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Owner: California98Civic
Black and Green: 1998 Honda Civic DX Coupe
Displacement: 1.59 L
Fuel type: gasoline
Transmission: manual
Curb weight: 2262 lbs
Coefficient of drag: 0.32
Frontal area: 21.4 sq.ft.
Instrumentation: UltraGauge
Description: This car is a daily driver--a commuter and a long-distance runner. I have three goals: average 55+ mpg @ posted speed limits, make the car cheap to own by doing all repairs and maintenance myself, and save on costs associated with a newer car, such as value depreciation, car-loan interest, higher registration fees, & higher theft/damage insurance.

OEM data sheets:
Transmission swap: 1993 Civic CX (see below for details of the mod) with 93K miles on it (March 2013).
Odometer calibration: On my current 15" rims & 175/70 tires, GPS shows a 9% undercount on the OEM odometer. I used to see a 2.9% undercount (consistently) with 13" VX wheels & Michelin Defenders (175/70), which turned 917/mile (
Speedometer calibration: With the 13" tires I had a I also see a moderate speed over count. But with the 15" tires I am seeing a significant speed undercount of something like 7%. The 1996-1998 Honda Service Manual says the speedometer reads 60mph when the Vehicle Speed Sensor (VSS) turns 1,025rpms and the 1992-1995 manual says 60 mph at 1026 rpms of the VSS. The speedometer gears in the 1998 and 1993 transmissions both measure 90.6mm using vernier calipers. So the differences in speed and distance calculations are due to wheel/tire size combinations and the imprecision of the VSS/Speedo from the factory.(cite)
Drag figures as modified: Cd ~0.28 (an 0.04 reduction estimated using this Hot Rod Magazine article). Frontal area estimate 21.0 because of narrower, smaller tires and mirror delete (OEM was 21.4). And CdA estimate 6.00 (OEM 6.85).
Engine type: D16Y7 (106hp/103tq)
1998 OEM 14" tire: Firestone FR680, 185/65SR14 (23.5" diam. & 886 revs/mi.)
ECU: OBD2, Code P2E-L32
OEM Color: Flamenco Black Pearl (Code NH-592P).
Manufacture date & place: Tuesday, 1/13/1998 at the East Liberty, Ohio factory.
Current odometer reading: passed 250,000 on 6/2/2017 (passed 200,000 on 10/28/2012).


Subtracting the costs of ecomodding from my total savings by modding and hypermiling, I saved about $3323 from 2/2011 through 5/2017). However, keeping the car is also an "ecomod" that saves plastics, metals, and money. Additionally, I avoid a few hundred bucks a month in loan payments, approximately $500-$700/year in costlier insurance, and thousands per year in depreciation on the value of a new vehicle or even a five-year-old used vehicle. Ecomodding is also how and why I began learning DIY auto repair. I do all the servicing and repairs for this car, saving on professional mechanics' labor charges. A car does not get much cheaper to own while pulling 60+ MPG.
Build Thread: Black & Green modding thread (1998 Civic DX Coupe base)
Current Mods: HYPERMILING (adjusting the driver nut is the single most effective "mod"):

I usually use EOC and P&G on surface roads, and a mix of these and on the freeways. I also adjust routes, trips, and departure times for MPG as much as my commuter schedule allows.

AERODYNAMIC (most effective first):

Rear diffuser
2.5" lawnedging airdam
Side skirts v2.0 (cut rain gutter, flat black paint)
Full upper grill block (v2.0) & 80% lower block (v1.2).
175mm wide tires all around (stock was 185).
Passenger mirror replaced with internal convex. Wheels skirts version 3.0
(see version 2 & version 1).
Mudflap delete.
Passenger-side wiper delete (and RainX application).
OEM antenna moved behind windshield, which is painted black at the top with plasti-dip
Thrush Turbo muffler (smaller than OEM, better for planned belly pan's rear diffuser).

MECHANICAL/ELECTRICAL (most effective first):

1993 Civic CX transmission with 93,000 miles on it (installed when odo read 203,000 miles). In fifth gear it provides a 20% rpm reduction over my stock DX coupe gearing, and about a 25% reduction in rpms in 4th gear. Compare ratios here. And here is how I dealt with one PITA part of the swap.

An injector kill switch
Tires inflated to 60psi.

An "Externally Powered Electrical System" (I plug the car in when I'm home). The set-up combines an alternator on/off switch, 10 LED bulbs, and a H4/HB2/9003 HID kit for the headlights, a deep-cycle Odyssey PC1200 battery with metal jacket & XSP-586 SAE post adapters, and a 25-amp on-board battery charger. For notes on why the 25 amp charger is important see this post.

A Warm Air Intake (WAI).

Alignment set to "zero toe"

Advanced ignition timing to 14 degrees BTDC (currently back to the stock 12*).
15" 2007 MINI 7-hole rims (12LBS)
NGK single-platinum spark plugs.
Radiator/grill ducting (v.1.2).
Fully synthetic Mobil 1 "Fuel Economy" 0W-30 (5w-30 currently).

