question about a/f ratios

[born2drv]

What would happen if you ran the car in a lean burn mode (a/f ratio of 20:1 for example) when cruising on the highway at 55-75mph with no boost?

the reason i'm asking is that's how my 2001 honda insight is setup. i was reading up on it, and that it has an extremely high a/f ratio of 22:1 only in lean burn mode on the highway.... the drawback was that the exhaust temperatures are much higher and the NOx is much higher as well (which is why they have a very expensive catalytic converter that costs $1500 from the damn dealer!)

So I'm wondering what would happen if the supra ran in the 18-20 a/f range with no boost at highway speeds, would the exhaust temps or engine get very hot? could it detonate even with no boost? how do you know how much you could push the a/f's safely for maximum efficiency?

 

[supra90turbo]

AEM supports this if i'm not mistaken.
Given variables, anything other than positive manifold pressure and xx% throttle position, it goes into lean burn if set up that way.
Roll into the throttle and it snaps out of it and goes right into your actual set fuel map.

 

[boostadikt]

kind of a good question, my experience is that if my car is above about 17.5 even cruising it misfires and just no good. i thought about trying to tune really lean like this for cruising but then asked myself what if? would it really be worth it to ruin my expensive motor to save 10$ a month on gas? your insight was engineered from the get go to handle extremes in gas saving, with the supra i just dont know. thats my 1 and 1/2 cents

 

[mrnickleye]

Extreme heat in the cumustion chamber when lean. Lean mis-fires means wasted fuel, and power loss.

 

[itr206]

anything above 17.5 or so as said above will missfire even at part throttle.
I tested this already.

 

[drjonez]

no problems doing a more lean cruise.....though you'll never get to 20:1 on the 7M. you'll need a combustion chamber specifically designed for it + direct injection + other junk. a lot of MKIV guys w/the AEM run 17:1 or so (as already stated).

 

[Nick M]

The Insight catalytic converter was made for that cars air fuel ratios also.

 

[drjonez]

excellent point.

 

[born2drv]

thanks guys....

will a very good catalytic converter help the exhaust run cooler or is it purely for emmissions only?

i'm thinking of getting an egt gauge and tweaking the a/f's to be as high as possible for highway cruising....i do care about the environment too, but getting peak efficiency on the highway is my main goal

 

[itr206]

I never understood why people with sports cars that modify them for more power are soo worried about gas mileage.
You have an Insight. who cares about the difference in gas mileage from 14.7-15.0:1 to 17:1 in your Supra? Its honestly not worth all the extra effort your going to put into it.

As far as the enviroment. fuck it. there is much worse out there. your car aint gonna hurt it any more.

 

[born2drv]

lol i do care about the environment... that's why i have a 3" cutout pre-cat and a muffler... its boost activated, so when i cruise along i'm a good citizen with low emissions and noise... when i stomp on the gas she opens up and becomes a monster

i also live in california, the land of the portable emission testers that test you as you drive by.

plus i'm just anal like that, i want everything in my car to work at 100% peak efficiency, or as close as possible.

 

[vas85]

anything above 17.5 or so as said above will missfire even at part throttle.
I tested this already.

How do you guys adjust the A/F ratio? I think mines running a little rich not 100% sure, I just cant plank the foot down, i have to rather "lean" into the throttle and it surges like a monster but im takin it down to my trusted mech to put a boost guage so I know how much its boostin at exactly, get it dyno'd and tune it.


If changing the A/F ratio isn't that hard then I wouldn't mind knowing .

 

[GotTurbos?]

How do you guys adjust the A/F ratio? I think mines running a little rich not 100% sure, I just cant plank the foot down, i have to rather "lean" into the throttle and it surges like a monster but im takin it down to my trusted mech to put a boost guage so I know how much its boostin at exactly, get it dyno'd and tune it.


If changing the A/F ratio isn't that hard then I wouldn't mind knowing .

what do you have fuel controller wise?

 

[vas85]

what do you have fuel controller wise?

Not really sure, i've got just whats pasted in my sig, thats all i'm aware of on a motor with 118,000ks / 73k Miles.

What is normally needed to do that??..

 

[GotTurbos?]

you need some type of fuel computer, the apexi S-AFC seems to be the most popular ive noticed among the bpu mk3 people, here are some you can look at:

http://www.mvpmotorsports.com/Templates/frmTemplateM7.asp?SubFolderID=926&SearchYN=N

thats not all your options, but you can look there and read up on the functions and such.

Jon