Lean AFR's to Increase Spool?

[1992awdlaser]

If your gauge is reading 20psi then you need to do two things.

1. Check for boost leaks after the maf.
2. Calibrate the maf.

If there are no leaks then you currently need to bring a slider up 28%. Don't know which slider since you didn't capture mafraw.

If you have the extra money laying around a map sensor will make tuning the gm maf soooo much easier.

After the maf is calibrated we can add more timing in to make more power. Then when you turn up the boost you will just have to take each timing slider down about 3* to start off with. Then if everything looks good timing can be added back in.

 

[99gst_racer]

Thanks guys. Yeah, the only reason I logged BoostEST is to see how close (or how far off) it is. I know I need to calibrate my GM MAF. I'll research about doing that today. Any good links to learn about what to do and how it all works? (<----- I feel like a newbie asking that - I'll just on the Link boards and see what I can find)

 

[turbosax2]

Thanks guys. Yeah, the only reason I logged BoostEST is to see how close (or how far off) it is. I know I need to calibrate my GM MAF. I'll research about doing that today. Any good links to learn about what to do and how it all works? (<----- I feel like a newbie asking that - I'll just on the Link boards and see what I can find)

http://jeffgst.com/gmafcalibration2.html
http://jeffgst.com/gmafcalibration1.html
http://jeffgst.com/boostestcurve.html

 

[1992awdlaser]

Best how to I know of:
http://jeffgst.com/gmafcalibration1.html

If you have any questions I am glad to help.

 

[99gst_racer]

Quick question: I don't have any 5-bar sensors in stock here, but I have plenty of 3-bar's. Most of them say they are good to 30 psi, but 3-bar actually equates to 43.44 psi. What's that all about?

Also, in jeff's link, he uses 14.7 in his equation. I assume that's because that is atmospheric pressure at sea level. If I'm 1000 above sea level, would be be smarter to use the more accurate figure of 14.24 instead?

EDIT: I also boost leak tested yesterday to 35 psi and it holds it like a champ. No leaks.

 

[1992awdlaser]

Quick question: I don't have any 5-bar sensors in stock here, but I have plenty of 3-bar's. Most of them say they are good to 30 psi, but 3-bar actually equates to 43.44 psi. What's that all about?

1 bar of every map sensor that I know of is for atmospheric pressure. So, this leaves two bars to read boost.

 

[99gst_racer]

1 bar of every map sensor that I know of is for atmospheric pressure. So, this leaves two bars to read boost.

Ahhh, you're right. I guess I never noticed that they were all measured in psia (pounds-force per square inch absolute). I'll have to wait and order the 5-bar.

 

[turboglenn]

I also use less timing and more fuel to spool it's just the same as anti-lag and NLTS , both retard timing and one adds fuel..both allow me to open my wastegate in neutral, i don't think there's any better way to spool.

YOu may increase heat and maybe energy at a leaner AFR but i have to ask about these 2 things.

1.) although spooling at a lower RPM, have you checked your logs to see how long it takes to increase speed by the same amount of RPM.. Meaning, if you're spooled by 3500 RPM normally and it takes 2 seconds to go from 3k to 3500RPM, but you lean it out and spool by 3300 PRM but it may take more time to get from 3k to 3300RPM than it did to go from 3 to 3500 RPM because of lost power from a leaner AFR..Better torque on almost any motor is going to be created at about 12.5:1..Hopefully you guys get what i'm saying there...my datalog does 180 frames per second so i can see down to 10th's of a second as to how much time has elapsed.

2.) Go try and get out in traffic in first gear.. again this same lean situation in the low boost in a gear that won't load down the motor enough to bring boost on will result in lost power from a lean situation, again 12.5:1 for the most torque is a general rule of thumb... The reason i know these 2 things to hold true is beccause i've tuned to it time and time again trying to save fuel only to be disspointed in other areas of driving just for a slight gain in one department..not worth it IMO.

