How to tune for less turbo lag?

[spork]

well, I can't help you with your spool problem except to say, theres something wrong with your car. It shouldn't take that long to spool.

[Guest bastaad525]

well, I can't help you with your spool problem except to say, theres something wrong with your car. It shouldn't take that long to spool.

 

thanks

 

okay so who has any ideas why my car might be spooling slowly?

 

or better yet (and I know probably no one will try this for me) can someone with a stock T3 do this same test for me with a stopwatch and tell us what they get? Just cruise along, I usually try 3rd or 4th gear, holding a steady 3000rpm, then floor it, and count how long it takes from the moment you floor it to spool up to whatever boost level you're running.

 

Also please mention how much boost you're running for reference.

[yo2001]

T3 wheels are just heavier to get it to go to spinning. Inertia. Mitsu wheels in the SRT and EVO are thinner, lighter, hence better response.

 

You ought to see dual BB CHRA between fast shift, it'll hoover like 5 psi boost.

[thehelix112]

bastaard,

 

As previously mentioned a turbo works on pressure differentials, specifically, higher on the manifold side than on the exhaust side so here are some things that will either decrease the manifold side, or increase the exhaust side:

 

1. Wastegate creep! - just experienced the difference this will make. Used to get 4psi by 3250 but have to wait til 4500 for 11psi. Now I get 11psi around 3750. Hell of a difference. Fries the tyres in 4th at 60mph.

 

2. Restrictive exhaust. The std downpipe was designed to work with the std T3 so that should be ok. Also did this on my car. 2.5" press bent wouldn't boost past 10psi no matter what I did. 3" no muffler immediately went to 25psi+

 

I don't think running slightly rich will have as much of an impact as these two things.

 

Is the wastegate flap closing properly? To test this quickly just put a spring holding it shut.

 

How are you setting boost to 14-15psi?

 

2 full seconds is a joke. My 650hp turbo spooled faster than that with the aforementioned crap wastegate spring.

 

Dave

[zguy36]

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' date=' just like any other driven turbine(Electric generators on dams, ect).

 

Clifton,

You are close to understanding what is actually going on with a turbocharger, but are missing a few crucial points. There is not more air exiting the engine during combustion. There is however, much more volume. The mass that goes into the engine is the same as the mass that leaves the engine. During combustion, much heat is added through burning of fuel which causes the air to expand greatly. This is where you are getting confused. Even though the air now occupies more volume, it is still the same mass. This is what I mean when I say that heat makes the turbo spool. Without the heat of the exhaust, it would occupy much less volume and be a much lower pressure. This is what is wrong with your intercooled exhaust idea. When you cool the hot exhaust gasses back down, the volume decreases and the pressure also drops. I doubt you want me to spout the equations to back this, but if you would like I can go into a much more mathematical approach. You equated your system to the turbines in a dam. You are correct about the turbines in a dam using the kinetic energy to spin them. This works for them because water has a much higher density. With more density, it packs more kinetic energy into a small area.

 

I am not usually one to frequent forums because they do not seem to be a place of learning, but more of a place for spouting erroneous babble. If anyone here would like to learn about the correct thermodyamic principles behind how a turbocharger works, please ask. I would think four years of mechanical engineering classes and $50,000 in tuition would mean something to someone. Or, maybe I'll commit forum suicide and quit frequenting this board and let ingorance reign.

-jeremy-

[proxlamus©]

very interesting Jeremy..

 

it makes sense... hmm

[Bernardd]

 

I am not usually one to frequent forums because they do not seem to be a place of learning' date=' but more of a place for spouting erroneous babble. If anyone here would like to learn about the correct thermodyamic principles behind how a turbocharger works, please ask. I would think four years of mechanical engineering classes and $50,000 in tuition would mean something to someone. Or, maybe I'll commit forum suicide and quit frequenting this board and let ingorance reign.

-jeremy-[/quote']

 

Why do the sts systems seem to work so well? It would seem that with a bit of trial and error one can/could get a reasonable amount of power out of a rearmount turbo. Is it possible to calculate the volume/density/flow (whatever you call it) at the end of 6' of pipe as opposed to what it would be out of the cylinder head? Would that type of info be any good in sizing a rear mount system? I would like to turbo a newer car without fussing with a set of manifolds/turbo etc etc.

