and I appreciate getting to know you, it must have taken years to get this into your head. I'm starting to do my own work later in life 72. Don't have a long time left but want to have fun for the rest. Hoping for 13s sometime then maybe better. My 340 has edlebrock heads a rumpity cam. Sounds good but the overdrive trans (I think) kind of messes it up.
 
Well, I do all the work myself so the entire trans, converter, shift kit, shift switching, driveline shortening and all ran me about $350-400.
Some people don't like to talk about how much they spent or whatever, but I like people to know it can be done for a lot less than buying everything out of a catalogue and paying someone to mess it, ops I meant do the work.:D

The rest of the car is fairly unique with a lot of "one of a kind" solutions.
It's been fun. :D

Sorry if I hijacked the gears post.

View attachment 1714959661
 
Wow you've spent a fortune on your setup. I'm learning on my 72 dart 340 .391 rear and 4 speed overdrive. I don't think the overdrive trans is going to work pops out of third and makes whining noise. Thought I'd buy a four speed rebuilt from Brewer's they've helped me a lot. I'd be neat to have it done by someone you trust. Think I asked them once and they told me $1300 +freight. Then I was thinking of a 3.23 center in my 8 3/4 to cruise. Switch over to go draggin.
Don't do it. Don't put 3.23s behind the od. First gear will be just fine. And it will cruise real nice with the equivalent to 2.78s. But third will suck, and second almost as much. This is really a wrong tranny for a 340. To keep a 340 on the pipe requires a close ratio tranny, and the od is a very wide ratio. Not just wide but very wide.
With 3.23s, first will be good to about 52 mph@6500. Then when you shift into 2nd the Rs will drop to 3485, and the poor 340 is nearly 1000 rpm under it's torque peak(depending on combo of course, but 600 for sure). So in a performance situation,she will be a bit of a slug til it hits say 4200 which will be 63 mph.So for 11 mph, from 52 to 63 the poor 340 will struggle. Then it hits the pipe and sings to 97 mph, through the traps. Two gears. That is not the fast way down the road.
But ok, never mind the track.
Say you just cruise the car. With 3.23s 4000rpm is about 32 in first,60 in second. So then what is third good for? Going 5 mph to hit O/D?
Ok try another one; You are cruising along in 2nd at 35mph doing about 2345 rpm. That's nice right? But say you want to speed up. A 340 has little torque at 2345. A teener could have more. You're gonna have to lean harder on the gas to get moving. But downshift!, you say. Ok, well 35 in first is 4340. Now the 340 has all kinds of torque, but it is screaming.
The o/d tranny is a tranny to fit a low-rpm engine, with plenty of torque, in a low to medium performance application. So if your 340 has a teener cam in it and there is nothing left in it after 4500rpm, then this would be a good tranny for it;maybe even with 3.23s; but 3.55s would be better, and 3.73s even better, and 3.91s best.
FWIW;
I ran this tranny behind a warmed up low-compression teener and 3.55s. It was pretty good. But as you can imagine, the teener was sloooow. So I put a GearVendor unit behind it and learned to split gears. That was pretty sweet. But now I had double overdrive, sooooo you guessed it; out came the 3.55s. And in went 4.30s. Well that teener turned into a terror. But I found 3.09 x 4.30 a bit much as a starter gear, so in went 3.91s. That was the magic number. A starter gear of 12.08, and a cruiser of 2.165. with 7 useable gears. 90mph was 2400ish rpm. Yeah it pulled it.....
So to recap;
3.23s,plus A833od, plus 340 equals bad idea.And
3.91s,plus A833od, plus 340,equals sorta doable. Or
3.91s to 3.73s,plus A833od,plus stock type teener,plus GearVendor splitter equals great idea!
 
Don't do it. Don't put 3.23s behind the od. First gear will be just fine. And it will cruise real nice with the equivalent to 2.78s. But third will suck, and second almost as much. This is really a wrong tranny for a 340. To keep a 340 on the pipe requires a close ratio tranny, and the od is a very wide ratio. Not just wide but very wide.
With 3.23s, first will be good to about 52 mph@6500. Then when you shift into 2nd the Rs will drop to 3485, and the poor 340 is nearly 1000 rpm under it's torque peak(depending on combo of course, but 600 for sure). So in a performance situation,she will be a bit of a slug til it hits say 4200 which will be 63 mph.So for 11 mph, from 52 to 63 the poor 340 will struggle. Then it hits the pipe and sings to 97 mph, through the traps. Two gears. That is not the fast way down the road.
But ok, never mind the track.
Say you just cruise the car. With 3.23s 4000rpm is about 32 in first,60 in second. So then what is third good for? Going 5 mph to hit O/D?
Ok try another one; You are cruising along in 2nd at 35mph doing about 2345 rpm. That's nice right? But say you want to speed up. A 340 has little torque at 2345. A teener could have more. You're gonna have to lean harder on the gas to get moving. But downshift!, you say. Ok, well 35 in first is 4340. Now the 340 has all kinds of torque, but it is screaming.
The o/d tranny is a tranny to fit a low-rpm engine, with plenty of torque, in a low to medium performance application. So if your 340 has a teener cam in it and there is nothing left in it after 4500rpm, then this would be a good tranny for it;maybe even with 3.23s; but 3.55s would be better, and 3.73s even better, and 3.91s best.
FWIW;
I ran this tranny behind a warmed up low-compression teener and 3.55s. It was pretty good. But as you can imagine, the teener was sloooow. So I put a GearVendor unit behind it and learned to split gears. That was pretty sweet. But now I had double overdrive, sooooo you guessed it; out came the 3.55s. And in went 4.30s. Well that teener turned into a terror. But I found 3.09 x 4.30 a bit much as a starter gear, so in went 3.91s. That was the magic number. A starter gear of 12.08, and a cruiser of 2.165. with 7 useable gears. 90mph was 2400ish rpm. Yeah it pulled it.....
So to recap;
3.23s,plus A833od, plus 340 equals bad idea.And
3.91s,plus A833od, plus 340,equals sorta doable. Or
3.91s to 3.73s,plus A833od,plus stock type teener,plus GearVendor splitter equals great idea!
What the hell is a teener cam?
 
Sounds like a close ratio trans is what is need. I had one Ina GTO once and it did pretty good but....I need more. GTO beat 5.0 mousetangs but not MOPARS.
 
Teener=318
1969 teener cam spec; 240/248/114.. lift of .373/.399

All SB Mopes could benefit from a close-ratio gearset.....
In a 5 speed flavor.
3.09-1.92-1.40-1.09-.69 w/splits of .62-.73-.78-.63 to be used with a rear of 3.55
The 10.97 starter gear is very nice.and the 2.45 would be a fine cruiser, making 65mph=2000rpm. Perfect for a 230*cam
Or something similar
 
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