MPG maximizing - My new ZX2 project

Hey ya,

Just picked up a unmolested 1998 5 speed a couple weeks ago and am guinea pigging it to see what can be done to extract more gas mileage. Here’s the plan…

I have chosen a Mobil station and 90 mile freeway driving loop for this adventure, and have become quite proficient at filling up the gas tank until the gas is visible in the filler neck so i know exactly how much has been used.

I have limited my driving style to shifting at 3000 rpm and keeping the speed at 70mph, give or take 4mph either way (it’s not flat country out here and the car has no cruise control lol)
So far I’m five trips into this venture and have brought fuel economy from a 34.24mpg to 37.5mpg.

So far here’s the breakdown of the first 5 sets of mods…

Run 1: Car is as purchased, with 10w30 wal mart oil and fram oil filter, and almost new Goodyear Integrity tires on the base model steelies. Tire pressures were 30lbs, front and rear, and the trunk and passenger compartment were free of any additional weight items… I consumed 2.64 gallons. and ran the car at dusk, turning the headlights on about halfway thru the trip

Run 2: Weight removal bits… I removed the spare tire, jack, false floor, and carpet pad from the trunk. Under the hood I removed the motor mount dampers and engine lift hook, and inside the car i removed the steel sandwich plate inside the glovebox… about 50 lbs total. I also upped the air pressure to 38lbs in the front and 34 lbs in the rear. Headlights were on the whole time. Consumption was 2.58 gallons (34.88 mpg).

Run 3: Added 14x6 motegi alloys, installed lowering springs in the rear only to improve stance (sits level looking now instead of that Dodge Neon kicked in the ass look of the stock springs), and installed a zxtuner ultra udp while replacing a noisy idler bearing. Headlights were on and consumption was down… 2.44 gallons (36.88 mpg)

Run 4: Switched out oil to 0w30 Mobil 1 and a motorcraft oil filter, added a 170 degree thermostat, reset the pcm, and removed the lower resonator from the stock intake. I drove the car for about a week to get the pcm to start learning its parameters again. Headlights were on and now I saw 2.40 gallons used (37.5mpg)

Run 5: I added a hi flow elbow to the TB end of the stock intake and ran again… Hot day, no headlights, and 2.41 gallons used (37.3 mpg).

As for how the car runs, it’s a tad smoother than stock, with a noticeable boost in power (the 'ol butt dyno says about 10hp).

I have a few more plans for the mpg upgrades, and if any of you out there have any ideas or suggestions on what to do to increase mpg, i’m all ears.


since it’s a 98 it has a shorter fifth gear, I’d rather keep the emergency items like the spare tire and jack and instead swap out the fifth gear in the tranny for one from a 97+ escort or tracer sedan. your cruising rpms should drop doing so

yes the sedan tranny would be a good mod - as for the spare and jack, a can of tire sealant and a AAA card are much lighter :wink:


and speaking of sedan tranny - all you really need is the 5th gear set, which can be replaced without removing the trans. True, you would not have the sedan’s 3.84:1 final drive, but the .72:1 5th gear over the .78:1 gear would be good for another 200rpm or so at 70mph.

Good start Rob. You might want to make sure the plugs are gapped right, fuel filter/fuel pressure is good, pcv is good. I would jack the tires up to at least 32-35 for maximum efficiency. 5th gear swap is always a plus if you have time as well.

-How are you liking the car overall?

this car is really tight - it has that '98 feel… the one of more solidity and substance (due to additional structural brackets and soundproofing). No rattles, the car tracks straight as an arrow, and is 10x more comfortable than my manual steering, eibach, and drag radial equipped s/r.


the next step is new plugs and FR plug wires, meshing up the front grille, and bumping tire pressure to 40psi. I don’t think I’m gonna do the gear change since i’m not keeping the car for long - once i’m done with this little adventure i’ll sell and replace it with another zx2 to mess with.


where’s the additional sound deadening in a 98? I’ve heard they have more, but I was just wondering where it’s at, I have a 98 and eventually I’d like to dynamat it

more bricks of foam in the rear side and door panels, rubber gaskets around the taillamps, additional plastic trim parts, and more dense seat foam than the later model seats are the most noticeable differences between a 98 and later years.

Dynamat? Boy that stuff is heavy. From a performance perspective Dynamat is the enemy lol. I prefer cardboard egg crates, expandable foam, as well as pillow batting to help reduce road noise.


this is true, I just swapped a mtx into an atx’s home, so I’ve got a ton of weight savings I need to negate anyhow :lol:

im hoping to see better mileage with my n/a zx2 as well :]

its all about light weight, less drag, and low rpms when making good mpg numbers. i should take my 2250 lb s/r on the 90 mile “eco-cruise” just for shits and giggles. i think it would actually do quite well considering the large cams and hi rpms it runs at 70mph.


Is that your race scort? S/R one?

yeah - my original s/r - the one thats been the zxtuner guinea pig all these years. still running strong on the original modded motor and the 4 spider trans that was put in 50k miles ago.

wow man that thing keeps on living hahaha. Glad to hear you still love that car. Post some pic’s up of your cars sometime

the original s/r is a sorry sight - one sideswipe due to a parking lot hit and run, followed up with an attempt by a mobile body shop to fix, combined with the last hit by a woman with a mexican d/l driving a navigator who decided to make the right hand turn as i was making a left on a green arrow from the other direction. add infrequesnt car washes and a 4 year hiatus sitting in my driveway, and a set of scion steelies on the rear with drag radials on the front and you get the picture…

anyways, back to the mpg thing… here’s a map of my eco-cruise trip if anyone cares to see. elevation changes from 1600ft to 300ft above sea level… copy and paste the full text

[url=] ... ress::1/l:[/url]:[20100-20499]+Box+Springs+Rd:Riverside:CA:92507:US:33.9475:-117.30195:street:Riverside+County:1/l::[2890-2913]+la+Sierra+Ave:Riverside:CA:92503:US:33.88945:-117.46475:street:Riverside+County:1/l::30000+Rancho+California+Rd:Temecula:CA:92591-2964:US:33.50752:-117.140099:address:Riverside+County:1/m:hyb:7:33.746017:-117.343978:0:::::/io:1:::::f:EN:M:/e

dang that looks like a fun drive but man does it go down quick on sea level. Does your ears pop all the time hahah?

naw - its only 1600 ft - Cajon pass at 4190ft on the 15 north is the ear popper…

Another update…

Run 7: Upped the air in the tires to 40psi, added Ford Racing Wires and new Motorcraft plugs gapped at .055" and I netted the same 37.5mpg… I should have seen an improvement but i think the low temp thermostat might be fighting my mpg cause. i’m going to change out the 170 t’stat for a 180 t’stat and see if that helps the cause. The car is running great, lots of off the line grunt.


Have you tried smaller plug gaps? I recently replaced my fuel filter and replaced the plugs with some oe .05 gap plugs and I’m seeing 40+ mpg’s highway w/ NGP0 on 93 octane