Air Fuel Ratio and Timing for Boosted 3400

[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.

Attachment 6134

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.

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[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.

passive boost spark map.jpg

[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.

passive boost spark map.jpg

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.

[TGP37]

From what I am reading/learning, an EGT Gauge can help with boosted AFR's. I read the higher the EGT's under load equals more power. Especially a turbo as the heat is the primary force that drives the turbine.

So leaning the AFR under boost will increase EGT's. Likewise adding fuel will bring temps down. Unless your beyond stoich going lean, but if the engine is running leaner then stoich in boost......there is a bigger problem, lol.

AleroB888: An EGT will be a blessing if you want to lean out the AFR's. But it isn't an exact science, as I learned. Placement of the EGT Sensor will determine over all temps. This is why I mounted mine as close as possible to CYL6 (the assumed hottest cyl).

Now, I'm curious of the max safe EGT for our engines? Anyone know?

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

I found upgrading to a larger diameter fuel line reduced restriction which in turn boosted the fuel rail pressure. That could be a cheaper solution versus new injectors above 36 lb/hr. Stock I was around 43 psi. With a -6AN Braided Stainless (3/8") my fuel rail pressure jumped to 60 psi. I also have a high flowing fuel pump, but not high pressure. Only need basic adapters at the rail and fuel filter.

Or get a WOT-TECH Adjustable FPR

Or get a boost referencing 6:1 FMU