1973 340, want more power.

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rumblefish360 said:
Search member "webby" for a 3.91 complete set up.
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Thanks!
He has this for sale....
8 3/4 3.91 Sure grip 489 New Nodular Iron Case
New sure grip unit, bearings, u bolt style yoke. Ring and pinion, crush sleeve eliminator, new nodular iron case, forged caps, billet adjusters ,professionally set up.
$1150.00 plus shippiNng

This is 225 usd less than the dr diff.... But is the dr diff one "newer"???

Also, this one from webby will fit my car for sure?

Thanks!!!
 
to find the gear ratio of the vehicle. Put the back up on jack stands. Put the car in nuetral. make a mark on the driveline or pinion yolk and on the inside of the tire where you will be able to keep track of revolutions. turn the drivline. keep track of how many time the driveline must turn to make one full revolution of the wheel. Done! 3.23 to 1. 3.91 to 1. etc. etc. etc.
 
clementine said:
to find the gear ratio of the vehicle. Put the back up on jack stands. Put the car in nuetral. make a mark on the driveline or pinion yolk and on the inside of the tire where you will be able to keep track of revolutions. turn the drivline. keep track of how many time the driveline must turn to make one full revolution of the wheel. Done! 3.23 to 1. 3.91 to 1. etc. etc. etc.
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After calculating my numbers accouting for the open defferential... I think i am at 3.23
 
When you swap gear sections out, look on the ring gears side for the ratio stamped in it.
 
I have never had a problem with ether. WEBBY is a good fella and cheaper. I have purchased from him before. If there is any questions, ask them direct.
Who you decide on is your choice.

If you want to check the ring gear stamping before ordering, that's your call. If it helps your mindset, do it.
 
Oh! If have also ordered
From Dr. Diff before as well and there was no issues ether.

Both have excellent reputations
 
open diff= 2 rotation of tire and count driveline turns. suregrip, both tires need to be of the ground, turn tire "1" turn and count how many turn the drive line turns.
2.76 =2 and 3/4 of a turn on the drive shaft. 3.55- 3 and 1/2 turn of the drive shaft.
simple and you will know without pulling it!
 
If I was drag racing all the time, the 3.91 gears would make sense. But, let's go over again how are you using this car.... You say 99% street but is this street racing? Or just cruising? If cruising, you are probably not going to be happy in the long term putting that amount of $$ into a 3.91 gear set that makes the car noisy and vibrates more at highway speeds, and drops gas mileage a lot. All of the engine operations will now be moved HIGHER in the RPM range, which is opposite of what you seemed to want to do earlier (post #24).

We have been talking about a lot of things but your use of the car keeps falling out of the picture. Bad advice and decisions flows from not clearly staying focused on what you will do with the car.
 
nm9stheham said:
If I was drag racing all the time, the 3.91 gears would make sense. But, let's go over again how are you using this car.... You say 99% street but is this street racing? Or just cruising? If cruising, you are probably not going to be happy in the long term putting that amount of $$ into a 3.91 gear set that makes the car noisy and vibrates more at highway speeds, and drops gas mileage a lot. All of the engine operations will now be moved HIGHER in the RPM range, which is opposite of what you seemed to want to do earlier (post #24).

We have been talking about a lot of things but your use of the car keeps falling out of the picture. Bad advice and decisions flows from not clearly staying focused on what you will do with the car.
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But I wana go fast!!!

I will not be doing much highway. Maybe once a year. I don't think I would mind the noise. My daily driver ram 1500 has 35 shaky tire and bro exhaust with no resonators.

However, I was under the impression that 3.91 is a good compromise for street/strip.
 
Cudafever said:
here is a chart that might help you out. i guest on tire height at 25"
sorry i made a mess of this but you can go on there sight and do some figuring on you one


Engine Speed (RPM) MPH 3.91 Gear MPH 3.23 Gear MPH 2.76 Gear

3500 RPM 66.58 MPH 3.91

3000 RPM 69.08 MPH 3.23
2500 RPM RPM/MPH From Gear Ratio Calculator by Wallace Racing
67.38 2.76

Here is the sight if you want to play around with gear ratio and tire size.
RPM/MPH From Gear Ratio Calculator by Wallace Racing
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That is cool. My rear tire is 255/60/15. I was going to get 275/60/15 at some point. The 255 is 27" and the 275 is 28" - acording to a online tire height calculator.
 
