I have a 99EX that gets somewhere between 32 and 35MPG on the highway, running pretty much stock except for an AEM intake and the wheels...the tire diameter is a little smaller than stock. I had a nice Greddy SP on there that didn't sound too loud...until some moron rear-ended me and crimped my aftermarket midpipe...I'll be rewelding a new exhaust soon, but I want to also explore other options.

What kind of mileage could I push with a VAFC? Anything? How about if I converted to an OBD1 ecu? I chipped my friend's p28 and was interested in the fuel/air tables when we were constructing a ROM. Any advantages to running hondata over a VAFC, particularly for gas mileage? The costs add up as I drive between school and home semi-frequently, and that's about 230mi round trip (plus the other driving that I do during the week).

Thanks.

 

By the way, don't message me telling me that you want to swap heads (It's happened in person enough.)

 

if you want better mileage get bigger tires. this works, really it does. if you have a standard shift, drive in the slow lane all the time. civic can get around 49 mpg at a constant 55, i've read.

 

I was forced to drive a long stretch at 55-60mph one time with little braking, and to be honest, my mpg sucked that time, I don't know why. I used almost an entire tank of gas at THOSE speeds, whereas in the 65-75mph ranges, I had a few mpg better. I don't know why though, but that doesn't bother me.

I am looking into changing from Konig 16's to Si 15's and getting slightly larger tires, but still, I want to optimize with the computer, ideally getting in the 45+ range at 75mph. When I first installed my aftermarket exhaust, and before the new wheels, I cruised at 75 for 220 miles and drove in Atlanta for about 20 and still had 41mpg.

 

why not just get a VAFC and take out a little fuel and see if that helps.

 

this thread is crazy, and not in a good way

Bigger diameter tires than stock help? How? It's pretty controversial, and there is definately a law of diminishing returns going on.

What do you think adjusting air fuel ratio's is going to do? You want to add less fuel? Great idea, except that you'll make less power. Which means to go the same speed as you usually go, you'll have to hit the gas more, and dump more fuel in it.

Something's wrong with your measurements if you get worse mileage at 55 than you do at 70, it's that simple.

 

read up on http://www.pgmfi.org, you can certainly tune for better mileage if you want to put in the work.......

 

Add less fuel, yes. As I have read, the ECU makes the engine run a little rich for emissions or whatever reasons. I don't want to be wasting that gas. I'd rather decrease fuel or add air.

 

According to a report by Energy and Resources Group / University of California at Berkley, specifically on Honda Civics, it's mostly about the transmission gearing.

Link is here: http://enduse.lbl.gov/info/Honda.pdf


Time for a VX swap + lean burn pwnZ j00!

<edit:> Also, commenting on your change of wheels above, lighter wheels would give you less rotational mass. Every little bit counts. May 14" HX wheels are an option for long trips?

 

Tire pressure, alignment, the car's mechanical condition, and driving style make more of a difference than tire size and a VAFC.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b20zej1 &raquo;</TD></TR><TR><TD CLASS="quote">if you want better mileage get bigger tires. this works, really it does. if you have a standard shift, drive in the slow lane all the time. civic can get around 49 mpg at a constant 55, i've read. </TD></TR></TABLE>

Bigger tires means the speedo will be off and be slower. ie the speedo reads 55 but you are really doing 65. Also you are moving more rubber. So you may think you are getting better gas milage but you really aren't. Now if you are moving from a 14" to a 15" you aren't going to see any noticeable difference. But bigger tires do NOT mean better gas mileage

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by parasonic &raquo;</TD></TR><TR><TD CLASS="quote">Add less fuel, yes. As I have read, the ECU makes the engine run a little rich for emissions or whatever reasons. I don't want to be wasting that gas. I'd rather decrease fuel or add air.</TD></TR></TABLE>

Your avatar says you live in atl, any idea how you're gonna pass emissions?

 

The car is registered in Tennessee. Plus, I really wouldn't care either way if it were registered here either. Just put the stock exhaust on one day out of the year, an hour or two of work, worth it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Falqon &raquo;</TD></TR><TR><TD CLASS="quote">
What do you think adjusting air fuel ratio's is going to do? You want to add less fuel? Great idea, except that you'll make less power. Which means to go the same speed as you usually go, you'll have to hit the gas more, and dump more fuel in it.

Something's wrong with your measurements if you get worse mileage at 55 than you do at 70, it's that simple.</TD></TR></TABLE>

1. Your thoery of less power is indeed correct, less feul = less combustion = less power, but that dosnt mean you have to hit the gas more to get higher speeds, it simply means it will take longer to accellerate to those speeds. the RPM at those speeds will be the same in the same gears regardless of Air/Feul ratios, just the output getting there will have less power, thus slower acceleration

2. You are wrong again. Depending on the transmission, if the gear ratio is high on 5th, then he could be pulling too low rpm in 5th gear, thus pushing real hard to keep that speed, thus using more feul, whereas if he is in an optimal RPM range at or around 70 (usually when the engine is quiet), feul usage is more efficcient

