Choosing EPA Ratings for Highly Modified Automobiles

[SVOboy]

Anyway, this idea has come up before. What EPA should we compare against when we modify our cars? I'll state two situations, what I think should be done, and why, and we can have a vote with reasoned responses as to our votes, and if we can come to consensus, we'll institute a policy. Good stuff, right?

#1:

I modify my CRX DX Auto by converting to MFPI and a manual HF transmission. FE soars 11MPG to ~50MPG. Should I have really awesome X over EPA by comparing to what my car began as, have medium response as I make some hybrid DX/HF EPA rating, or get my % over (under) trashed by picking the closest set-up? I feel that I should be able to keep my original EPA ratings because I worked hard to take what I had and make something more of it, and that should be shown in some way. If I made a hybrid it would more closely resemble driving ability, and if I just picked the HF (which is what I did) it would make some sense but ultimately not work out very well in any sense. I liken my transmission swap to basjoos's aerodynamic modifications; do we force him to change his EPA because he car is fundamentally different that the CX it began life as? The answer is no, he earned that % over EPA by making his car into a caulked up, aerodynamical machine.

#2:

Jared puts a D16Z6 into his CX. Same possiblities as with my case. I forget what he chose as EPA, but what should we do with him? I say he uses the CX EPA figures, because much like people who drive their CX very hard and get lower than EPA mileage he chose to use a more powerful engine and more shortly geared tranmission in order to achieve greater acceleration. Why punish the fast driver or the driver with some aerodynamics killing body kit and not the person who thoughtfully chose to lower their FE in search for acceleration?

I assume you know how I feel about the situation. If I can work to put a new transmission in and benefit from it in terms of FE I should also benefit from it in terms of bettering what I began with, which shows as % over EPA. Just like adding an undertray or engine block heater, a transmission or engine should be no different. We do not adjust for route, temperature, or any other factors.

The main conflict I find here is the concern over people who switch cars to better FE. This is ultimately the greatest sacrafice, and should be treated so. That's why people like Dan and Compaq still post their retired cars' statistics in order to show that they are progressing, which I think is rather fair.

Please give me your thoughts.

[Matt Timion]

It may end up being an individual decision, but my feeling is as follows:

The car I purchased was a 1989 Civic LX. So far I have put lightweight wheels on it, a d15z1 (civic VX) engine, and a CRX HF transmission. There is no car that even closely resembles my car. The Civic VX (from which the engine and wheels came) is a hatchback and is much lighter than my car. The CRX HF (From which my transmission came) is not only lighter but much smaller than my car.

I have a four door sedan.

We are creating frankenstein vehicles. Some of us add engines, transmissions, wheels, undertrays, or even caulk. Some of us change driving habits, or even remove our seats to have a lighter weight vehicle.

In the end the best measure of our improvement is to compare against the original EPA estimates. A modification is a modification. The only way to really measure progress is to see what the starting point was, so I vote for that.

[tomauto]

The people who try to earn that extra mpg here should be rewarded with their improved figures. After all, some of the mods here were not easy. Even though the car has changed it should still have its factory EPA numbers.

[ketel0ne]

I may be missing the point, it is 3:45am here, but isn't this gassavers.org. It isn't about adding acceleration or being the fastest.

MetroMPG could decide tomorrow he wants a turbo Suzuki Swift GT engine and setup, his mpg would reflect that, and negatively, I might add.

[Compaq888]

I think it should be the stock EPA numbers that the car came with.

[Matt Timion]

Originally Posted by ketel0ne

I may be missing the point, it is 3:45am here, but isn't this gassavers.org. It isn't about adding acceleration or being the fastest.

MetroMPG could decide tomorrow he wants a turbo Suzuki Swift GT engine and setup, his mpg would reflect that, and negatively, I might add.

I think you're missing the point of the question.

Let me rephrase it.

You start with a bone stock 1991 CRX DX Automatic (like SVOBoy did).

You change the transmission to a CRX HF transmission, making it a manual transmission. You also swap in a new engine, which forces you to switch to obd1 (previously you were pre-obd).