Check some of these things out and let me know what your logs show you for elapsed time from one RPM to the next during spool and also tell me if you don't feel a loss in 1st gear when trying to get out in traffic at 1/2 throttle. Maybe it's a DSMlink thing where the way the ECU works in some way might benefit from being told to put in less fuel, IDK *shrugs*

 

[99gst_racer]

^^^ My findings seem to be the same for you, but I'm going leaner. The more lean my tune is, the better off-boost response I get. My car has never been more fun to drive in first and second gear, pre-boost, then it is now. When it was rich, it would climb to boost slowly, and sometimes stumble on itself at around 4K. As a matter of fact, on the standard Link tune, I couldn't even exceed 4K RPM's until I took fuel out of it. It would stumble at 4K so hard, I couldn't increase RPMs with any amount of load. It was pouring fuel into the cylinders. Everytime I've taken out fuel, my car has responded better and better, in both boost and pre-boost.

This method worked on my 50-trim set-up as well, and I believe I have dyno graphs (somewhere) to show the difference....

 

[turboglenn]

Well, how rich were you? I mean i'm only running about 13.2 - 113.5:1 under the first 5 psi or so. Then richen up to about 12 or so untill i'm past 14psi then go into the 11's

 

[r1991_4g63t]

2.) Go try and get out in traffic in first gear.. again this same lean situation in the low boost in a gear that won't load down the motor enough to bring boost on will result in lost power from a lean situation, again 12.5:1 for the most torque is a general rule of thumb... The reason i know these 2 things to hold true is beccause i've tuned to it time and time again trying to save fuel only to be disspointed in other areas of driving just for a slight gain in one department..not worth it IMO.

did this make it run like crap in 1st sometimes 2nd under normal driving but runs fine under "spirited" driving?

 

[mach4g63t]

I still am curious... when leaning out like this to increase roll-on boost response, is it safe to use this same tune when coming off the line with Anti-lag at the track, or should this be a sort of roll-on, highway driven tune only? Since Anti-lag builds boost before leaving the line, I understand that it probably wouldn't benefit much, but how dangerous is it to the motor if kept like this and then yanked from the line full boost? Does it matter since you're leaving the line at a higher rpm (launch@ ~5k) then where this lean range occurs?

 

[1992awdlaser]

I still am curious... when leaning out like this to increase roll-on boost response, is it safe to use this same tune when coming off the line with Anti-lag at the track, or should this be a sort of roll-on, highway driven tune only? Since Anti-lag builds boost before leaving the line, I understand that it probably wouldn't benefit much, but how dangerous is it to the motor if kept like this and then yanked from the line full boost? Does it matter since you're leaving the line at a higher rpm (launch@ ~5k) then where this lean range occurs?

You can safely use this same tune at the track.

 

[mach4g63t]

Well, if 11.5 is the ideal range that people shoot for in a safe tune- what is the limit you can lean it out and still make power and not worry about melting down your motor?

 

[1992awdlaser]

Well, if 11.5 is the ideal range that people shoot for in a safe tune- what is the limit you can lean it out and still make power and not worry about melting down your motor?

If you are going to lean it out for better spool you will want to do so when there is no boost or almost no boost present. This will keep it safe. I woulldn't go leaner than 11.5:1 on pump gas when you are in boost. For no boost 14.7:1 and for a little boost 13.5:1 is the leanest I would go.

 

[mach4g63t]

Good to go. That makes sense.

Now, let's switch it a second... when it comes to race gas. I can get C10 110 octane for like 7 bucks a gallon, not a bad deal, I think. I will eventually be tuning my car on this for a fun track tune and some nasty passes. I understand that race gas burns slower, fending off knock, allowing for more boost and a higher timing curve. Is it the same when it comes to the AFR ratio, though? Would you also want to keep it within the same bounds as pump gas? 11.5 or so for WOT boosted pulls and 14.5 for cruise? Thanks for all the help!

 

[1992awdlaser]

Good to go. That makes sense.

Now, let's switch it a second... when it comes to race gas. I can get C10 110 octane for like 7 bucks a gallon, not a bad deal, I think. I will eventually be tuning my car on this for a fun track tune and some nasty passes. I understand that race gas burns slower, fending off knock, allowing for more boost and a higher timing curve. Is it the same when it comes to the AFR ratio, though? Would you also want to keep it within the same bounds as pump gas? 11.5 or so for WOT boosted pulls and 14.5 for cruise? Thanks for all the help!

