Okay, i am all about best economy too, not in boost but while cruizing. I was reading on PGMFI that some dude tuned his car getting 40+ miles per gallon and running mid 15 afrs crusing with part throttle. Right now i am in the 13.5 range cruizing part throttle, level road, 70 miles and hour, 3800-4000 rpms, 16-19 hgs, with base timeing that b16s have, 450 dsms. I ran one tank never hitting boost once, driving grandma style and i am getting around 27mpgs. How lean is good, can i take it to 14.7 or even a little higher as long as i listen for det What do you guys suggest. Also what is ideally the best afr under a load in vaccuum, espescially right before getting into boost??

its a 2000 civic si.

 

14.7 is what the stock o2 sensor *tries* to get the afr at, so why wouldn't it be ok?

I've run low 15's with no problems. This was on an 8.8:1 compression ratio engine tho.

I tuned an h22 that would start to hear detonation at anything above 15 with 93 octane.

 

DUH! i don't know what i am thinking :1 . I do read that alot of people keep it at 13.5 in vaccuum, i guess its cause they dont want to mess anything up. SO then under a load in the vaccuum side but almost wot, would 13.5 be a good area or little richer or leaner

 

Bone runs his super lean, on his d15.

 

at 70 at about 4k 15 vac i run 15.0 at high load about 13.8 with 9.0 cpr

 

vac afr's like stock, once you get to 0 you better start adding some fuel or something. why throw your mileage away?

 

Run it as lean as possible without misfiring...

Nothing is going to detonate, part throttle cruising...there just isnt enough cylinder pressure to make that happen.

 

yea, i ran my d15b super lean cruising. i had a super small turbo that boosted in every gear no matter what. i dont remember what the afr's were but i was getting 35mpg's with a 50/50 mix of city and highway driving. one i start driving again in march i will be shotting for 40mpg's highway. if there is no load on it, then it will be hard to hurt it

 

i usually cruise mid 15s until about 7hng, then its about 13.5-ish until i hot boost

 

Remember when you want to run leaner the burn takes longer so advancing your timing will be advisable.