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.....

[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.

[AleroB888]

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.

[ATTACH]6134[/ATTACH]

Interesting, that's for a turbo, right? I'll study that one a bit, might try the last row and smooth it into the rest of the table.

[TGP37]

Interesting, that's for a turbo, right? I'll study that one a bit, might try the last row and smooth it into the rest of the table.

Here is a spark map I used in the beginning of my tuning. It is pretty passive except for the top end, which is worked into the Lumina spark map.

Can't upload excel doc's for some reason. 60degreev6 webpage won't allow the file type. SO heres a pic of it.

[AleroB888]

Here is a spark map I used in the beginning of my tuning. It is pretty passive except for the top end, which is worked into the Lumina spark map.

Can't upload excel doc's for some reason. 60degreev6 webpage won't allow the file type. SO heres a pic of it.

[ATTACH=CONFIG]6138[/ATTACH]

That's within a degree or so of the map I am now using, in the lower right corner. I believe Ben had mentioned some time ago that if you go past 20* in the 3400, it won't make more power, so not to go past that even if no knock occurs. Can anyone verify that?

Also, is the only reason for running richer for the safety of the engine -- that is, to avoid knock?

I am wanting to try it at 12.5 to 12.8 AFR, because the duty cycle of my 36 lb. injectors is lower ( and more comfortable) there, and less fuel would be consumed. That is a concern because I suspect the fuel pump canister may be running dry before the end of my 1/4 mile runs.

And of course, if it makes more power at the higher AFR, I'd take that..............

[Joseph Upson]

That's within a degree or so of the map I am now using, in the lower right corner. I believe Ben had mentioned some time ago that if you go past 20* in the 3400, it won't make more power, so not to go past that even if no knock occurs. Can anyone verify that?

Also, is the only reason for running richer for the safety of the engine -- that is, to avoid knock?

I am wanting to try it at 12.5 to 12.8 AFR, because the duty cycle of my 36 lb. injectors is lower ( and more comfortable) there, and less fuel would be consumed. That is a concern because I suspect the fuel pump canister may be running dry before the end of my 1/4 mile runs.

And of course, if it makes more power at the higher AFR, I'd take that..............

20 deg max is probably the point at which max performance potential is achieved theoretically and actually. If that's the case you'll gain nothing by increasing timing beyond that point just because you can do so without detonation. Doing so could possibly put you in a situation where the bearings among other things are being over loaded causing them to fail prematurely.

For example, if you rotate the crank until the piston is at TDC and then hit the top of it with a rubber mallet, the chances are pretty good it will not move downward, if you rotate it away from TDC about 20 deg for example and repeat the proceedure, the piston will move downward. The first scenario is what you want to avoid exposing to high forces because at that point you have the least amount of give in a situation where SOMETHING has to give. Basically you don't want to exceed the spark timing advance that can be most productive or you start approaching the point where you are trying to stop the piston and move it in the opposite direction.

As for AFR under boost, until you have a good comfortable understanding of it stay on the rich side. It does help fight detonation and cooking your piston rings and valves. http://autospeed.com/cms/A_1595/article.html

[1988GTU]

Also, is the only reason for running richer for the safety of the engine -- that is, to avoid knock?

Not the reason, but it tends to help. What over fueling is supposed to do is drop combustion temps, which in turns helps avoid er band aids you from kr.

I am wanting to try it at 12.5 to 12.8 AFR, because the duty cycle of my 36 lb. injectors is lower ( and more comfortable) there, and less fuel would be consumed. That is a concern because I suspect the fuel pump canister may be running dry before the end of my 1/4 mile runs.

Time to upgrade to a higher output injector set while taking care of any other fuel restrictions.

And of course, if it makes more power at the higher AFR, I'd take that..............

Do do that. Fix the root cause, as you might find. Your motor might possibly prefer tuning for it to run richer than leaner and that means fixing the situation to enable more fuel consumption.