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Hello! I own a 1991 Honda CRX HF. Not the lightest HF but still gets good mpgs. Ever since I heard about this car I had wanted one and now I am wishing I would have waited to get an 88(the lightest 2nd gen CRX).

So I bought the car with 192,000 miles on it and it had no intake whatsoever and the exhaust was thoroughly rusted out. First thing I did was to buy a cheap CAI off of ebay and put it on. It is a 3" tube and my Throttle Body is only a 2". Also I needed an exhaust and heard that header produces more power by "scavenging" so I decided to get one. Unfortunately I bought off ebay and most of their stuff is cheap crap. So the muffler did not last which required me to go to an exhaust shop and buy an entirely new muffler(200+ bucks).

So this is my question: Since I was not able to do any MPG tests when i bought the car, did buying a CAI and a Header with magnaflow muffler increase my MPGs or lower them?

Btw on a recent trip south I got 64.1 MPGs. I was trying to hypermile all the time, but I ended up pissing off everybody on I-5.

The header is debatable. The ECU detects warm air temps and can lean the fuel mix out. So no, the CAI typically will not help the mpg. You still got great mileage though. Congrats on that and getting the HF.

Welcome to CleanMPG! The link in my sig will get you pointed to some great reading here.

ohh thank for the welcome!

I am on other forums but they are mostly all crazy about performance. I just like getting crazy mpgs in my CRX.

Like I said I wish i could have done a baseline MPG run but I didn't even have a Intake. I now wish I had not bought the car as it was not in the best of shape. But now I find I cannot part with it.

The 88 CRX HF was actually lighter about 150 lbs lighter and with that i would probably get close to 70 if I really stretched it. But many ricers out ther buy the 88 HF and swap in bigger engine and ruin the car for what it was built for.

People install cold air intakes to achieve a colder, denser air charge, hence more maximum power. But if you're driving carefully, there's no need for more power. A hotter air charge offers numerous efficiency advantages, so my engine breathes hot air off the exhaust manifold.

If you can convert the CAI to a WAI there should be a noticeable improvement in FE.

the stock air intake takes the air right off the top of the exhaust manifold. But all models of 2nd gen CRXs did that, even the Si's. I assume this was the safest spot to avoid water getting into the intake. But I have to think that the reduced resistance going from a stock setup to a smooth tube would have to increase MPGs right?

I will post a pic of a stock engine bay and my engine bay:

MY Intake:
http://i73.photobucket.com/albums/i217/Vg_Ace/Honda/DSCF3386.jpg
don't mind the stupid breather cause I have fixed that by now.

Stock CRX:
http://i73.photobucket.com/albums/i217/Vg_Ace/Head-Gasket-Replacement-on-91-Honda-Civic.jpg

No, lower restriction intakes/filters don't improve MPGs (http://www.metrompg.com/posts/air-filter-part-2.htm).

but they do improve HP and torque, generally speaking of course.

Welcome to CleanMPG!

I had a K&N with an adapter, though not a true CAI, I installed in my 2002 Pontiac transport It wasn't mounted 100% solid as the mounting bracket was from another vehicle, but it was enough for me to run some test tanks. I observed about 1mpg improvement all other things being equal.. route, trips, time of year.

Since that worked fairly well I recently bought a Fram Air Hog replacement filter for my Montana's stock airbox. The Air Hog is Fram's version of K&N washable high capacity filter. Its a K&N type filter manufactured at the same size as my stock airbox filter size. It was $8 on Amazon Auto.

My tests were less scientific than the one in the link in the post above. But since I am planning to drive this thing another 80k - 100K and the filter was $8, it was a no brainer. Across several tanks and months the mileage has not gone back down. My theory is that beyond total maximum volume of air, which is admittedly low when Hypermiling, the velocity of the air can increase more quickly during starts.. I think the term is volumetric efficiency. My montana is heavy for its v6 and starts have always been mpg craters for me. Not sure on my theory but the simple answer is that it did help me.

The CAI won't improve PART THROTTLE FE which is what we are actually measuring.
It can improve full throttle HP and Torque and there is a chance it would improve full throttle FE.

The reason is that any decrease in before the throttle plate intake resistance is simply countered by your foot(or the ECU in modern drive by wire vehicles) shutting the throttle plate a bit and increasing the throttle plate resistance so the total restriction to flow is more or less the same as it was before you put the CAI on. If the total restriction isn't the same, then you will get a bigger charge in-bigger bang more TQ, and you'll end up with MORE RPMS- and a HIGHER SPEED at a given load.
Now if the CAI trickery allowed such a great improvement in intake flow that you could put it in a higher gear to take advantage of the higher torque then maybe you could get a tiny increase in mpg. But in general part throttle FE is generally in the highest gear, or even if it isn't the ECU won't allow a taller gear.If your car is a MT generally you can't shift much sooner(and get fever total revolutions) by virtue of the slight torque increase. In theory you might get a few less revolutions by being able to shift sooner in a MT, but it will be so little, and the CAIs generally are not as well designed as the oem intakes in respect to part throttle low rpm intake tuning that the net result is rarely/never improved FE.
They-the designers- generally maximize these CAIs for high rpm full throttle flow, not lower RPM part throttle flow. The OEMs max them for low rpm part throttle flow and drive-ability.

