What is an OK AFR for part throttle cruising under boost?

[mbarryracing]

Figured I'd throw this out here to my fellow TY members with more of a profound knowledge when it comes to boosting...
I am in the process of dialing in the AFR's with my ID1000 injectors and when I am cruising at between 20-40% throttle I am building anywhere from 4-7 psi of boost running along. My question is what AFR is acceptable under boost at part throttle load? Considering I have cool intake temps (below 20 C) and controlled coolant temp, with fresh 91 Oct pump gas.
Currently have it running between 13:1 and 13:7 hoping to maintain some fuel mileage, but should I be running richer?
It shouldn't be detonating because the cylinder pressure isn't high being it's just cruising and not under big load...

Thanks.

 

[suburban]

i would be 12.7-12.8 with that kind of cruise boost.

 

[TurboTime]

You are correct. I also run about 13.5 during half throttle. Its within specs...

 

[kinger]

I run about 12.0-12.9 little rich I know but it runs so perfect I figure a little extra safety is ok. When I leaned it out to 13-14afr cruising then it got VERY lean in the switch points of the GEMS. Again that is my GEMS unit your running a fancy motec or something right?

 

[Wildman]

Re: What is an OK AFR for part throttle cruising under boost

Figured I'd throw this out here to my fellow TY members with more of a profound knowledge when it comes to boosting...
I am in the process of dialing in the AFR's with my ID1000 injectors and when I am cruising at between 20-40% throttle I am building anywhere from 4-7 psi of boost running along. My question is what AFR is acceptable under boost at part throttle load? Considering I have cool intake temps (below 20 C) and controlled coolant temp, with fresh 91 Oct pump gas.
Currently have it running between 13:1 and 13:7 hoping to maintain some fuel mileage, but should I be running richer?
It shouldn't be detonating because the cylinder pressure isn't high being it's just cruising and not under big load...

Thanks.

Hey Maury do you need that kind of boost when cruising or is that just what your turbo is making? The reason I ask is if you want better mileage set-up your closed loop boost control to use TPS vs Load (boost). Make it so anything below 60% (example) it will only allow 1 to 2 pounds of boost and then run in the 14 to 14.2 AFR just cruising almost as if its a N\A motor. You can have your cake and eat it!

We run a hot trail sled like this with a Motec. Barely any boost until you want it which is normally past 60% throttle then full tilt at 95% (I'm sure you know you can configure the TPS tables up to 14 cells for a lot of options). You can stage it in on the table. There are many more boost parameters you can use with the Motec I believe two full 3D tables completely user definable at the same time.

You don't have to worry about fuel quality either with this as much nor detonation while cruising nice and lean for max economy.

 

[Omega_5]

For part throttle, boost situations, I generally aim for a 'naturally aspirated power enrichment'. Meaning, I aim for 12.8, but accept between 12.5 and 13.2. I'd suggest bumping it up a small bit to be safe.

To be fair, many boosted road vehicles won't go into power enrichment until about 75% throttle. I'd never do that on a sled, as they can load up pretty fast when you run off trail.... but it's peace of mind knowing what most engines are capable of.

With that said, are you controlling the fuel based on load (MAP), throttle, or a combination?

 

[mbarryracing]

I am using a Motec M400 from Martin, very very accurate and defined as you want it to be.
My main fuel table and ignition table are RPM vs Throttle % with a secondary load fuel table that is MAP pressure (boost) vs RPM. This is what I am tuning now, very easy.
There is also a secondary ignition table for MAP to pull timing out, but that is pretty much a standard table and don't need to mess with it.
Both fuel and ignition have compensation tables for intake air temp and coolant temp, as well.

OK, so I probably should add some fuel to the lower boost levels and et it around 13 or under? I already have 11.5 at WOT, so all good there.

 

[Omega_5]

I guess I should have looked at your mod list.

Seeing as your using a real ECU, adding about 3.7% to the area you mentioned (in the RPM vs throttle table) will probably get you right on the 13:1 mark.

It's worth noting that you might want to watch the AFR on your next ride at the same throttle / RPM, under no boost. If the change causes the sled to go rich under vacuum conditions, you might have to reverse the change and bump the MAP compensation table instead.

 

[mbarryracing]

All my changes have been to the MAP comp table, specifically the 125 to 150 kpa cells. Not even touching the main fuel table (naturallly aspirated)...
Got it dialed in so part throttle - no boost is 13:1 and part throttle - boost under 6 psi is at 12.5:1, anything with boost levels higher then 7 psi drifts down towards 11.5:1.
I really like this Motec.