Aerocivic - how to drop your Cd from 0.31 to 0.17

[JimIsbell]

Originally Posted by MetroMPG

Hi rifraf -
2) The lever for the hand throttle is to provide very fine throttle control when cruising. It's a mod that enables a more efficient driving technique.

When you get fuel consumption instrumentation in your car, one of the very first things you notice is the relatively BIG jumps in fuel consumption from incremental changes to the accelerator position. Changes that are literally imperceptible to the butt-o-meter will show up on an instant fuel consumption display.

The hand control permits much finer adjustment of the throttle once up to cruising speed. It may also be more comfortable to use than feathering the throttle by foot for long periods.

I have found an easier way around that problem in my 2000 Insight (65mpg lifetime average). If I wear sticky soled shoes (rubber) I find it difficult to remain in Lean Burn mode and my mileage suffers. If I wear leather soled cowboy boots my mileage greatly improves because the accelerator is operated more smoothly.

[Cd]

From what I have read, a 10% reduction in Cd will result in around 5 % rise in F.E. .

Since the AeroCivic started out as a 5th gen. Civic CX hatch, the Cd would have been .31 stock.

Since the car now has a DX engine in it, the EPA figures for a DX would be 42 MPG highway using the old EPA method.

Since your motor has so many miles on it now, your actually highway mileage might be closer to 40 MPG highway.

Since you decreased your Cd down to ".17 ", you reduced your drag by around 55 % .

If I am understanding the math correctly, that means an 11 MPG improvement from your aero mods.

Is there some formula that I am missing, because it looks as if the car would not be able to do better than 55-60 MPG.

I'm asking because of the statement that you made about getting 95 MPG :

" 95 mpg is what I typically get while driving at a constant speed from 30 to 65 mph on a flat road in 80 degree F temperatures with well broken-in tires "

With the engine running, the gas pedal pressed down, and the car in gear, what is your mileage on a level stretch of road ?

I have a hell of a lot of respect for what you have done to the car, but I'm really confused about how that you can get that car to achieve 95 MPG on a level stretch of road with no hypermiler tricks being used.

Thanks ! You are an inspiration to us all.

[Daox]

Originally Posted by Cd

From what I have read, a 10% reduction in Cd will result in around 5 % rise in F.E. .

That statement alone is very subjective. It a very general statement accounts for a certain amount of time spent at low speeds where aero doesn't have as large of an effect on FE. If you drive lots of highway (as he does), it will have a much larger effect.

[basjoos]

Although the 5th gen Civic 4-door sedan has a Cd of 0.31, the shorter, blunt-tailed 3-door hatch has a higher Cd of 0.36.

Even though my car has a DX engine in it, the transmission is the taller-geared unit used in the VX and CX, so the EPA figures for the DX wouldn't apply. I found that the DX engine (installed when my car was still otherwise stock) has a lot more punch at high rpms than the stock CX motor, but didn't reduce the mileage as long as I minimized my visits into high rpm territory. So the mileage increasing effects of taller gearing trumps the mileage reducing effects of higher power, at least with the Honda motors that need to reved high for max hp.

This past summer, with close to 100,000 additional miles on the motor, with newer and a different brand of tires, and E10 gas, I was getting 85 to 90mpg on a steady speed cruise at 65mph on a level road. This is down from the 90 to 95mpg I used to get on my previous set of tires, straight gasoline, and a less aged motor. I'm not using any hypermiler tricks when driving at a constant speed on a flat road, those are reserved for urban/suburban driving and when driving on hilly roads. I've never gotten any mileage improvement with the pulse and glide technique on flat terrain on the few times I've tried it and as a result don't use it except in city driving or hills with their unavoidable stops or downhills.

Like Daox said, aero effects are most significant at highway speeds. What my aero mods have done is to let me get the same mileage at 65mph that I used to only be able to get at 45mph. I didn't have a SuperMID installed in my pre-aero days, but I'm sure if I had it installed at the time, I would have had no problem getting 95mpg while driving at a constant 40mph on a level road in the summer. I certainly don't have a problem doing that now. What my aero mods have done is allow me to get about the same mileage through a wide speed range from 30mph to 65mph and then rolling off at 70mph and above, as opposed to having the mileage start to roll off above 45 mph back when the car's Cd was stock.

[Cd]

Originally Posted by Daox

That statement alone is very subjective. It a very general statement accounts for a certain amount of time spent at low speeds where aero doesn't have as large of an effect on FE. If you drive lots of highway (as he does), it will have a much larger effect.

Right - at non highway speeds, the F.E. change will be even less. Weight then becomes the main factor to consider, and would finally outweigh any aero benefits.



Perhaps I'm not understanding what you are saying.

[Cd]

Originally Posted by basjoos

Although the 5th gen Civic 4-door sedan has a Cd of 0.31, the shorter, blunt-tailed 3-door hatch has a higher Cd of 0.36.

.

This is a copy .... of a copy, of a copy of a magazine article that I no longer have. If you can make out what it says through the water damage, the sedan is.32, while the hatch is.31 ( and VX slightly lower )

[MetroMPG]

Cd: the main issue is that you can't compare EPA ratings against readings taken at a constant speed. (Even considering the Aerocivic has a drivetrain that the EPA never tested in the first place, as Mike points out.)

The EPA's "highway" fuel economy rating is actually an entire simulated "trip" - from rest, then varying "highway" speeds (up and down, in a range from 30-60 mph), and then to rest again.

Comparing that rating to actual MPG @ some steady speed is apples to oranges.

I'd even say that most cars will significantly exceed their EPA highway ratings where MPG is measured at a steady 60 mph.

[alohaspirit]

yeah, i believe it was the 6th gen hatch that had the .36

[basjoos]

Originally Posted by Cd

This is a copy .... of a copy, of a copy of a magazine article that I no longer have. If you can make out what it says through the water damage, the sedan is.32, while the hatch is.31 ( and VX slightly lower )

My error. That .31 for the sedan and 0.34 for the hatch were some values that I had ran across on a Honda performance site on the web about 5 to 10 years ago and got stuck in my head as the values for the 92-95 Civics. So this thread needs to be relabeled " Aerocivic - how to drop your Cd from 0.31 to 0.17" to be more accurate.

[MetroMPG]

Thread title updated.