[WANTED] 2.76 open differential 741 or 742 case, 8 3/4 axle
- Thread starter Brooks James
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Charrlie_S
Well-Known Member
Got a 2.76 open, 742 case. Need to get it out and take it out of the "can" and check it. I really don't know what is a fair price, so shot me an offer if interested. In your favor, don't need to ship it, as you are fairly close to me.
Pm on the way
Good to know I'm looking at one at Charlie's in Ocala has tommorow.
His initial report is that it's extremely clean, perfect gear mesh pattern.
Reason for 2.76 gear search, less fuel consumption
EV's will eventually be the largest sales overall has cars for $11000
The government is panicked to slow the onslaught of extremely cheap EV that follows their edict of the Chinese, inexpensive up front, disposable, just buy another, which is feed.
Bidens suggestions tariffs, etc, which ultimately the consumer will pay for @ 15 , 000.per car
My point, I will cruise my 360 mag as long as there's gas, then onto natural gas, which the US has huge reserves of.
Life, liberty and the pursuit of happiness is what the Constitution guarantees us.
The American right to cruise your car is as American as the same as baseball, hot dogs, apple pie, and ice cream, Mopar, and Chevrolet.
Take that from me, and there will
Definitely be a problem.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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If your looking to better the fuel economy of an already hopped up engine, with "a bit of a cam in it", I got some Bad news James. Any SBM with a bit of a cam, that has already been optimized for fuel economy, will lose fuel-economy as the rpm goes down, for two reasons;
1) Cam-timing and
2) lack of optimum Ignition timing.
You cannot do anything about the cam-timing other than replacing the cam. But
I can tell you exactly the lowest rpm that you want to run, and the ignition timing to run with it; it's easy;
1) Put a vacuum gauge on the intake.
2) then rev the engine up until the vacuum peaks, and fix it there. This will be between 1800 and 2600 with just about any street cam
3) grab the distributor and advance the timing until the rpm reaches it's highest point.
4) then go back to finding the highest vacuum, by reducing the rpm until the vacuum starts to drop, then
5) back to timing; advance or retard for the highest rpm.
6) now, record the Ignition timing and the rpm. Then put everything back where you found it.
7) as to the results; what you got here, is the most efficient and lowest rpm and accompanying timing for your particular combo. It is the first time that the air is going thru the engine, and not getting pushed back into the intake on the compression stroke or getting sucked out the exhaust valves on the overlap cycle. Finding that was easy. But as to the timing, what did you get? My guess is it was over 50 degrees and could be as high as 60*.
Making a non-computer controlled distributor make that number, at less than about 2200 rpm, is darn near impossible;
and if you don't get the timing up there, then, the lower the cruise-rpm gets to be, the further from optimum it's fuel-economy will get...... and the less fuel-economy you can expect, with any additional decrease in rpm.
It soon becomes an exercise in futility and eventually the fuel economy just gets worse.
I have already done the homework for you;
having installed a dash-mounted, dial-back, timing module,
with a range of 15 degrees, that I can add or subtract ignition timing on-the-fly.
At one time, I had both the Mopar A833 overdrive box, and the GVod behind it, and so, with two overdrive ratios, I could directly compare fuel economy, in direct, or in first-over, or in second over; all at the same cruising speed, and with, on-the-fly adjustable ignition timing, in the range of 50 to 65 degrees.
Then, on the next cruise, I would install a different rear gear, and repeat the exercise.
What I discovered is that my engine liked a particular combination of rpm and ignition timing , almost no matter what the roadspeed was, and I figured it out as described above.
You wanna guess where I ended up?
2240 rpm @ no less than 56*@65mph.
Can you build your Mopar distributor to make that number at 2240 rpm?
No you cannot.
I got pretty close tho; but the resulting curve still needs to have the right Power-Timing, the right Part-Throttle timing, and a decent Idle-timing.
Here's how I did it;
1) I modded my vacuum advance to the max which on mine was 22 degrees. @TrailBeast got 24 out of his. This left 34 to get out of the Flyweights plus initial.
My combo is a 4 speed so 14* is the most I will run at Idle, and 12* is preferred, leaving 20 to get with the flyweights, which is easily doable at 3200 or so, but I need it at 2240 rpm. I made a two-stage curve that hits 28* at 2800, which according to my timing map, is .78* per 100rpm, so then, at 2240 this is 11*. To that I add the 14 Idle, and the 22Vcan, to get a total of 47*. To get the rest, I use my Dial-back, which has a range of up to 15 degrees for a possible max of ~63 degrees.
