What is the real difference between the auto and standard pinions?

[jerd_hambone]

Anyone know exactly how much of an acceleration difference? MPG gains?

I have an auto gear that I'm considering swapping into my car, as I don't have the space or place to drive like a maniac, the car will be my daily, and will rarely see any spirited driving.

I'd use it mostly to keep rpms down, considering we have stop lights every 1/16 mile, standard speed limit is 35-45, and I'll probably rarely take the car over 55-70 mph.

With gas prices well over $3 a gallon here, I'll take a hit in the seat of the pants to save a hit in the wallet, unless it will be so slow that I'd not be able to bare it haha

[Pete_89T2]

Difference in gear ratios can be found on Mazdatrix site FAQ, see ref:

http://www.mazdatrix.com/faq/ratios.htm

It's a 3.90 (auto) vs. 4.10 (all manuals except GTU-S, which is 4.30). Don't know what that would translate to in a MPG improvement, if any. It may well hurt your accelleration enough where you'll find youself flogging it just to get out of your own way, which would likely make your MPGs worse. Especially if you have hills to deal with. IMHO, don't bother - you would be better off picking a beater econobox as a daily driver.

[TitaniumTT]

I dind't notice that much of a decrease in MPG going from the 4.1 to the 4.3, but there was definately an increase in acceleration. The higher the gear, the more torque you can put down, so the less torque you need from the engine to make the same acceleration changes. If you can keep a light foot, it will help with mpg on the highway.

[jerd_hambone]

I know the difference in ratios, and all that.

And like I said, I'm not going to be ripping through gears just top stop every 8th of a mile. I drive like a grandma, even when I drove a built V8 car. People always complain about how I drive. Even in my Cutlass and my old GTU, I rarely hit the speed limit by the time I got to the next light.

I despise highway driving here because I have to pass the most advanced weigh station in the US or something and it never fails to get bowled off the road by retarded truck drivers.

Honestly, I enjoy taking 25 and going through town, even if it means I have to leave 15 minutes earlier.

How much is the actual difference between rpm vs mph?

[RETed]

If you are really worried about MPG, just get another car...
We don't buy these cars for their gas efficiency.
It's really useless to debate gas efficiency on these things when you can get daily drivers that will top 35mpg+ all day long.


-Ted

[jerd_hambone]

See, the problem people don't realize is this, here, a 92-95 Civic sells for between 3k and 5k.

I don't have the funds to put into another car. And it's completely unreasonable to spend money on a new daily, when I'll be traveling 60 miles a day at the very most.

What I'm mainly asking is the loss of acceleration really bad, and I'd like to have an experienced opinion on the results. Not an opinion on what the car was made for. I know very well that 7's get rather poor mpg's. I'm not debating that at all.

So, to clear things up, can someone with experience having the 3.9 gears in an S4 N/A 5 speed tell the results and offer a comparison on the 3.90 versus the 4.10? How different is the acceleration with the 3.90 versus the 4.10?

Like I said, I won't be blasting through the gears, just to have to hammer the brakes to slow down. Triple T is the only one who has really offered any sort of real experience, but the difference between his car and mine is night and day.

[RETed]

That's the problem...
You want your cake and eat it too.
Problem is that money is the solution.
You don't have it.

Who says you gotta buy that particular Honda?
Geo Metro
Ford Festiva
Nissan Sentra
Toyota Corolla
All of those get great gas mileage and don't cost an arm an a leg.
Keep in mind that resell values are close to 100% if you buy the right vehicle.
Who said it has to be "sporty" or "cool"?
We're talking strictly about gas mileage here.

You'd be lucky to get 1 - 3 mpg due to the rear end change.
Is it worth it?
I don't think so.
You still gotta deal with the labor - or are you paying someone else to do that too?
More money wasted...
You'll maybe get 5 mpg gain if best case scenario - all freeway cruising miles.
So, you're barely hit 25mpg...
The above cars hit 30mph city and easily hit 35mpg+ on the freeway.
Figure out the easy 10mpg difference, and we're talking lots of gallons of gasoline saved per year.
This means hundreds and even $1,000+ saved during a year - there's your daily driver cash right there.

Analysts are predicting $4.00 / gallon for gasoline this year in parts of the U.S.
RIGHT NOW IN HAWAI, I PAY $3.70 FOR A GALLON OF GAS.
There are parts of Hawaii that have broke $4.00 / gallon already.
You will not get pity from me when you complain about gas prices.

The FC is not an economy car.
It should be banned to mention "gas mileage" and "RX-7" in the same sentence.
If you can't afford the gas, you shouldn't be driving the car in the first place.


-Ted

[jerd_hambone]

Ted, I am not on a quest for more mileage, please read my entire post before you reply.

Those cars may be cheaper, but the availability is an issue. I am not looking for a different car, nor am I looking for increased mileage. I am looking for a comparison on the acceleration of the two. I assumed about 3-5 mpg gain at most, and I am more interested in hearing about the acceleration difference.

You are just repeating a moot point, which was moot the first time you stated it. I didn't say that I can't afford gas, I didn't say I'd be paying anyone to do the swap, I just would like a comparison on the differences because I have both rears right here.

