Honda Insight Tail Extension Project

[Cd]

Jim - your work on it was a real inspiration.
I really appreciate all of the testing information you provided.

What would you estimate the cD was with the tail, based on the data you got from it ?

[3-Wheeler]

Originally Posted by Cd

Jim - your work on it was a real inspiration.
I really appreciate all of the testing information you provided.

What would you estimate the cD was with the tail, based on the data you got from it ?

Hi Cd,

I had to do some digging around for some really old data files. I thought that maybe I had some old coast downs using the GPS to check Cd of the addition of the tail. No dice.

But I did find an A-B test for gas mileage here...

https://ecomodder.com/forum/showthre...tml#post203744

From this you should be able to calculate the effective Cd of the tail.

I estimated that air drag and rolling resistance are equal around 45 mph. The A-B test was done at 56 mph.

Jim.

[Cd]

Jim, I tried to input some of your data into the aero and rolling resistance tool https://ecomodder.com/forum/tool-aer...resistance.php
However, I don't know some of the variables, such as your final weight and such.
When you have a moment, can you input some of the data to get a rough estimate of the final cD ?

BTW, If i understand correctly, a tail like this would only show an increase of 4.3 MPG on a car like mine that got 42 MPG at that same speed you traveled.
( And likely much less, since each cars body shape is different )

I'm a bit confused when you all say you are getting over 80 -90 mpg when traveling at 56 mph.
Stock, your car got around 55 -60 mpg at that speed, correct ?
Is the 80 -90 -100+ mpg using tricks, like coasting, or coasting with the engine turned off ?

[3-Wheeler]

Originally Posted by Cd

Jim, I tried to input some of your data into the aero and rolling resistance tool https://ecomodder.com/forum/tool-aer...resistance.php
However, I don't know some of the variables, such as your final weight and such.
When you have a moment, can you input some of the data to get a rough estimate of the final cD ?

BTW, If i understand correctly, a tail like this would only show an increase of 4.3 MPG on a car like mine that got 42 MPG at that same speed you traveled.
( And likely much less, since each cars body shape is different )

I'm a bit confused when you all say you are getting over 80 -90 mpg when traveling at 56 mph.
Stock, your car got around 55 -60 mpg at that speed, correct ?
Is the 80 -90 -100+ mpg using tricks, like coasting, or coasting with the engine turned off ?

Hi Cd,

********* Topic 1 - MPG **********

I'm going to respond to your question about the Insight's typical mpg first. When Darin had his Insight, he generated the following data.



Notice at 56 mph, he is getting 89 mpg. This is the typical gas consumption at a steady speed with no special "tricks" going on at the time. When we talk about getting over 100 mpg, then typically the "tricks" are involved while driving at the same speed.

********* Topic 2 - Fuel Usage **********

The statement "BTW, If i understand correctly, a tail like this would only show an increase of 4.3 MPG..." can be elaborated.

Your typical MPG is stated as 42 Miles/Gallon. Let's switch units to Gallons/100 Miles.

42 Miles / 1.0 Gal = 1/42 Gal/Mile * 100 = 2.38 Gal/100Mile
The Insight gets typically 90 mpg, or 1.11 Gal/100Mile

So if I build a tail that increases mpg by 10% to 90*1.1 = 99, then consumption is 1.01 Gal/100Mile.

If you build a tail and get 10% better mileage, then your consumption is 42 * 1.1 = 46.2 mpg or 2.16 Gal/100Mile.

Now let's compare our fuel consumptions with tails:

--------MPG Gal/100Mile Change (Gal/100Mile)
Insight-99.0----1.01--------0.10
Cd -----46.2----2.16--------0.22

Notice how your tail helps to reduce gas consumption much better than the same with the Insight.

********* Topic 3 - Insight Cd **********

I looked at the Cd generator and see that there quite a few assumptions about input parameters. It makes me leery of trying to fill out those boxes. However I can say that adding the tail raised the typical body weight of the car by 40 pounds or so. I still had the IMA battery installed.

If you have further questions about filling these boxes please let me know.

Jim.

[aerohead]

For my MY 2000, M-5 transmission Insight, as a non-hybrid, from Denton, TX, to Oklahoma City, OK and back, at a constant 65-mph, with air conditioning ON, the car returned 52-mpg for the roundtrip ( what my 1984 CRX got at 55-mph, without air conditioning ).
The 'green' Insight, is turbocharged, if I remember correctly. Julian could verify that.
At the February 2, 2019 visit, the owner conveyed to me that he had witnessed up to 80-mpg. I do not recall all of the particulars. He was in from out of state, and as happy as I was for the visit, I didn't want to keep him from quality family time.
His plan was to cosmetically restore the tail, and have it color-matched to the 'new' Insight.
Jim's design feature, which allowed for the use of the rear hatch really impressed me, as did all of it.

[JulianEdgar]

Originally Posted by aerohead

The 'green' Insight, is turbocharged, if I remember correctly. Julian could verify that.

Yeah, Sam's car is turbo'd.

[AeroMcAeroFace]

Obviously a turbo allows more fuel into the engine, but does it make any difference to cruise MPG? The IMA presumably doesn't do anything at cruise, or maybe it does boost and while doing so allows the engine to go into lean burn.

Theoretically, ignoring that you have to accelerate, is a turbo insight going to get better or worse MPG at a constant speed cruise?

[JulianEdgar]

Originally Posted by AeroMcAeroFace

Obviously a turbo allows more fuel into the engine, but does it make any difference to cruise MPG? The IMA presumably doesn't do anything at cruise, or maybe it does boost and while doing so allows the engine to go into lean burn.

Theoretically, ignoring that you have to accelerate, is a turbo insight going to get better or worse MPG at a constant speed cruise?

Theoretically, a turbo will always improve mpg at a constant speed because more of the heat energy of the fuel is being utilised ie not so much wasted out of the exhaust. That more than outweighs increased back pressure.

But that's theoretical only. I've had both mpg gains and losses on different cars I have turbo'd.

[aerohead]

Originally Posted by AeroMcAeroFace

Obviously a turbo allows more fuel into the engine, but does it make any difference to cruise MPG? The IMA presumably doesn't do anything at cruise, or maybe it does boost and while doing so allows the engine to go into lean burn.

Theoretically, ignoring that you have to accelerate, is a turbo insight going to get better or worse MPG at a constant speed cruise?

An observation:
1) on the roundtrip to Oklahoma City, without the IMA, I was forced to downshift from 5th, to as low as 3rd gear, on all the rolling terrain, in order not to impede traffic on the interstate.
2) turbo boost would have effectively increased displacement, power and torque, by virtue of the overpressure charge density.
3) it seems quite reasonable that, a turbo would help compensate for the lack of electric boost, lessen the need for downshifts, and end up improving mpg, as current EcoBoost, SkyActive, Dura-whatever, small displacement turbo'd engines are doing. Engineers have vigorously pursued them since 1973. You're basically purchasing something beyond a COSWORTH racing engine of the 1960s, with 100,000 + -mile durability.

[Piotrsko]

Actually Cosworths were reliable. You could get one for a vega and as long as they weren't beaten hard, they held up, according to friends that had one. But that's putting a race horse hitched to a garbage cart.