However, at 14* Idle-timing, I need to get down to 5* for parading, so 15 less 9 = leaves just 6 for cruising. and 6 plus 47= only 53. So I made a judgement call; what was more important to me; idling at 500, letting the engine smoothly slug along at it's chosen pace of 3.6 mph, or getting those last 3 degrees of cruise timing. I choose parading.
If I go on a long trip, I just advance the timing for the trip, and retard it back at the other end; a minor inconvenience.
So then, my combo currently runs 3.55s x .78GV=2.77s
If your engine combo is the same as mine, then yours would also like 2.76s; But the question is, if it is the same as mine, it will also need 56 degrees of cruise-timing, at 65 mph, to maximize the fuel-economy.
If you are running an auto, and say yur running 3.23s, and your engine is probably idling at say 18*, then 65= 2600rpm, and
by 2600 you probably have a dozen mechanical and maybe another dozen in the Vcan, for a total of say 42*. If your combo wants 56 degrees, then you are only 14* short. But at 2600, it is not gonna ask for the same number as at 2240, cuz the engine is already up, out of the dirty zone.. Maybe it only wants 52 degrees, and so, at 42*, yur only 10* shy.
But say you install those 2.76s, and your engine wants 56* now, but the best you got is still 42*, so now yur sweet baby is 14* off the mark. 4* more off than before.
But what if your cam is a lil bigger than mine (276/286/110 advertised) ? and now it wants 58*, then yur 16* off the mark.
I'll tell you what, those last 3 degrees don't count nearly as much as the first three. They count for about ONE mph of cruising speed. So whatever gas-pedal your combo was needing at 65 mph with 3 degrees short timing, adding the three is gonna punch yur speed up to 66mph. If you then close the throttles a hair, to slow back down to 65, you will be burning a tiny bit less gas. You will NEVER see this on the vacuum gauge, which is why I never use it for anything but diagnostics. But I can just barely see one mph on my speed-O.......................
------------------------------
Point of the story is this;
If your cruise timing is currently 10 degrees or more off optimum, just fixing that will be worth more than a swap from 3.23 to 2.76s. which by the usual math is worth about 7% max which might work out to what? 1 mpg? Hardly worth the bother and expense.
------------------------------
however, taking this to the extreme, I once geared my car to go 85@2100. Which was the lowest rpm that she was efficient at. And on the subsequent point to point trip, at about 2100, she made 32 mpgs, with a tuned for the occasion carb.
That combo was an 11.3/1 367 with a 223@050 cam, pushing 195 psi.
That gear combo was 3.55 x .71 in the main, and .78 in the GVod equals a final road gear of 1.97.
That set-up was about 10 mpgs better, than in regular trim with 3.55s x .78= 2.77, and 65=2240.. Butum, that carb was not streetable lol. As soon as I got to where I was going, I swapped the 750DP back on. Hallelujah!.
1) Cam-timing and
2) lack of optimum Ignition timing.
You cannot do anything about the cam-timing other than replacing the cam. But
I can tell you exactly the lowest rpm that you want to run, and the ignition timing to run with it; it's easy;
1) Put a vacuum gauge on the intake.
2) then rev the engine up until the vacuum peaks, and fix it there. This will be between 1800 and 2600 with just about any street cam
3) grab the distributor and advance the timing until the rpm reaches it's highest point.
4) then go back to finding the highest vacuum, by reducing the rpm until the vacuum starts to drop, then
5) back to timing; advance or retard for the highest rpm.
6) now, record the Ignition timing and the rpm. Then put everything back where you found it.
7) as to the results; what you got here, is the most efficient and lowest rpm and accompanying timing for your particular combo. It is the first time that the air is going thru the engine, and not getting pushed back into the intake on the compression stroke or getting sucked out the exhaust valves on the overlap cycle. Finding that was easy. But as to the timing, what did you get? My guess is it was over 50 degrees and could be as high as 60*.
Making a non-computer controlled distributor make that number, at less than about 2200 rpm, is darn near impossible;
and if you don't get the timing up there, then, the lower the cruise-rpm gets to be, the further from optimum it's fuel-economy will get...... and the less fuel-economy you can expect, with any additional decrease in rpm.
It soon becomes an exercise in futility and eventually the fuel economy just gets worse.
I have already done the homework for you;
having installed a dash-mounted, dial-back, timing module,
with a range of 15 degrees, that I can add or subtract ignition timing on-the-fly.
At one time, I had both the Mopar A833 overdrive box, and the GVod behind it, and so, with two overdrive ratios, I could directly compare fuel economy, in direct, or in first-over, or in second over; all at the same cruising speed, and with, on-the-fly adjustable ignition timing, in the range of 50 to 65 degrees.