[zguy36]

Bernardd,

 

I did a search for the STS system that everyone keeps talking about. After looking at their website, I have a clearer understanding of what is missing here and to help you all understand.

 

From what I saw, the STS system mounts the turbo at the rear of the car in order to reduce heat fatigue on the turbocharger parts and to also reduce heat in the engine compartment. My first response to this is that heat in the turbo is not that bad if properly handled. They showed a picture of a glowing turbo, and that is bad if you shut the engine down without letting it cool, since it burns the oil inside of the cartridge. If you let it cool properly, there will be no problems with oil burning, and this I assumed you all already know.

 

My replies to what STS says will be in normal text and their words will be in bold.

 

Directly from the website of STS:

http://www.ststurbo.com/f_a_q

 

Doesn't heat create the velocity in the exhaust gasses to spool the turbo?

No, heat doesn't create velocity. Heat creates volume. If you look at any of the physics laws for gasses, you will find that pressure and volume and heat are related. PV=NRT is a popular one, The V isn't for velocity, it is for Volume.

 

All that is said here is 100% correct. In a given turbocharger system, there is a given amount of mass flowing through the system. When the mass flowing through the system is hot, it occupies a larger volume. Pushing a larger volume through the same size nozzle causes a larger velocity through that nozzle. So, if you are running a given mass of exhaust gas through your turbo, the hotter the mass is, the more volume it has, therefore giving rise to a larger velocity through the given nozzle.

 

 

 

The turbine housing is what creates the velocity. The scrolling design that reduces the volume of the exhaust chamber as it scrolls around causes the gasses to have to increase in velocity and pressure to maintain the same flow rate.

 

 

 

Also 100% correct. The design of a turbine housing takes a larger diameter and necks it down to a smaller diamter, aka a nozzle. As I said before, if you are running a given mass through the nozzle, you want the largest volume to be occupied (by heating the charge) before it enters the nozzle.

 

 

 

Hotter gasses have more volume, thus requiring a higher A/R which in effect means that it starts at say 3" and scrolls down to approximately 1". Lower temperature gasses are denser and have less volume, so they require a lower A/R housing which would start at the same 3" volume, as the turbine housings use standard flanges, and scroll down to say 3/4".

 

 

 

Also 100% true

 

Now if you were to reverse the housings in application, the conventional turbo would spool up extremely quick, at say around 1500 rpm but would cause too much backpressure at higher rpms because the higher volume of gas couldn't squeeze through the 3/4" hole without requiring a lot of pressure to force it through. On the reverse side, the remote mounted turbo with its cooler denser gasses, wouldn't spool up till say around 4000 rpms but once spooled up would make efficient power because it doesn't require hardly any backpressure to push the lower volume of gas through the larger 1" hole.

 

Also 100% true. The problem is that this company is trying to sell you their product. They have only given you one side of the story to make their product seem much more apealing. Yes, this rear mounted turbo system will increase performance but it won't do it in the most efficient way. They are not accounting for the energy lost from the exhaust as it cools before it gets to their turbos.

 

Lets start from the basics. The compressor in a turbo requires X amount energy to give you boost. This X amount of energy must come from the turbine in the exhaust flow. All of this energy comes from the expansion of gasses. This happens in the turbo because before the turbine wheel, the gas is very hot (large volume) and pressurized. It enters the turbine housing which is in essence a nozzle restricting the flow. This increases the velocity of the gasses and before it hits the turbine wheel, then expands to a much larger volume (low pressure) after it leaves the wheel. This expansion process increases the volume of the gasses and decreases the temperature. The beauty of a turbine is that it converts this heat energy to kinetic energy.

 

In a conventional system, the air entering the turbo is very hot. Heat is energy, and we must not forget that energy cannot be created or destroyed, but can be wasted. Compared to the STS turbo system, a conventional AR ratio is very large. This means there is less of a restriction in the exhaust.

