Engine RPM on Auto 4Speed vs Standard 5 speed.

The transmissions gear ratios determine what the engine speed is at any given vehicle speed, so two different transmissions with different #s of gears and ratios will produce different results.

Logic says it is certainly possible that the engine speed will be different in a manual and a stick. There are a couple of reasons. The gear ratios in the transmission are often different in an automatic and a manual, and the differential gear sets are also different ratios. I've seen the same vehicle get 3.73s in the diffs of a manual trans, and 3.07s in an automatic.

Whether this translates to different engine speeds requires one to do the math, and the tire size would enter into the calculation.

Thanks! I am just wondering if the five speed or the 4speed auto has better gas milage on highway......I might find some charts and stuff....

Kenny

It used to be true that an automatic had a shorter gear ratio than a manual. I looked on Toyota's website, and for the Tundra, they list the same differential ratio for both auto and manual. They only list a manual trans for the V6, the mileage is 1 mpg better with the auto in town and mileage is the same on highway. I would assume by this, given tires are the same, that engine speed would be really close in town and the same on highway. YMMV, davidj92

different

Not really, it is the final drive ratio in OD that determines the cruise RPM, not the number of gears in the transmission. Genrally automatics have a taller OD than manuals do so they tend to have lower cruise RPMs. Axle ratio is also a factor here.

So, with EVERYTHING being equal, a 4 speed auto should have better gas mileage than 5 speed if crusing on highway at equal speed...... right?

Thanks Kenny

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Generally all things being equal, manuals tend to get better MPG because there is less overall power loss in the transmission. In like vehicles I have never seen automatic beat a stick in MPG in the real world unless you are not good with a stick.

With all ratios being equal, the 5 speed manual will give better. Autos lose a lot in the torque converter.

Yes and it takes at least 3 to 5 hp to run the hydrulic system in a auto tranny too before you factor in other auto tranny losses. Newer automatic are better but a stick will beat it especailly on the hiway. I put well over 200K on a 91 Camary with a stick and I regulalry got in the high 30?s on hiway at 70 to 75 MPH and a few times over 40. Cars with automatic will not do near that well. The smaller the engine and car, the more noticable it is. In a big heavy draggy SUV, the differnece will be less.

Many times, in traffic, I've wished I had an automatic transmission. Probably 90% or my driving is stop and go, city-type street driving, to and from work. There's one stretch of road where I have to wait to turn left. The line can be up to quarter of a mile long, waiting for the turn light. The whole stretch is on a 4% or so up grade, so when traffic stops, it's in with the clutch, and on the brake untill traffic inches ahead a few feet. That's when I wish I had an automatic... :>))

But what-the-hey, I've owned my '88 22R pickup since it was new and do OK with the 4-speed tranny (yup, they had 4-speed trannys then as well as 5-speed)... :>))

Really? Cite your source for this because I KNOW you do not have such data from your own bench tests. Does it really take 3-5 hp to generate and maintain 50-120 psi line pressure? What about your engine? There's an oil pump there too, which generates 60 psi.

IF it does, the difference is very small. There is no slippage in any automatic equipped with torque converter lockup.

Yeah right. Are those Canadian kilometers to liter, improperly converted to Imperial gallons and then reported as US gallons?

-Philip

How did we get from tranny losses to engine oil pump losses??? All automatics consume power, a smalll one with a 4 banger will consume 3 to 5 hp and big one can use more yet. You have the pump losses and the oil shearing losses in clutches that are not enage engaged as a automatic leaks power through it all the time (take drive shaft of and put it neutral and watch the output shaft spin fast at a idle.

"Philip" wrote:

No so because you still have the interanl losses that are higher than with a manual.

"Philip" wrote:

If you do not want to believe me that is your bussiness and your loss. US gallons using 89 octane or better, 75w90 gear oil in tranny and engine timing about 6 degrees advanced over stock on a 2.0 Liter engine. Car was totaled in a freak wreck and I do miss it. I had 40 PSI T type tires on it too withl very low rolling resitance and it was the best coaster I ever had as it had low drag. Toyota made a big deal out thet car that year saying that it only took 11 hp for it to maintain 55 MPH because of improvements in aero drag and wheel bearing design. (it also came with hi presure T type tires from factory) Last trip it went on before it was totaled it got almost 39MPG averaging about 70MPH or less. On one tank going through the high plains of Montana and Wyoming in the high thin air it got 41.5MPG. I drove that car for 220k miles so I knew what it would do MPG wise. Around town it would do the low 30?s if you babied it or in the high 20?s if you stepped into it a lot.

As a general rule of thumb, a manual will always give better mileage than an automatic. The variations on this rule have more to do with the way you drive than how the transmission works. Frankly, my suggestion is to get the transmission you prefer to drive, and forget about the fuel mileage. If your daily drive is in stop-n-go traffic, the mileage is going to be more a function of how much time you are stopped than going.

