Actual gas mileage of VX to CRX HF Swaps - Fuelly Forums

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Old 10-16-2008, 02:13 PM   #1
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Actual gas mileage of VX to CRX HF Swaps

In this post, I'm looking for those who've actually performed an actual D15Z1 engine into a CRX HF, while trying to determine both the actual city and hwy mileage that they've been able to achieved. If you've done this, please chime in. I like many others would like to hear about your results.

So far in my most recent post, I've been told that a realistic expectation could average somewhere in the high 40's for city mileage & somewhere over 60mpg consistently for hwy mileage. 60mpg on the hwy is impressive to say the least; but why such a disparity for city mileage? Is anyone able to confirm this? Given that the CRX HF is significantly lighter than the VX, plus having better aerodynamics, I would have presumed that such a swap would lend the city mpg closer to the mid 50's.

Thank You.
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Old 10-16-2008, 07:15 PM   #2
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First, I have a 90 HF, but have not done the swap so I cannot directly answer your questions from experience, but the main reason the VX's get better hwy mileage is you can keep the car in lean burn, which is more difficult in city driving. As far as what kind of numbers you get I think is more up to your driving. If you go through the garage, you'll see some VX's averaging ~45mpg and others in the mid 50s or higher. While there may be some aero mods on these cars, I'm guessing the biggest difference is in how they are driven.

I'm getting ~43mpg in my HF, which compared to other HFs on this site is pretty low and I'm sure most of that has to do with my driving. I average 75mph on the fwy and do not baby the car in city driving and other then letting it coast downhill, do not do any hypermiling techniques. I'm guessing that if I did a VX upgrade and didn't change the way I drive I probably would not see much of a difference in mpg. I think it would be naive to believe that just the engine swap would miraculously get me in the 50mpg range. It could even get worse if I started using the extra 25 or 30 hp the VX engine has.
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Old 10-17-2008, 12:41 PM   #3
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CRX HF to VX comparison

Quote:
Originally Posted by Davo53209 View Post
In this post, I'm looking for those who've actually performed an actual D15Z1 engine into a CRX HF, while trying to determine both the actual city and hwy mileage that they've been able to achieved. If you've done this, please chime in. I like many others would like to hear about your results.

So far in my most recent post, I've been told that a realistic expectation could average somewhere in the high 40's for city mileage & somewhere over 60mpg consistently for hwy mileage. 60mpg on the hwy is impressive to say the least; but why such a disparity for city mileage? Is anyone able to confirm this? Given that the CRX HF is significantly lighter than the VX, plus having better aerodynamics, I would have presumed that such a swap would lend the city mpg closer to the mid 50's.

Thank You.
Hi,

It is not possible for me to say what pure city driving is on my CRX VX because I have never done city driving alone nor have I ever recorded pure highway driving. All records on the CRX VX have been taken with an addition of 33% of the vehicle's weight added during the road tests. My gas log explains. I installed a 12 gallon CRX SI fuel tank that replaces the 10 gallon tank. On one tank of gas, under those conditions, I can drive in excess of 740 miles. This is why it is unrealistic for me to drive that many miles in city driving. I know that many people would say that you can fill up after driving only 50 or 100 miles but I have found large discrepencies in calculation under short driving conditions due to gas pump variations. And, at the mileage my car gets that is only three quarters of a gallon of gas to about a gallon and a half. That leaves large room for error. With the use of the A00 ECU I have never gotten below 55 miles per gallon under any condition. That includes racing other cars.
In the future I do plan on making a pure hypermiling trip to see how well I can max out with this vehicle. The reason there aren't any recent posts to my mileage log is because I am in the middle of aero mods so it is not driveable at this time. It has taken a long time because customer cars take precedence over my car.

