How can I reduce turbo lag? [Archive] - SaabCentral Forums

: How can I reduce turbo lag?


Aero_adam
6th December 2005, 09:20 AM
As the title - how do I reduce turbo lag. My thoughts were:


Smaller turbo (not favoured = lower max power?)
lower inertia internals (titanium impellers?
hybrid turbo - 360 degree thrust bearings and low inertia impellers
Freer flow filters
Freer flowing intercooler
re-balanced turbo
Freer flowing exhaust (reduced back pressure)
The only thing that gets tiring these days is a fairly major turbo lag of around a second or more. How do I get around this? There must be a number of things can be done to help this available at different financial costs. Ideally, I don't want to sacrifice any power for spool up time.

There must be some good options available. The only one I know of is the Abbott racing hybrid turbo available exchange at 425. What else.

DrBoost
6th December 2005, 11:13 AM
Hej !

You say that you've got a turbo lag of about a second, let me ask you the following, when you experience this turbo lag, in which gear are you, engine rpm's and throttle position ?

Bladey
6th December 2005, 12:16 PM
i'd have thought that the ecu would be one of the factors contributing to 'lag' cause isnt that what ulitmately controls how and when the turbo spools up and so on.. not that i know :P

Aero_adam
6th December 2005, 01:31 PM
Hej !

You say that you've got a turbo lag of about a second, let me ask you the following, when you experience this turbo lag, in which gear are you, engine rpm's and throttle position ?

It occurs whenever the engine is at low revs = less than 2000 rpm. Obviously in the lower gears the engine picks up quicker than the high gears. I want to minimise the time to get from no boost to maximum boost in all gears. Ideally from idle.

When I take some video of the hirsch performance I'll get a time for the lag.

Adam

Aero_adam
7th December 2005, 07:17 AM
Done a little digging and got some leads that may be worth following up:


Turbos with ball bearing instead of plain bearings spin up faster.
Subaru impreza (among many others) share our turbo (TD04-14T) so there must be dowzens of ricers with hybrid turbos. (I found one company, APS, that make turbos that seem to do exactly what I want) - spool up quickly.

This is not a power thing - only the response of the turbo.

Bladey
7th December 2005, 08:34 AM
sounds most interesting adam... keep digging very interesting...

imagine hirsch stage 2 and an upgraded turbo.. provided that the ecu doesn't mind.. could be pretty amazing


thus.. i'd love to know if after having stage 2 hirsch, would switching to the upgraded turbo that abbot use, do the trick?

boenka
8th December 2005, 04:52 AM
Like this thread since i have the same issue in daily commuting but i am afraid that the existing turbo wont help much in solving the problem.
You have a manual transmission so why not drive in a lower gear if you look for a sportier drive, it will keep the atmospheric part of the engine more performant and you will be quicker in the right powerband. Also the lag will not upset the cars stability that much.
If i look at the power and torque curve of our car (hirshed or not), the party starts at 2500 rpm for real. The Hirshed one is even a little better than stock.

Or why not just drive faster all the time? :cool:

Regarding the scooby, that one is only going from way higher revs as our 9-3 if you see its power and torque curve so no solutions there.

Aero_adam
8th December 2005, 01:10 PM
I read one piece about ball bearing hybrid turbos with 360 degree thrust races (in-place of plain bearings) can reduce the spool up speed by 600 rpm. That would be fantastic.

I am not wanting to change the power of the engine, just the responsiveness. I don't want to be driving around in a low gear all the time. With the hirsch tune the pull in third is awesome and in fourth is certainly spirited. I just want to be able to follow a line of traffic and when an opportunity appears to overtake, punch the throttle and go. Punching the throttle and waiting two seconds for it to collect its thoughts is not ideal.

If I can get a turbo that spools faster (better bearings and a reduced inertia impeller) then that would be great.

mike saunders
8th December 2005, 02:56 PM
It occurs whenever the engine is at low revs = less than 2000 rpm. Obviously in the lower gears the engine picks up quicker than the high gears. I want to minimise the time to get from no boost to maximum boost in all gears. Ideally from idle.

