1973 340, want more power.

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Ok stupid question.. when I turn thebrear wheels thendrive shaft does not move. It is in park now. Put in neutral? With e brake? Seems dangerous. Just back is jacked. I have the jack on the rear axl.
 
Hmmmmm
Turning the tire around once.. the drive shaft does not even make two trips around. For the drive shaft to make two trips around the tire need to rotate about 1.25 times.

This does not seems good.
 
Try putting one wheel on the ground and turn the driveshaft while counting wheel revolutions. More accurate. I would almost lay money on the fact you have 2.94 gears in a 73. 3.23 if you're lucky.
 
Lustle said:
So an all around street machine is basically what you are after. I will say this, if you get 400+, expect to start making suspension/chassis/tire changes. Or you will never put it to the ground. I run 245's on the back of my scamp, and can absolutely burn them at will in any gear. And thats with a snubber and SS springs. I will need to go cal-tracs and spring relocation or even mini tub if I want to really plant it.

The best way to find out gear ratio is to jack it up and put the transmission in neutral. Make a chalk mark on the drive shaft. Then spin the tire. Keep an eye on how many times the tire spins vs how many times the driveshaft spins. That gives you your ratio. EX: If you turn the tire once, and the driveshaft turns 4 times, you're in the 4.10 area. It will also help you tell if you have an open differential or not. If you turn one tire and the other turns the same way, or not at all, that's sure grip. If it turns the other way, open differential. If it is open, you'll have to block the one tire to figure out your ratio.

Your current gears might be great for highway driving. But a gear change will definitely help you get that neck snap you want. Common street gear is between 3.55 - 4.10. But once again, it's all in the whole combination. If you change rear gears, you should get a better converter. If you change cam you should change rear gears and compression. Etc etc etc. It all works together. The best thing you can do is figure out everything about your car. Know every last nut and bolt.
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Can you post a link to a good converter to match up to the 3.91 gears?
 
Richard McLaughlin said:
Can you post a link to a good converter to match up to the 3.91 gears?
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This is who I went with: Performance Torque Converters - Specializing in Race Converters & Transmissions Design & Manufacturing

But you can talk to Lenny at ultimate. Or Pro torque. Or anyone who makes custom converters. I suggest filling out their spec sheet IN FULL. And they will get back to you with a price and timeframe. Then the converter will be built to your EXACT specs. My custom converter from PTC was LESS than an off the shelf B&M unit. Built to my exact car. Billet front. 9.5 inch. 3000 stall. Good for the street. It was very easy to work with them.
 
Richard McLaughlin said:
I did have one wheel on ground.
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You're not doing it quite right: do it again as below.
nm9stheham said:
3. For an open rear axle, you need to block the other wheel so it does not turn. Then rotate the wheel near to you exactly two turns, and count the number of driveshaft rotations. That will be your rear gear ratio.
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From your former results it sounds like a low 3 gear ratio.
 
Well, a very discernable improvement in acceleration. Nothing comes without a price: with the higher rear gear ratio, the engine will rev more when cruising, will be noisier in the car (usually considered a bonus by the younger set LOL), and use more gas. Top end speed will be more limited. So choose wisely. At some point, you can get the rear gear so high as to just spin the tires too easily.

The SureGrip (Mopar-speak for a limited slip rear differential) will make it grip more surely.... a marketing term that really works! A nice upgrade for just about all things.
 
Hold on to your horses, from what I can gather, you have a 340 with an 8 3/4 rear in a 74 Duster. What a great combination! Before you do anything, tune that thing to the max. If there is a hint of miss anywhere up to 6,000 rpm, get new high quality cap, rotor, platinum plugs, and Taylor Spiro Pro wires. Gap the reluctor to factory spec and set timing to 10 degrees BTDC. Next if you have highway gears, 2.76 or 2.94, we used to run 3.23 for a daily driver cruising at 70 mph all day long. If you are not on the highway much try 3.91s. Get rid of the Holley and get a Quadrajet or a TQ. Make sure your carb opens all the way when you mash the pedal. Factory air cleaners are as good as anything, don't waste your time or money. Try to do one thing at a time, so you know what works and what does not. Since you have an 8 3/4 rear you can get the whole center section and swap them back and forth. And yes, get a Sure Grip.
 
66fs said:
Hold on to your horses, from what I can gather, you have a 340 with an 8 3/4 rear in a 74 Duster. What a great combination! Before you do anything, tune that thing to the max. If there is a hint of miss anywhere up to 6,000 rpm, get new high quality cap, rotor, platinum plugs, and Taylor Spiro Pro wires. Gap the reluctor to factory spec and set timing to 10 degrees BTDC. Next if you have highway gears, 2.76 or 2.94, we used to run 3.23 for a daily driver cruising at 70 mph all day long. If you are not on the highway much try 3.91s. Get rid of the Holley and get a Quadrajet or a TQ. Make sure your carb opens all the way when you mash the pedal. Factory air cleaners are as good as anything, don't waste your time or money. Try to do one thing at a time, so you know what works and what does not. Since you have an 8 3/4 rear you can get the whole center section and swap them back and forth. And yes, get a Sure Grip.
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Thanks!
if it is not to much trouble, can you post links to examples (ex: links to buy the product) to these products: high quality cap, rotor, platinum plugs, and Taylor Spiro Pro wires.

Also, a link to a "whole center section" for 3.91 gears and suregrip....

Thanks!!!!
 
Richard McLaughlin said:
Most likely my next mod. What is the Benifit of this one vs my old
Mopar one? Excuse my ignorance
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What is your old MoPar one?
A custom converter is for your set up exactly. The converter I had done @ Pro Torque is a 2400/2500 stall. It will drive like a normal converter but not bog down the engine and its performance. It was made for the combo.

This is the only place I know of that has and sells complete bolt in ready to go 3rd members. Mopar 8 3/4" (8.75) 489 Case Third Member
 
rumblefish360 said:
What is your old MoPar one?
A custom converter is for your set up exactly. The converter I had done @ Pro Torque is a 2400/2500 stall. It will drive like a normal converter but not bog down the engine and its performance. It was made for the combo.

This is the only place I know of that has and sells complete bolt in ready to go 3rd members. Mopar 8 3/4" (8.75) 489 Case Third Member
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Sweet! I like that idea of bolting in the 3.91 and sure grip with "one part"...

Not sure about my converter.. Not home at the moment.
 
I was going to say, look in the classified mechanical parts for sale, you can also look on eBay or some of the vendors here. Dr Diff I believe. Summit Racing for the other parts.
 
Richard McLaughlin said:
Right. So putting in 3.73 or 3.91 I would notice a massive improvement correct??

Also should I change it to sure grip as well??
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if your making any kind of power, im thinking the sure grip will net a better result then the higher gear BECAUSE a higher gear will burn one tire quicker then you do now BUT a sure grip will distribute the load and actually get your car moving
 
diymirage said:
if your making any kind of power, im thinking the sure grip will net a better result then the higher gear BECAUSE a higher gear will burn one tire quicker then you do now BUT a sure grip will distribute the load and actually get your car moving
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Looks like ill be doing the sure grip and 3.91 anyway...
 
sounds like a plan

perhaps, while the axles are out, you may want to upgrade the wheel studs as well
 
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