I've been lax on the CRX VX because I also picked up a 1986 CRX HF and had to refurbish it first. It was in really rough shape. It even required rebuilding of the circuit boards that control some of the fuel management functions. It is a federal version HF and has both a wide-band five wire LAF sensor and a lean-burn feature even though it is carbureted. I know this sounds strange because it sure did to me. But, it is real, and I have an all-around-average MPG of 55. The lowest I've ever seen is 49 (local driving, many cold starts) and this one I did take on an all-out hypermiling trip--250 miles long--and received an awsome 68 mpg. This was with two adults on board. I have experienced in excess of 60 miles per gallon many times with this vehicle. Many of you might wonder why do the VX swap when you can get mileage like this out of a stock CRX HF. The answer is: The VX allows you to have your cake and eat it, too. In other words, with the VX you don't have to suffer the gutless woes of high mileage vehicles. It not only gives you superior over-all average mileage, but it climbs hills and accelerates effortlessly. Additionally there is not large descrepency in mileage due to cold conditions and short distance driving, as there is with a carbureted engine.

A couple of points I would like to make, because I've heard questions in the past regarding these areas: The VX does go into lean-burn in every forward gear. I know this because just by pure accident the installation of an external fuel pump in my CRX VX fuel system notifies me (with a sqwall) when the fuel pump meets the extra resistance of lean-burn conditions. This is evident even when I drive through town in the low load conditions and the D15Z1 engine leans out. The factory Honda service manual also states that the minimum speed requirement is three mph. The other thing I hear a lot is that the D15Z1 is weak on acceleration. I agree with this if you are comparing a Civic SI and a Civic VX in a drag race. But if you are installing a D15Z1 into a 1985 CRX HF, you are installing a 58% higher horsepower rated engine into a 400 lb lighter vehicle than a VX. That's a vehicle with an impressive 19 lbs per horsepower. Many of today's vehicles have much worse ratios and don't get anywhere near the mileage or performance.

My opinion is that the large variation in the advertised city to highway MPG was originally written on the window sticker to cover those individuals that like to accelerate from stop light to stop light in the manner of many teenagers (and some old folks, too).

