# Getting Better MPG in your SR20



## lovemyser (Mar 14, 2003)

I'm doing this write up because no one has ever done it before. I would like it to be a Sticky since so many people ask questions about it.

1. Immediate improvement: Keep your foot out of it! Focus on keeping your RPM's under 3k when you are shifting. There's a reason they call it "give it some gas!" 

2. Cost less improvement: Try not to carry so much stuff in your trunk the less weight the better. 

3. Tire pressure: This is a friction improvement, the less friction the less you have to press the peddle. Try keeping your tires at Maximum PSI. Around 25-40lbs.

4. Higher Octane gas: You pay for it extra for it, but...the lower the combustion the better the power. Also there is octane booster which is also good for cleaning out your fuel rails and other things like that.

5. 300ZX Twin Turbo fuel filter: These always seem to help. Because so much fuel is designed to flow thru these they let the car get better gas mileage with out having to force it through the fuel filter. Direct Bolt up.

6. O2 Sensor: Arguable the most popular mod for Gas mileage, its around 60.00 and a fairly easy install although it requires a special socket that you can rent from say autozone for free.

7. Regular Tune Up: Can beat these! New NGK plugs(don't forget to gap them) and wires, air filter(I've heard wix are the best paper filters and can be had at O-reilys), Fuel filter.

8. Synthetic Lubricants: Any mod where there is going to be less friction is going to increase longevity of the motor and increase MPG. 

9. Taller/shorter tires: This is dependant on wither or not your a highway driver or a city driver, taller tires will give you better road MPG while shorter tires will give you better city MPG.

10.Clean Your throttle Body: The smoother the air going into the motor is the better the mileage. Use a Carburetor/throttle body cleaner and a light scrub brush, you might even want to take it off.

11. Reground the MAF: You want to get a around 2 mv. Search for more detail on how to do this.

12.Parasitic Loss: Any parasitic loss mod will help, underdrive pulley, a/c delete, the list goes on.




The last thing I want to show people is how to calculate MPG. 

1. Top of your gas tank.
2. Drive until your ready for gas again, say 250 miles.
3. Top of your gas tank again. Say you put in 8.346 gallons
4. Divide 8.346 gallons into 250 miles for the answer of...29.954 MPG.


Like I said gas mileage is a popular question and I would like it to be a sticky if possible.


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## BennittoMallito (May 20, 2002)

OK sure but... 

5) I looked up the part # last time, and I could have 2 or three regular old SE-R fuel filters for the price of one from a TT. Why not just change it more?

8) Regular dino engine oil is ok. It costs so much more to use synthetic that the cost saved on gas is negated. Again 2-3 oil changes on regular oil for one with syn. and new oil is better than old oil anyway. People argue the same about premium gas too. Synthetic Gear oil is a must for SE-R's.

10) Cleaning TB does more than just smooth airflow, but I hate physics. 

Good list though. I hate it when people post asking how to calculate mpg. Or saying I get 213 to like half way between...


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## Jeff (Oct 17, 2002)

A lot of these tips can be used for many cars out there. Good info!


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## lovemyser (Mar 14, 2003)

Yes these can be used for other vehicles, but as you can see I went into specific mods for a specific type vehicle. Besides SR20's are the only ones I care about  :cheers: 


As far as the other guy, you have two people in this dear sweet world optimist and pessimist, "The optimist proclaims that we live in the best possible worlds, and the pessimist fears this is true." 
The point was not to price everthing out and grade it from there, the point of this thread was to give people a list of things they could do to improve their gas mileage, I didn't want to go into an argument of why dyno oil is better than synthetic oil(numerous studys prove that synthetic is better, we've done threads here on it, and 18.22/5 quarts for mobil one for a thing you love doesn't seem to me to be a big deal). This was to give people viable options on what they can do to improve their mileage, I included it all from free to not worth it.


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## mille-16i (Jun 16, 2004)

You forgot header and free flowing exgaust this will help alot and most people want to do this anyways also a CAI will help some, cooler air burns more efficently also it takes out the turbulance of factory air intake and again most people want to do this.


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## BennittoMallito (May 20, 2002)

If you don't save money what's the point? Its the old case of robbing Peter to pay Paul. 

#9 I don't get either. I know narrower tires have less resistnace. Why would the tire height improve fuel economy? You actually have a different rolling diameter so its no longer a true reading of actual distance travelled. Is it the effective gear ratio?


