CRX hf mpg

does anyone know why the 1990 hf crx model gets 46-50 mpg, while the 1991 hf model gets 32-36 mpg. Why was the drop so dramatic, werent the cars made the same way, or is my info just wrong. Any help would be great.

does anyone know why the 1990 hf crx model gets 46-50 mpg, while the 1991 hf model gets 32-36 mpg. Why was the drop so dramatic, werent the cars made the same way, or is my info just wrong. Any help would be great.
My 91HF with 115K gets 49.5 mpg on the freeway!
Mods. Homemade ram air intake, Si exhaust manifold and exhaust, Sounds wicked but in feel it is not. If I wanted it to go faster I would put a B motor in. Thats not why I bought it though. 48 mpg is why I bought it. I just modded it to improve air flow. That helps mpg too!

i wanna upgrade a car so it has ridiculous gas mileage like 55-60 mpg, and i was thinking of starting with the crx hf (a 90 or 91). I understand the air intake system, which makes airflow more effiecient would help the mpg, would a B16a swap help mpg? How about an MSD ignition? has anyone tried a this project based soley on mpg? with gas prices the way they are id like to buy parts for this hf that would improve hp, but help mpg as well. Any thoughts...thanks

if you are looking to make ridiculous MPG, dont use a b16a. you are gonna be taking a hit stock for stock going from a d15 to a b16a. and then you are also gonna be eating gas even more everytime the engine goes into VTEC. if you want great gas mileage, stick with the HF engine, and do a few airflow mods, igntion mods, cooling mods, and exhaust mods. then try to tune the engine to run as lean as you can safely. the closer to 14.5:1 you can get the better.

try using hotter sparkplugs to get a more complete burn, and upgrade the coil and put an MSD box on it to get more powerful spark. run higher octane gas too, itll allow you to run leaner without detonation.

I would actually get a EG hatch, VX model (base, i think), which if kept under 60, will get close to 60 mpg stock.

The gas milage of the hf is mostly the tranny. I did a ZC 1.6 ltr sohc vtec swap in my hf and kept my tranny and as long as i baby it and keep it in 5th on the freeway running a steady 80mph 85 mph and still got 45 mpg. Thats a 89 tranny that i have.

alright so airflow and ignition upgrades would help.......how about carbon fiber parts, If i threw a carbon fiber hood on with some carbon fiber fenders this would drop the weight of the vehicle and help mpg too, right? And i would get the cf hood w/ scoop for better engine circulation, does this sound good?

I hear the mugen engine chips help mpg too, is this true, ive never installed one but i hear they give horse power gains. Are there any bad sides to these chips?........sorry bout all the questions.....any help would be well appreciated...

yea anything that will help lower the weight will help increase MPG.

also, a good engine for mpg and power is the obdII JDM D15B, it costs alot but it makes as much or more hp then any other D-motor(its rated ~125hp i think) but is still able to get ~50mpg highway. It has 3-stage VTEC.

You dont really want to increase the airflow; more airflow=more hp=less mpg.

about ignition mods; i would avoid the msd box; lots of people put that in there NA motors and noticed the engine runs crappier. Its more of for boosted apps. If anything just upgrade the wires, coil(to something like a MSD blaster coil with the distributor cap), and platinum or iridium plugs.

explain to me how increasing airflow decreases gas mileage? think about it, airfuel ratio is the measure of air to gas. the best ratio is stoichometric, 14.5:1 and thats 14.5 parts air to every 1 part gas. so why would putting more air in equal worse gas mileage if he isnt doing anything to up the fuel?

well with my b16 and the ls trans i get pretty damn good gas mileage. I filled my tank like 3 days ago and have gone 170 miles with half a tank still left. Thats equals out to about 39 mpg. It probably also has to do with the fact that I don't beat on my car very much, and I stay out of vtec for the most part unless im passing someone or feel like driving spirtly. I think its acutally getting better mileage than when I had the d16a6, but i also kicked the shit out of that motor too LOL.

explain to me how increasing airflow decreases gas mileage? think about it, airfuel ratio is the measure of air to gas. the best ratio is stoichometric, 14.5:1 and thats 14.5 parts air to every 1 part gas. so why would putting more air in equal worse gas mileage if he isnt doing anything to up the fuel?

for a given amount of air, it takes 14.7 parts air to fuel for the best efficient burn right? now if you increase the air, you will have to increase the fuel; if you dont itll be leaner then 14.7(which is worse then running rich). most systems are already designed to work around 14.7, so if the engine notices its getting more air; it's going to add more fuel. And if the system is "dumb", itll still be sending the same amount of fuel before, but since more air is introduced, itll also be running lean but with the same MPG.

i dont think theres many car manufacturers that actually tune their ECUs to run at stoich. its too risky. most of them run slightly rich.

and if its already running slightly rich, if you lean it out by introducing more air and tuning to get it closer to stoich, then you will get better gas mileage. it wont still get the same MPG simply because the amount of gas injected at a given load will be less.