SVOBoy's question is this: When entering your EPA numbers into the garage (www.gassavers.org/garage) for your vehicle, should you use your original EPA estimates (what you started out with) or should you somehow construct a new EPA estimate derived from the cars you took the parts from.

In SVOBoy's case he started with a 1991 CRX DX Automatic. He put in a CRX HF transmission, which gave him around a 11mpg improvement. In his garage should his EPA value (city/highway/combined) be that for a CRX DX Automatic, or a CRX HF, since mechanically his vehicle now resembles a CRX HF more than a CRX DX Automatic.

Hope this makes sense, it's also late here

[krousdb]

What about this situation?

I started with a Del Sol DX. I modified my body style from a 2 door targa to a three door hatch which changed the Cd from 0.38 to 0.31 and reduced weight by 100 lbs. I added a rear seat. I swapped the D15B7 for a D15Z1. I swapped the DX tranny 4.06 FD to a ZX tranny, 3.25 FD. I also applied rust to my rear wheel wells along with various dents and dings but retained the original color. My Del Sol DX is now a HB VX and my cost was negative $1500. So what do I use? 34/36/38 or 48/51/55? I chose to use the EPV figures for the car that mine most closely resembles. As a result, I have increased my FE but decreased my % over from 84% to only 36%. Quite a severe penalty for seeking to improve one's FE.

I understand the arguements, and that modding your car for better FE should be rewarded. But what about those who make what Matt referred to as the ultimate sacrifice and switch cars?

Modding the vX will have much less dramatic effect than the Del Sol because the Honda engineers have already added the mods as stock features which are already reflected in the EPA numbers. For example, the VX already has the grille blocked off and already has a partial undertray and a rear diffuser. It already has a 192F thermostat and it warms up super quick so an EBH would have little effect. It came with lightweight wheels and skinny tires so what I have today will make a much smaller difference. The car has nothing left to do for weight or drag reduction except for a full bellypan and removing the drivers side mirror.

So we have quite a dilemma here..... One sticky issue being that some cars' EPA figures include very little in terms of FE mods while other cars' EPA figures include factory installed FE mods, what I have referred to as built in FE. The playing field isn't level to begin with so why should we expect to end up with something level?

Anything, I chose the worst case scenario for me which is the 48/51/55. As such, I went from #1 on %over EPA to not even in the top 10.

Whatever everyone decides is OK by me.

[MetroMPG]

Originally Posted by krousdb

The car has nothing left to do for weight or drag reduction except for a full bellypan and removing the drivers side mirror.

Ahem.... rear wheel skirts, smooth wheel covers, tire deflectors, front wheel arch gap fillers, partial boat tail... ahem....

[krousdb]

Originally Posted by MetroMPG

Ahem.... rear wheel skirts, smooth wheel covers, tire deflectors, front wheel arch gap fillers, partial boat tail... ahem....

My average speed is 35 MPH. How much do you think that stuff would get me? Certainly not 80-100 like you.

The point of a partial boat tail is lost on me, at least on the hatchback. There is already a tail / spoiler on the back which I assume is there to promote separation of the flow.

[MetroMPG]

Originally Posted by krousdb

My average speed is 35 MPH. How much do you think that stuff would get me? Certainly not 80-100 like you.

True. But I just figured if you see the utility of doing a belly pan, then it just seems logical to do other aero things as well.

The point of a partial boat tail is lost on me, at least on the hatchback. There is already a tail / spoiler on the back which I assume is there to promote separation of the flow.

The roof extension is good for getting clean separation, true. But a boat-tail would taper the car's shape even further than stock, so where it ends, the trailing wake would be that much smaller. Kamm figured: assuming laminar flow and the proper tapered shape, the optimum area at the very rear of the vehicle should be 50% of the vehicle's maximum projected area.

I'd be surprised if you didn't net at least a couple of percent FE improvement just with skirts, smooth wheel covers & carefully applied wheel/tire deflectors.