The air/fuel ratio for cruising should always be bouncing around 14.7:1 no matter what gas you are using. WOT with race gas you will be able to lean it out some more. With race gas I first put the boost where I want it and then get decent peak timing in the low 20's. Then I will lean it out some until I see knock then richen it up slightly.

On pump gas I personally aim for 10.8:1-11.2:1 air/fuel ratio. I do this because almost always timing will make more power than leaning it out. If I leaned it out then I wouldn't be able to get as much timing. This is when a dyno is good so you can see what the car likes. On the dyno you can tune for max timing with say an 11.2:1 air/fuel ratio. Then you can lean it out until it knocks. Then back the timing off to get rid of the knock and lean it out some mor. This way you can see if your car likes a lot of timing and a air/fuel around the 11.2:1 or if it likes a leaner air/fuel and slightly less timing.

 

[turboglenn]

did this make it run like crap in 1st sometimes 2nd under normal driving but runs fine under "spirited" driving?

Yea, that's basically what i'm saying, mid throttle acceleration in lower load gers suffers from the lean condition, especially first where there's not enough load to spool a larger turbo until almost 5500 RPM.. I know my 57 trim in first gear getting out into traffic doesn't make more than a few psi untill after 5k, and i normally don't rev that high just to get into traffic so any lean spots in the first few psi in that gear hurt greatly (at least on stand alone cars i've tuned)

But in 3rd you won't notice this because the motor loads fast enough to get past thea lean condition of the first few psi almost instantly when you get into it, but try it in first and yuou'll see what i mean

That's why i have to ask "how lean" are you guys talking about? I mean if you're into 11's under teh first 5 psi, yes you're loosing something from being too rich.. Tuning is a fine balance and you will find different afr's do different things at differenlt levels of load on the engine. Refer to my post above for what AFR's i use for particular boost/load areas. These are what i've found to be the best balance of economy, power and overall performance balance

Well, I gotta go work for a few hours...

 

[Black_Bullet]

FWIW; Yesterday I put the car on 12.5 afr during the first couple load gm/rev rows in my tune ( which means im richer than normal ) and i advanced the timing a couple degs in that area and the car did indeed pick up better and felt much torquier than before... Going leaner, like keeping the afrs in the 14s during spool didnt feel as strong to be honest, and going way richer than 12 was even worse...
Though, My turbo already spools about as fast as its going to get, but I noticed the difference in 1st gear, and when at a really low rpm before theres any boost....
Im going to lean it back out, but I was playing with my maft and I recalled this thread and thats why I wanted to experiement with different AFR's. So for those with a huge turbo thats laggy I can see were "spool-tuning" can be benefitial.
On a turbo smaller than a 18g I dont see it to be worth the effort though, since this tune is richer than my normal settings. Just my take.

On pump gas I personally aim for 10.8:1-11.2:1 air/fuel ratio. I do this because almost always timing will make more power than leaning it out. If I leaned it out then I wouldn't be able to get as much timing. This is when a dyno is good so you can see what the car likes. On the dyno you can tune for max timing with say an 11.2:1 air/fuel ratio. Then you can lean it out until it knocks. Then back the timing off to get rid of the knock and lean it out some mor. This way you can see if your car likes a lot of timing and a air/fuel around the 11.2:1 or if it likes a leaner air/fuel and slightly less timing.

I agree.
Ive been shooting for 11.2-11.4 afr's, but this maft doesnt like consistency.
For what most of us pump gas guys are after, I think closer to 11.3 is most ideal according to something I was reading about burn rates at different air fuel ratio levels.
Timing does make up a lot for a rich afr though, but heavy boost makes even more power then timing.
But ive read that how much timing you need is based off a LOT of other things and thats its a lot different for every car...

Ive always wondered what would be better though ( given both scenarios have the optimum afr and wont detonate)
* High boost + high timing and low compression ( 8:3ish and lower)
- Or -
* High boost + high compression ( 9:1 + ) and low timing.

 

[JeffGST]

Lean + High Timing = Better boost response

Why? Because heat and pressure spool a turbo. The more pressure there is the faster the turbo spools.

The only time low timing spools a turbo quicker is when you activate Antilag. But this is a EXTREME case of ignition retard. Instead of spooling up in the 15-25 degrees of advance, ALS retards timing to negative 10 degrees of timing or 10 degrees ATDC. That is a huge difference since the spark is occuring so late, that the combustion pressure escapes right out the exhaust valve.

