Thread: Dyno graphs - BAD afr? - looking for some help

First off, a little background on my setup. For the December runs I had a JDM highport swap with S4 cams, UR pullies, Thermoblock spacers, JWT popcharger, wrapped SSAC with 2.5" downpipe, Catco 3" high flow cat, and a 2.5" mandrell bent catback exhaust. Timing was set at 19 degrees. I also have a JWT flywheel and an SR16 tranny if that makes any difference (I wouldn't think it would matter). The changes made from the Dec runs to the Jan runs were a JWT ecu with the pop program for premium fuel and rev limit raised to 7950, timing moved from 19 to 15 as jwt recommends, and finding & fixing a vacuum leak that was causing a rough idle even after the new ecu was installed. Here are the graphs:



I was very dissapointed with the Dec runs, and while I'm happy with the increases in both power (+6.5 hp) and torque (+11 ft-lbs), I was honestly expecting more than 150 hp. I didn't have afr numbers for the Dec runs, but I had a bung installed pre cat on the exhaust so that afr's could be watched.



I honestly don't know a lot about afr numbers, but was told that I am dangerously lean. I picked up a adjustable fpr, fp gauge, and a new fuel pump from Greg V, and while I can install these on my own, I don't know what setings I should be at in terms of fuel pressure, afr, etc.

I met a few guys at the Atlanta dyno day in January that seem knowledegable about this and one offered to help me out, but I lost his number. Any help here?

I don't see how those AFR's translate to "dangerously lean" conditions. On turbo, hell yes! On N/A? Not as much. Looks like you're at stoich pretty much thru the powerband, IMO.

I would say to bump your fuel pressure just a smidgen and richen your AFR to a high 13 to mid 14 at WOT pulls

I'm by no means an N/A guru, so I could be way wrong. All that aside, I STILL don't see how those AFR's are "dangerously" lean.

Not dangerously lean, but with S4 these high AFRs are unneeded. Go to the 13s by bumping your fuel pressure. Dunno, try 52 psi with AFR hose disconnected and see.

Not really dangerously lean. It is much harder to damage an N/A motor due to lean condition. You are running much leaner than you should be for max power though. You're looking for anywhere from 13.5-14.5 for decent power. I believe max power is found somewhere around 13.5 - 13.7. I've aimed for 13.5 in my N/A tuning (possibly the only N/A with stand-alone at the moment).

15: is very lean, stoich is at 14.3-14.7:1 depending upon season, age of fuel etc.
aim for 13:1 to start, then check how well its running and slowly edge to 13.5:1 to see if it runs better or worse. The fuel pressure will bring the flat from 4.5K onwards back down some, but just an FPR may not make it flat all the way.
Dont forget each cylinder is running slightly richer or leaner than any other, so an average of 15:1 may be quite bad on one cylinder.

Really carefully check the exhaust system for leaks, borrow an egt gauge and measure the wideband temperature, if its not a wideband, then the number is meaningless.


Mike

can you guys look at this AFR graph, please?

http://www.sr20-forum.com/showthread.php?t=3669&page=2

id say that that afr is safe, far from ideal but yes its safe. you could add a little more fuel pressure to keep the leanest point under 14:1 until you get it tuned and flattned out