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ACEL 06-24-2020 03:12 PM

1999 Acura EL or Civic EX sedan - dropping Cd from 0.33 to below 0,20
Welcome to my 21 years car improvement adventure,

I am starting this thread to report on the evolution and advancement of the modifications brought to my 1999 Acura EL. The Acura EL was built with the same engine and basically the same mechanical components as the Honda Civic EX Sedan in North America. The EL was, on the outside, a replica of the Honda Domani in Japan but with a North American power plant. The EL was only marketed in Canada.

I am the first owner of the car purchased in July 1999.

Cd = 0,32 1996-2000 Honda Civic sedan

Cd=0,34 estimated by automobile-catalog

Engine D16Y8 stock, 5 gears manual

Tires: 195-55R15 (wider than the 14 inches tires on most Civic of the time)

Tire pressure : 32 psi all around

Weight with only the driver : 2550 lbs

Mileage Canada Energy - Same as EPA

Highway 7,5 L/100km, City 9,7 L/100 Km, Combined 9,7 L/100 km
Highway 24 mi/US Galon, City 31 mi/US Gal, Combined 27 mi/US gal

Year 2019, Spring to Fall, not used in winter, combined mileage 6,9 L/100 Km

Actual odometer reading in excess of 232 000 Km, 144 000 miles

Even compressions, no oil burn, LRR General Tire RT43, new brakes all around

YEAR 2020 GOAL :
Bring combined mileage down from 6,9 L/100 Km to 5,4 L/100: from 34.1 mpg to 43,6 mpg US or better.

Since 1999, the car went through different phases of modifications.

(Continued on next entry)

Welcome to my 21 years car improvement adventure,


ACEL 06-24-2020 03:48 PM

Continued : 1999 Acura EL or Civic EX sedan - dropping Cd from 0.33 to below 0,20
The car improvements went through 5 phases

1. Finding out the car was actually eco-friendly
2. Searching for means to repeat the best mileage reported
3. Mods inspired by products claims and performance magazines and forums
4. Mods inspired by solid advice : EricTheCarGuy and (J.Edgar)
5. Aerodynamics mods supported by trials and monitoring data

Phase 1. Finding out the car was actually eco-friendly

First, for all my cars since 1977, I have a log book and record every fill and distance on fill. This meticulous logging and mileage computation alerts me to maintenance needed. For this particular car, I believe that only about 20 Litres (5 gal) have not been recorded in almost 21 years of use.

I purchased the car on Acura claims of better mileage than the Civic sedan and IIHS good results for crash tests. I shopped a lot on the web at the time.

During summer 2000, a highway trip of more than 600 km resulted in a 5 L/100 Km mileage (47 mpg). My driving was agressive, speeding at times at more than 150 Km/h (95 mph), using the air conditioning at times. The car was loaded with my second other and our luggage for a whole week. The car was still under warranty and going to the dealer for mandatory inspections. After the next inspection, the mileage dropped and I suspect the dealer mechanic did something to set the car to standard parameters.

Still, when one was enlightened once, one wants to get back in grace! I was driving the car mainly on highways and started searching for means of improving the mileage. It took years to get as good a mileage as that warm day of summer 2000. I entered Phase 2. Searching for means to repeat the best mileage reported



ACEL 06-24-2020 04:03 PM

Continued phase 2: 1999 Acura EL or Civic EX sedan - dropping Cd from 0.33 to below 0,20
Phase 2. Searching mods to get steadily the best mileage ever

Internet and Google are my friends for a long time. I scoured the web for years when I could afford the time with a super busy professional schedule.

First mod was a K&N air box filter, supposed to let more air flow through the engine (probably in 2000 or 2001): little improvement on mileage, less air restriction?

Then, I went from regular 5w30 oil to synthetic oil same grade, sure improvement on mileage and better car performance (since 2002).

Then, hotter spark plugs to promote more complete gas combustion, little improvement on mileage (around 2005 at first and through 2012)

I did not have enough time to myself to search and find solid evidence to support proposed improvements. From 2000 to 2012, the available money was scarce and I rather learned to control the "nut behind the wheel" and got fairly good mileage.

After retiring in 2012, I got into phase 3


ACEL 06-24-2020 04:41 PM

Phase 3: 1999 Acura EL and Civic EX sedan
Phase 3. Mods inspired by products claims and performance magazines and forums

After retiring in the end of 2011, I decided on the pass time of working on this Acura EL aging car. The car had always had a good handling. It was fun for sporty high speed driving. It is even the only car I did not fall asleep in! And it needed love.

