How to tune for less turbo lag?

[Thumper]

Well I'm starting to tune my motor and my main concern is turbo lag. My turbo is more than capable of outflowing my injectors so my limiting factory will be them then the stock bottom end. My signature has my specs and i'm running msns-extra 25v2. I have read that in some cases lower timing during boost build up helps since this increases egt's. I have read increasing timing helps because it gives the car more power = more energy = more exhaust gases to spool the turbo. Another theory I've read is during boost build up run engine slightly leaner which in turn increases egt's as well. I have my initial timing at 24, then during vacuum it slowly ramps up to 39 by 3000rpms. Then I retard timing roughly 1.2 degrees per psi. So what do you suggest trying more timing, less timing, more fuel, less fuel, etc...? Thanks

[myplasticegg]

If it is a drag car, throw a 50 shot of nitrous on it. If it is a street car, enjoy the lag as a "traction builder"

[oinojo]

yes tuning is crutial to the response of the car. When i turboed my 02 civic si, i had turbo lag between the time i installed it and the time i spent on the dyno. I normally would have full boost by 5200rpms before the tuning, and after i had full boost @ 3800. This was done using a Turbonetics T3/60-1 turbo. This thing was enormous for a *eco* vtec honda 4 cylinder.

[Clifton]

Exhaust flow spools turbos not heat. Heat is just a byproduct of power. More timing will make more power. More power = more exhaust, more exhaust flow = faster spool.

 

If you have 12 psi by 3100 rpms I wouldn't worry. When will you be below that rpm when racing or really in it? In 4th I can get 5 psi by 3k and I thought mine spools fast for it's size.

[Thumper]

If you have 12 psi by 3100 rpms I wouldn't worry. When will you be below that rpm when racing or really in it? In 4th I can get 5 psi by 3k and I thought mine spools fast for it's size.

 

You are right I am quite happy with 12psi at 3100rpms but if I could tune it so it was at 2700 that would be even greater. Also because of my bad piston skirts and soft hydraulic lifters I don't want to go above 6000rpms so every little bit will help. If I can't then I can't but if I can I can.

 

Thanks for the advice but I am not interested in NOS and I know that tuning will help turbo lag that is the reason for my question. Thanks

[Pyro]

When I was running a stock T3, it would be at 5 psi at 2300 rpms and 10 to 12 psi at 2800 rpm. But it didn't start to pull until 3000 rpms anyways. So lower spool rpms doesn't didn't mean less lag for my car. So, it had boost but didn't start to go move like a turbo cr until 3000 rpm.

 

I recently got my bigger turbo to start spooling to 3 or 4 psi at 2800 rpm and 8 to 9 psi at 3000 rpm (up from 5 psi at 3000 rpm) by leaning out the mixture with 28 degrees of timing (no boost retard). The lag is now a little more than stock but that could also be caused by the stage 1 turbo cam.

[zguy36]

Clifton,

 

I must say that your theory on boost could not be any more incorrect. The amount of air flow does indeed create more boost, but it is the heat that is the main driving factor. As the hot exhaust air goes from high pressure (before turbo) to low pressure (after turbo) it is much cooler. This change in energy is what is transfered through the turbine. Simple thermodynamics and turbine theory. A quick way to prove this... take you car up to fourth gear, build full boost. While you foot is still in the throttle (don't let up) reach out and turn your ignition off. Your boost will drastically drop even though your engine is still pumping just as much air as before.

 

The way to tune for fast building boost is the same way to tune for power. Correct air/fuel ratios and proper ignition advance for power is also correct for building boost quickly. These values are dependent on your setup and how much boost you are running.

 

-jeremy-

[Clifton]

Clifton' date='

 

I must say that your theory on boost could not be any more incorrect. The amount of air flow does indeed create more boost, but it is the heat that is the main driving factor. As the hot exhaust air goes from high pressure (before turbo) to low pressure (after turbo) it is much cooler. This change in energy is what is transfered through the turbine. Simple thermodynamics and turbine theory. A quick way to prove this... take you car up to fourth gear, build full boost. While you foot is still in the throttle (don't let up) reach out and turn your ignition off. Your boost will drastically drop even though your engine is still pumping just as much air as before.

 

The way to tune for fast building boost is the same way to tune for power. Correct air/fuel ratios and proper ignition advance for power is also correct for building boost quickly. These values are dependent on your setup and how much boost you are running.

 

-jeremy-[/quote']

 

If you shut your ignition off with your foot in it obviously it will obviously loose spool. Cylinder pressure under load is over 1000 psi. That's alot of volume that is lost. According to your theory, STS systems shouldn't work very well either. The heat created at 3k and 6k rpms is the same but at 3k you will have quite a bit of lag due to the low exhasut volume. Try holding a propane torch on the turbine wheel and see how fast it turns, then use room temp compressed air. Correct afr's and timing build boost faster because you are making more power wich produces more volume. Just like a 5L motor will spool a given turbo faster than a 3L motor at the same rpm. More exhaust volume, not more heat.