On the bright side your engine bay looks nice-clean-so just stick with what you have.Careful about reoiling that filter- if it is an oil type-don't over oil when you clean it.

Charlie
PS The headers-slightly different story, but generally aftermarket headers are design for full throttle high rpm flow, not part throttle lower rpm flow drive-ability. It is really tough to beat the OEM engineers in respect to part throttle FE- even with older vehicles like your Honda. The Honda engineers were/are pretty good- better than the aftermarket engineers.

Weight loss, lower RR tires, and driving style modifications generally deliver much more than any engine type mods. Regearing -in some vehicles-works also.Honda generally short gears their MT cars-they run more RPMs than they need in top gear. Your vehicle was a mpg vehicle, so it is probably geared pretty tall for a car-small 4 cyl- of that era-maybe 2500 RPMs at 60 mph? Some ran closer to 2800-rpms at 60 mph.

the stock air intake takes the air right off the top of the exhaust manifold. But all models of 2nd gen CRXs did that, even the Si's. I assume this was the safest spot to avoid water getting into the intake. But I have to think that the reduced resistance going from a stock setup to a smooth tube would have to increase MPGs right?

I will post a pic of a stock engine bay and my engine bay:

MY Intake:
http://i73.photobucket.com/albums/i217/Vg_Ace/Honda/DSCF3386.jpg
don't mind the stupid breather cause I have fixed that by now.

Stock CRX:
http://i73.photobucket.com/albums/i217/Vg_Ace/Head-Gasket-Replacement-on-91-Honda-Civic.jpgGood news! The intake that's been installed on your car is a warm air intake. The stock intake breathed from a pipe right above the radiator, drawing in cold air through the hood gap. The new intake is sitting in relatively warm, ambient engine bay air.

Now if you seal up part of your radiator grille for better aerodynamics and faster warmup, you'll be able to keep the ambient engine bay air even warmer. You should look up some grille blocks that people have done for this purpose.

@ phoebeisis

Actually that RPMs is where the HFs really shine. The HF transmission was geared VERY high. So much so that many tuners actually take that trans, or simply the 5th gear and put it into their cars.

At 60 MPH I am just a hair under 2000 RPMs. I have photos to prove it.

But when you were talking about RPMs let me ask you this. When I put the header on my car I noticed that at the same speed ~60 mph my RPMs were lower than when I had it stock.
The same thing happened with my 2005 Kia Spectra 5. When I bought that car new at 60 MPH the RPMs would be about 3100. Now with a CAI and Header the RPMs at 60 MPH are a hair over 2600 RPMS. Now I talked to some mechanics and they told me this is impossible. They told me that if you are travelling a certain speed the you can calculate how many RPMs you will be based on whichever certain gear you are in.

But I know the RPMs dropped after the mods. What happened?

The only thing that could have changed ratio is tires changed or tire wear. That many rpm would have taken a tire size change. Other than that, an electronic anomaly had to have occurred.

I agree with the mechanics otherwise.

yes but how did it occur on both of my cars from different manufacturers?

Well perhaps it was all in my mind.

@ phoebeisis

Actually that RPMs is where the HFs really shine. The HF transmission was geared VERY high. So much so that many tuners actually take that trans, or simply the 5th gear and put it into their cars.

At 60 MPH I am just a hair under 2000 RPMs. I have photos to prove it.

But when you were talking about RPMs let me ask you this. When I put the header on my car I noticed that at the same speed ~60 mph my RPMs were lower than when I had it stock.
The same thing happened with my 2005 Kia Spectra 5. When I bought that car new at 60 MPH the RPMs would be about 3100. Now with a CAI and Header the RPMs at 60 MPH are a hair over 2600 RPMS. Now I talked to some mechanics and they told me this is impossible. They told me that if you are travelling a certain speed the you can calculate how many RPMs you will be based on whichever certain gear you are in.

But I know the RPMs dropped after the mods. What happened?

If those vehicles have manual transmissions then yes it impossible to do what you are saying. It's a mechanical coupling and can't vary without clutch slip.

However with an automatic it is possible that the converter wasn't locking at 60 but does now.

That is a good suggestion Worthwads. Is there a common mod that you have done on both cars? Electrical, mechanical, or fluids?

It depends on the vehicle if f/e will increase or decrease after those mods. For my car ('05 Toyota Corolla), after I went back to the stock OEM parts, my f/e went up quite a bit.

The K&N filter helped my '97 Escort wagon too.