shone190

Hi guys,

I was wondering, is there any MPG difference between these three transmissions in everyday city driving, in the same car off course?

440roadrunner

Of course there is

But are you talking about an OVERDRIVE A-833 or a straight through "standard" A833?

The TKO is an OD box

shone190

Standard A833, but I don't know why is this important because in the city I will never shift in OD

TVLynn

I would suspect better mileage with the TKO600 due to the closer spacing of the gears

shone190

Me too, and off course because there is no slippage at all

Lets include a little math in calculations

On highway with my 3.23 differential, 26.7 wheel diameter and A727, at 2000rpm speed will be 49 MPH, probably a 45MPH because of slippage (non lockup A727) which is not included in calculator. With the same setup and RPM, but with TKO600 (0.64 OD) instead of A727, speed will be 77MPH.

So, let's say that fuel consumption with A727 is 14MPG at 45MPH. At the same rpm with TKO600 speed will be 71% faster. Per time unit, both cars consume the same amount of fuel, because of the same RPM. For the same distance, lets say 60 miles, A727 will need "to work" 80 minutes and TKO600 will need 46 minutes, that's 57% A727 working time, and 43% less fuel consumption
For 60 miles, A727 will need about 16.8 liters (4.43 gallons) and TKO will need 9.7 liters (2.56 gallons).

So 14MPG with A727 will be 24MPG with TKO600 at 2000 rpm constant speed

Maybe there is some "space" for corrections because of larger wind resistance at higher speed, but lets say that fuel consumption will be around 50% lower.

Simple math, right

If we use Gear vendors unit with 0.78 OD, there will be about 22% smaller fuel consumption on the highway, no matter what RPM we use for comparison. So, if you have 14MPG with A727 at 2000rpm, you will have about 18MPG with GV+A727 at 2000rpm.

TVLynn

I was referring to the A833 compared to the TKO. TKO should be better even without the overdrive

Coronet 500

I would like one of those Tremecs, are you thinking of getting the 2.87 or the 3.27 first gear.

shone190

2.87, anything more than that and first gear with 3.23 rear diff will be almost unusable with 493 stroker

demetri

Your Math is a bit off . 45mph/.64=70 mph. But actually, your torque converter slippage will be almost negligible at 2000 rpm and part load, if you have stock converter. Fuel economy calculations are not that simple.


You will probably get 15-25 % better fuel economy, depending on driving. But you will have to offset that with the frequent and more expensive rebuilds of the 4 speed. The gear vendors is probably a better solution. Another way is to change your differential ratio to a 2.76 and keep the 727.

shone190

I don't think so.

A727 has no lockup converter, so it will always be a slippage, let's say around 7%. At 2000rpm A727 (3.23 rear and 26.7 tire) - 49MPH, include slippage it wil be around 45MPH. At 2000rpm TKO600 (0.64, same rear and tire) = 77MPH, there is no slippage, so it will be 77MPH. In the same car (with different only transmissions) fuel calculation is just that simple, nothing complicated.

demetri

At 2000 rpm and only road load, the slippage of the no lockup converter is near negligible. About 1 % or less. You can easily confirm that. Just raise your rear tires and put the transmission in drive. Take the engine to 2000 rpm and observe your speedo. There is essentially zero load, and the slippage is zero. Then, drive your car on a level road, and take it to the same indicated speed. Now, there is a bit of load. Yet, you will see that your tach shows essentially the same rpm. If you put more load on the engine (but not enough to downshift) you may see 100-200 increase, but that is not steady state, your car will be accelerating.

At much higher rpm, your converter slippage will be low, even at full load.

Modern cars have lockup converters because they use high stall converters. But back then, because there was no lockup, they designed the converters to have high efficiency.

Fuel consumption of the engine depends not only on rpm, but also on load. The principal reason why the fuel consumption improves when you add the OD is that the engine operates at a higher load and lower rpm for the same road load. That allows reduced manifold vacuum, so the pistons fight vacuum less during the intake stroke (this is called pumping loss). Predicting this fuel economy benefit is very complicated, and it really depends on a lot of things, including the driving cycle.


The main benefit of the OD is that it will make high speed driving more relaxed and allow your engine to last longer. If you like to drive fast, it will improve your top speed too. But I have heard from many that the 4 speed autos designed for small blocks just cannot handle the torque of the 440.


You are also making a mistake on how you are calculating speeds. A 0.64 ratio on OD will reduce rpm at the same speed by 36%. Or vice versa, at the same engine speed, your car will be traveling at x/0.64. 0.64 is a very radical OD ratio. Usually, they are between 0.80 and 0.70.

Gorts 5th

The best thing I ever did was retro that 47re into my 5th ave... with 3.90 gear 2000 rpm lock up stall, city driving or any speed under 45 mph she turns 2000
the lock up and od I con trol with switches and relays
the combo is fun fun fun with a push of a button LU OD in city cruisin with other rodders not to mention the fuel eccono. Every thing stated below is true based on my real world exsperence
i will add though this set up needed diffent fuel / timming, ratio / curve...tune than the 727 set up I used earler.

rcknrolfender79

Since your going with a 493 stroker there probably isn't much of anything thats gonna help your gas mileage, noticeably at least (unless your going with a fuel injection setup, which would be the best thing you could do for better gas mileage). I'd say just go with which ever one appeals to you most.


Not 100% but your estimate of 14mpg and 24mpg above seem.... well WAY too high for a 440 and even higher for your 493 stroker. My Coronet R/T is running a 440 4 speed (A833 no OD). 750 Holley double pumper... little bigger cam, headers, and aluminum intake. Dana 3.54 rear end. May have some head work done as well not sure on that though. On highway at a constant speed of 65 mph the best I can get is 10 MPG. In town... 5 -7 mpg. The motor in my car is probably a very mild build next to your 493. Anything you do to a motor to make it more powerful will always use more gas. More power requires more air and more gas. With a really good fuel injection setup and the right gear ratio you may get close to 14mpg (but I very highly doubt that). Unfortunately that motor will never see 24mpg... a brand new 5.7 hemi barely sees that good of gas mileage. If your not going with fuel injection you can pretty much promise yourself that 493 wont get any better than 10mpg and thats if your lucky.

To get that motor anywhere near decent on gas you'll probably have to take some huge power losses, which would pretty much make your stroker kit a waste of money and time. 493 stroker and gas mileage just aren't two things that go well together. You'll be able to pass everything except a gas station though.

Gorts 5th

My milage average s 12 -15city only highway improved 15 18 I dont have any solid numbers ... I havent ran a tank long trip since the conversion , but at 80mph with LU engaged she turns 2200 rpm with 1/4 throttle the cams effective curve in my combo pulls from 22-6500

rcknrolfender79

Small block?

Gorts 5th

Yea 318 518 3.90 nice combo w/ 2000 stall and lockup
the avatar pic of the motorI have the retro of the trani posted here under my big swap..i think I wiil double chk that title.