Then, on the next cruise, I would install a different rear gear, and repeat the exercise.
What I discovered is that my engine liked a particular combination of rpm and ignition timing , almost no matter what the roadspeed was, and I figured it out as described above.
You wanna guess where I ended up?
2240 rpm @ no less than 56*@65mph.
Can you build your Mopar distributor to make that number at 2240 rpm?
No you cannot.
I got pretty close tho; but the resulting curve still needs to have the right Power-Timing, the right Part-Throttle timing, and a decent Idle-timing.
Here's how I did it;
1) I modded my vacuum advance to the max which on mine was 22 degrees. @TrailBeast got 24 out of his. This left 34 to get out of the Flyweights plus initial.
My combo is a 4 speed so 14* is the most I will run at Idle, and 12* is preferred, leaving 20 to get with the flyweights, which is easily doable at 3200 or so, but I need it at 2240 rpm. I made a two-stage curve that hits 28* at 2800, which according to my timing map, is .78* per 100rpm, so then, at 2240 this is 11*. To that I add the 14 Idle, and the 22Vcan, to get a total of 47*. To get the rest, I use my Dial-back, which has a range of up to 15 degrees for a possible max of ~63 degrees.
However, at 14* Idle-timing, I need to get down to 5* for parading, so 15 less 9 = leaves just 6 for cruising. and 6 plus 47= only 53. So I made a judgement call; what was more important to me; idling at 500, letting the engine smoothly slug along at it's chosen pace of 3.6 mph, or getting those last 3 degrees of cruise timing. I choose parading.
If I go on a long trip, I just advance the timing for the trip, and retard it back at the other end; a minor inconvenience.
So then, my combo currently runs 3.55s x .78GV=2.77s
If your engine combo is the same as mine, then yours would also like 2.76s; But the question is, if it is the same as mine, it will also need 56 degrees of cruise-timing, at 65 mph, to maximize the fuel-economy.
If you are running an auto, and say yur running 3.23s, and your engine is probably idling at say 18*, then 65= 2600rpm, and
by 2600 you probably have a dozen mechanical and maybe another dozen in the Vcan, for a total of say 42*. If your combo wants 56 degrees, then you are only 14* short. But at 2600, it is not gonna ask for the same number as at 2240, cuz the engine is already up, out of the dirty zone.. Maybe it only wants 52 degrees, and so, at 42*, yur only 10* shy.
But say you install those 2.76s, and your engine wants 56* now, but the best you got is still 42*, so now yur sweet baby is 14* off the mark. 4* more off than before.
But what if your cam is a lil bigger than mine (276/286/110 advertised) ? and now it wants 58*, then yur 16* off the mark.
I'll tell you what, those last 3 degrees don't count nearly as much as the first three. They count for about ONE mph of cruising speed. So whatever gas-pedal your combo was needing at 65 mph with 3 degrees short timing, adding the three is gonna punch yur speed up to 66mph. If you then close the throttles a hair, to slow back down to 65, you will be burning a tiny bit less gas. You will NEVER see this on the vacuum gauge, which is why I never use it for anything but diagnostics. But I can just barely see one mph on my speed-O.......................
------------------------------
Point of the story is this;
If your cruise timing is currently 10 degrees or more off optimum, just fixing that will be worth more than a swap from 3.23 to 2.76s. which by the usual math is worth about 7% max which might work out to what? 1 mpg? Hardly worth the bother and expense.
------------------------------
however, taking this to the extreme, I once geared my car to go 85@2100. Which was the lowest rpm that she was efficient at. And on the subsequent point to point trip, at about 2100, she made 32 mpgs, with a tuned for the occasion carb.
That combo was an 11.3/1 367 with a 223@050 cam, pushing 195 psi.
That gear combo was 3.55 x .71 in the main, and .78 in the GVod equals a final road gear of 1.97.
That set-up was about 10 mpgs better, than in regular trim with 3.55s x .78= 2.77, and 65=2240.. Butum, that carb was not streetable lol. As soon as I got to where I was going, I swapped the 750DP back on. Hallelujah!.
Last edited:
matthon
Well-Known Member
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I hear you loud and clear.
Sold my pig rusty computer controlled multiple module $200 just to diagnose garbage 2008 full size truck to get away from all the bs.
Lucky for me, my 64 wagon, my daily driver now, came with a 2.76 Sure-Grip and a 318 poly 2 barrel.
Fantastic on gas, great cruiser and highway car, plus headers and dual exhaust for that rumble.
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