A727 vs A833 vs TKO600 - MPG

[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?

[Troy]

Well the TKO has overdrive so that should definitely improve things! Not so much if you're only in the city and constantly shifting gears. The 833 has less "parasitic" loss then the 727 so it should be slightly better - if you can keep your foot off the gas!

Troy

[shone190]

Translated into numbers or percentages if it is possible?

[c00nhunterjoe]

Varies so much its hard to say. City driving they would all be pretty close.... well ..... depending on what you call city. Driving in rush hour in new york city? Or cruising 35-40 with minimal stops?
  It also depends on your rear gears. But for a generic city vs highway you can say that the 727/833/tko will all be within a mpg of each other in traffic and low speed drivi g. Out on the highway doing 70-75 the tko will pull ahead due to the overdrive. How much depends on how thirsty your engine is but figure the 727/833 is 1:1 and the tko's are usually .80 in final gear yielding maybee a 4-500 rpm drop.

[shone190]

Forget city MPG and 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

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.

[Troy]

RPM is critical. When my Six Pack opens the outboards cruising at about 3,100 RPM, gas mileage gets cut by about 25%. Same with 4 bbl carbs - stay out of the secondaries! This is why anything with an overdrive is better on the highway (unless you like driving 55-60 mph). Of course, with an OD there is a tendency to put steeper rear axle gears in which hurts low speed mileage. In traffic with lots of starts and stops my mileage is only slightly better than half of my highway cruising mileage (17 vs 11). That has a lot to do with the impulse to mash the pedal though! I get reasonably good mileage on back roads where I can maintain a fairly steady 40-60 mph speed. City driving around here is a lot like the second scenario so I doubt any of the transmissions will be significantly better than any other - although I'd still give the nod to either manual transmission just due to lower friction.

My Barracuda with the 318, automatic, and 2.76 rear gears would get 23 mpg on the highway. In town it was fairly good as well but performance was mostly a joke. If you want something with much more power your *average* mileage is going to be fairly close no matter what combination you choose (except under ideal situations for a particular setup).

In the city, EFI will likely have more impact on fuel mileage then transmission selection.

If you're looking to justify the purchase price with increased fuel mileage it's probably not going to work. I spend 70-80% of my driving time on the highway or medium-high speed back roads so an overdrive is the best choice *for me*. I like shifting so the automatic is out (even if I had an OD version like the A518). The good news is that I have the cars and parts that I need so it doesn't cost me anything extra to get what I want. Leaves more money for gas!

Troy

[flyinlow]

When I went from a 727 to a 518 my road gas milage went up about 2-3 mpg. I do live rurally so  I use the OD most of the time. (.69 OD with lock up)