In researching the CRXs and VXs I found that Honda had many variations of the seemingly "same" vehicle. That leaves a large range of personal experience by all of the different people driving in all of the different regions of this planet. For example: There are Japanese VXs, California early '92 VXs, California late '92 and '93 VXs, California '94 VXs, Federal A00 VXs, Federal A02 VXs, and even more variations on the first gen CRXs and even additional variations on the 2nd gen CRXs, some of which are alterations in chassis design to meet safety regulations that increased the weight of the vehicle. I hope this helps answer some of your questions.
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Old 10-19-2008, 02:44 AM   #4
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The other thing I hear a lot is that the D15Z1 is weak on acceleration. I agree with this if you are comparing a Civic SI and a Civic VX in a drag race. But if you are installing a D15Z1 into a 1985 CRX HF, you are installing a 58% higher horsepower rated engine into a 400 lb lighter vehicle than a VX. That's a vehicle with an impressive 19 lbs per horsepower. Many of today's vehicles have much worse ratios and don't get anywhere near the mileage or performance.
I agree with you about the power to weight ratio, but not the acceleration. 92HP, 97ft-lb torque in a car that weighs less than 2000lbs actually makes for a better power to weight ratio than can be found in your typical base four cylinder cars today. BUT, there is more to acceleration than power to weight ratio. In the case of the D15Z1, the transmission gets in the way of any kind of decent acceleration. The problem is that, in order to get the tall fifth gear for economical freeway cruising, you have to get the HF transmission. And this leaves you with pretty much the WORST gears 1-4 that you can imagine. Rather than having a decently short first, second, and third with a wider gap between 3-4 and 4-5, the HF transmission gives you a REALLY tall first gear and a second gear that is TWICE as tall. By the time you reach third, you are about as tall as fifth in an SI. And at fourth, you are as tall as fifth in a DX. So all the REALLY big gaps between gears are where you least want them - in the lower gears, which you use while trying to accelerate in the city. It all just makes me wonder what Honda was thinking when they designed this transmission.
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Old 10-19-2008, 08:48 AM   #5
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I agree with you about the power to weight ratio, but not the acceleration. 92HP, 97ft-lb torque in a car that weighs less than 2000lbs actually makes for a better power to weight ratio than can be found in your typical base four cylinder cars today. BUT, there is more to acceleration than power to weight ratio. In the case of the D15Z1, the transmission gets in the way of any kind of decent acceleration. The problem is that, in order to get the tall fifth gear for economical freeway cruising, you have to get the HF transmission. And this leaves you with pretty much the WORST gears 1-4 that you can imagine. Rather than having a decently short first, second, and third with a wider gap between 3-4 and 4-5, the HF transmission gives you a REALLY tall first gear and a second gear that is TWICE as tall. By the time you reach third, you are about as tall as fifth in an SI. And at fourth, you are as tall as fifth in a DX. So all the REALLY big gaps between gears are where you least want them - in the lower gears, which you use while trying to accelerate in the city. It all just makes me wonder what Honda was thinking when they designed this transmission.
Your premise regarding the gearing in the HF is correct; however, though it will bolt up to the D15Z1 it is problematic to use it in the swap because to go into lean-burn you need VSS (vehicle speed sensor) connectivity. That can be attained by using a CX or any of the third gen Civic transmissions. I used the CX. I know there are others working on coupling the HF to the D15Z1 through the VSS in the instrument cluster, but I haven't heard of anybody with a perfectly running swap that has gone that route. If anyone has one of these VX engine to HF tranny swaps working problem free please let us know about it. I'm not asking for hear-say, just info from the individual who has the working vehicle, and how they accomplished the VSS interface with the HF tranny. My first post is just for those who don't have a chance to know and want to know how completely pleasurable the CRX VX is to drive. In my opinion there should be more to high mileage vehicles than just high mileage alone, especially at the expense of driveablility. A point of gear ratio and racing I'd like to make: I have won many a race while driving down the street because the guy next to me could downshift only one gear and I could downshift two because of my taller gearing thereby giving me the advantage. Not all acceleration contests start from a dead stop.
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Old 10-19-2008, 10:25 AM   #6
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Originally Posted by soletek View Post
Your premise regarding the gearing in the HF is correct; however, though it will bolt up to the D15Z1 it is problematic to use it in the swap because to go into lean-burn you need VSS (vehicle speed sensor) connectivity. That can be attained by using a CX or any of the third gen Civic transmissions. I used the CX. I know there are others working on coupling the HF to the D15Z1 through the VSS in the instrument cluster, but I haven't heard of anybody with a perfectly running swap that has gone that route. If anyone has one of these VX engine to HF tranny swaps working problem free please let us know about it. I'm not asking for hear-say, just info from the individual who has the working vehicle, and how they accomplished the VSS interface with the HF tranny.
I have successfully done that swap, I just ran the wire from the vss in the cluster that normally went to the B16 pin on the obd0 ecu to the B10 pin on the P07 ecu and it works perfectly. The ecu doesn't care where it gets a vss signal from, the transmission or the speedometer, as long as it gets one. Your post is actually the first time I've ever heard there was a problem with doing this. I've got over 10k on my swap and lean burn works great. This is in a 90 hatch, you may run into problems with earlier crxs that may not have a vss at all. I have no idea when Honda started using them.
As for the gearing, I agree that 1st could be (a lot) lower, but otherwise the gearing is fine, you can always downshift and run the rpms up if you need to accelerate faster.
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Old 10-19-2008, 01:36 PM   #7
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Thanks for the info. nowhhs. I did the swap with a 1985 CRX HF California version which does create the need for extra effort, carbureted and all.