[Bernardd]

I run 45deg's advance until the boost kicks in. That brought my spool down by 800rpm. Previously I ran 30degs max with no boost. Afr's are low 13's to high 12's before boost at wot. I have a small amount of meth/water inj starting on boost so perhaps I can get away with more than most so this just a guideline. More timing = quicker spool in my experience.

[yo2001]

There was a thread about this before. More timing (max timing no ping) will give most power. Since you are giving more power (torque, high cylinder pressure) you rev faster leading to more exhaust flow. Higher rpm more exhaust flow, more spool. But if in case the same rpm (like two step) less timing will spool the turbo due to its heat. (heat=energy)

 

Tune for max timing = most power.

[Tony D]

"You are right I am quite happy with 12psi at 3100rpms but if I could tune it so it was at 2700 that would be even greater."

 

Don't confuse Boost Threshold with Turbo Lag. What it appears to be here is that you want full boost at a lower rpm, which means lower threshold.

 

You can artificially tweak some of those parameters like Bernard suggests by running advance one way or the other. I know I could get 17psi at 1000rpms on a stock turbo with a 5ATDC timing setpoint and flooring the pedal for full fuel. Turned the turbo into a gasturbine. Also will melt down your wheels, blow holes in your housings, make them glow orange cherry red at idle while doing so, melt the braze joint on the oil feed line... etc etc etc...

 

Nothing is free, for keeping the car on boost instantly, drive the vehicle in the proper gear for the speed you are at, otherwise size the turbo for the threshold rpm value you want full boost to occur. Anything else is a patch for an improperly applied turbo, changes can be done, but the temps at the turbine will increase and life may be shortened. Flatshifter WRC Anti-Lag Turbos don't last very long compared to stuff not subjected to that abuse!

 

I agree with the last few posts: most timing will optimize power. Optimize power, not necessarily trim threshold using timing.

[zguy36]

If you shut your ignition off with your foot in it obviously it will obviously loose spool. Cylinder pressure under load is over 1000 psi. That's alot of volume that is lost. According to your theory, STS systems shouldn't work very well either. The heat created at 3k and 6k rpms is the same but at 3k you will have quite a bit of lag due to the low exhasut volume. Try holding a propane torch on the turbine wheel and see how fast it turns, then use room temp compressed air. Correct afr's and timing build boost faster because you are making more power wich produces more volume. Just like a 5L motor will spool a given turbo faster than a 3L motor at the same rpm. More exhaust volume, not more heat.

 

Clifton,

 

"If you shut your ignition off with your foot in it obviously it will obviously loose spool. Cylinder pressure under load is over 1000 psi. That's alot of volume that is lost. "

 

An engine is a constant displacement pump. If you shut down the ignition, the engine is still turning and therefore still drawing in air and pumping it out the exhaust. Yes, the cylinder pressures do indeed drop, but that is not because of a loss of airflow. Cylinder pressures drop because there is no combustion (heat creation) in the cylinder chamber. Cylinder pressures w/o combustion are ~150-200psi and with combustion ~500-1500psi depending on throttle opening and boost.

 

The only difference is boost comes from the amount of heat that is being ejected through the exhaust. With ignition off, you still are pumping the same amount of air, just the air is cold. You get no boost. With ignition on, you are pumping the same amount of hot air and you get your turbo to spool up. You are correct in that it does take an amount of air to spool the turbo, but that air must also be hot. Remember that work is being done by the turbo and must come from somewhere. The compressor side of compressing the exact same amount of air as is being released through the exhaust side. What goes in must come out. This is not theory, it is the laws of conservation of mass an energy. If it was mearly air velocity driving the turbo, then the same amount of power would be transmitted to the turbine as the compressor would consume to pressurize the intake. That assumed a 100% efficient thermodynamic cycle, which is not the case. The extra energy comes from the temperature difference between the inlet to the turbine and the outlet of the turbine. If you still do not understand, I can reference some thermo equations and diagrams to help. I am at work now and do not have access to my thermo book. (I am a mechanical engineer)

 

Now for the question at hand originally posted here. How to tune for best spool. Since you engine is constant displacement, you cannot really change how much air is being pumped unless you make changes to the engine itself to improve volumentric efficiency. If you are just trying to tune the engine, this is not what you are striving for. If you want the turbo to spool the fastest, tune the engine how you would normally tune. Any changes that would make a turbo spool faster would be outweighed by how poorly your engine runs as the result. For example, anti lag systems. These are great for off throttle, but not what you want during full throttle. Systems that retard timing and richen fuel mixtures to the point of constant backfire will spool the turbo. In this case, you are burning tons of fuel in the exhaust just before the turbo in essence making a jet engine out of it. When this is going on though, the engine is not making power, just building boost. That is the beauty of the system because it builds boost on decel, when you would normally lose boost pressure, then switches back to normal fuel and timing curves when power is required again. Anyway, I hope some of that helps.

[Tony D]

Systems that retard timing and richen fuel mixtures to the point of constant backfire will spool the turbo. In this case, you are burning tons of fuel in the exhaust just before the turbo in essence making a jet engine out of it. When this is going on though, the engine is not making power, just building boost. That is the beauty of the system because it builds boost on decel, when you would normally lose boost pressure, then switches back to normal fuel and timing curves when power is required again.