Richard McLaughlin said:
That is cool. My rear tire is 255/60/15. I was going to get 275/60/15 at some point. The 255 is 27" and the 275 is 28" - acording to a online tire height calculator.
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Click on that link i posted and play around with it........it will help you make a decision on tires as well as gear ratio
when i still ran my car on the street, i had 3.91 and 235/75/15 truck tire on the back and 26 slick that i raced at the track with.
Even with 28" tires you were the slow one on the freeway.
 
Cudafever said:
Click on that link i posted and play around with it........it will help you make a decision on tires as well as gear ratio
when i still ran my car on the street, i had 3.91 and 235/75/15 truck tire on the back and 26 slick that i raced at the track with.
Even with 28" tires you were the slow one on the freeway.
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Did you dislike your 3.91 or did you find it a good highway/street/strip balance?
 
If your not going this be on the Hwy. much, 3.91's are fine and with the tall tire, not to bad of a combo.

The "Good compromise" gear choices are 3.23 & 3.55. Normally MoPar's do not come with 3.73's. But those are the 3 ratios considered to fall into that category. And tire size (height) has a play in that as well.

I have run 4.10's for decades. I last had 255/60/15's out back and IMO, it was excellent for the build, car & performance intended. I had no issue being on the Hwy. Of course, I did not travel very fast. 60/65 mph was the cruise speed. The car was a manual and the tack ran around the 3300 area. I do not under any way consider that spinning the engine high for Hwy. driving for the build that it was and the set up it ran. A lot of people cry like they have a baby at that.

If that's to much for you.......
 
rumblefish360 said:
If your not going this be on the Hwy. much, 3.91's are fine and with the tall tire, not to bad of a combo.

The "Good compromise" gear choices are 3.23 & 3.55. Normally MoPar's do not come with 3.73's. But those are the 3 ratios considered to fall into that category. And tire size (height) has a play in that as well.

I have run 4.10's for decades. I last had 255/60/15's out back and IMO, it was excellent for the build, car & performance intended. I had no issue being on the Hwy. Of course, I did not travel very fast. 60/65 mph was the cruise speed. The car was a manual and the tack ran around the 3300 area. I do not under any way consider that spinning the engine high for Hwy. driving for the build that it was and the set up it ran. A lot of people cry like they have a baby at that.

If that's to much for you.......
Click to expand...
Perfect!
 
That will fit your application.
That is a good strong differential.
You will notice a big emprovment on your
"Get up and go "!
 
Richard McLaughlin said:
But I wana go fast!!!

I will not be doing much highway. Maybe once a year. I don't think I would mind the noise. My daily driver ram 1500 has 35 shaky tire and bro exhaust with no resonators.

However, I was under the impression that 3.91 is a good compromise for street/strip.
Click to expand...
Rear gear selection is something that goes along with the use of the car. If ripping or tearing is what you want to do, then go high! Look at what YR uses: 4.56 LOL! The term street/strip gets used in a lot of different ways, and means different things to different people. So when I hear 'street/strip', I ask what the person really want to do.
- The higher rear gear increases the torque to rear tires and that make the car accelerate harder.
- The engine RPM's are higher.
- Fuel mileage is lower.
- The ultimate top end speed is lower.

I'm just wanting you know the tradeoffs. As RF360 sez, the 3.55 seems to be the most popular compromise gear for these cars. As he also sez, the engine rev's with the 3.91 is gonna be OK to 60-65 mph, not to 75 mph; the fuel mileage will be down. If you are not cruising long distance much, and don't care about fuel mileage, then it won't be an issue.

FWIW, the right engine combo would work very well with 3.55 gears or even your 3.23 gears. I had a small block set up for a very broad torque, and, even with 3.08 rear gears, it outran 440 GTX's all day long . The same engine with 3.55's would just spin the tires more. So there are different approaches to your goal. But the engine work to get THERE is a lot more complex than a rear gear swap, so a rear gear swap may well be the perfect first step for you.

BTW, several people have commented about having the engine tuned, and in particular, working on the distributor advance curves. As a next project, I would urge you to start reading through a lot of threads here about ignition timing and working on the distributor advance curve. That is a cheap way to pick up a very noticeable amount of low end and mid range torque. It is also a good starting point to begin learning about the innerds of engines, and would be a good 'gateway' to more complicated engine upgrades.
 
yellow rose said:
The best street/strip compromise gear I've found is the tried and true 4.56. The perfect street strip gear. It's what I use.
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I have 4.88's in the Duster now. Put put around town and rip it up on the back street strip. Not really good for anything in between. But I do like them.
 
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