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## Tavel (Aug 21, 2004)

just a clear up. mileage reading is not based on actual distance traveled, therefore it doens't matter what size the tires are, the mileage reading will still be correct. think of it this way: if the car is moving an actual distance of 1.2 miles for every 1 mile the odometer says, then the car is still doing the work to make it move 1 mile when it says its moving 1 mile. essentially, the reading is accurate because none of the scales have changed. 

it is the final ratio between axel and wheel diameter that determines stress load for an engine in certain situations(namely city or highway driving).

however, if you want to know actual distance traveled, than you need the right size tire.


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## lshadoff (Nov 26, 2002)

Tavel said:


> just a clear up. mileage reading is not based on actual distance traveled, therefore it doens't matter what size the tires are, the mileage reading will still be correct. think of it this way: if the car is moving an actual distance of 1.2 miles for every 1 mile the odometer says, then the car is still doing the work to make it move 1 mile when it says its moving 1 mile. essentially, the reading is accurate because none of the scales have changed.
> 
> it is the final ratio between axel and wheel diameter that determines stress load for an engine in certain situations(namely city or highway driving).
> 
> however, if you want to know actual distance traveled, than you need the right size tire.


Don't tell me that size doesn't matter. 

Gasoline mileage in the US is based on two readings, the number of gallons reading on the gas pump and the odometer reading in the car. We'll assume the gas pump reads correctly. 

You are saying that the odometer reading is not based on the actual distance travelled, which is correct. It is based on the number of revolutions of the speed sensor (whether it is a cable or electronic). The tires rolling on the ground cause the speed sensor to rotate. The odometer is calibrated to display the distance travelled by knowing the exact number of revolutions the stock tire makes to cover one mile and the number of revolutions the speed sensor makes for each revolution of the tire. 

Suppose, now, that you change your car's tires to tires with a larger diameter. The number of revolutions it takes the new tires to cover one mile is now smaller because the diameter of the tire is larger. However, the odometer does not know the tires were changed, and displays a number of miles which is too low. Now when you fill the tank, it will calculate to be a smaller number of miles per gallon because the miles reading is erroneous. 

The difference is usually a few percent. If you had Kumho Ectsta Supra 712 tires in the stock size (195/55 15) on the car (revolutions per mile = 870) and replaced them with 205/55 15 (revolutions per mile = 858) the change would be 1.4%. 
[Numbers taken from Kumho tire specs on www.tirerack.com] 

But, with the new tires your car travels a greater distance for each revolution of the engine. This should improve the gas mileage. Suppose it goes from 30mpg to 31mpg. That's a 3.3% improvement. However your calculated miles per gallon improvement would be 3.3 - 1.4 = 1.9% improvement, because the odometer is not measuring the distance correctly.

Knowing the difference in diameters of the two tires, you can calculate a correction to the measured miles per gallon.

So, size does make a difference.

Lew


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## lovemysan (Jan 31, 2003)

I tried to talk lovemyser into putting this in. Most Odometers are not correct. One of the first things you should do is simply compare the odometer to mile markers over 100 miles and then figure the percentage that it is off. If its 3.2 miles off then thats 3.2% just add that back when your figuring your mileage

Whats important here is that the odometer is consistent! I run taller tires all the time ,1.5" taller, because it does improve your economy. Especially if they are narrow. A tall, fat tire won't help that much because you won't to keep rotational mass down. 

195/75 14 verses a 205/75 14


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## lovemyser (Mar 14, 2003)

BennittoMallito said:


> If you don't save money what's the point? Its the old case of robbing Peter to pay Paul.
> 
> 
> 
> > Yes but...Both of the points you mentioned are viable performance options as well so they have multiple functions, so nobody is robbing peter and paul is better off. And Ishadoff summed up your other question very nicely.


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## lshadoff (Nov 26, 2002)

I have a problem with several of these. 


lovemyser said:


> I'm doing this write up because no one has ever done it before. I would like it to be a Sticky since so many people ask questions about it.
> 
> 1. Immediate improvement: Keep your foot out of it! Focus on keeping your RPM's under 3k when you are shifting. There's a reason they call it "give it some gas!"
> 
> ...


There is a sticker either on the driver-side door or door pillar with the manufacturer's recommended tire pressure for your car. If the pressure is lower than this, the tire will run warm and have more friction, thus taking more power to make it roll. If it is significantly higher than this, the rolling friction decreases, but the tire wears unevenly (wears out the center, moreso in wider tires), necessitating more frequent tire changes which negates some of the savings from better gas mileage. 


lovemyser said:


> 4. Higher Octane gas: You pay for it extra for it, but...the lower the combustion the better the power. Also there is octane booster which is also good for cleaning out your fuel rails and other things like that.