I started to read the forums on mods like turbo and cold air intakes and lighter wheels and low rolling tires and whatever could make more power. This "grocery getter" was not peppy enough on hilly roads and that bugged me. Also the car was less silent than in its first years. Noisy is not comfortable.

So, I started with the sound insulation stuff and spent most of 2012 season. The sound proofing allowed to determine the performance summer tires were the main culprit to my ears discomfort. I decided the car was having some rust and having a second car the Acura could rest during the winter.

2013-2014 money scarce in retirement. Still, I procured and installed a short cold air intake instead of the air box and got some mileage improvement. I later discovered in my readings that the short cold air intake is rather a warm air intake allowing less dense air to enter the cylinders. It probably also helped me realize that more power requires both more air and more gas. Thus, pursuing the power development, I was abandoning my old goal of better mileage.

2015 a new complete body repair and paint job, lighter alloy wheels and low rolling tires. Wow, the little Acura is getting peppier! Less weight and low rolling tires and the car accelerates better and mileage improve again.

2016-2017 The winter last almost 6 months in Quebec City Canada. It is a long time to read and decide on maintenance and checks and also decide if the car is worth continuing on improvements.

Also, during the fall of 2016, I went to work on my brother in-law pickup and got back into self confidence that I can maintain and most of the time fix my cars myself. I worked on his clogged plastic engine air intake manifold, a complete engine tune-up, complete rear drum brakes job. I guided myself with Youtube and the likes of Chrisfix, EricTheCarGuy and others.

So, I entered phase 4. Mods inspired by solid advice


ACEL 06-24-2020 04:42 PM

Phase 4: 1999 Acura EL and Civic EX sedan
4. Mods inspired by solid advice : EricTheCarGuy and (J.Edgar)

First 4 wheels brake job in this Acura life (221 341 Km)

Reduce lost power and fuel wasted
Polishing activities are borrowed from the performance phase

- Throttle cable readjusted
- Air conditioner compressor and fan control: switch off under heavy load
- Air conditioner cabin temperature controlled by thermostat
- Fuel injectors checked and cleaned
- Ground cables and fixing points checked for continuity and cleaned
- Original fuel filter replaced (221 341 Km)
- Throttle body cleaned and polished (new gasket)
- Intake manifold mouth and part of runners polished (new gasket)
- Knock sensor replaced (broke when intake manifold removed)
- Intake air control valve replaced (from junk yard)
- Air intake mouth relocated to bottom front grille (highest pressure zone)

- Upper grille blocked, lower grille partly blocked
- Air dam (lawn edging) first part of season
- Homemade front bumper lip and spoiler replacing air dam
- Home made side skirts (house vinyl siding board)
- Rear trunk lid low height spoiler from junkyard Civic 2006
- Splash guards removed on 4 wheels

Unfortunately no partner to perform tuft tests, just observations and mileage logging

Engine withstands lower revs cruising in all gears
Acura gear change recommended RPM is 3000 passing 1st to 5th gear
Now gear change as low as 2200 RPM, cruise as low as 1600 RPM

Car is far more stable in cross wind or being passed by a large vehicle (both ways)

Engine coolant temperature is affected by the upper grille block but is maintained between 87 and 95 Celsius on the highway. I remember from reading Julian Edgar in that engine coolant temperature between 90 and 95 Celsius is optimum for combustion thus for power and mileage.

Measures and data logging
Android phone using “Torque Pro” app to improve driving skills and check on engine operating parameters like coolant temperature, GPS speed, RPM

Mileage from fill logging, highway speed around 100 Km/h – 61 mph, summer driving

Best mileage highway with air dam : 4,48 L/100 Km, 499 Km ride (52 mpg US, 310 miles)

Best mileage with front bumper spoiler 4,74 L/100 Km, 523 km ride (50 mpg, 325 mi)

Season mileage combined: 6,9 L/100 Km, 8240 Km (34,1 mpg US, 5120 miles)

Mileage Canada Energy - Same as EPA

Highway 7,5 L/100km, City 9,7 L/100 Km, Combined 9,7 L/100 km
Highway 24 mi/US Galon, City 31 mi/US Gal, Combined 27 mi/US gal

6,9 L/100 Km combined vs EPA estimate 9,7 L/100 Km, I am winning!

