Ziff951

Okay, I finally got the laptop hooked up to the Mafterburner and started dialing in the AFR's... Great to be able to do it 'real time'...well, in between driving portions...

My questions start with the AFR for 'cruising' time. In the posts I've read, the term 'cruising' and 'under' or 'off' boost are thrown around a lot. To clarify, is cruising considered ANYTHING 'off' boost? Meaning, even if I'm at a highish rpm, but not under boost, or load, is the leaner number still okay? I've gathered that fuel comes on at certain loads (since rpms don't = boost) ie:, not rpm specific, so as long as my AFR goes into the healthy range as soon as I hit boost, that should work, correct?

Next, when I am under boost, is the richer ratio the same if it's just starting to boost all the way through WOT, or should it have a 'richening curve' as the boost climbs?

Lastly, can someone point me towards info about the ideal AFR for cruising and WOT? I've read a couple dozen threads and have found that people tend to say 15-17 for cruising and 11.5-12.5 for WOT....can anybody that's really knowledgeable confirm some numbers or point me to some studies I can read?

Right now I'm running at about 14.7-16 at cruising (anything off boost, even higher rpms with no boost) and about 11-12.5 on boost.

Thank you guys for all the help. I know I'm asking a crap load of questions, I just want to make sure I don't grenade my engine. I'm hungry for knowledge and the tuning day today was a blast and not as complicated as I thought it would be.....(except for the ideal numbers thing...)

Feel free to PM me if you don't feel like posting a giant response.

Thanks again,
Stephen

87' 951 with LR 340 package.

Rogue_Ant

For cruising / light-load, which pretty much means anything not in boost, shoot for ~14.7:1.
At ~15psi of boost, you should target between 11.5 - 11.8, for best power and safety.
From 0psi of boost to that 15psi, should be a gradual slope from cruise AFR to WOT AFR.

If you are running more then 15psi, I would go a little bit richer yet, such as low 11's.


-Rogue

Tom M'Guinn

Like R_A said -- 14.7 off boost and mid to high 11's on boost. Assuming you have your stock oxygen sensor, the DME will try to adjust your air fuel ratio as you drive to get it to 14.7, since this is the so-called "stoichiometric" ratio -- i.e., the point at which you have just the right amount of fuel for the oxygen available, no more, no less. (Google it for endless theory.) Because of the closed-loop system getting it to 14.7 off boost, as long as your tuning is in the ball pak, the DME will take you to 14.7. However, the car generally runs better (less surging, etc.) if your tune is as close to 14.7 as possible before the DME steps in to bring it back to 14.7. On boost, the car runs in open-loop, meaning the DME does not help to get the ratio where you want it. I generally shoot for it to be into the mid 12's by the time I have 5psi, and then mid to high 11's by full boost. Octane, timing, altitude, leaks, etc. can all factor into it though...

Ziff951

Awesome. Thanks for the feedback, guys. That's what I'll dial it in at. I'll also shoot for a gradual richening as boost increases. Thanks!

Stephen

Ziff951

One more question. When I come back to idle, at a stop light or whatever, the AFR is really rich...then it slowly steadies back out to 14.7...is that normal?

I've got the 340 kit from LR....MAF, turbo, 55lbs injectors, etc...

Tom M'Guinn

How rich, and how long does it take to get to 14.7? Does it matter if you just came off boost or if you were just cruising before going to idle?

Ziff951

It doesn't matter if boosted prior or not and it takes maybe 5-10 seconds, varies though. It usually goes down to 10.1 then works its way back up to 14.7...also, it can feel a little stumbly while it's in that state...probably due to the extra fuel.

Rogue_Ant

Sounds like a couple of issues...
When tuning, you should disconnect the O2 sensor - this way you are not fighting the DME's close-loop control.
Also when in gear, you let off the throttle your WBO2 should show infinite-lean. This is because the DME cuts fuel during drop-throttle. But this only works correctly if your TPS is good and adjusted properly.


-Rogue

Ziff951

I'll check the TPS, and, yes, the WB02 does go infinite lean on lift throttle.

So, I should just pull the 02 wire before the low end tuning? That won't interfere with the Mafterburner readings or anything like that? Just making sure. Thanks!

Stephen

Rogue_Ant

Pulling the O2 wire should not interfere with the MafterBurner.

toddk911

Can the stock O2 be disconnected without getting under the car?

spyder348

todd you dont work on cars do ya? lol yeah the connector is under the back of the manifold, round connector looks like the diag. port mounted on the rear of the valve cover.

toddk911

LOL, hey Spyder!

Well, I have never messed with the stock O2 other than changing it out from under the car.

spyder348

to change needs to be done from under yes but disconnect up top.

toddk911

Does disconnecting the O2 auto put the DME in open loop?

And if so, should we always be tuning with the O2 disconnected to keep the DME "adjusting" out of the picture?