WEIGHT REDUCTION (probably most effective in city/P&G driving):

251lbs removed (to approx 2011lbs* curb weight):
9.7lbs VX wheels (replaced 18lbs alloys), 9lb thrush muffler (replacing 18lb OEM), AC, rear seats, power steering, and numerous other things small and large.

* = Includes 33lbs for front passenger seat delete (often reinstalled).

ECOLOGICAL FOOTPRINT: Some hypermiling techniques might raise certain emissions when engine is running. But radically cutting overall fuel consumption reduces the average emissions per mile. Cutting fuel consumption in half also halves my contribution to demand for fuel, which produces pollution in production and very high emissions in distribution via super tankers (3, 4, 5).


EM project library link.

Sites for parts, besides my local Autozone and O'Reilly: a, b, c, d, e, f, g, and h.

Tires & wheels (besides ebay & Craig's List): a and b. Grassroots Engine Management.

Calculators: standard deviation, Ohms Law, & drag HP losses


Lighter rear brake drums from 1st Gen Insight (if replacement needed one day): Insight drums weigh about 4.6 lbs ea and the Civic OEM drums are a little over 6lbs *


Would consider a Boomslang harness (BF08003 for the 1996-1998 Civic) and an APEXI SAFC2 in order to produce my own version of "lean burn," but it would require converting to a wide-band O2 sensor and an EGT sensor. That would not be easily reversible for California emissions tests.

Lighter flywheel (perhaps from a VX or HX) when the clutch finally fails. The stock DX flywheel is about 20lbs and the stock VX is about just under 16lbs. A Ralco RZ Aluminum Flywheel is only 7lbs. (interesting PDF article on possible benefit)

Lightweight stock sized, standard belt layout crank pulley (Unorthodox Racing Part #0220610612) or a single belt conversion, possibly experimenting with Unorthodox Racing Ultra R underdrive crank pulley (part #030610502). An undampened aftermarket crank pulley seems unlikely to harm an inline 4 engine.

Possible wheel swaps:
13" CRX HF OEM (higher RPM & just under 13lbs)*
13" Civic VX 8 spoke (higher RPMs but only 9.7 lbs.)
14" Civic HX 8 spoke (approx 11.75 lbs)
14" first generation Honda Insight (11lbs)*
14" Civic Hybrid 2003-2005 (approx 14 lbs)
14" x 4.5", 4x100, 46 Offset, 56.1 center bore (2014 Mitsu Mirage)
15" Mini Cooper R81 Imola 7-hole (12.1 lbs)
15" Mini Cooper R86 star-spoke (15 lbs)
15" Mini Cooper R96 7-spoke (13.8 lbs)
15" Enkei Classic J-speed (14.1 lbs)
15" Enkei RP-F1 (9.5 lb)*
15" Kosei K4R (10.7 lb)*
15" Konig Helium (11.2 lb) 40mm offset, hub bore 73.1mm*
15" Acura Integra GSR (94-95, 16lbs)
Other size specs to double-check for any possible swap: Offset 35-45; bolt pattern 4X100; lug size 12mmX1.5; hub center bore 56.1mm minimum (larger needs spacer rings). For more info see 1, 2, and 3 (for general wheel size data across models). More weight info here.

OEM Light bulbs for possible LED swaps:
Headlight: 9003 (done with HID)
Parking Light: 3496
Front Turn Signal: 3496
Rear Turn Signal: 7440
Tail Light: 7443 (done LED)
Break Light: 7443 (done LED)
High Mount break light: 7440 (done LED)
License: 168 (done LED)
Back Up light: 7440 (done LED)
dome Light: 168 5w (done LED)
Gauge lights: 194 3.4w
Indicator lights: 74 1.4w

Brake drag reduction mod: drums and discs.


Rear wheel skirts (brackets)
Lower forward stagnation point with expanding foam
Rear box cavity or flat rear trunk lid spoiler


Head gasket (done 5/2018)

Acid-washed Catalytic Converter with citric acid. Also see this thread (DONE August 2016, July 2018).

Bleed brakes and inspect pistons because possible brake dragging (done 1/2017).

Front main seal replace (done summer 2016).

Timing belt (done 8/2015)

Add grounding wire (done summer 2015).

Drive axles replace (done 5/2013)

Driver window whistle (fixed May 2017).

Replace hood release (done 2016 & redone May 2017)

Cabin fan intermittent failure (replaced motor 3/2018)

Driver exterior door handle (replaced 3/2018)

Driver window crank shaft (repaired 3/2018)

Fix rapid/slow directional signal problem (done 3/2018)

Suspension bushings replace.

Rebuild DX trans using VX final drive gear and a rebuild kit from Synchrotech or another company.

For fun: maybe a seat replacement someday. Maybe also repaint the car someday.

Official Fuel Economy Ratings
EPA city 27 mpg(US)
EPA highway 34 mpg(US)
EPA combined 30 mpg(US)

Actual Fuel Economy Performance
Lifetime 61.51 mpg(US)
Last 3 tanks 66.34 mpg(US)
90 days 64.33 mpg(US)
View Fuel Log
Last updated: Aug 15, 2019

Trip Log
AV 64.7378 mpg (US)

(Created: 2011-03-06 10:29:32 / Modified: 2019-08-15 19:35:24)

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