Planned modifications not performed

Replace 195-55R15 tires by 195-65R15 tires:higher, narrower, larger diameter for lower revs at same speed

Catalytic converter and muffler not replaced to accommodate 2.25 inches headers and tail pipe to reduce exhaust restriction - improve gas flow

Continued with phase 5. Aero dynamics improvements

ACEL 06-24-2020 10:02 PM

Phase 5: 1999 Acura EL and Civic EX sedan
5. Aerodynamics mods supported by trials and monitoring data

Finally, I am getting there. Driving behavior and mechanical mods brought some good results. Time to add some improvement in the aerodynamics field.

For starter and since the beginning of 2019, I read a lot of scientific papers on the web. What works. What works better? What is the most recent knowledge about a particular road car aero topic?

I also purchased Julian Edgar, 2018, Modifying the aerodynamics of your road car, SpeedPro Series, Veloce Publishing, England : Step-by-Step instructions to improve the aerodynamics of road cars.

Secondly, modifications monitoring methods and tools

Fuel log: from the first fill of this car in 1999, I log every fuel fill and distance covered to compute mileage and check on car maintenance need.

Digital dashboard: standard car dashboard is so weak on information that I use an ELM 327 Bluetooth OBD2 adapter and Android phone or tablet app TorquePro or RealDash: both apps allow real time engine monitoring and datalogging of parameters, direct from car ECU (Engine Control Unit), like coolant temperature, gps speed, RPM, throttle % opening, intake air temperature, instant and long time mileage and else: mileage can be calibrated. OBD2 adapter cost less than 20 US$, each app pro version costed below 10 US$ (free version of apps log less parameters but are still usefull).

Digital differential manometer to measure air pressures on the car body in various points: allowed to relocate the air intake mouth in the front “dead zone” of higher air pressure: also useful to evaluate the air intake tract components, from mouth to throttle body, to reduce restriction and improve the flow of air to engine.

Tufts test: assistant required for pictures or small movies using a smartphone: observations of tuft movements and positions frame by frame with some movie viewing app or movie editing app better done on larger computer screen. I use an Apple MacBook and Quicktime player to review frame by frame and extract interesting frames with a screen capture for further examination.

Dust test: to better see actual vortex deposited dust areas on car panels and choose correction, e.g. separation edges

“Throttle stop” method to evaluate modifications according to Julian Edgar on Youtube 2020 :

Drag improvement speed difference computation proposed by Julian Edgar on Youtube in 2020:

Fuel tank filled to the brim, every fill in 2020: no two fuel pumps are the same and will stop at the same filling level thus introducing errors in mileage. From this 2020 spring, I fill the fuel tank to the mouth. I stop when I see fuel about to pour out. That way I am sure the difference between fills is minimum and get accurate mileage measurements.

Test facing low or no headwind on flat straight road when possible
. It seems that testing with tail wind and gusts "steals" air from the engine thus results are not as good as when facing low wind speeds. I will have to check on that with the manometer.

Now, modification, testing, measuring, data logging, approving or disproving modification, next modification and loop…

(Continued with some actual results)

ACEL 06-27-2020 01:33 PM

Phase 5: Aerodynamics results: 1999 Acura EL and Civic EX sedan
Aerodynamics modification results

But for the first modification package (following) every mod is evaluated against the “throttle stop” results of the previous modification.

1. Under belly, upper grille block, 45 psi tires, side skirts, 4 wheels deflectors: throttle stop speed increase, 15,2 %, drop in Cd estimated 32,6 %

2. Folded external mirrors: throttle stop speed increase, 2,6 %, drop in Cd estimated 4 %

3. Tires overinflated from 32 PSI to 45 PSI: throttle stop speed increase, greater than 2 %, drop in Cd estimated 2,5%

4. Wheel covers: throttle stop speed increase, greater than 4 %, drop in Cd estimated 8,1 %

5. Vortex generators installed: throttle stop speed increase, 2 %, drop in Cd estimated 2,5%

6. Rear wheels “boat tails”: throttle stop speed increase, 1-2 %, drop in Cd estimated 2,5 %

If computing against the estimated Cd=0.34

Adding all the estimated reductions per modification comes to 52,2 %

May be or may be not a real total reduction, if “may be” then means a new Cd= 0.17

“Strange” result obtained with the first set of modifications (under belly and else), with filling the gas tank to the brim before and after the trip, with rear wind, the highway mileage computes to 2,15 L/100 Km (about 110 US mpg) OMG, Holy something! What went on this 234 km ride? Some of that fuel went to a 20 km country road at 70 km/h speed and I got stopped by a patrol car on the highway for part of the rear underbelly dropping to the pavement: stop on highway means I had to resort to heavy acceleration to merge in traffic and get to cruise speed of about 100 Kph.

