I've always thought that I didn't have enough horsepower for my setup (street port, holley carb, etc.), so I decided to get the car dyno tuned.... bolt the car on, hook up the A/F sensor, and start the car... The guy running the dyno says that something's not right... The A/F ratio is 20:1.... hm.... He starts a baseline pull, and immediatly shuts it down when he notices the A/F ratio isn't moving.... Well, to make a long story short, The end of the dyno session saw us going up 14 sizes on the jets to get a 12.5:1 ratio, and we're still not done yet... ran out of time to start playing with the A.P. size... I don't know what Racing Beat was thinking, but I'm sure glad I didn't blow my motor....

Dan

 

Lean won't kill a N/A engine!

 

that's interesting, i've always wondered about my jetting while i bolt on stuff like headers etc. was there a performance difference after updating the jets?

Alvin

 

I'm a professional engine diagnostition and one of the things I've noted is that the Rotary will run somewhat well with an A/F so lean it's nuts.

Vernon

 

that is becuase it does not really detonate but it will burn up th apex seals and make them brittle lol.

 

If this is the case, then did I screw something up? Should I run it leaner?

Dan

 

for an n/a, I'd think that AFR's right around 13:1 would be great..

 

For WOT, run 13.5:1. For cruise and idle run close to stoich (14s).

 

how would a typical joe (without access to a dyno) figure out his a/f? Also, this reading would have to be taken before the cat right?

 

You dont need a dyno, you need a broadband lambda!

 

For loaded conditions, 1/4 mi MPH numbers or, if there's no dragstrip near you, a clear road and an honest eye on the tach and a stopwatch will get you dialled in. Target A/F is not important, best power is.

For cruise conditions, run just barely rich enough that it doesn't misfire. This is way leaner than a mere 20:1.

At idle, run it just slightly richer than as lean as you can make it. Usually this is richer than stoich since rotaries don't idle too well.

 

Again, does this mean I should've left the jetting alone? Did I just take a step backwards? Someone please tell me before my dyno session tomorrow... We need to get the A.P. set up for the new jets!!!

Dan

 

No, run a slightly rich mixture under power or you'll melt down the motor. Lean mixtures burn very hot. It's ok for light cruise and idle when there's not much heat but not for any power level above that.

Vernon

 

i have a full RB exhaust, is there an O2 bung on the header, or would i have to have a shop put one on (the car came with the full exhaust)?

 

Being an average Joe,I always got my mixture by turning the screw CCW till it started to stumble, then CW till it ran rich. After that, I put it about in the middle, erring a little to the rich side by a half turn or so. That was my poor mans solution and it worked pretty well.

 

Suparslinc, that addresses the idle, but doesn't address the jet size in the carb, I'd like to know whether i'm running a good a/f mix when i'm driving hard, not just at idle.

 

if the guys equipment is right you need to go with the jets giving you more fuel

 

for an n/a setup you really should stick to around low 13 - 13.5 afr's. maybe even high 12's. if you're on the dyno you will see what is working the best, just go with what nets you the best powerband. but definately keep it away from being anything higher than 14's under WOT.

 

Endurance racers would run full power in the 16:1 range for best economy...

Lean don't hurt N/As!

 

I know the narrow band O2 sensor isn't the most accurate thing in the world, but at idle I generally register nearly no voltage what so ever (in fact at an auto-x one of the instructors asked if the car was on (pointing at the blank O2 gauge). While cruising the closed loop causes the meter to bounce between blank and just under "stoich" and at WOT I register just a touch above "stoich" on the meter. True this is the EFI GSL-SE, but it's the stock ECU doing this

I'd say that way lean shouldn't be an issue under idle and cruise conditions, but you don't wanna be at 20:1 if you're looking to make power, and you probably don't want to be there while at WOT either. That said, I don't think you broke anything.