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[TTC]

I was out tuning a bit with Minor threat and we did some cruise stuff to help get a bit better fuell mpg. Turns out i wasnt running enough timing and I was making very little vacuum during cruise.  What im wondering is what do most of u fellas aim for at cruise for afr and timing.


For afrs Ive read that you an almost lean it out till it bucks, so i figured cruise at something like 15.1 15.5? but the timing thing has me stumped. Its not likely to detonate at such a light load. So how do you know when to back off?  ON the road is a bit tougher , but im guessing i can go roughly till i dont see it making any additional power ?

Brett can probably explain it to me, but im curious what u naggers think. on my 85 4age turbo

After some tweaking we came up with this.

[Joseph Davis]

Cruise AFR is primarily determined by combustion chamber and atomisation.  I understand ignition can have a lot to do with it, but when dealing with the ever-familiar Honda I see some engines starting to stumble in the 15s, others 17-18 AFR - one was an LS the guy claimed 46 mpg, I was surprised.  Anyway.  Give the setup what it likes.

As far as timing, the "bigger bore likes more timing" adage seems slightly amplified, compared to WOT, be a degree or three.  Also, CR and presence of EGR make a difference - as does AFR, lean might want more timing.  Frankly I don't hear many/any part throttle cruise timing pings.  I think its the sort of thing you want to steadystate on the dyno and tune for best cruise at torque, but knowing jack shit about your motor I want to say set cruise timing to 38-42 deg and forget it until you buy time on a loading dyno.

[TTC]

I'm surprised he got up to 17-18afrs.... You would think it would lean out and buck, I guess I could just keep backing off the fuel till it does so and add it back in.  One curious thing tho is EGTS at cruise, depending on how lean you go I wonder how hot it will get with little to no load. 

I'm also assuming that when you are for instance on the highway and the road starts climbing a bit, you wont exactly be in your cruise bins.  However, you probably arent to far off, so it might be a good idea to leave those outer bins a tad bit richer? 

Ideally id like to do it on the dyno, but frankly its to expensive atm. Just finished Uni so soon ill be able to finally tune my cars cam gears as well. 

If it helps my motors very similar to the miata 1.6.

Thanks jd.

[98vtec]

i saw up to 17.5 AFR without misfire with my old h23vtec.  Was running RDX injectors at 55psi.  it could go 40mpg set at leaner cruise such as 16.5

[Joseph Davis]

I'm surprised he got up to 17-18afrs.... You would think it would lean out and buck, I guess I could just keep backing off the fuel till it does so and add it back in.  One curious thing tho is EGTS at cruise, depending on how lean you go I wonder how hot it will get with little to no load. 

It wasn't just that one car, I see it a lot.  My D16Y5 Type-R would do it.

EGTs might be a little warmer in the 16's, not that it matters since at a cruise your engine is making 13-18 whp aka not enough power to tax the cooling system, but general rule of thumb based on the engineering literature is that past 17:1 both temps and combustion pressures fall way off. 

i saw up to 17.5 AFR without misfire with my old h23vtec.  Was running RDX injectors at 55psi.  it could go 40mpg set at leaner cruise such as 16.5

Those are Bosch cores, I think?  I went to do the break in on an 85mm NA motor for one of the local roadrace guys tonight that has some pink '03 SRT-4 injectors, I'm hoping his shit goes down like that.

[TTC]

Ive heard that as well, that after a point, the burn gets so lean it gets cooler.

[crttaz]

I know on my old D15B7 that Blundell tweaked the timing and fuel maps on, I had to start blocking the radiator to get it up to temp. If it was 40 degrees out of colder I'dd fully block the grille opening and 1/2 the radiator.

[98vtec]

I'm surprised he got up to 17-18afrs.... You would think it would lean out and buck, I guess I could just keep backing off the fuel till it does so and add it back in.  One curious thing tho is EGTS at cruise, depending on how lean you go I wonder how hot it will get with little to no load. 

It wasn't just that one car, I see it a lot.  My D16Y5 Type-R would do it.

EGTs might be a little warmer in the 16's, not that it matters since at a cruise your engine is making 13-18 whp aka not enough power to tax the cooling system, but general rule of thumb based on the engineering literature is that past 17:1 both temps and combustion pressures fall way off. 

i saw up to 17.5 AFR without misfire with my old h23vtec.  Was running RDX injectors at 55psi.  it could go 40mpg set at leaner cruise such as 16.5

Those are Bosch cores, I think?  I went to do the break in on an 85mm NA motor for one of the local roadrace guys tonight that has some pink '03 SRT-4 injectors, I'm hoping his shit goes down like that.

yea, they are bosch style.  Same core as the ID injectors.