Air Fuel Ratio and Timing for Boosted 3400

[AleroB888]

I'd like to know what AFR in boost this site's members have successfully used for these and similar engines. Please give specifics on your setup.

Also please include "target afr" setting used in PCM to achieve result and the manufacturer of wideband O2 sensor used; 1- or 2-bar MAP.

And the timing at WOT, plug gap used.
Thanks in advance.....

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[TGP37]

T3/T4 .50/.63 3100v6 SFI
8 psi = 11.3-10.7 AFR
4 psi = 11.8-11.2 AFR
0 psi = 12.2 AFR

AFR slides -0.6 over 15 seconds.

I plan to refine these further after the manual swap is complete. Getting a whole new tune.

For fun, I've set idle at 13.5 AFR and it idles very well, feels better but isn't fuel economical.

[Dave96z34]

8 psi = 11.3-10.7 AFR

That's way to rich and will foul plugs quick and up having random misfires. 12 is more like it.

[90BlueZ]

That's way to rich and will foul plugs quick and up having random misfires. 12 is more like it.

That's not rich enough to foul plugs at all. No random missfire either. I've ran mine that rich before. Now, I run about 11.6AFR at 10psi. Can drop to low 11 to high 10 without issue.

[1988GTU]

10.5 area for about 19.5 lbs I think 11.9 was ideal for mine motor at 10 lbs.

[TGP37]

I do run it on the rich side but not too rich. 11.3 is the afr for the most part, it slides into the high 10's after several seconds and high RPM's to help cool.

I'd rather foul plugs and spend 15 minutes changing them out versus replacing the pistons, rings, bolts, etc. And after some time getting to learn the engine again after the manual swap and other modifications I'll bump up the AFR until I hit power loss or 11.8 AFR.

1988GTU, thats good to know. So you think I will be safe at 11.6-11.8 AFR at about 8-12 psi?

[1988GTU]

11.2-11.5 would be what I'd try out and go from there. I am running 110 octane, so keep that in mind.

I do run it on the rich side but not too rich. 11.3 is the afr for the most part, it slides into the high 10's after several seconds and high RPM's to help cool.

I'd rather foul plugs and spend 15 minutes changing them out versus replacing the pistons, rings, bolts, etc. And after some time getting to learn the engine again after the manual swap and other modifications I'll bump up the AFR until I hit power loss or 11.8 AFR.

1988GTU, thats good to know. So you think I will be safe at 11.6-11.8 AFR at about 8-12 psi?

[TGP37]

Yeah, 11.3 is the base line AFR while in boost. I run 93 octane and the knock sensor is functional. I decided to use Keith Black Hypereutectics instead of forged. Hypers can handle the boost well, just don't hit detonation or it's over. But to prevent issues, the rings were gapped for moderate boost temps so I don't rip the crown to pieces. So it is a trade off, my clearances are tighter but the ring gaps increased slightly. Man was that a day, gapping rings. Spent the better part of all day gapping just right. Had them more accurate then what they were shipped as.\

Because of that I feel the extra fuel is justified to help control temps, especially since the top ring is smaller now.

[AleroB888]

Thanks for the responses. I'll throw in some observations on recent test scans I've done.

Engine and tranny are stock 3400, boost peaks at 11 psi at the upper intake manifold. Total charge temperature rise is between 6 - 18 degrees F., depending on ambient conditions. Fuel injectors are 36 lb. GM (from supercharged Buick Riv).

I am able to use up to 20* of timing advance at WOT without knock. In the past I have usually used 18*, but is there a consensus on what is optimum for this engine?

I haven't dyno'd in a great while, iirc the actual AFR was reasonably close to the Target AFR set in the PCM. Now assume for the sake of discussion that Target AFR is close to correct at 12.0. Here are 4 typical WOT scans, each with a different Target AFR:

Target afr .... IPW ........... IDC
13.1 ........... 16.9 ........... 85%
12.5 ........... 18.4 ........... 90%
12.0 ........... 19.7 ........... 93%
11.5 ........... 21.0 ........... 99%

Those were done on different days, but you get the idea. No misfires showed up, no KR. I did not intend to try it at 13.1 AFR, but I typed in a positive adder instead of negative one time. Still did not get KR, though.

The car had about the same "feel" for the different AFR settings. But if I'm getting no KR, would it be worth the risk to chase a few more HP by going up to say, 12.7?

This was for a fixed Target AFR, but I might go back to the "sliding afr" method. That makes sense as the engine tends to build up heat on long WOT runs.

[TGP37]

I agree w/ the sliding AFR. I slide two ways, the AFR gets richer over time & slides 0.2 AFR leaner at higher RPM's (leaner burns faster)

Here is a Spark Map I got from a poster at HPTuners/forum. His spark setting is pretty extreme and I won't use it BUT, the last three rows were dyno proven spark degrees at about 10 psi boost on a 3400v6. I've incorporated those figures into my spark map before and it worked great for boost. Anymore and I got knock.

Spark Map.bmp