would a speed density tune be better for my truck? do i have to convert to a 2 bar MAP? What are the advantages of a properly tuned speed density tune? Thanks-TIM

 

Do you still use your MAF? If so is it maxed?

For *me*, speed density is better for FI, because of the increased granularity of running a 2 (or 3) bar map sensor and doubling the size of the VE table.

Does 1bar MAF tuning work for FI? Sure. Absolutely and with great success.

Here's the difference between the two:

MAF: Your VE table becomes less important when under boost. The PCM relies on the MAF reading to calculate the necessary fuel. Where this can get dangerous is if you are maxing out the MAF (pushing more air than it can read) and the PCM is fooled into thinking you have less air coming in that you actually do, and it tunes you lean.

You also have 1bar of granularity in the VE table, so you can't manually add more fuel (which is ignored after 4000rpm anyway in a MAF driven PCM) for boost, without adding the SAME amount of fuel FOR ALL BOOST LEVELS. A 1bar VE is the exact same as an NA ve table. You can effectively add fuel for boost by adding to the 105kpa column, but you then treat everything from 0 boost to your max boost to exactly the same VE settings (as found in the 105kpa column).

2BAR SD: This method ditches the MAF altogether, which means your tune must be BANG ON RIGHT. There is no MAF anymore to act as a safety net for the VE table, so 100% of the fueling for all RPMs comes from your VE settings. The benefit is that you get twice the granularity of a 1 bar tune. You can now tune for all boost and vacuum levels your engine will see (up to 2bar of course).

This means you have a column for each 5kpa of boost you add over 105kpa and can tune for boost exactly as you tune for vacuum operation. This is a more precise tune, and a tune that is more in your control than a MAF tune.

It's also 6x more work, much more fragile to ambient temp changes, mods, etc.

 

thanks for the explanation Eric ! I'm going to try a speed density tune. Got A friend with a similar vehicle we are going to try it out.

 

What kind of tuning software are you going to use? I really recommend EFI Live for this -- it makes it so easy to get your VE table.

 

great explanation turbo!!!! I am in open loop 2bar sd right now. (open for ve cleaning/tuning) you couldn't be more right about the ve needing to be dead on. I am also commanding 13:1 while doing this, but it blows me away what a +1 at 150kpa 5600rpm will do to your afr.

 

if you can go to a custom operating system..on your fueling you go by the commanded fuel vs rpm.. you can change your A/F at any rpm and map pressure.. cruising down the the highway i have mine set to 15.5 A/F and i get some really good gas mileage down the highway..

 

The thing that confuses me about the whole speed density thing is the two WOT tables. There's the PE and BE tables, and one's supposed to take over the other for certain scenarios. What scenario? It seems that if the PCM knows how much boost is there, then why couldn't you have a WOT VE table, not one that's rpm dependent.

 

Vanilla,

I haven't run a PE table for about a year -- with SD and a dialed in VE table there's not much need of PE.

 

Really? So do you use the Boost Enrich table at all? How does it all work with your LTrims? Do you even have to worry about them if you're not using the MAF?

 

dont even worry about them...