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Old 04-15-2012, 04:26 PM   #1 (permalink)
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WOW losing lots of mpg from poor aero.

I swapped a vx motor into my 96 civic hatch. I bought the vx donor car without a title. I liked the idea of 2 airbags, A/C, and the 96 hatch looks cool.

I've been slightly unhappy with highway performance. I can only go about 55-60mph to maintain lean burn with slight grade changes. At 65mph it really doesn't like to to stay in lean burn. I find that I either have to kinda pulse above 70 and then go in lean burn and slowly lose speed over a few miles, or must slow down to just maintain the lean burn. Well not only is that annoying, but I don't like driving 5-15mph slower than the rest of the traffic. I want to be able to maintain 65mph and stay in lean burn.

Today I stumbled upon this calculator
Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
and this list of aero numbers Vehicle Coefficient of Drag List - EcoModder

I had no idea my car had a .762 CDA, the original 92-95 hatch the swap came from is 6.36, a crx is 5.57 and insight is 5.0, prius is 5.83. My hatch is as bad as my fiance's 03 Toyota Camry for CD.

Things to note, a crx is more aerodynamic than a prius, pretty cool. I plugged in the CD and A figures found on the 2nd link into the calculator and kept weight at 2400lbs, and same efficiencies ect. I just wanted to see the difference between the aero.


Well at 60mph the results are:
96 hatch = 38.70mpg
92-95 hatch = 46.56mpg
crx = 50.13mpg
insight = 54.23

I know my car can get about 50mpg at 60mph, so that means I should see a considerable boost if I swapped the vx back into a 92-95 hatch or crx chassis. I know i'm 12mpg over and that won't directly correlate to 62mpg in the crx, but it should be quite a bit more than 50.

Most importantly I want to stay in lean burn at 65mph. Any stock vx owners out there, that don't do pulse and glide and don't have huge aero mods done and can tell me if they have problems staying in lean burn at 65mph?


Last edited by steffen707; 04-15-2012 at 04:32 PM..
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Old 04-15-2012, 04:56 PM   #2 (permalink)
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I got this quote from link 2000-2006 Honda Insight - Top Speed

"At highway speeds, the airflow around a vehicle becomes turbulent. Turbulent air generates considerably more drag than smooth-flowing (laminar) air. In addition, as speed increases, the power required to overcome turbulence-induced drag rises exponentially. To combat the effects of drag, Honda engineers designed the Insight’s body to be highly aerodynamic. Its 0.25 coefficient of drag (Cd) is one of the lowest of any mass-produced automobile in the world. In comparison, the Honda Civic Hatchback, with roughly the same 1.9 square-meter frontal area as the Insight, has a Cd of 0.36, and needs around 32 percent more power to operate at the same speed as the Insight."

Holy cow, 32% more power. I know a crx isn't an insight, but the calculator suggests the insight would be 40.12% higher mpg at 60mph, the crx would have 29.53% more mpg at 60mph.

Roughly 3/4 of the gain in the insight, so maybe 3/4 of 32% is 24% more power needed to keep my 96 civic at 60mph than a crx at 60mph? That's a lot of extra power needed.
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Old 04-15-2012, 08:56 PM   #3 (permalink)
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Quote:
Originally Posted by steffen707 View Post
I swapped a vx motor into my 96 civic hatch. I bought the vx donor car without a title. I liked the idea of 2 airbags, A/C, and the 96 hatch looks cool.

I've been slightly unhappy with highway performance. I can only go about 55-60mph to maintain lean burn with slight grade changes. At 65mph it really doesn't like to to stay in lean burn. I find that I either have to kinda pulse above 70 and then go in lean burn and slowly lose speed over a few miles, or must slow down to just maintain the lean burn. Well not only is that annoying, but I don't like driving 5-15mph slower than the rest of the traffic. I want to be able to maintain 65mph and stay in lean burn.

Today I stumbled upon this calculator
Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
and this list of aero numbers Vehicle Coefficient of Drag List - EcoModder

I had no idea my car had a .762 CDA, the original 92-95 hatch the swap came from is 6.36, a crx is 5.57 and insight is 5.0, prius is 5.83. My hatch is as bad as my fiance's 03 Toyota Camry for CD.

Things to note, a crx is more aerodynamic than a prius, pretty cool. I plugged in the CD and A figures found on the 2nd link into the calculator and kept weight at 2400lbs, and same efficiencies ect. I just wanted to see the difference between the aero.


Well at 60mph the results are:
96 hatch = 38.70mpg
92-95 hatch = 46.56mpg
crx = 50.13mpg
insight = 54.23

I know my car can get about 50mpg at 60mph, so that means I should see a considerable boost if I swapped the vx back into a 92-95 hatch or crx chassis. I know i'm 12mpg over and that won't directly correlate to 62mpg in the crx, but it should be quite a bit more than 50.

