Tuning for Timing vs Tuning for Boost

Once you get beyond a few psi of boost, your goal is basically going to be to set the timing as high as you can get it without knocking (at least, if you're running straight pump gas). So really it becomes a question of how much boost you should run. There's two ways to answer that question:

1) Turn it up until you stop getting additional power.

2) Look at how much everyone else is using, and just go with that.

I tried #1 until I reached #2, and then I chickened out.

For me that was 18.5psi, but I had a FMIC.

Most of the research I've done indicates for power, you want to run as much boost as you can within your turbos efficiency range with as lean of an air fuel ratio as you can get away with. From there timing should be dialed in to work with the above without knocking.

Many people that upgrade to say a 16g without fueling upgrades are unable to hold as much boost due to running out of fuel up top. In those cases people have dialed boost down and added timing and likely not lost very much power.

There are many ways to go about it but what most people don't get initially with OEM turbo and stage 2 setups is that going from 17 or even 16.5 psi at 2800-3600 rpm to 18 psi is really not adding a lot of power to the car as it gets through that RPM range very quickly. IMO you're better off running 17psi and holding it as far through the rpm range as is possible. 18+ psi is possible but you're really beating up the turbo for not a lot of gain.

Most of the research I've done indicates for power, you want to run as much boost as you can within your turbos efficiency range with as lean of an air fuel ratio as you can get away with. From there timing should be dialed in to work with the above without knocking.

 

Many people that upgrade to say a 16g without fueling upgrades are unable to hold as much boost due to running out of fuel up top. In those cases people have dialed boost down and added timing and likely not lost very much power.

 

There are many ways to go about it but what most people don't get initially with OEM turbo and stage 2 setups is that going from 17 or even 16.5 psi at 2800-3600 rpm to 18 psi is really not adding a lot of power to the car as it gets through that RPM range very quickly. IMO you're better off running 17psi and holding it as far through the rpm range as is possible. 18+ psi is possible but you're really beating up the turbo for not a lot of gain.

Thanks! I was talking with a tuner who tuned my friend's car (same Stage 2 setup as mine, except stock mufflers and restrictor pill) with a target boost of 15psi, and he focused on increasing timing rather than boost. Also, his engine load ranges go up to like 3.2 It felt very smooth, but like there was some power missing from it.

Like I said in my first post, I remember hearing that you can do one or the other...but want some input on that.

Like I said in my first post, I remember hearing that you can do one or the other...but want some input on that.

Nope - that is a false dichotomy. To understand why, you have to understand a couple things about tuning.

The really key thing is that if you are running pump gas, and running non-trivial boost, your maximum timing advance is limited by knock. What I mean is, adding timing will add power, right up until the motor starts knocking. So, no matter what boost level your tuner chooses, they are going to increase the timing advance to a level just below the knock threshold.

I think that what gets people confused about this is the fact that the knock threshold is inversely proportional to boost. So, if you add boost, you have to run less timing to avoid knock - or if you reduce boost, you'll be able able to run slightly more timing without knock. So it looks like an either/or choice. But in fact the tuner doesn't really get to decide between running more boost or running more timing - the tuner chooses one of those (a boost level or a timing advance), and the motor chooses the other.

If you're visually and numerically inclined, this image might help...

http://i193.photobucket.com/albums/z151/Legacy_NSFW/Tuning/v126-Timing.png

That's the total ignition timing advance that my car was running about ten reflashes ago.* You can ignore the dark bands, that's just where my mouse happened to be when I took the screenshot.

The numbers on the vertical axis are RPM. The numbers on the horizontal axis are load - the number of grams of air that were ingested with each intake stroke. As boost goes up, load goes up.

I came up with the timing table by finding the knock threshold at several different boost levels. Notice that the timing advance automatically tapers as load goes up. If I turn the boost down, I automatically get more timing. If I turn the boost up, I automatically get less timing. When I choose the boost level, the motor tells me how much timing it will allow at that boost level.

Or I could say "I want to turn up the boost until the knock threshold at 4000 RPM is a little more than 10 degrees" and then I'd end up with whatever boost level produces a load of about 3.45 grams.

I don't get to choose both. Whichever one I choose, the motor tells me what the other one has to be. If I don't use what the motor wanted, I'm either leaving power on the table or blowing up the motor.

* For the tuners in the crowd: that's the base table plus the dynamic advance table. I've added 2-4 degrees at high load (4.0ish) since I took the screenshot. Load values shown are probably about 10% higher that what you'd see if I was scaling my injectors the way Subaru does it, but I used ID's scaling.

You're forgetting a few things. Boost changes with the gear and will also will change at least a little bit with the weather. There are compensation tables to adjust the boost controller based on ambient conditions.The knock threshold can vary with the weather and driving conditions as the water, oil, and intake temps change. There are compensation tables but you can't really get them all "perfect."

The trade offs between adding more boost + less timing vs less boost and more timing are best found on the dyno. In my experience the more modified engines, especially those with cams etc, need to run less timing to remain safe. The really built engines can make a ton of power with little timing advance.

You're forgetting a few things. Boost changes with the gear and will also will change at least a little bit with the weather. There are compensation tables to adjust the boost controller based on ambient conditions.The knock threshold can vary with the weather and driving conditions as the water, oil, and intake temps change. There are compensation tables but you can't really get them all "perfect."

All true, but how are these things relevant to the OP's question? Why must he understand them in order to understand the answer?

Because tuning boost is harder than tuning timing. Boost takes time. You have to scale back timing, up the target boost, guess and check the wastegate and turbo dynamics controls to stabilize boost, then check and readjust fuel slightly. Then add back in timing until you feel haply, or hit knock threshold.

Or just +2 part of the timing table and check knock, one step at a time. There are a lot of lazy tuners. I have seen Cobb do this at their Plano location. Guy comes in with an HTA Green, wanting to switch to E85. They spent so much time replacing his clutch, they just turned up his timing table and sent him home. Lazy. But the customer has no concept of efficiency islands or cylinder pressure, so everyone is happy. It pays to know.