The D16z6 does not need anymore than 87 (unless heavily modded.) It has a 9.2:1 CR ... c'mon guys. I ran 87 on my 9.6:1 D16Y8.

Only the high compression need the premium.

 

Amen, mantis. I ran 87 octane in my old D16Z6 for 195k. Read your manual again, sure you can put 91-93 octane but 87 is just fine. Now some cars like my Maxima's for example, need a minimum of 90-91 octane. Ask my wife, she did'nt take my word for it and learned the hard way. She bought gas at a racetrack gas station because it was cheap. She filled up her SE with 87 octane and went back home. Later that day she went to the car, started it, and it died. It kept doing it. I was at it for two hours that night trying to figure out WTF was wrong and then finally she says, "well, I filled up with regular today because it was cheap, would that have hurt something?" So, I run to the zone and get some octane booster slap in there, and what do you know, she purrs like a kitten. But in general, most inline 4 honda motors can use 87 just fine for normal operation.

 

B16's and B18C's need the premium

 

if you're new plugs, ignition coil, wires, fuel filter... what could cause bad gas mileage?

they're just normal bosch plat's i'm getting 26 at best for mixed driving on a d16z6 auto... and i can't figure out for the life of me why i'm getting sheity mileage. intake and exhaust are the only mods.

 

Compression ratios alone do not dictate which octane of gas to run, timing has also a lot to do with it. Stock timing curves for a D16Z6 are fairly aggressive, they also run very lean in the midrange RPMs in order to get good mileage (15.5 to 1 under light cruise). You can safely run a D16Z6 with regular and the timing bumped back a few degrees, but it's not going to run close to the way it can. I do agree that you should run the lowest octane gas that your car can handle without pinging - running premium in cars designed for regular usually carbons up the engine quite a bit.

 

In another thread, you said you had some 'other' ECU program. This most likely advances timing and adds fuel which will require the premium.

A stock/lightly modded D16 needs nothing more than regular. You must have the wrong manual for your car because I know the sohc does not need premium.

 

All I know is I can't put the 10% ethanol blend in my car or the CEL light comes on. If I put in 87 or 92, it runs fine. I called Honda and they said that just because the manual does't say you can't put it in, doesn't mean you can either. :dunno:

 

I had problems with regular gas before I modded anything on the drivetrain. Maybe it was the MTBE in the fuel that was hurting - I now live in an area that doesn't dictate adding MTBE for emissions purposes.

 

Thanks for the opinions guys. I still never heard anyone say what difference it would make if the plugs weren't gapped just right. Also, my exhaust has no cat, I have a test pipe instead. Would this have much to do with the black smoke?