T70FD

I going to get some tuning done soon and would like to know what kind of Air/Fuel Ratio is good for a single turbo on pump gas. I was thinking of 11.5 to 12:1 or is that to rich? This will be on a chassis dyno so the Air/Fuel ratio will need to be a little rich to counter act real conditions correct?

Silver7

I would definitely not tune it any leaner than 11.5. I am going to keep mine in the low 11s

RICE RACING

I would agree with Silver7, If your ignition can handle it then low 11s or high 10s is the best for durability, reducess ALOT of heat stress on the turbo and goes along way to cooling the engine/apex seals (stop chamfering of the edge).

If you have std ignition you will need to run it near 12:1 just to get it to fire, this problem gets worse as you start to make over 450BHP.

You can run near the 12:1 if you use something like water injection, but I have found that if you do not then either your turbine wheel will eventualy melt the tips right off (unless you have a real exotic turbo) or if you are using ferrous seals (non ceramic) you will either or have prematurley worn apex seals and excesive wear on your side seals (gap between corner and side seal) both of which will cause low compression.

shinjuku

ok Rice Racing what would u say would be the leanest u could go with water inj at WOT??

Silver7

By standard ignition I assume you are referring to stock ignition? I was not aware that the stock ingnition was not capable of firing properly when the a/f is tuned rich. Maybe it is time for me to upgrade my ignition system.

Anthony Rodrigues

Since 1986 2nd gen rx7, Australian delivery vehicles on a chassis dyno (complete vehicle), will run 11.4 down to 10.8 AFR with no ignition problems. The standard gen2 coils have been run successfully above 25psi without missfire or any signs of detonation. The key to this is in the way the coils and ignitors are being driven. We currently have them on an RX4 13b running 9.7@142mph. Cannot say the same for FD coils.
I have found that the power increases gained from leaning from 11.7 to 12.1 or leaner not to be worth the trade of in reliability that has been already mentioned.
Regards-Anthony

RICE RACING

leaner is not better when running pump fuel, better for engine builders mainly

SPOautos

So what about FD coils? With a a/f of say 11.2 how far can you go with a totally stock FD ignition system?

Thanks,
STEPHEN

machinehead

So what is a good general rule for A/F ratio? You want to run as rich as you can without causing missfire?

Anthony Rodrigues

SPAutos,
The reason why I cannot say the same for FD coils is that I have never pushed these units to their full potential. A factory car will consistently run into the mid tens without missfire once their factory ecu temp corrections etc.. Although this is at relatively low boost pressures as they will also reduce boost with extreme air temps(track racing). I believe that Siguel has one of his workshop FD's running factory coils being driven by a Microtech that sees 25psi and a small shot of N2O. Dont qoute me on that as I am only repeating what Ihave been told.
Before I had my dyno or an accurate AFR I tuned my car at the track by having it just off rich missfire and had good results. Please keep in mind that this was a long time ago and we had far inferior ignition systems therefore making the misfire point alot leaner than we could run now.
You cannot give a blanket target for AFR, as your boost levels are increased you must run richer, fuel octane can also determine AFR requirements. Starting rich and slowly leaning it out until your EGT's or plug readings tell you to stop will normally giveyou success.
Anthony

SPOautos

So basically if tuned right you think a 3rd gen SHOULD be able to run 15psi on the stock twins with the stock ignition set up. That would net somewhere around 370ish RWHP. You feel like the stock setup and prob handle that?

I'm not familiar with the stock 2nd gen set up, what is the difference in the 2nd and 3rd gen ignition set ups?

Thanks,
STEPHEN

1000HP20B

SPO,
I have run FD coils using MW igniter and old Microtech DIGI years ago on an R100 with 13BT running 16psi and 30hp N2O, we ran it at 11.6 A/F and never had any missfire problems, the car ran 10.20's all day every day for a couple of years of racing .
As Anthony stated the factory AFR's on a stock S/4 are into the 10's and well into the 10's on mildly modified units, I hav'nt had any experience with rich missfire problems on any on my dyno except where the ignition timing was over retarded.