Tr0LL

Does retarding the timing yield better gas mileage?

The reason I ask is because I set my timing to about 17 (in between the middle mark and the other mark) and my gas mileage dropped from 30mpg to 19-22mpg. I noticed the distributor seemed really advanced (leaning towards the firewall a lot), so I just put it more towards the middle (haven't rechecked timing yet) and drove about 100 miles and poored gas again to check gas mileage... that was the ONLY change I did and now I'm back to 30mpg. I get gas at teh same place and didn't change anything else. When I first put the b20 swap in, i was running the wrong ecu (P28 vtec) and I was still getting 28mpg. Then I got the a LS ecu and been getting 28-29mpg also.... then I use the timing gun to advance my timing to 17 and all of a sudden my gas mileage drops SIGNIFICANTLY. I also notice my car isn't as responsive as it used to be. I will recheck timing with the light as soon as I can, but until then......

Retarded timing = better gas mileage?

doctorsohc

It's usually the other way around - advance = better mileage, retard = worse. You had mentioned that you were running a P28 ECM in your car... P28s run fairly lean in stock maps, so that coupled with a little more timing will give you much better fuel economy. I usually set P28 equipped cars a little more advanced than stock and run premium fuel - usually 2-4 degrees more depending on mods... if you have a B series with higher compression usually less (higher compression means faster burn of air/fuel mix). I've seen mileage up to 39mpg on some D16s by doing this and get roughly 38 hwy with my modded D16Z6. As far as responsiveness goes - more initial advance will make an engine more responsive as long as you have enough fuel to compensate for tip in throttle. P28 stock fuel maps are this way - you can get the stock size tires to bark in 2nd gear on a P28 civic when you goose the throttle! :naughty: It sounds like your timing is too retarded on your car if you have poor throttle response - if it's too advanced it will start to ping noticeably, unless you have a knock sensor - then the ECM will just crank back the timing. If you feel like experimenting you could also try relocating your AIT sensor (intake temp) - sometimes you can squeeze another 1-2 mpg with that alone. A common misconception is that more is always better with ignition timing - too much timing will decrease WOT power and can also wear out your bearings in your engine, even if you don't hear detonation.

Tr0LL

i actually have a b20b in my car... not a d-series.....

and i got around 28mpg with the p28...... but average about 30 with the ls (pr4) ecu......

the p28 ecu ran with the engine check light on though. it was for the vtec stuff (obviously because the b20b is non-vtec)...

Anyway, just weird how I dropped 10mpg. I mean timing can affect gas mileage, but 10mpg? that is a lot....

90AccordEX4

Could you elaborate. I am always looking for an extra 1-2MPG! I am currently averaging ~32mpg and have gotten as much as 37.5.

1stGenCRXer

It really depends on what grade of gas you use. Lower octane rating'd fuel burns faster than gasoline of a higher octane rating. If you gain fuel economy from retarding the timing, then you're probably using a lower grade of fuel than was originally intended for the engine, and once you've retarded the timing, the engine is able to better use the fuel burn to move the car. With a higher octane rating, you can get a longer useful fuel burn, so you'll need a bit of advance compared to a lower grade fuel.

At the same time, you can advance the timing to get a better throttle response, but throttle response doesn't equate to more power or better economy, just better throttle response. However, if your timing is advanced too far to make the best use of the fuel while burning, it'll get the piston moving faster, but not really have any follow-through. That make any sense?

doctorsohc

On a D series engine you can find the air intake temp sensor in back of the intake towards the timing belt side - has a two prong plug on it held in with two philips screws. Buy another sensor from honda and install this in your CAI or factory airbox away from the engine leaving the old one behind to plug the intake. Extend the harness to reach the sensor and you're done. Works very well in hot weather - hondas hate heat! This works for two reasons - ECM senses cooler air and gives more ignition timing, also leans out air/fuel at cruise. The only downfall is on a cold day you will get a richer running engine, so just plug the connector back in the old sensor when the outside temp goes under 50 or so degrees.

doctorsohc

In your case I'm sure it was a combination of less fuel and more timing. BTW B series engines don't get the fuel mileage D series get b/c B series engines have more internal friction loss from having 2 cams and make their hp in the upper RPM area which doesn't spell high gas mileage, although I've seen B18bs getting low 30s in stock trim with a PR4 ECM - must be the extra torque down low. But anyways, low 30s to the gal is very respectable for a B series!

doctorsohc

you're right - the only way you benefit from a certain grade of fuel is to have igntion timing set accordingly.

When you advance to far, peak cylinder pressure occures when the piston is still on the compression stroke = detonation! on the other side, when you retard timing you get better top end power b/c of this reason: the faster an engine revs, the more timing it needs to completely burn the fuel in the cylinder (this can be up to 25 degrees more than base timing!), so when you retard timing you get more push on the downward power stroke of the piston like you stated in your quote, but less follow through, i.e. lots of push at one point (retarded timing) as opposed to a steady push through the whole power stroke (advanced timing). It also has to do with the rod to crank angle and bore/stroke ratio of the engine you have. I hope I was able to explain it well enough.

Tr0LL

ok..... it's been a few gas fill ups since i posted and i can confirm that lowering my timing does wonders for my gas mileage.... could there be something wrong with my ignition system perhaps?

the thing is..... using a timing light, at 16 degrees at 750rpm, i get 19-24 mpg..... basically crappy gas mileage.....

when lowering the timing to about 14 degrees, it instantly jumps back up to 29-30 mpg and the car feels a lot faster... this is of course with NO other changes....

i tested this for 2 months now..... i would run it at 14 degrees.... 29-30 mpg..... go back to 16 degrees and my gas mileage drops significantly to 19-24mpg....... then just last week i decided to lower it to 14 degrees again and bam... 29 mpg from today's fill up.... my driving varies, but even if i drive like a grandma, i could never hit more than 25mpg with 16 degrees timing.....

??? - i am confused....

oh and i'm using 87 octane btw..... and i have the lower compression b20 which is designed for 87 octane (which is 8.8 or 9.2 compression depending on which b20 theory you believe in)... maybe later i'll test it again at 16 degrees and try 91 octane and see if gas octane is the reason here.....

1stGenCRXer

Octane most likely will be the reason that you'll see.

The bottom line is that you're going about it the right way, experimentation, because each engine is different and will respond differently depending on what fuel grade and driving style you use.