i know that most cars are close to stoich, like 12:1 or 13:1, but very few cars run closer to that simply because there needs to be a padded area to keep the engine from running lean and running hot.

i still say improve the airflow, improve the cooling, ditch the HF manifold and go with one from another d-series, get hotter spark, and probably an AFC and wideband o2 sensor to tune as lean as possible.

i think im gonna start looking for a car to try this on. i may try it with my del sol.

and if its already running slightly rich, if you lean it out by introducing more air and tuning to get it closer to stoich, then you will get better gas mileage. it wont still get the same MPG simply because the amount of gas injected at a given load will be less.

you dont want to do that, as ive stated before because running leaner is more dangerous than running rich. If your engine is running rich itll be better to take away some air. example: a d15b will also have potential for lower MPG than a 1.8l B18B right? this is because the d15 cant take in as much air as the b18b(assuming the a/f are the same); thus not needing as much fuel create a combustion. This is also why you get better MPG with part throttle vs. full throttle(less air!).

remember the ECU runs off of a map that looks at vacuum and throttle position. Then the amount of fuel injected will be modified by other inputs(such as the O2 sensor, load, etc.). btw, the o2 sensor in the Hondas are narrow-band; so theyll only tell the engine whether its richer than stoich or lean. Giving it more air is going to make it want to inject more fuel.

what would make the engine inject less gas at the same load? Only way is to alter the fuel map.


i know that most cars are close to stoich, like 12:1 or 13:1, but very few cars run closer to that simply because there needs to be a padded area to keep the engine from running lean and running hot.

12:1 and 13:1 is rich, lots of tuned NA motors run around 13:1. lots of engines do run stoich at under 50% throttle(you can look at the base Honda fuel maps and see this) but run a little richer only during warming the car up.

this is exactly why i said that the ECU would need to be tuned. if you alter the fuel maps, then you can run as lean as safely possible.

and the only reason upping the air would also up the gas is because the ECU sees the increase in air and adjusts for it.

im sure there are cars that occasionally do hit stoich, but every one ive ever seen on a wideband analyzer ran slightly rich. think about it, why would a car company want to put themselves at risk by setting their ECUs to operate at stoich? all it takes is a few anomalies and itll run lean and burn something up. my guess is its slightly rich for insurance against lean overheating and detonation. in fact, nissan had a recall on altimas a while back that i worked on. it was because the ECU was running a tight ship on A/F ratios and it was melting the cat, damaging o2 sensors, and cooking oil. the parameters for A/F were so tight that engine temp was soaring. we had to reprogram every ECU, and on a lot of them, replace cats, o2 sensors, and oil. and a few of them needed new engines because of it. now the ECUs run a bit richer to make sure this doesnt happen again.

when i say lean it out, i dont mean to go past stoich, i just mean getting it as lean as possible without damaging anything. airflow does effect gas mileage negatively, just look at how much a dirty airfilter effects it. you can lose 10% gas mileage from a dirty filter, since you have to basically open the throttle plate more just to get the same amount of air through as with a clean filter. and remember that the more you open the throttle, the more gas the ECU injects.

so by that logic, improving the flow of air will help gas mileage. because now you are opening the throttle less at a given load, but still getting enough air in, so the ECU isnt going to dump gas.

i think you and i actually agree on more points than we disagree, and i think we might just be misunderstanding each other on the points that we disagree on. i will say this, its the most interesting things ive been involved on on AF.com in a while

the engines run a little rich because the map is altered or modified in a passive way(like load, engine temp, etc.), but the actual fuel table is set for stoich under 50% throttle...atleast on many Hondas(im not too familiar with the Nissan systems). .

yes i agree with you, but when people say "upgrade the intake" its usually the piping and routing(mainly ram-air and cold-air types), which will usually harm mpg. but if its just the filter, that would work good. A good intake for a good MPG car is one that wont choke the motor(make it work harder to suck in air) and one that wont give the engine more air then it needs for cruising(this is why the hybrids use a electric motor to help with acceleration; the engine would be weaker in the higher rpms/higher throttle angle).

yea i would definately agree that an optimal air/fuel (not to rich or lean) would help mpg. I also think lowering the car a bit would help reduce air resistance and in result help mpg too. I would also want to replace the radiator with a del sol version for weight reduction as well. Im considering removing the whole ac system too........but anyways about lowering it, ya think this would help mpg, drop it like 1.5-2.5"

any other ideas???......thanks

itll prolly improve higher-speed downforce without drag increase(less air under the car), but that's about it.

I have a CAI and I think my mpg is pretty decent with it... engine doesn't choke or work hard to suck the air up. I don't have to floor it all the time. The car is ghetto tuned to run the way that suits my driving... no a/c, lightweight pulleys and flywheel, stage 1 clutch, header, full exhaust with a silencer with my trottle adjusted just right... even with the cam, I'm still getting about 35mpg.