The next best mileage result for a 231 Km ride is 4,0 L/100 km or 59 US mpg

On the mechanical front, 0w20 synthetic motor oil is in use for 2020. Tires to higher, narrower less dragging tires have not been replaced. Catalytic converter and muffler have not been replaced yet. Will wait till more discretionary money available or worn out parts. Sigh!

As soon as possible, modifications description will be presented with pictures and cost estimates.



California98Civic 06-27-2020 04:17 PM

Subscribed. There is a lot to digest here but I am impressed. And I have had my 98 Civic since June 2001, so I am only a little behind your 21 years. Love Acuras. I'll be back to see more.

ACEL 06-29-2020 10:26 AM

Acura EL 1999 picture as out of storage in May 2020
2 Attachment(s)
This is a profile view of the car just out of storage before a "dust test". The car is showing the front spoiler that acts as an air dam for the front wheels; unseen is the belly pan, front part from spoiler to wheel shafts and direction links in aluminium, middle part in choroplast, rear part is a 6 degrees diffuser also in chloroplast. The car is also equipped with vertical deflectors in front of the rear wheels and OEM side skirts are extended down by 2 1/2 inches with painted vinyl gutter split in halves (see picture, costed 5 $ at hardware store).

The front spoiler is only 120 mm (about 5 inches) above ground. The middle part of the car is about 150 mm (6 inches) and as flat as possible: the exhaust from headers to rear is not covered. From the rear suspension links, a "diffuser" sweeps up by 6 degrees attached at the front with "zipties" and affixed to the rear plastic bumper cover with self taping screws : no more brake parachute effect from the rear bumper cover! Total height from ground under the rear bumper cover is 30 cm (12 inches). I guess the car "rake" and the "venturi effect" are improved.

ACEL 06-29-2020 10:45 AM

Front upper invisible grille block
2 Attachment(s)
This is my second attempt at an upper grille block as I am working under aesthetical constraint from my 42 years partner: "the car has to look good or you can't do it or you will have to remove the ugly modification".

The bottom spoiler is tolerated on promise that I will remove the fabric tape and finish it shiny when the body filler goes on special.

So, instead of my first work at an external grille block that hid the grille and the Acura crest (picture), I went around and blocked the grille from behind with black choroplast held by some "big monkey" fabric tape (picture).

I suppose the aerodynamics effect of having the grille blocked from the back rather than the front is not that much. I suppose a boundary layer builds up at the surface of the grille features and serves the same purpose as attaching some solid material in front of the grille to block it. So air flows up the grille area "sliding" on the boundary layer.

A mask on the top wide slot under the upper grille where the licence plate should sit adds to the air blockage. Invisible to the left of this blocage is the air intake mouth that collects air for the engine (more on that later).

These grille blockages give pretty much the same results for the engine coolant temperature as the previous in front of the grille blockages. The previous and actual grille blocks cover the same areas. So the coolant temperature on highway gets from 82 to 95 Celsius when outside temperature ranges from 16 to 36 Celsius (180 to 203 F when outside temp from 60 to 97 F). The cooling fan kicks in at 97 Celsius (208 F). Going up a hill or with an heavy load at speeds under 70 km/h makes the coolant temperature go up to turn the fan on. Generally on highway the coolant temperature is maintained between 90 and 95 Celsius (194 to 203 F) which I read somewhere is the ideal temperature window for complete combustion.

As the belly pan works with the grille block to maintain a certain temperature in the engine compartment, the front of belly pan stops about the oil pan and in front of the wheels shafts and direction links. Before the second part of the belly pan, a belly wide opening is left for the air warmed in the engine compartment to exit under the car as it was initially engineered. The outsides of the middle pans are attached up to OEM side skirts with self taping screws and the front and inner sides are attached with zipties wherever there is a solid attachment point allowing.

Coolant temperature data is read from the car computer (ECU) through an OBD2 Bluetooth adapter and the data is logged on an Android phone or tablet. Coolant grade is good for up to 115 Celsius (240 F) and engine oil is synthetic 0W20.

On the aerodynamics side, the grille block was not evaluated separately from the belly pan, the in front of the rear wheels deflectors and the 45 PSI inflated tires. The preliminary combined result of drag reduction for the all these mods is 32,6%. The 45 PSI inflated tires were later compared to the Honda recommended 32 PSI inflated tires to yield a 12% drag reduction with the latter.

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