Is your transmission final drive ratio Federal 2.95 or California 3.25? What is the horsepower rating on the D15B VTEC-E, is it the same as the D15Z1?
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Old 10-19-2008, 02:47 PM   #8
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Its the 2.95, which is probably the reason for my tall first gear. On the other hand, I wouldn't want a lower 5th, so I won't change it out. I'm turning about 2200 at 70mph and have more than enough torque to be comfortable there.

As far as I know, based on the research I did before doing the swap, the horsepower is the same as the Z1. On the other hand, there are some minor differences, I think the intake is slightly different for example, but the internals are the same. I'm sure its close.
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Old 10-19-2008, 05:30 PM   #9
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Quote:
Originally Posted by nowhhs View Post
I have successfully done that swap, I just ran the wire from the vss in the cluster that normally went to the B16 pin on the obd0 ecu to the B10 pin on the P07 ecu and it works perfectly. The ecu doesn't care where it gets a vss signal from, the transmission or the speedometer, as long as it gets one. Your post is actually the first time I've ever heard there was a problem with doing this. I've got over 10k on my swap and lean burn works great. This is in a 90 hatch, you may run into problems with earlier crxs that may not have a vss at all. I have no idea when Honda started using them.
As for the gearing, I agree that 1st could be (a lot) lower, but otherwise the gearing is fine, you can always downshift and run the rpms up if you need to accelerate faster.
Excellent, this is just the kind of dialogue that I was hoping to get. So what kind of gas mileage would you say that you've been averaging in both city and freeway driving?
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Old 10-20-2008, 12:11 AM   #10
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Originally Posted by soletek View Post
Your premise regarding the gearing in the HF is correct; however, though it will bolt up to the D15Z1 it is problematic to use it in the swap because to go into lean-burn you need VSS (vehicle speed sensor) connectivity. That can be attained by using a CX or any of the third gen Civic transmissions. I used the CX. I know there are others working on coupling the HF to the D15Z1 through the VSS in the instrument cluster, but I haven't heard of anybody with a perfectly running swap that has gone that route. If anyone has one of these VX engine to HF tranny swaps working problem free please let us know about it. I'm not asking for hear-say, just info from the individual who has the working vehicle, and how they accomplished the VSS interface with the HF tranny. My first post is just for those who don't have a chance to know and want to know how completely pleasurable the CRX VX is to drive. In my opinion there should be more to high mileage vehicles than just high mileage alone, especially at the expense of driveablility. A point of gear ratio and racing I'd like to make: I have won many a race while driving down the street because the guy next to me could downshift only one gear and I could downshift two because of my taller gearing thereby giving me the advantage. Not all acceleration contests start from a dead stop.
Although I have not yet completed my D15Z1 swap, I have done MANY swaps of more performance-oriented motors in the past. And I have never, I repeat NEVER had a problem using the electromechanical VSS in the stock 1988-1991 instrument panel. No check engine lights. And no failure of VTEC to switch over. I just don't see how things could be any different with a D15Z1 vs a B18C in this regard. After all, both the electronic VSS of 1992-1995 vehicles and the electromechanical VSS of 1988-1991 vehicles produce the same four pulses per revolution. In other words, it is not necessary to deal with the trouble and expense of using an electronic VSS in a 1988-1991 car.

As for the transmission, one thing I have considered is using an HF transmission with second, third, and fourth gears from a DX transmission. This, of course, would not deal with the horrid, clutch-burning first gear of the HF transmission (since ALL D-series transmissions use a first gear ratio of 3.25:1). But it WOULD help the 1-2 shift by bringing second gear from a way to wide ratio of 1.650:1 to 1.894:1. This would eliminate that nasty bog you get when shifting to second, and having RPMs drop by a half. And by bringing third from 1.033:1 to 1.259:1, and fourth from .823:1 to .937:1, the transmission would be MUCH easier to live with. Yes, there would be a large gap between fourth and fifth. But because this shift would be made after you are already traveling at high speed and done accelerating, it would not be a problem.
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