The gearing in the diffs will counter the gearing in the trans, and the end result at speed will be pretty close to the same. The auto is easier to drive, but the manual will give better mileage in stop-n-go.

I asked you to CITE YOUR SOURCE for the amount of horsepower required to generate oil pressures. You chose to duck that request.

Cite your source for that figure. And what difference does it make what engine is driving an automatic?

Half truth. Bands do not drag. Clutches do have a small amount of drag due to ATF's viscous drag when cold. This is very small when the fluid had reached operating temperature.

Sorry you failed to grasp the fact that with a lockup torque converter, there is no slippage in an automatic when the torque converter is locked up.

Sorry ... am not buying some old Camry getting 40+ miles per US gallon.

I can't cite by quantity exactly how much horsepower is lost at each step, but I know there is work being done inside the transmission that does not contribute to forward motion, therefore it is a loss. This is basic logic.

The biggest heat generator in a slushbox is the torque converter, and the most heat is generated during heavy acceleration - this is why they plumb the fluid flow out of the torque converter directly to the transmission cooler.

Same logic that says if you have waste heat you are absorbing into the engine coolant and dumping out of the radiator, that waste heat wasn't used to propel the vehicle down the highway, therefore it is a loss.

That one has been proven many times, but you are limited in improving that by 20th century mass-production materials technology of cast iron, copper, steel and aluminum components, and the lubrication systems - let the engine run hotter to lower those thermal losses, and the engine melts - or the bearings gall and lock up.

The transmissions for cars with larger engines are scaled up physically larger to handle more torque and horsepower throughput, therefore the losses should scale up (somewhat) proportionally.

IOW, "I choose to reject your reality and substitute my own."

That's fine and dandy, but don't expect it to stand up to critical analysis. When an auto box is hot you might not have a whole lot of drag from the internal components, but that torque converter is still up front with it's frictional losses creating heat like a banshee whenever it isn't in lockup mode.

Sit there stopped in Drive, and all the engine's useful power output is being turned into heat in the torque converter.

Hate to break it to you, but until you get up to 45 MPH plus highway cruising speeds the torque converter is not in lockup mode, so the friction losses are present up to that point.

How about a full-size tag-axle Dolphin motorhome on a Toyota V6

5-speed chassis that was consistently getting 20-plus MPG highway? When automatics were lucky to see 16 - 18? That one is hard to deny.

Bottom Line: If you have the same size engine, same size vehicle, and same basic driving methods, Sticks consistently get notably better fuel mileage than Automatics. This can be proven. Correction: This has been proven, but I'm not going looking for the studies right now.

But the US automakers don't want to sell sticks for several reasons

- because the exhaust emissions tests end up worse from all the over-run during shifting, whereas an automatic shifts under power and the EFI can more closely control the emissions. And you have people toasting clutches and grinding gears to death, and then trying to get them fixed under warranty.

And add to the mix all the lazy and/or stupid people who either can not learn or refuse to learn how to drive a stick properly. It is not difficult to learn, but you would be amazed at the number of people who will admit to not being able to do it - and there are even more who can't, but wont cop to it...

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You are making assumptions. You do not appear to understand how hydraulic clutches operate or when. So your "logic" is really a rationalization.

There is no heat generated in the torque converter when it is locked. It is in the lockup mode that EPA fuel consumption measurements are taken (largely, 48 mph, steady cruise).

You use the word logic incorrectly. Now, there is no oil cooler in 99% of cars equipped with automatic transmissions. There is a *heat* *exchanger* in the cooled radiator tank. So the engine imparts heat to the transmission until such time as the engine coolant and transmission fluid have equal temperatures. During those rare times when the transmission fluid temperature is higher than the engine coolant, heat is then transferred to the engine coolant. When the torque converter is locked, there is no heat generated.

What the engine does thermally has nothing to do with the transmission. Stay focused.

You really don't know that to be the case to any meaningful degree. It's just your academic claim.

Another half truth. When there is a 100 rpm slippage at 40 mpg with the torque converter unlocked, little heat is generated. But to maintain the same speed while ascending a hill (say 400 rpm slippage), then heat is generated. NEITHER condition generates heat comparable to a standing start full throttle acceleration when there can be upwards of 2,000+ rpm slippage. Or when you are conducting a 'stall test.'

This statement is misleading. At idle, in Drive, closed throttle ... the engine is not producing much power. The slippage rate is typically 600 rpm. This is not going to overheat the transmission ... ever.

Not universally true at all. I have a 2003 Corolla that under light throttle shifts to OD/lockup at 41 mph and does not unlock the torque converter until as low as 37 mph, light throttle.

snip

In the hands of the average driver, the difference has become very small and in fact the convenience of the automatic in commuter traffic or when the driver truly is not particularly skilled, the auto is preferred.

On this point, we mostly agree.

You suspect this.

Thank you for supporting my earlier contention that the net difference in MPG between manual and automatic is tiny. :^)