Correct Air/fuel ratio

How could you check air/fuel ratio? I mean, I'd like to see what would be the most adequate type of air intake for my exhaust.

Before I changed my Exhaust, I was getting 380kms(236 miles) per tank.
After the exhaust, I'am getting 325kms(302miles) per tank.

I was using a K&N filter.

Right now I'm trying the regular paper filter and it's not looking good in terms of mileage. (Note: I'm not doing mods solely for mileage).

Could people post or PM me what mileage they're getting with mods?

PS. my exhaust is 2" from the flange back with 2 hi-flow flowmaster resonators and a magnaflow muffler.

[y2dgone]

custom CAI with K&N cone filter, port matched exhaust manifold, PCV breather, NGK plug wires, e3 plugs, magnaflow high flow cat, flowmaster 40 series muffler, 2.25" full exhaust piping, 99 mazda miata 15x7 rims, nitto tires, carpet removed, trunk interior and paneling removed, KVR front rotors and pads, H&R lowering springs

need to add transmission cooler and under drive pulley

45mpg on the highway

I'm far from that many mods.

But how many miles on a tank on average?

[y2dgone]

good question, i havent judged that in a long time but i can usually go from tulsa to st louis on a tank which is about 400 miles

[aveosummit]

400/11=36.3636363636mpg

from what i know the ratings for mileage are different from the usa and canada.

i didn't want this to be an endless mileage post.

how could i check to see if i have the best air/fuel ratio?

[exodus]

use an air/fuel meter?

how can you tell i'm not a mechanic.

could one of those hypertech or superchips computer programmers be used to help in the air/fuel ratio?

[exodus]

how can you tell i'm not a mechanic.

could one of those hypertech or superchips computer programmers be used to help in the air/fuel ratio?

Not familiar with the specific products you're talking about, but adjusting the fuel maps on the ECU will be able to change the ratio... (a fuel map is basically an instruction manual... for X amount of air, add Y amount of fuel)

[y2dgone]

400/11=36.3636363636mpg

But of course that all depends on how I'm driving