 

Dang, who else said that? LOL!

[yo2001]

Anti lag also needs O2 to ignite the fuel good so 0 throttle antilag needs an aux. air valve.

 

Just to keep the poeple less confused with WRC antilag and dragracing launch control antilag

[zguy36]

Haha.... you beat me to the punch! I was still typing before I saw what you said.

-jeremy-

[Guest bastaad525]

what are some other causes of lag? in a small turbo like a stock T3. Obviously, restrictive exhaust, and I guess retarded timing can increase lag, but what else?

 

what effect does fuel mixture have on lag?

[thehelix112]

Turbocharger work on pressure differentials.

 

You are both right.

 

Hotter gases occupy more volume. In a given container (the exhaust manifold), more volume of gas results in higher pressure.

 

Dave

[Clifton]

Clifton' date='

 

"If you shut your ignition off with your foot in it obviously it will obviously loose spool. Cylinder pressure under load is over 1000 psi. That's alot of volume that is lost. "

 

An engine is a constant displacement pump. If you shut down the ignition, the engine is still turning and therefore still drawing in air and pumping it out the exhaust. Yes, the cylinder pressures do indeed drop, but that is not because of a loss of airflow. Cylinder pressures drop because there is no combustion (heat creation) in the cylinder chamber. Cylinder pressures w/o combustion are ~150-200psi and with combustion ~500-1500psi depending on throttle opening and boost.

 

The only difference is boost comes from the amount of heat that is being ejected through the exhaust. With ignition off, you still are pumping the same amount of air, just the air is cold. You get no boost. With ignition on, you are pumping the same amount of hot air and you get your turbo to spool up. You are correct in that it does take an amount of air to spool the turbo, but that air must also be hot. Remember that work is being done by the turbo and must come from somewhere. The compressor side of compressing the exact same amount of air as is being released through the exhaust side. What goes in must come out. This is not theory, it is the laws of conservation of mass an energy. If it was mearly air velocity driving the turbo, then the same amount of power would be transmitted to the turbine as the compressor would consume to pressurize the intake. That assumed a 100% efficient thermodynamic cycle, which is not the case. The extra energy comes from the temperature difference between the inlet to the turbine and the outlet of the turbine. If you still do not understand, I can reference some thermo equations and diagrams to help. I am at work now and do not have access to my thermo book. (I am a mechanical engineer)

 

[/quote']

 

There is more air exiting the engine when during the combustion. Fuel has energy and that mixed with oxygen and ignition makes an expolsion that produces alot more volume than if there were just air alone being pumped thorugh. The fact that the exhasust is hot is just a byproduct of the combustion. Someday when I'm retired and bored I might intercool my exhaust and hang the turbo out back like STS to show that it is volume and velocity the spins it, just like any other driven turbine(Electric generators on dams, ect).

 

 

what are some other causes of lag? in a small turbo like a stock T3. Obviously' date=' restrictive exhaust, and I guess retarded timing can increase lag, but what else?

 

what effect does fuel mixture have on lag? [/quote']

 

What are you talking about, lag on the stock T3. How much faster do you want it to spool, off idle? ALL turbos have lag. Try a postive displacement SC. To answer your last question though. Peak tuorque occurs around 13.2:1. More power, more exhaust, faster spool. Look at any dyno with equal motors and turbo and you'll see cars that run richer spool slower. This is not therory.

[Guest bastaad525]

well MY T3 has lag. In any gear, if I hold the rpm at 3000rpm, just cruising hold that RPM steady, then floor it instantly, it takes around 1.5 to 2 full seconds before my turbo spools to 13-14psi where I have it set. Yes I've actually sat there with a stopwatch and timed it. Two... full.... seconds.

 

By comparison, my nearly stock, brand new SRT-4, if I do the same thing, hold 3000rpm then floor it, hits full boost of about 16psi in about half a second. I figure part of this is due to the SRT having a very small turbo, but the T3 isn't exactly large either, so a full extra second/second and a half to spool doesn't make sense.

 

My turbo is in good shape. There's no shaft play that I can tell, not side to side or back and forth. There's no oil seeping out anywhere that would suggest a bad seal or anything like that. I'm on the stock downpipe but everything past that is opened up compared to stock, with a mostly 3" pipe with some 2.5" thrown in, through a straight through glasspack, no muffler, no cat. Even before when I had just the open stock downpipe, it didn't spool that much faster. The SRT's stock exhaust isn't anything phenomenal, by comparison, with some pretty bad restrictions in it as well, so I'm not convinced it's the stock downpipe either.

 

Maybe it's something to do with the way my car runs rich when boost hits... but that's a funky catch 22. It only runs rich when boost comes on, but is it that it's running rich that's making the boost come on so slow?

 

So I'm left scratching my head... lots of guys have said how the stock T3 has very little lag (though I'm the first person I know of to actually sit there and TIME it )... well either something is wrong with my setup, or you guys are just very forgiving.

[stagefumer11]

I have the same problem. Lag. Im using a Rb20det turbo on my l20et with a FMIc and 2" piping, 2.5 Exhasut. And in any gear is lags. im onl running 11psi.

 

Nearly fully advance timing also