 

The STS system however, uses a much smaller AR ratio (smaller nozzle). The downside of their system is that all of that heat energy is lost in the piping to the turbo. Remember, that you are burning Y amount of fuel and their is Z amount of energy produced in this process. This burning of fuel creates heat and if you let that heat escape without harnessing it, you are losing potential to use it.

 

To make the turbine spin, there is the a given amount of energy needed. In the conventional system, this energy comes from the heat of the exhaust. If you allows that heat to escape (STS system), then the energy needs to come from somewhere else. This comes from pumping losses in the engine. As the exhaust gas leaves the engine, it is really hot. As it travels towards the rear mounted turbo, it cools down and the pressure drops. To bring this pressure back up, STS uses a smaller AR ratio (small nozzle) to bring the pressure back up. This pressure energy has to come from somewhere and it comes from pumping losses in the engine. On the exhaust stroke of the engine, more energy is required of the pistons to push the exhaust out. Energy is not free, cannot be created or destroyed. It is your choice as to whether or not you want to use what is already given to you.

 

If you have any more questions or need more clarification on something, please ask.

 

-jeremy-

[thehelix112]

Can we get back to the topic at hand perhaps?

 

The question I think was whether we want to advance our off-boost timing or retard it to get earlier spool up?

 

I think the answer to this question is retard, ala anti-lag systems. The reason why these work is the massive pressure increase which occurs during combustion is not being used to drive the piston downwards but is instead directly exiting the head and increasing the pressure in the manifold and driving the turbocharger.

 

What does this mean for you and me. If you retard your timing a lot in your pre-boost maps you turbo will spool a lot and your engine will run like a piece of crap off boost.

 

I will have a play with this when I get the boost control sorted. It would seem that massive retard in pre-boost maps will cause the turbocharger to spool and can then go back into proper advance so the engine can make some power. The question I have is whether it will oscillate backwards and forwards? Ie, if i retard my timing so much that it'll make 10psi @ 2000rpm on moderate throttle, and it does, this then pushes the map into proper advance @ 2000 which then means the turbo is spinning down as it doesn't have the gas to drive it, as soon as it gets below boost it'll go into retard and spin up again.

 

Maybe thats why WRC cars only have anti-lag for throttle-off applications.

 

Maybe a compromise and having moderate retard down low, but not so much that the car runs like a slug will spin up the turbo a little faster and have it blend into proper power advance when on boost?

 

Dave

 

zguy36, forums are often a place for **** talking, but there are always a few people interested in learning. Please stick around, you obviously know what you're on about.

[zguy36]

thehelix112,

 

Sorry for taking over your post. I think it is hard to fully grasp the concepts of your question unless the basics are answered. I'll be the first to admit that I don't know the answers to your question, but do think you should play around with your tuning to find out.

 

You are thinking that retarding your timing to get more boost at low RPM might be useful. I would be inclined to think that the power lost from retarding the timing this much would not outweigh the benifit of the extra boost being built. In answer to your question about ocscilating back and forth, yes and no. If you try to do this, make a good note of what your boost is at full throttle through the RPM. If you retard the timing to build boost higher than normal timing would, then bring the timing back when the boost is built, it will drop back to the normal boost curve with normal timing. So say you get full boost at 3000rpm... you retard the timing so you get full boost at 2500 rpm. If you are still at 2500 rpm and you put your timing back to normal, your boost will drop back to normal as well since it is the retarded timing that is making the boost happen. As I said before, I don't think the benifit of the extra boost would outweigh the lost horsepower due to retarded timing. High boost+retarded timing isn't as good as lower boost+regular timing. It wouldn't be too difficult to map this though for a quick check. Just make your timing curve retarded at low to no boost levels with a high throttle opening. Leave the timing values at their normal settings below 85% throttle opening. This way you won't get bad drivability and can still test out the idea. Let me know how it works.

 

-jeremy-

[thehelix112]

Jeremy,

 

We are saying the same thing about timing equating to boost. I think it will be a matter of walking the fine line between using the combustion for power (more advanced) or for boost production (less advanced). If we get boost production then we have more combustion to split between maintaining boost and making power.

