Kevin T. Wyum

I'm not too worried about the light boiling after shutdown.

I'm starting to think my lambda sensor might be far enough down stream to be reading a little leaner than it really is. .75 to .77 of stoich 11:1 to 11.3:1 really runs like **** on pump gas 93, really drags. At about .79 to .82 11.5:1 to 12:1 it runs crisp and pulls like a monster. This is of course at 14psi or so. I adjusted maps a bit trying to move everything to about .78 and put in some race gas and it ran like ****. heh. Really need to lean it out for race gas. Any opinions on ratios that other people have been using? I'm also curious where people have been mounting wide range sensors.

Kevin T. Wyum

After some reading I discovered I hadn't thought about something with respect to displayed AR, overlap. It hadn't occured to me that charge air could enter the exhaust and cause leaner readings than were really taking place during combustion. I can think of some arguments against it, such as the exhaust pre turbine should have as much or more pressure as the intake charge, since it has to turn the turbine doing the compressing to begin with, which would result in the known exhaust contaminating the intake charge during overlap. This is my first bridgeport so I'm a little hesitant, but the observational data and gutt feel supports the reading leaner than it is. At anything close to displayed 11:1 the car is a pig but as I move to displayed 12:1 it pulls more like I would expect it to. With turbo cars there is a saying that sums up my real fears here, with reference to leaning things out "They feel best just before they blow." I don't feel like chunking Ianetti apex seals in a quest to find out just what AFR is good in this case : ). I think I'm just going to bite the bullet and try for tuning to just under 12:1 displayed. In my youth reinventing the wheel was a thrill, now it's just something more I won't have time to fix.

Kevin T. Wyum

Kevin T. Wyum

P.S. Sheesh, I just went back to look through my datalogs from runs in 1998 (hard to say for sure since garage laptop battery is really lame and loses date) before the turbo failure happened. I think I am obviously reading much leaner than it is. I'm floored I didn't blow the motor back then. I've got runs to 8500 RPM at about 22psi with lambda readings between .85 leaning to .91 by the end of the run. That's between 12.5:1 to 13.3:1 If that were real I can't imagine the motor would have held 22psi even with C16. Did I mention I hit 8960 RPM : )

GoodfellaFD3S

iTrader: (213)

Good info Kevin, keep it coming

CCarlisi

Do you think cross referencing your 02 readings with an EGT would help to clear up the uncertainty?

Kevin T. Wyum

CCarlisi, yup that's the best course of action, the problem is placement of the probe. I'd actually like to use two with one after each turbine to keep an eye on any problems with one leaning out etc. might have saved my destroying the rear turbo the first go round. The other issue is more of a petty thing, I'm not sure if I have any active inputs left on my Motec to include an EGT sensor output. It's much more pleasant to adjust a map while sitting at a desk and looking through the graphs instead of remembering the temps were about this at about that for which run at which fuel pressure etc. Anyone know what the output signal of EGT's are? I assume they work by change in resistance with temp.

Who's a good source of EGT's now days? I seem to remember the normal sources like Jegs, Slummit etc. not reading high enough for us, Pegasus now?

Kevin T. Wyum

Howard Coleman

iTrader: (6)

hi kevin,

i just returned from a nonstop 1900 mile trip to N J to pick up my motor. it should be running in a couple of days after i get my eyeballs uncrossed...

https://www.rx7club.com/showthread.p...2&page=1&pp=15 w regard to loggable egts... i suggest your read the above link. Jeff has posted a simple circuit that will generate 0 to 5/10 volts. also take note of an excellent K thermosensor probe. a simple deal to make for next to nothing.

stay away from the poh-leese.

howard coleman

Kevin T. Wyum

Well looks like I'm going to pull the motor out. I'm not going to risk Ianetti seals etc. on a guess with the Lambda readings. I'm going to put 2 EGT's in, one at each turbo, thankfully I have two spare inputs with calibration and conversion tables on the Motec. So I'll be able to log the EGT's along with everything else (I want to make sure I can see if one rotor is going lean, not just the average of two). I think I can even set some added fuel / ignition trims based on the input as well, although I doubt I will.

Anyway I can't get at it while they're on the car and I've got some exhaust leaks on the manifolds that, again because of the tight fits, I can't get in there to torque to proper specs while everything is in the car. Not sure how long it will take since I really have a hard time spending more than an hour or two at a time on anything lately. I would certainly hope to do it all before it gets too cold here.

Kevin T. Wyum