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Discussion Starter #1 (Edited)
The D16Z6 engine (D16Z6 #1) that was original to my 1995 Honda Civic EX coupe (EJ1) threw a rod with with around 243,000 miles on it.

I found a good running '95 Civic EX sedan (EH9) with about 168,000 miles on its original D16Z6 for an engine donor.

The compression numbers for the donor (D16Z6 #2) were:

#1 = 205
#2 = 195
#3 = 215
#4 = 210

Compared to 140-150 psi when last checked for D16Z6 #1. I believe that 195-215 psi are on the high side indicating carbon buildup, which makes sense with for a car driven by an older female art teacher and the cheapest gas she could find based on the mismatched no-name tires that were on the car but the rings and valves had to seal that pressure and it passed smog check pretty easily.


DZ16Z6 #2 in 1995 EH9 - completely stock, smog check by prior owner. Spark plugs were in bad shape with huge gaps.


D16Z6 #2 in 1995 EJ1, smog check fail #1. Stock D16Z6 intake (thoroughly cleaned manifold and throttle body) from D16Z6 #1, new Purolator A34799 air filter, new NGK ZFR5J-11 gapped @ 0.045 inch, DC Sports 4-2-1 CARB header, cat from EH9, EJ1 resonator, custom 2" exhaust with Dynomax 17742 muffler, fresh Redline 5W30 in engine, 44 psi cold 185/60-14 tires. Same engine block, head, distributor as when tested in EH9 chassis. Different ECM, different sensors, different wiring harness, different exhaust, different intake, corroded VSS connector, warm engine but only drove 5 minutes on freeway, Chevron 87 fuel and then idled for 5-10 minutes before it went on the smog dyno.


D16Z6 #2 in 1995 EJ1, smog check fail #2. New Walker Cal Cat, new O2 sensor, new VSS connector (which restored VTEC and 7400 rpm rev limit), a little more effort in getting and keeping the exhaust hot, only 5-7 minutes of freeway but 4000 rpm in 4th the whole way.


D16Z6 #2 in 1995 EJ1, smog check pass easily. Replaced cheap replacement PCV valve with oem Honda part from the EH9 intake, new distributor cap and rotor, stock exhaust manifold with heat shields, stock downpipe, "winter blend" Chevron 87 and a big effort to get the cat hot and keep it hot, 30 minutes freeway normal driving, two exit freeway loop full throttle 7000 rpm shifts touching 100 mph and onto smog dyno with less than two minutes idling.


Last successful smog check with D16Z6 #1 for comparison, tired and abused engine 75 minutes freeway before smog check, DC Sports header, stock intake, Walker Cal Cat.

I expected to breeze through the smog check with the much fresher engine, was really stressful trial-and-error not knowing whether I was wasting my time swapping parts, only theorizing that the changes were steps in the right direction. With the stock exhaust manifold and downpipe, the exhaust gases ahead of the cat and the O2 sensor are hotter. I'd expect it to pass with the header so long as I got the cat hot and kept it hot but I am going to play it safe and duplicate this setup and procedure next time around, failed smog checks hurt.

Interestingly, judging by the CO2 numbers, the engine was more efficient with the Fail # 1 and Fail #2 tunes than when it passed.

Hope this helps someone else.
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