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?

 

Are you sure you're setting it to 17 deg BTDC and not 15 deg BTDC?

 

pretty sure... push distributor towards firewall = advance...... towards front/headlights = retard......

right?

 

Oh...... and EVEN if it was at 15 instead of 17, a drop of 10mpg??? that is a lil extreme dont' you think? I know timing can affect gas mileage, but damn.... 10mpg is a BIG drop...

 

I saw no difference in mileage with the timing adjusted... if anything, mileage should slightly increase as you're making more 'free' power and therefore making the engine slightly more efficient at using injected fuel more fully.

Are you sure you didn't somehow trigger the engine to go into severe timing retard? I know the P28 doesn't have a knock sensor but if something else caused it to go on the fritz so that it pulled massive amounts of timing I'd expect terrible mileage.

 

i am using a pr4 ecu now (obd-1 non-vtec ecu) from an integra ls...

i just used the p28 for a while. used to get like 28mpg with the p28...... now i'm getting 30mpg.....

got 19-22mpg when I adjusted timing to 17... car ran good, just got crappy gas mileage...

now it's at ??? (i just retarded the timing a bit) and it's back to 30mpg, but the car doesn't feel as responsive...

 

any hp increse has a trade off. an increase in hp would tell you that more fuel and air are being sucked in. fudgin with the timing is going to make you run leaner or richer. i think gas mileage would change ,but not that much. i'd kill for 19 miiles per gallun

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by redneckstanger &raquo;</TD></TR><TR><TD CLASS="quote">any hp increse has a trade off. an increase in hp would tell you that more fuel and air are being sucked in. fudgin with the timing is going to make you run leaner or richer. i think gas mileage would change ,but not that much. i'd kill for 19 miiles per gallun</TD></TR></TABLE>

I think that's true in some cases, but not in the cases where, like adjusting the ignition timing, you're simply trying to recover more 'wasted' energy... the engine's just blowing the gas out the tailpipe anyway, so adjusting the spark ignition time simply allows more of that wasted gas to burn and propel the vehicle. I don't think that means that any more gas is going in, but just that more of the gas going in is being used.

Now if he was using a B&M adjustable FPR or some sort of fuel-enrichment device you'd be right...

 

Ignition timing adjustment won't change the amount of fuel injected...

 

it affects gas mileage though..... i'm pretty sure it does.... not a LOT... but it does affect it.....

anyway, it's just weird how mine dropped by 10mpg......

 

I would say something else changed also in your case, dude. I'm telling you, I adjust my timing up and down and left and right all the time and have seen no mileage increases or decreases. The same goes for my brother's B16A, and the same goes for my girlfriend's SE-R. It just shouldn't make a difference, really.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HardLowrdRanger &raquo;</TD></TR><TR><TD CLASS="quote">Ignition timing adjustment won't change the amount of fuel injected...</TD></TR></TABLE>
It should, indirectly. Retard the timing and the engine makes less power. So you open the throttle a little bit more, in order to keep driving at the same speed. This lets in more air; ECM sees TPS & MAP changes so it injects more fuel.

 

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.....

 

well with timing at 17btdc i get 33mpg mix driving and higher 30's freeway.... so i guess thats the sweet spot.. for my engine

 

Sounds like you've been detonating. That can be felt as lost power.

 

could it be that when you RETARD the timing...the car is SLOWER so you drive slower therefore burning less gas...and when you ADVANCE the timing the car is FASTER so you accelerate faster? just a thought...

 

Making more power on the same amount of fuel injected means better mileage because it takes less time to accelerate to a given speed

This is why MPFI cars see the ECU continually attempting to advance the timing to the threshold of detonation. It's the most efficient way to run.

 

You have probably been pinging. Try with 91 octane and then post your mileage