The best way to test this data, is on the dyno with a MAP sensor. I have tuned many cars that show increases in boost response through this lean and high timing method. This achieves the most efficient burn and produces the hottest and most pressurized burn possible.

 

[Tarantula]

I started a thread on DSMTalk on this but my scenario is a bit different. I use a mix of E85 and I use the FP3052. I boost about 25psi. While tuning to perfect acceleration I found that I get so much better spool up by making it rich down before 4500-5000rpms than leaning it out. First gear is just a blink and second gear is amazing. The boost comes on hard and strong. Now I can't play with timing numbers because I am not on link. I have a keydiver and it follows stock timing maps. I have zero knock everytime. My max timing is 15-16 degrees. My timing always dip to about 9 degrees when going WOT than climb to 15-16.
If I lean out the mixture closer to 12 A/F ratio down low, my spoolup is smooth. Spoolup with A/F ratio in high 10's result in a hard hitting faster spoolup. Maybe because I'm using E85 that my results are different since E85 makes more power slighlty rich? But wanted to add my experience to the mix. Now after 5K I lean out the fuel but have not gone to its max lean yet. I want to try to get 12 up top to make more lbs/min. So far my max has gone close to 40lbs/min on stock cams/stock head/valves.
Heres my thread if you want more details. Rich A/F down low spools turbo faster. - DSMtalk Forums

 

[slipstream808]

Yes, you've got it exactly. Your results will be different because of the different burn characteristics of E85. I wont tell you anything to do because you've experimented, know what you are doing and getting results you want. Now if you can one day get the ability to adjust timing then yeah, come back cause you'll have more fun and adjustability to play with.

 

[phunny]

JeffGst, on pump gas what a/f's do you shoot for pre-boost and up to full boost?

 

[synchronic]

99GST has it totally right when it comes to retarding timing to spool faster. It becomes a problem of diminishing returns. You get to boost faster, but your engine isn't on the pipe because you're dumping cylinder pressure into the exhaust that could be harnessed by the cycle. Besides, the big negative is increased temps on the exhaust components, namely the turbine wheel. And considering that plenty of time is spent off-boost cruising, it will shorten the life of your exhaust mani and turbo.

I think that you would get way more benefit retarding the exhaust cam gear. It all comes down to cylinder pressure and using as much of the burn as you can.

 

[OneLove]

What you want to do is retard the timing and add fuel pre-spool.

Retarding timing will make it spool faster. It does this because more of the heat from the power stroke goes into the exhaust manifold. I will try to explain each.

When timing is advanced the spark ignites the air/fuel mixture at a sooner point. This gives the mixture more time to burn in the cylinder. Most of the heat from this will be absorbed by the engine itself. The reason this makes more power is because the mixture has a longer time to burn before the piston reaches tdc. Since it has more time to burn it is going to make the pressure pushing down greater. This is where the exrta power comes from. More pressure downwards when the piston is at tdc. This is also why advancing timing can create knock or pre-ignition.

Retarding the timing makes the mixture start to burn closer to tdc. This will make less power since the mixture has less time to expand before the piston reaches tdc. Retarding will cause some of the mixture to be burning when the piston is moving down and when moving up on the exhaust stroke. Since the mixture burns later the heat has less time to be absorbed by the engine and as a result it will go into the exhaust manifold which will help spool the turbo. The mixture burning during the exhaust stroke also causes the turbo to spool sooner since the mixture is burning with the exhaust valves open. This is how antilag works, it retards timing so the mixture is burning when the exhaust valve is open.

When you add the fuel, the mixture will be burning longer since there is more fuel to burn. This will also cause the mixture to burn when the exhaust valves are open which makes the turbo spool faster. When the spark plug first goes off all the fuel doesn't burn right away. The fire spreads outward away from the spark plug. Since the flame spreads outward it takes time for all the fuel to burn. So, if you add fuel there is more fuel to burn which equals more time it takes to burn all of it. That translates into some of the fuel burning when the exhaust valves are open. This is another way of knowing how adding the fuel help.

If you don't understand i will try to make it clearer for you.

Very informative post, Thankyou. Im gunna give this a shot tonight.