75-76 Aluminum 833 4 speed Overdrive trans questions ?
I have 2 identical aluminum 75-76 aluminum a body 833, 4 speed transmissions, one complete with factory shifter and rods
1. How much hp/torque will they handle
2 How much with modifications
3. Weak links/poor engineering
4. Availability of parts
5. Reliability/durability
6. Value
7. Requires its own bell housing ?
As to these questions;
1) since my engine seems to be making over 400hp, and more that in torque, I gotta say at least that much, lol.
2) there are no mods that I know of, to increase reliability
3) the mainshaft od gear is the weak link.
The poor engineering is the exceptionally wide ratios. 3.09/.73=4.23= 423% range. This is too much, IMO, for just 4 gears. I installed a GVod behind it and started splitting gears, for Seven useable gears. IMO, this was two gears too many, lol. But it did allow me to run those broken boxes for many more years, as six-speeds
4) I buy spares at swapmeets
5) leave it parked in the garage and never worry
6) I have paid as little as $50, and as much as $100. When yur walking, $400 will be cheap.
7) yes and no. the factory retainer is 5.125od and requires it's own housing. I have heard that the retainer can be cut down to the next smaller size, but I have not seen an SBM housing that ever had the next smaller hole. So then you got lathe the hole out to fit your cut-down retainer; and then you gotta bring everything back into alighnment by dial indicating it and moving it to where it needs to be, then you still gotta figure out how to make it stay there.. BHs are cheaper by far, than going thru that rig-amarole.
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8) BTW as a streeter, and at WOT, you will be mostly concerned with Second gear. The right Roadgear to run with a stout 360 is about 6.50 to 6.80. The gear in the trans is 1.67, so then the rear gear will need to be ~6.70/1.67=4.01, rounds up or down to 4.10s/3.91s. I recommend the 3.91s, which will get you 65=2310 with 27" tires.
Now, the starter gear will be 3.91 x 3.09=12.05, which is way more than any 360 needs. But worse, IMO, is when you shift.
In my combo with 3.55s;
Around town I usually shift at ~2800, which is 20mph. With the Commando, shifting into Second brings the Rs down to 1740, and my 367 easily pulls that. But when I had the od box, the Rs dropped to 1510, and of course, the engine had to struggle for a bit. To overcome that, I had to rev it to 3220 to get back to 1740 on the shift. No big deal right? Well except that 3220 was now ~24mph.
But at WOT, shifting at 5500(40mph), the Rs dropped to 2970.... that's a serious drop, and now the car is getting into wind-resistance.
so then, in the combo of A833od and 3.91s, whatever engine you have in there, it's gonna need some balls to pull hard from 2970.
Finally, with 3.91s and 27s, 2970 is 36mph, 4500 is 54mph and 5500 is 67mph, so this is a pretty good Second gear for city driving, with the right combo of cam, to cylinder pressure, to cubic inches.
I'm saving parts to build an economy package engine in case gas gets and stays crazy. I have a stock bore 273 (68), an Edelbrock 318 Street master, and a 400 cfm AFB. I have a 2.94
8 3/4 carrier, in conjunction with the .79 OD ratio should be about a 2.30 final ratio, which should put me at 2000 rpm at 80 mph
The od ratio is .73.... not .79,
and I can tell you this, your 273 is not likely to make any better hiway-only fuel mileage at 65= 1740 than at 65=2200............. because the stock-type distributor cannot deliver enough ignition timing at 1740, but can, at 2200.... albeit barely.
Furthemore, the engine will struggle longer and harder to get up to speed with the 2.94s and 1.67 Second gear.
Furthermore, in town, in Second gear, and 2.94s, 30mph is ~1830rpm. If the engine even pulls your car at 1830, it's gonna take considerable throttle to do it. If it gets up on the mainjets, say goodbye to fuel mileage.
Furthermore, trying to get to cruising speed using Second gear, is gonna take a lot of throttle initially, and or, for a long time, and so ........ say goodby to fuel economy......... again
The 273 has the potential to be a great lil fuel-miser, but IMO, you are not working the angles right with this combo of A833od and 2.94s.
This trans/gear combo will need a stinking boatload of cylinder pressure to even tickle fuel-economy, and it's almost not possible with a 273. I mean with closed-chamber iron heads, even shaved, you are limited to about 160/165psi on best gas, and Ima thinking you want to run 87. This will NOT, IMO, be possible with this trans/gear combo. or if you do swing it, it's gonna be more expensive than it's worth.
IMO, with this combo of trans to gear, you're gonna need very high cylinder pressure to be efficient, and that points to an alloy headed 318, at least.
If I'm right, then you have a decision to make, which is this;
to keep the 273 she'll need one of two things, either; gears closer together, and/or not handicapped by the 2.94s .
Since you already have the 273 and the 2.94s,
my vote would be to get a close-rario/standard-ratio, 4-speed with a lower first gear ........ like the commando, and then slow down a little.
2.94s will get you 65=2380 with 27" tires. This will require about 56 degrees of timing to be efficient, which is doable with a stock-type distributor. The Commando 3.09 low gear gets you a starter gear of 9.08 which will get you to 3600=32mph, on the 1-2 shift, the 1.92 Second gear will be
2240, and the 273 can pull that all the way to 50=3570 rpm. On the 2-3 shift, the Rs will fall to
2560, and third will get you 65=3330. and then Fourth drops to
2380.
Now; gather up the data. Your powerband for this, has to be from ~2240 to max of ~3600.
So if you build your engine to work in that zone, getting fuel-economy is a sure thing.
BTWs,
> the cam for this is the stocker, which may already be in the engine. But if not, there's better ones to be had,
> a 318, driven the same way, in this circumstance is likely to get BETTER fuel economy because you can build it to a higher pressure with way less money, and with the higher pressure, it will accelerate harder on the same throttle-opening. Or said another way, it will accelerate the same as the 273 with LESS throttle-opening. In this case, less is more, lol.
Here's the thing, the 273 can be made to really sip fuel, but it's not something that you can just throw together. Whereas pistons for the hi-pressure 318 are easy to find.
> pressure can be made three ways; your options are; cubic inches, Static compression ratio, and intake valve event timing. Pressure is directly limited by the onset of detonation, which is directly related to, the octane of the fuel you want to burn, and together with the temperature in the combustion chamber.
> While getting the 273 to run 80@2000, and still get fuel-economy may be possible, IMO, it will Not be possible on a Throw-it-together budget.
> however, this does Not preclude you from throwing it together just see what happens if you already have all the players.
I did exactly that from winter/2000 to about 2005 with my winter-engine; a smog-era 318 with a quick freshening, the A833od and 3.55s. But wait, with a GVod behind it, Yes it pulled 65=1600. But I installed a Thermoquad, a small-port Iron intake, and headers. and I wasn't after fuel economy. Rather just something to drive while I freshened the 367 every winter.
Not once did I check the fuel economy, mostly cuz the daily commute barely got the engine warm.......
Mr. James I could be wrong.