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Zekers &raquo;</TD></TR><TR><TD CLASS="quote">
Bigger tires means the speedo will be off and be slower. ie the speedo reads 55 but you are really doing 65. Also you are moving more rubber. So you may think you are getting better gas milage but you really aren't. Now if you are moving from a 14" to a 15" you aren't going to see any noticeable difference. But bigger tires do NOT mean better gas mileage </TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by stevel &raquo;</TD></TR><TR><TD CLASS="quote">

what a bigger tire can do is effectively lower your overall gear ratio. You know how rear end cars have 3.10 gears and 4.55 gears. That's the final drive ratio. A 4.55 gear will spin the motor to more rpms at the same speed as say a 3.10 gear. For example, at 70 say the 4.55 gear the motor is turning at 4000 rpms. At 70 a 3.10 gear may be turning the engine at say 2500. It's the same principle with FWD cars as they have FD ratio's but it's all in the tranny. Well, changing tire diameters can do the same thing. A .5" or 1" change in overall tire diameter can make a difference in rpms. If i wanted better gas mileage I would change to a 14" rim and get 185/70/14 tires or even bigger. They're narrower so less drag and they have a larger overall diameter so at the same speed the rpm will be lower. And while you are right that the speedo is off, you can buy a speedo correction gizmos that will compensate for the larger diameter tire so your speedo is accurate. Everything else you said is pretty much incorrect. A bigger tire will have the motor turning less rpms at the same speed there by increasing gas mileage.

s</TD></TR></TABLE>

Acually, you are both quite incorrect. Larger tires WILL NOT modify speedo. I have covered this before in topics past, but the physics behind it are as such:
For a larger wheel to spin one full rotation compared to a smaller wheel, more torque is required by the engine for this full rotation. Thus being said, the speedo will compensate by computing the torque requirement relative to the number of rotations. Just to let you know, the ECU is smart and it knows how to do math.

Now on the other hand, Lighter wheels and thinner tires will effectively reduce drag (less friction), and lighten the veichle enough to see gain in feul efficiency

EDIT: Its not all about gear ratio's, it also concerns Power requirements and output

 

Lets try exampleby exageration.

In this thread, 'bigger tire' means larger circumfrence, not width; true, it they should've said 'taller' instead. Anyways - put 12" old Geo Metro wheels&tires (or whatever size they use) on a Civic, at 65 it will be turning out well past a few 100 rpm's MORE than what the Civic's stock 14's did. Higher rpm will logically lead to more fuel consumption (unless the ecu leans it out, doubtful), and at the very least, increased engine wear (however small, its there).

Put on dubs (assuming you can fit them ) and your doing probably 1000 LESS rpm's (very rough est.) at 65 than the stock 14's.

The other side of the coin - increased rotating mass - shouldn't be of much concern unless your motor is severly lacking in torque. Rotating mass, in the very simplistic of estimates, equates to adding double it's mass to the static weight of the car when talking about accelleration (and in this case, preventing decellereation). Although in worst-case it will make any other 'improvements' harder to see, do many people notice much of a mpg decrease after adding a sub & amp to their trunk?

To show how reduced power via ecu air/fuel adjustments won't equate to you having to jam on the gas more (and in essence use the same amount of gas), drive around in a 300whp gs-r at 75 in 4th gear. Does the integra need the near-300whp it has at those rpm's to stay at that speeds? Hell no - my old shadow could do that with a worse drag coef. and 70hp. Leaning it out to decrease HP will help, assuming you don't need the amount of HP your engine supplies at the given rpm/cruising speed.

I'm looking forward to doing this for my LS/Civic since I need much less hp/torque to maintain 75mph (with winter 13's) than the LS is supplying at 4000 rpm. I'll admit its different with a swap since it was made to push a heavier car with bigger wheels (ie different final drive ratio *at the wheels), but most civics have power to spare at most rpm's (to cruise, that is, not accellerate ) Didn't mean to **** no anyone's leg, just type enough bs to avoid some confussion - hopefully.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Apocolipse269 &raquo;</TD></TR><TR><TD CLASS="quote">

1. Your thoery of less power is indeed correct, less feul = less combustion = less power, but that dosnt mean you have to hit the gas more to get higher speeds, it simply means it will take longer to accellerate to those speeds. the RPM at those speeds will be the same in the same gears regardless of Air/Feul ratios, just the output getting there will have less power, thus slower acceleration

2. You are wrong again. Depending on the transmission, if the gear ratio is high on 5th, then he could be pulling too low rpm in 5th gear, thus pushing real hard to keep that speed, thus using more feul, whereas if he is in an optimal RPM range at or around 70 (usually when the engine is quiet), feul usage is more efficcient</TD></TR></TABLE>

1, if you decrease fuel at a given rpm to the extent that you lose power, then you will lose the ability to sustain that rpm as easily as before, therefore you will be using more fuel to obtain the same speed that you did before. Your reasoning is flawed, the rpm can be the same but the horsepower sure won't be.

2, I have never seen a stock honda engine that couldn't handle 5th easily at 55mph. The simple fact is even if your right (and I don't believe you are) then downshifting to 4th and bringing your revs up while still going 55 is going to be much easier aerodynamically than going 70.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Apocolipse269 &raquo;</TD></TR><TR><TD CLASS="quote">
Acually, you are both quite incorrect. Larger tires WILL NOT modify speedo
</TD></TR></TABLE>
3, Now you're really showing off ignorance, increase the circumference of a tire and it will affect the speedo.

 

I agree with your stuff man, but the ECU is stupid. It does NOT compensate for a change in tire size. How I figured this out?

Today, I was on 75. I timed how long it took to get from one yard stick to another. That was 45 seconds exactly. That equates to exactly 80MPH. However, my speedometer read exactly 85MPH the entire time since it was flat and I was watching it. A bunch of exactly's, but I was really careful...and didn't round.

 

I coulda told you that, the ECU has nothing to do with the speedo.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by parasonic &raquo;</TD></TR><TR><TD CLASS="quote">By the way, don't message me telling me that you want to swap heads (It's happened in person enough.)</TD></TR></TABLE>
haha cmon forrest u know u want that b7 head... 41mpg

 

Bite me. You're not getting my head.

 

looks like i'll have to buy my head, as usual. thats the only way ill be able to get it lol