Wrong. Higher octane gas burns slower. I am unfamiliar with what lower combustion is. The octane specified by the manufacturer is the gas to run. Any higher octane is a waste of money. It will not yield better gas mileage or more power (unless you have modified your engine in a way that requires higher octane to avoid detonation). 


lovemyser said:


> 5. 300ZX Twin Turbo fuel filter: These always seem to help. Because so much fuel is designed to flow thru these they let the car get better gas mileage with out having to force it through the fuel filter. Direct Bolt up.


Wrong. As long as the filter is not plugged, it will provide enough gas to run your engine under all conditions. A filter capable of higher flow than your engine can use is a waste of money. 


lovemyser said:


> 6. O2 Sensor: Arguable the most popular mod for Gas mileage, its around 60.00 and a fairly easy install although it requires a special socket that you can rent from say autozone for free.


Replacing the O2 sensor when it is functioning correctly is a waste of money. If your gas mileage has dropped suddenly, it is worthwhile testing the sensor as a possible cause, and replacing it if defective. 


lovemyser said:


> 7. Regular Tune Up: Can beat these! New NGK plugs(don't forget to gap them) and wires, air filter(I've heard wix are the best paper filters and can be had at O-reilys), Fuel filter.


Tune ups should be done at the manufacturer's recommended interval. A tune up also should include checking the timing and idle speed. Set the timing to the most advanced setting specified by the manufacturer. For the B14 SR20DE it is 17* BTDC. Use only factory wires. All the cheap aftermarket wires cause problems on this engine in a short period of time. 


lovemyser said:


> 8. Synthetic Lubricants: Any mod where there is going to be less friction is going to increase longevity of the motor and increase MPG.
> 9. Taller/shorter tires: This is dependant on wither or not your a highway driver or a city driver, taller tires will give you better road MPG while shorter tires will give you better city MPG.


Why would shorter tires give better mileage at low speed? The principle is the same at all speeds. If you lower the number of revolutions the engine makes to go 1 mile, you increase the gas mileage. 


lovemyser said:


> 10.Clean Your throttle Body: The smoother the air going into the motor is the better the mileage. Use a Carburetor/throttle body cleaner and a light scrub brush, you might even want to take it off.


Actually, several intake manifolds are designed to make the air entering the combustion chamber swirl (including the B14 SR20DE).

Consider this if all else fails. To do it properly, the intake manifold should be removed and degreased. Why would you want to put all that gunk through your engine to burn it? There are many posts on NF about engines running poorly after running a solvent through the intake. 


lovemyser said:


> 11. Reground the MAF: You want to get a around 2 mv. Search for more detail on how to do this.


I would check the ground on the MAF if the engine is running poorly. Why ground it if it shows a low resistance? 


lovemyser said:


> 12.Parasitic Loss: Any parasitic loss mod will help, underdrive pulley, a/c delete, the list goes on.


Very light wheels and tires are another of these. 


lovemyser said:


> The last thing I want to show people is how to calculate MPG.
> 
> 1. Top of your gas tank.
> 2. Drive until your ready for gas again, say 250 miles.
> ...


How repeatably can you fill your tank? To the nearest 0.001 gallon? I doubt it. Just fill your tank exactly the same every time to get the best mileage calculation. Suppose you can fill the tank repeatably to within 1 quart (0.25 gallon). If you added 12 gallons and went 300 miles, this is 25mpg +/- 0.5mpg. An acceptable precision. It is ludicrous to calculate gas mileage to 5 significant figures.

Lew


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## lovemyser (Mar 14, 2003)

Ok....I'm not even going to try a response to that.


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## asleepz (Feb 24, 2004)

No the odometer is going to say that you have better gas mileage but you really don't

Here's a experiment.

1.2 miles = 1 mile on the odometer.

Put it on some type of roller that would calculate distance and drive lets say 300 miles from what the cars odometer says.

In reality you would've drove 360 miles.

Now with this being said in NO way are you getting better gas mileage, your just driving a farther distace than the car would think.

Say 10 gallons will get your 300 miles normally from what the odometer says. Well to get that same 300 miles in reality you used 16 gallons to get that same reported 300 miles. 

In NO way would it make gas mileage any better unless the wheels that you put on (obviously aftermarket) weighed less.


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## lshadoff (Nov 26, 2002)

SKD_Tech said:


> No the odometer is going to say that you have better gas mileage but you really don't
> 
> Here's a experiment.
> 
> ...


That's exactly what I said. I said, "it will calculate to be a smaller number of miles per gallon". That is worse mileage.

Lew


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