Hi guys, I have a 1998 Z28, bone stock except aftermarket 18x9.5 rims with 274/40R18 tires. What kind of gas mileage should i expect? Rate now i am getting 220km to the tank on average driving not hard at all. In town gas mileage. Will an air filter and spark plugs and wires help me at all?

 

I get about 22 miles per gallon around town in my M6. You can expect to do a little worse (not much; maybe 20-21) if your car is an auto.

Plugs and filter might help a tiny amount, but nothing noticeable/measurable. If you're lucky it might get you another half a mile per gallon.

An airbox lid ($100) and a catback exhaust ($300-$800) might get you 1mpg together (I have both), and they'll add horsepower and make your car sound better too.

 

Not to be rude, but you'll have to quantify your mileage with better accuracy to fully evaluate your problem.

Ben T.

 

I'll typically see 20-21mpg in the city and I've hit 30 on the freeway doing 75-80mph. That is with an air lid, cat back. As was stated above, plugs and wires might get a little more, make sure your tires are properly inflated, and don't use cheap quality gas. I was using Valero and averaged 250 miles on a tank, switched to Exxon and am seeing 300 on a tank. Makes a HUGE difference. I have a 6 speed, that get a little better than auto.

 

on my last fill up I managed to put in about 39 L and got 271 km out of it.

I was driving like a lunatic though for almost 75 km of it, doing 2nd gear and 3rd gear chirps on a whim and pulling WOT blasts in 2nd and 3rd gear...

the rest was spent doing city driving for the most part.

I tend to keep very detailed logs of every fill up I do, each fill up IS a fill up and trip meter is used to record mileage between fill ups. Cost per mile, miles per cent, L per 100km, the whole enchilada is calculated by my spreadsheet. This is for the taxman as I write off my fuel heh.

City driving has nailed me as low as 14mpg for bumper to bumper traffic jams for 2+ hours. City has averaged around 18 mpg for the most part, combined as much as 22-24 on avg and if I ever manage a long drive I feel confident it can do at least 28mpg, perhaps even 30.

 

220 KILOMETERS per tank??? How much are you putting to the tank each time?

220 kilometers is less than 137 miles. If you fill the usual 12-14 gallons, I'd say you are definetely wasting a lot of gas.

I get 270-320 MILES per tank and that usually translates to be about 21-23 miles per gallon. Which is not bad at all for a daily commuter with LS1 and manual transmission. I got just about the same mileage with my A4 LS1, too.

TS

 

Get some accurate readings for your next few fill ups. Each time you fill up your car note the trip meter reading and write it on the receipt. Reset trip meter to zero. Make sure you try to fill up your car as consistently as possible. I always go to the second click of the pump then add a little bit to the next dollar. It's give or take half a litre per fill up, but I try to keep it consistent.

Then with mileage in hand and amount used at last fill up calculate mileage then. Note it will be your second full tank that will give a more accurate idea of your mileage. Try to fit in at least 3 fill ups before posting back on what your mileage is. Then we can try to help you determine what needs to be changed (driver or part in car) for mileage.

 

I guess i must be doing something wrong because i average about 160 miles per tank... thats about 12-13 gallons on fill up... i must be doing something wrong...

 

last few times i have checked it....that's with the cam...

mild city...not really stop and go...but all slower stuff...mostly 45mph...very little 55mph. and all short trips

18-19mpg

highway, mostly 75-80mph with about 1/4 of it straight 55mph:

24-25mpg

last trip was about 50/50 highway and city...and the city was downtown miami and some very slow small beach town 30-35mph stuff...with the ttops off the whole time which hurts mileage a little (i've tested it)

23.3 over a 284mile trip

not bad for 400rwhp

 

That's a horrible way to be consistent.

The only way to be reasonably consistent with your fillups is to always fill up at the same station, and the first time the pump stops, you're done. For best consistency, use the same pump every time.

To be perfectly consistent, you'd have to run the car dry, put in a known quantity, reset the trip odometer, and run it dry again. But that's bad for your fuel pump, so don't do that.

 

I get 20-22 avg. about 30 hwy.

 

yeah i measured teice now and im averaginf 200 KILOMETERS per tank!!! To me that is horrible, i would at least expect 300 km in town driving and i have not run the car remotley hard. I need help! I also run 87 Octane gas. Would a higher octane gas make my car faster? thanks

 

Use premium gas. It will help your gas mileage and horsepower, although not enough to get you up to 300km.

How many gallons (or liters) are you putting in when you fill up? I get the idiot light when there are still ~4 gallons in the tank, and it bugs me, so I usually only put about 11 gallons in when I fill up.

 

I get around 12-15 around town - have a converter...
and 24 on the freeway.

i average about 210 miles / tank.

***keep in mind*** for LS1 cars: 98's had a 15.5 gallon tank, 99-02 had a 16.8 gal tank

 

I failed to mention the stick to one gas station and same pump, when you're trying to fill to the brim each time, you can get the fill up pretty dame close where you are only off by less than a litre. This is why I tend to stick to mpg mileage as that 0.xxx is more or less within something known as "standard deviation".

As long as you keep that in mind, you can be consistent, even science has to take into account that no 2 experiments will be the same so you work with standard devaition to take that into account.

If I was to really get into it there are so many things that can cause deviation, the ride height of your tires decrease over time with usage, the air temps vary from hour to hour, humidity varies, the roads you drive on are not the same, the formulation of fuel from even the same pump, the way you drive...

the list is almost endless... this is why its an average AND not a definite reading, but it will be a good indicator as to if all those deviations are in your wallets favor not.