When I take some video of the hirsch performance I'll get a time for the lag.

Adam

Adam, you're shifting too quickly....

Best way to avoid lag is to use your gearing properly, just as others have said. You should be in a low enough gear to enable the engine to stay in its powerband, which, for the 14T starts at about 2,500 rpm, which is pretty fast for that size turbo. (Please check me on that...)

Extend your 1st gear shift to 4,000 or 4,500 rpm and the drop to second should be more than 2,000 rpm, allowing you to boost immediately or to only feel a heartbeat's worth of lag. (I'm using a bigger TD04HL-16T with SQR software and have learned to let the turbo spool...) The hardest thing to get used to is re-tuning your ears to gauge the right shift point

Unfortunately, lag is the inherent tradeoff of turbocharging. You could certainly go to a ball-bearing turbo. The Garrett GTBB series is excellent, albeit expensive. Longevity is an issue because it can't be rebuilt if it goes kaplooey!

T7 and T8 aren't as forgiving to items like manual boost controllers, which are commonly used in T5 cars to increase boost in early gears. You could be a pioneer and install a supercharger like those in the ION Redline, but that would be a LOT of work for only a little gain in responsiveness.

Try the longer shift points for a couple of weeks and see what you think...

And get used to downshifting when you want that immediate rush....:cool:

MudMover
8th December 2005, 03:28 PM
How about a 2nd turbocharger? Not sure how you'd cram it in - but a smaller unit for the initial pickup (less inertia etc.) and then a larger unit for the oomph we all love!

I think there are quite a few cars out there with 2-stage turbocharging.

Again, a bit of a pioneering thing to do.

I haven't driven the Aero, but my HOT 900 used to be a PIA wrt turbo-lag. Sadly the only option I could afford was to modify my driving style - and if that meant sitting behing a queue of traffic in 3rd (just in case) then that's what I did - at least our engines are smooth enough to do that without rattling our fillings out - even if it is at the expense of economy. Although I don't think that's the solution you're after! ;)

Phil

DrBoost
8th December 2005, 05:37 PM
Hej !

As I suspected, the turbo lag described is normal, as designed.
A result of the existing h/w. AND, probably most importand, of very little importance when it comes to "racing" either a the traffic lights or on the track. When operating the engine within the "normal active rpm band" turbo lag is not an issue.

So, what can be done, is opening up the exhaust side. This will probably give the best results. Possibly fitting an E-turbo, then turbo performance is brought to "the next level". Turbo lag will be an unknown word....
Power on demand, without "delivery time".

Using TiAl turbines can be one option, however probably not as good as people in general think. TiAl turbines needs to be designed with thicker blades, normally resulting in fewer. Inconel (the normal stuff) or even better Mar M 247B will make it possible to design a turbine wheel with nice slim blades. Fewer thicker blades will make the efficency to suffer.

Twin turbo, two stage, is also one way to go. Can be "interesting" to control. If you succed to control the "evil twins" you will be rewarded....

IF you want to reduce lag, OR increase the TORQUE at no/low boost conditions, make your engine breathe unrestricted.
Now, I would like to go to bed, i've had a long day.... V6's and a V12 all day long...

Aero_adam
9th December 2005, 05:22 AM
Thanks all.


Don't get me wrong - I know why the lag is there and I don't think it is especially bad for a powerful turbo car - in fact it gets on boost pretty quickly.

When I want to drive quick I do hold gears longer and change straight in to the boost zone - however I bought a Saab because I can also get good performance from the thick torque band. If I had wanted to rev the nuts off the car I would have bought something Japanese that made nice noises when revved hard.

Freer breathing sounds like the tip from Dr Boost - so possibly looking at the inlet might be an option - or the intercooler.


Dr Boost - would there be any issue changing the intercooler to something with less back pressure? Does T8 get upset if I start changing things on the inlet side of the engine?