I'm not asking for pity on gas prices, just stating a fact that gas is well into the $3 range and I live in a poverty stricken town with a $7 an hour minimum wage. Just a fact.

So, please, if you can't stay on the topic I am asking about, I will end the thread and ask for a comparison elsewhere and you can troll another thread.

I respect you because you have a lot of knowledge, but this is supposed to be a place where one can get info, but you have a very strict "my way or the highway" deal going on. And it makes the forum less friendly.

So, back on topic, does anyone have any experience with the different ratios, that can give me an accurate description of the acceleration differences?

[diabolical1]

can't speak on the Gen II cars, but i've owned Gen I cars with similar final ratio differences (3.91 versus 4.08). i will say this, if you were to put a stopwatch on it, there may be a discernible difference, but as far as my tooling around town was concerned, i didn't notice a difference.

as far as gas mileage was concerned, i can't say i noticed a difference there, but in all fairness, i only started tracking mileage qunatitatively when i was running the 13B (Dell'Orto and exhaust) with the 3.91 rear and i averaged 24 to 25.5 MPG on the highway. i didn't feel i needed to calculate city mileage because i commuted almost exclusively on the highway.

i hope this helps you some.

[NoDOHC]

You will take about 0.2 seconds longer to reach 60 MPH at full throttle. (8.5 to 8.7 seconds).

If you never exceed 35 mph, you will see NO mileage gains at all. The tall gears only help you once you get into 5th gear. if you are shifting into 5th gear at 35mph in a stock ECU RX7 with 4.10 gears, you are probably hurting your mileage.

You will end up accelerating to a higher speed in each gear with the taller gears, so you will not save gas at all.

The 3.9:1 gears will give about 2 mpg highway, about 0 mpg city.

If you want better mileage:
Advance your timing (if it is NA - not a good idea with turbo)
Remove power steering
Remove air pump
Avoid revving past 3500 rpm
Avoid exceeding 30% throttle
Avoid excessive lugging (>10% throttle when below 1800 rpm)

I got 28 mpg highway and 24 city very consistently (in the summer) doing this with my stock ECU RX7. (Haltech would give 35/30 on the 6-port).

[jerd_hambone]

So, the acceleration difference isn't that horrible? It really isn't a big gear difference. I know that some people act like it would make the car so slow that it would be ridiculous to drive.

[RETed]

Originally Posted by jerd_hambone

I'm not asking for pity on gas prices, just stating a fact that gas is well into the $3 range and I live in a poverty stricken town with a $7 an hour minimum wage. Just a fact.

Last time I checked, the federal minimum wage was $7.25 an hour.
If you're getting paid $7 / hour, it's illegal, unless it's a commission and / or tips earning position.

BTW, Hawaii might not be the poorest area, but it's the most expensive to live in.
A gallon of milk breaks $7.
Gasoline on the neighbor islands have already broken $4 / gallon.
A loaf of bread is $3.
Hawaii has the highest COLA index in the nation - 26%?

Back to the topic...
Acceleration wise, I doubt most will feel the difference.
The complaints about the 3.9 rear is mostly due to the combination of the 3.9 rear *and* the automatic trans.
You cannot get a 3.9 rear with a manual trans from the factory.
If you have a very sensitive butt dyno, you might feel the acceleration difference.
Is that what you're looking for?

Really, there is no significant, positive reason to go with a 3.9 rear with a stockish 13B...


-Ted

[diabolical1]

Originally Posted by jerd_hambone

So, the acceleration difference isn't that horrible? It really isn't a big gear difference. I know that some people act like it would make the car so slow that it would be ridiculous to drive.

for your purposes? no. i'm pretty sure it won't make a stitch of difference.

as far as how people act, i think this is one of those times when you need to do your own thing. obviously, i can't speak for someone else's experiences (and perceptions), but i sense a bit of an exaggeration in reports of a vast difference. i've driven my Rx-7s all up and down the east coast, with both rear ends, and the acceleration and fuel consumption were virtually identical.

unless you need a new rear, or it's for the experience, or some other personal fulfillment, don't waste your time swapping. you're not likely to see any appreciable differences.

[jerd_hambone]

Originally Posted by RETed

Last time I checked, the federal minimum wage was $7.25 an hour.
If you're getting paid $7 / hour, it's illegal, unless it's a commission and / or tips earning position.

BTW, Hawaii might not be the poorest area, but it's the most expensive to live in.
A gallon of milk breaks $7.
Gasoline on the neighbor islands have already broken $4 / gallon.
A loaf of bread is $3.
Hawaii has the highest COLA index in the nation - 26%?

Back to the topic...
Acceleration wise, I doubt most will feel the difference.
The complaints about the 3.9 rear is mostly due to the combination of the 3.9 rear *and* the automatic trans.
You cannot get a 3.9 rear with a manual trans from the factory.
If you have a very sensitive butt dyno, you might feel the acceleration difference.
Is that what you're looking for?

Really, there is no significant, positive reason to go with a 3.9 rear with a stockish 13B...


-Ted

$7.25, I couldn't remember the change. Haha. But yeah, I know that HI is expensive as hell. I had to look for honeymoon prices to there once.

And yes, that was exactly what I was looking for.