Most importantly I want to stay in lean burn at 65mph. Any stock vx owners out there, that don't do pulse and glide and don't have huge aero mods done and can tell me if they have problems staying in lean burn at 65mph?
If your talking 65 mph with a flat road and light wind and summer temps than yes I get leanburn at 65 mph. I don't drive at 70 mph but I would doubt it .Not without a strong tailwind

If your talking 65 mph going up a grade and adding throttle to maintain speed than no leanburn. I get leanburn down till I go below 41 mpg ( 5th gear ) on the instant mpg.

I can tell you that my vx will get 57-58 mpg at a true 60 mph as I have hundreds of miles on a dead flat road with my mpguino. If I see 60 mpg than I have a tailwind and if I see 55 mpg I have a headwind. It really is as simple as that on a flat road . I really wish more people would give speed and wind when they talk highway mpg because as you know it makes a huge difference.
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Old 04-15-2012, 09:05 PM   #4 (permalink)
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Quote:
Originally Posted by turbothrush View Post
If your talking 65 mph with a flat road and light wind and summer temps than yes I get leanburn at 65 mph. I don't drive at 70 mph but I would doubt it .Not without a strong tailwind

If your talking 65 mph going up a grade and adding throttle to maintain speed than no leanburn. I get leanburn down till I go below 41 mpg ( 5th gear ) on the instant mpg.

I can tell you that my vx will get 57-58 mpg at a true 60 mph as I have hundreds of miles on a dead flat road with my mpguino. If I see 60 mpg than I have a tailwind and if I see 55 mpg I have a headwind. It really is as simple as that on a flat road . I really wish more people would give speed and wind when they talk highway mpg because as you know it makes a huge difference.
Yeah i meant with a flat road and light wind. I'm surprised you have lean burn at 41mpg in 5th gear. With my car if i'm losing speed and i keep giving throttle to maintain speed, my mpg will drop to about 48mpg and then if I give any more throttle it will drop out of lean burn and fall to 34-36mpg.
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Old 04-15-2012, 09:51 PM   #5 (permalink)
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A couple points:

I'd be a little cautious about buying a car with no title, especially a Civic since they are so often stolen.

Also, perhaps the laws are different where you live, but in many places it is illegal to replace your engine with an engine from an older car. Your Civic is OBD2 and VX engines are OBD1.
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Old 04-15-2012, 10:15 PM   #6 (permalink)
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Quote:
Originally Posted by Crazy88 View Post
A couple points:

I'd be a little cautious about buying a car with no title, especially a Civic since they are so often stolen.
I wasn't too concerned with the car. It was in poor condition and owned by a potato farmer, hardly the kind of car that is is stolen. If it was a riced out civic with a gsr turbo motor and slammed with a body kit, I might be worried.
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Old 04-16-2012, 06:29 PM   #7 (permalink)
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VX

I believe that at the time the VX came to market,that the National 55 MPH speed limit was still in force.The VX would have been calibrated for this speed for the Federal Test Procedures at EPA Mobile Sources in order to optimize the EPA HWY rating.
By operating the car at 65 mph,your asking it to perform in an environment that it was not optimized for.
You may want to follow basjoo's lead with the aero.You'll get your lean-burn for sure!
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Old 04-16-2012, 07:12 PM   #8 (permalink)
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Don't forget the next gen cars weigh about 10% more as well. That can't help either.

Alignment is of utmost importance as well. Anything increasing effort at cruise will contribute to keeping the car from being in lean burn.
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Old 04-16-2012, 07:20 PM   #9 (permalink)
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Quote:
Originally Posted by hondaguy72 View Post
Don't forget the next gen cars weigh about 10% more as well. That can't help either.

Alignment is of utmost importance as well. Anything increasing effort at cruise will contribute to keeping the car from being in lean burn.
Was the VX like 2080lbs? I suppose you're right. My car with full tank of gas and my 180lbs weighed in at 2480 or 2460 last week. Can't remember which.

So 60lbs for fuel and 180 for me, makes the car 2220-2240. So 6.7% more

I was contemplating taking it in for an alignment. I should read more on what you guys do. I though many cars "stock" had some toe in to give more stability at highway speeds. I have a friend that works at a shop, he would dial it in however I asked him.
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Old 04-16-2012, 07:21 PM   #10 (permalink)
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Quote:
Originally Posted by aerohead View Post
I believe that at the time the VX came to market,that the National 55 MPH speed limit was still in force.The VX would have been calibrated for this speed for the Federal Test Procedures at EPA Mobile Sources in order to optimize the EPA HWY rating.
By operating the car at 65 mph,your asking it to perform in an environment that it was not optimized for.
You may want to follow basjoo's lead with the aero.You'll get your lean-burn for sure!
That would make a lot of sense. I'll have to sift through the garage on the forum and send some private messages to stock vx owners and see if they can provide any lean burn at 65mph info for me.

Of course aerocivic mods would help a ton, but I'm not sure i'm ready for all the laughs.

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