I'm going to be installing an SAFC on my '86 GXL in several weeks, and just want to know what AFR's I should be shooting for when I tune it. I'm thinking high 12's at WOT? Maybe low-13's?

Mods: CAI, TB-mod, RB true-duals and SAFC for tuning. Everything else is stock...

 

about 13.5:1 is the best starting point for any NA at WOT. The main tuning variable when changing compression is ignition timing and even that shouldn't change much.

For cruise, generally speaking, the AFR should be as lean as possible without causing the engine to stumble... around stoich. Tuning for partial throttle and cruise are much trickier than WOT as they take more data from sensors and dyno time to tune.

Do you have a wideband? It will make AFR adjustment EASY.

 

Yeah, I'll be street-tuning with a wideband. I won't be manipulating stock timing unless it's suggested.

Anyways, thanks for the response!

 

I wouldn't change the timing at all... as long as everything is set to stock specs you are great in that department.

 

on the s5 motors, we seem to end up at about 13-13.2:1 afr's up top. safc you can tune using the force, theres a point where you'll stop seeing gains on the butt dyno

 

Good deal. I appreciate this thread now, because I finally got the wideband and SAFC installed in my '86 N/A several days ago.

Surprisingly, this car is seeing pretty damn-good AFR's in light/mid-cruising below secondary-injector staging. Between 14.5-15.5... Seems to be in the low-13's in the upper-RPM's (stock).

Mods are now just the RB true-duals, TB-mod and a "true" CAI intake.

I'll be tuning it with a buddy tomorrow or the next-day for mid-13's during WOT, redline runs. Pretty close as is, but I'll tweak it because I can.


RANDOM NOTE: Redoing the grounds on this RX-7 yielded a noticeable butt-dyno increase in the low/mid throttle-response. Grounded all 4 ECU grounds (at the source) at the same time as the SAFC install. Also redid the tranny bell-housing to firewall ground with a thicker gauge AND grounded the pressure-sensor (factory early-s4 recall problem).

Loving the DD!

 

Question:

I am unhappy with my SAFC's throttle % reading... It says I'm at 100% throttle when I'm closer to 20%.

Should I hook up the throttle-sensor wire to the pressure-sensor wire instead? I've done this on turbo cars successfully in the past--I just want to know if it's recommended on N/A cars.

 

Seems like people with N/A tuning experience look at the SAFC TPS/pressure-sensor "debate" on both sides...

It's agreed that the pressure-sensor gives you a wider-range of tuning potential--but it's been argued that with an N/A it's basically pointless to even bother tuning the low-throttle map because the stock ECU does so well on it's own... Most people don't even bother, and just set the low-throttle map at 98% and their high-throttle map at 99%.

It's interesting; I am currently running NO stock 02-sensor to aid the ECU in it's light-throttle fuel-corrections--however, it's been doing a fantastic job under light-load conditions... Between 14.5 and 15.5 AFR's, just as if there were a stock 02-sensor helping.

That being said, the fuel-mixture gets quite rich as soon as the secondary fuel-injectors come online at around 3800RPM's. Under light acceleration the AFR's go from around 15.0 to 13.0 as soon as the secondaries come on.

That being said, I will be swapping to the MAP-wire before tuning, just in case I can have some more fun playing with it.

 

Yes... yes.... the madness is spreading!

No! Much much much leaner than that. Take advantage of the massive turbulence in there, make that sucker run LEEEAN and watch fuel economy soar.

 

The S4 TPS is morel like a switch then a potentiometer. Its purpose is mostly to distinguish idle for the ECU. The S5 has a full range TPS because it has the electronic OMP.

 

dude I made 172 rwhp with a hackjob SAFC install (in hindsight) and ghetto advancing the timing with the CAS. It's an SAFC. It has limited capabilities and little precision, but for an n/a it gets the job done. Hooking it to the pressure sensor on an NA won't make a difference. It won't make any noticeable difference in actual power numbers.

 

You've read about my 12A S2?

It stumbles horribly when autotuning any leaner than 13.5:1. This may or may not be to do with the timing I run (which is suggested by www.hitman.hm) which supplies a haltech timing map for a 12A mildport and the corresponding afrs.

This may or may not be to do with my map and rpm signal noise problems. Is there anything else it could be?

 

if the engine misfires, the WB will not give a correct number. it possible the misfire isnt really noticeable either.

car i'm thinking about gave mid 12's on the wb @12psi, with a slight stumble in the midrange (4000-5000rpms). it felt rich, but was really just too lean to run. richening it up, brought afrs to the mid 12's...

the engine should have no trouble running 14.7's cruising, if not more like 15's

 

I meant if i autotuned the car to 13.5:1 it would generally cruise fine. If I then tried to lean it out by autotuning to 14.7:1 it would misfire it places not across the board.

The car does have other problems tho.


I was wondering if certain timing could just be too agreesive for such a lean afr like that. And would more timing + more fuel give the same economy?

 

Go for minimum duty cycle. Whatever it takes to get the lowest duty cycle.

I went tuning with a friend of mine today. For the highway cruise tune I kept tweaking it leaner and leaner until it sounded "off", like it was missing a little. At that point the duty cycles would increase. So I'd richen it up just a bit - just enough to make it smooth and a hair more for good measure. I can cruise at 60mph at 10% duty cycle, which with 680cc injectors should mean about 30mpg.

On a whim, after getting to that point, I tweaked the tune richer until it hit stoich. My main highway cruising bin (Megasquirt) is a 40. I had to bump it up to 45 to hit stoich. So my cruising AFR is (45/40) * 14.7 or roughly 16.5:1 AFR.

I used the same method for WOT tuning to get to 12.5:1 AFR. He'd hold it at a given RPM and I'd knock fuel down until the O2 would switch lean. )Then shout OK LET OFF! ) Then multiply that resulting bin by (12.5/14.7) to get my figure. We did the top two RPM bins a little different (took a guess, accelerated through, took another guess, etc) and over the whole range I ended up taking a LOT of fuel out relative to what my base map was, and the fuel map looks more like how the power curve felt, which perversely makes the engine feel more linear, since the weak midrange isn't even weaker due to being *way* too rich.

I chose 12.5 because it should still be nice and cool. N/A seem to be really indifferent to AFR. Even after taking all the fuel away, I had him switch from the old map to the new one and I couldn't tell a difference zt the top end by seat of pants. But overall fuel economy should be vastly improved as well as keeping the plugs cleaner.

Now a new problem cropped up... rough/low idle after coasting to a stop, and big clouds blue smoke when accelerating away. Probably related to not having any kind of crankcase ventilation hooked up. Need to find that air pump bracket and rig up my crankcase vacuum system!