 

Will do some testing Autronic has nice datalogging so will be able to get some decent data for us to examine. I will also eventually have a crack at the Autronic anti-lag system and get some datalogs of that in operation so we can see exactly what its doing in terms of advance as rpm/boost change.

 

Dave

[Tony D]

Sounds like it's ocme full circle, and back to my definitions of Boost Threshold and Turbo Lag.

If you want the threshold lower, then size the compressor turbine package accordingly, and tune for efficient combustion. Also driving in the right gear for the speed will make threshold almost irrelevant. Don't try to tweak too much with timing or mixture, as ultimately you aren't efficently producing the power you would were you turbosized and fueld correctly.

 

If you want a "less laggy" turbo when driven correctly (with less than 1/2 second from no to full boost) then realistically you need to look elsewhere for that kind of response, lag will always be less than 1/2 to 1/4 second when sized properly.

 

Where full boost is made is boost threshold rpm.

Above boost threshold rpm, time to full boost is turbo lag.

Below boost threshold rpm, time to full boost is incorrect driving techinque!

[thehelix112]

Tony D,

 

I was just about to edit my post and say just that re threshold vs lag. I'm well aware of the difference but still made the slip up. Sorry all.

 

I would also like to echo your comment about incorrect driving technique. If you're complaining about it with regards to track work then you're in the wrong gear.

 

But its always interesting to think about these things.

 

Dave

[Tony D]

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.

 

That is exceedingly easy to answer: you have an improperly sized compressor section operating outside the design parameters!

 

JeffP's engine will go from 0 to 23psi in an eyeblink at 3000rpms using his last scroll compressor combintaion. 2500 actually....

With the new compressor there is a 500rpm higher threshold, so if he nails it at 2500 now, the car gets bost, but not full boost till 3500. If he nails it at 3500rpm, though, it goes from 0 to 25 instantly, just like before.

 

You simply have a turbo combination working so far outside the proper operating range, with so much volume to fill and such a small compressor filling it, it takes forever.

 

You really need to come down to Orange County and go for a ride in Jeff's Car! When you size it correctly, turbos are savagely efficient and responsive!

[Tony D]

BTW, my T3 pumping through triple mikuinis would go from 0 to 17psi in an eyeblink with the .43 housing on it at any speed above 1500rpm, with a choke at 5500rpm.

When I changed to a .63 A/R turbine housing, the runup to 15psi would take about the same time, less than 1/4 second at 3000rpms, probably 1/2 at 2500. It was considerably slower than when the smaller JDM housing was on there.

[Guest bastaad525]

Tony - then why does it seem I am the only person running the stock T3, at these boost levels, that seems to be getting this much lag? Or is it as I said, that everyone else is just very forgiving and doesn't really notice it? I really don't think it's my exhaust... even though it's not full 3" mandrel, it's still far better than the stock 280zxt exhaust. As for it having to fill such a large volume... there is a lot of extra volume there after I added the I/C and all the piping. It seemed MUCH laggier after the I/C install. I wish I had thought to time it before and see how fast it spooled.

 

By the way, I can get full boost at like 2500rpm if I punch it from 2000rpm in 3rd-5th gears. So I don't think it's 'wastegate creep'. Flooring it at anything above 2500rpm, it will go up to where I set it, usually with 1-2psi of spike.

 

I'm using a Grainger ball and spring style valve for a manual boost controller. What gets me is that this should theoretically decrease lag noticeably since it prevents any boost signal from getting to the wastegate actuator until the set boost level is reached.

[zguy36]

I think your lag problem has everything to do with your tuning. You said that it runs rich under boost, but how rich is rich? I am assuming you don't have an air/fuel gauge, but that might be something you should consider. I am running a T3/T4 hybrid, which should be worse than yours for lag since it has the same turbine with a larger compressor. My exhaust side is the same as the stock 280Z turbo but yet I build boost a bunch faster than you are talking about. I would check your mixtures and see where you are at.

 

-jeremy-

[thehelix112]

By the way, I can get full boost at like 2500rpm if I punch it from 2000rpm in 3rd-5th gears.

 

So you're telling us it takes 2 full seconds to get from 2000 to 2500?

 

:S

 

Oh and its still perfectly possible for the wastegate to be creeping. By creeping I mean being forced open by the pressure in the exhaust manifold, not being actuated by the intake pressure via the wastegate diaphram.

 

Dave

[Tony D]

My time in first gear was less than 2 seconds from a dead stop and hit redline, second gear was 3 or so seconds (again to redline) and then third was again on full boost as I hit the gas. I never dipped below 17psi unless I was drop-throttled.

The exhaust I was running was a mandrel bent 2.5" out of the stock turbo housing, into a merge that split to twin 50mm pipes. Technically this should flow equivalent to a 2.76" single, so it would seem I am more restricted than you are currently!

I would look to loose wastegate and the tuning, that is the only thing I can think of, with the .63 I was slightly slower to spool initially, and threshold went up from 1500 1700 to 2200 or thereabouts. But once on the cook above that point, if I floor it, it jumped to full (17psi) in a rapid sweep, you cant even get "onethousand" out of your mouth starting when you hit the gas before it was at full boost.

[Guest bastaad525]

well about the tuning, I have tuned on a wideband at a dyno. I'm using an RRFPR to give extra fuel. The thing here is that it ONLY adds fuel AFTER boost pressure builds up.

 

On the dyno, I had the operator floor the throttle at 2000rpm. Boost would start building instantly, and would hit full boost (12-13psi at the time) at 2800 rpm or so. Now on the wideband graph, the mixture was at about 12:1 up until about 3200rpm where it suddenly drops drastically to about 10:1. But notice, the boost has already spooled fully BEFORE the fuel mixture goes very rich. Now that I have looked over my dyno graph again and seen this, I can't see how the rich mixture is slowing the spool, since it only goes rich after full boost is reached.

 

Otherwise, the only 'tuning' I've done, since I'm on the stock ECU, is the timing, which I've advanced 2* from stock (22* BTDC).

 

The car is still quick, so even with the apparent lag it performs close to what it should be doing for the hp it put down and weight of the car.

 

I know a lot of you probably don't put any stock in them, but I did buy and try one of the most recent Gtech Pro SS meters. I have read several magazine and internet reviews plus have two friends now who've actually been to the track with a Gtech and all found them to be very accurate, within 1-2 tenths.

 

Well when I tested on the Gtech I was pretty consistently hitting 0-60 in 5.5 seconds and a 13.7 second 1/4 mile at 108mph, but mind you I could NOT launch the car properly and was getting horrible 2.5-2.7 second 60' times. I tested at least a good 20 times with that Gtech and got very consistent results on almost all of the runs with only a few that I really botched the launch or missed a shift.

 

On the dyno, the hp/torque curves look exactly as they should. Torque peaks at around 2800rpm and stays table top flat until 4200rpm. Again, that's with the operator flooring the throttle at roughly 2000rpm.

 

 

I appreciate the input guys but what would be REALLY helpful is if someone else with a T3 could go out with a stopwatch and time their spool time for me. 3rd or 4th gear, hold the throttle steady, RPM and 3000, then floor it and time how long it takes to hit full boost.

 

Because for everyone to comment how "wow 2 seconds is a joke" or "my turbo definately spools faster than that" it's all very relative and just perception until you guys actually time it.

 

The more I think about it though the more I think it's not THAT abnormally laggy... again, for comparison, my SRT-4, with a very small, much more advanced turbo made out of better materials, tested the exact same way, takes about .7 of a second to hit full boost, and my Z is doing it in almost exactly twice that with a much bigger older turbo and probably more restrictive exaust with that crap stock DP. It's still not GREAT, and yeah at this point I'm really suspecting the exaust or a wastegate that's not closing all the way, but isn't that bad either. That is, until someone times their's for comparison and finds that a stock T3 should spool in like .2 seconds or something like that

 

Well if it's the exhaust it doesn't matter because the car is still for sale and WILL be sold sooner or later, so I'm not investing any more money into upgrading it... but if it's something I could solve easily, maybe replacing the wastegate actuator or something like that, then I'll take care of it.