I enjoy the way the car drives, and the lag is not THAT bad - just one of the few things that could be improved. Yes it is a characteristic of all big turbo cars, it is a compliment to Saab that this is one of the few issues that I have.
I don't mind experimenting under the hood - but fabricating twin turbo set ups or switching to a supercharger is way more serious than I had in mind. At the end of the day I am just tinkering and need a reliable car daily.

johnc_22
9th December 2005, 05:16 PM
I am not wanting to change the power of the engine, just the responsiveness. I don't want to be driving around in a low gear all the time.

It's not about being in a low gear all the time but in the right gear at the right RPM's. This means not upshifting too early and not downshifting too late. One helpful thing is to teach yourself heel-toe downshifting so that as you hit a corner or curve where you have to reduce throttle you can smoothly match the engine speed to the higher RPMs in a lower gear by blipping the throttle as you downshift (while clutching). You are then in a lower gear at an RPM range where the turbo will spool almost instantly.

If you figure this out you will have even more fun with your car. If you already know how to do this then ignore me - my previous SAAB (Viggen) had a 5-speed but I (regretfully) went with auto this time due to Atlanta traffic gridlock, so I don't know how the 9-3SS behaves with a manual.

Hope that helps.

mike saunders
10th December 2005, 12:58 PM
It's not about being in a low gear all the time but in the right gear at the right RPM's. This means not upshifting too early and not downshifting too late. One helpful thing is to teach yourself heel-toe downshifting so that as you hit a corner or curve where you have to reduce throttle you can smoothly match the engine speed to the higher RPMs in a lower gear by blipping the throttle as you downshift (while clutching). You are then in a lower gear at an RPM range where the turbo will spool almost instantly.


Well said, John

Adam, in your first post you described "major turbo lag of a second or more." This is indicative of improper shifting, not of anything that needs to be done with the turbo or its plumbing. Freeing up the intake as Dr. Boost said will help the car, but the major determinant is driving habits.... I don't remember if the Aero I test drove has the silly "shift up" light, but if it does, the thing to remember is that this light is not an indicator of the proper shift point for power. It's a fuel-saving device. It purposely prompts you to shift early to increase MPG and to minimize the amount of boost produced, which requires more fuel. (I put a piece of black electrical tape over mine ! :cheesy: )

When puttering around town, I generally shift at just over 3,000 RPM and I can see and hear the boost drop (I have a BOV fitted)...but in these situations I don't expect to need the boost immediately. For around-town driving there's little need to pull out the ponies. On the highway, or passing situations, then expect to downshift ot shift later.....

DrBoost
10th December 2005, 02:33 PM
Hej !

Well, I'm afraid that if you really want a lot of torque, at low rpm's and high, the answer is: http://www.saab4fun.com/upload/uppladd/5683RRV12.jpg

With the basic h/w that you've got, don't expect any huge improvements in low end torque/quick responce. Dealing with the exhaust side of the turbo may give some, intake side and a better I/C, probably not. Tha I/C is not a major restriction at low rpm/load, the airmass flow is just soo low...

If you analyze the torque at low rpms, you will find that it's "fully acceptable" but the higher the max boost/torque is, the worse the lag will feel, even if the low end torque/responce is the same. I also must mention that the torque responce is under some conditions somewhat restricted/limited. Some "improvements" can be done here, however, it's my firm opinion that the torque responce is "modern", what can be expected of a car of today. The voilent behaviour found in turbo cars of the late 70's and 80's is just obsolete today. Well, IF heavy mod's are allowed, then we can get rid of turbo lag and increase low end torque...

Aero_adam
11th December 2005, 07:41 AM
Hej !

Well, I'm afraid that if you really want a lot of torque, at low rpm's and high, the answer is: http://www.saab4fun.com/upload/uppladd/5683RRV12.jpg


Dr Boost

Thanks for your words. I think that the V12 may make the stereing a little heavy and give it a tendancy to understeer when pushed....


Thanks all for the tips on driving - maybe I'll shift out of 5th gear around town.... (joke) Of course using the gears will make the car accellerate faster, but I don't always want to make my passengers feel like they are on a fairground ride. For example, if I am driving in town at 25mph in third gear and I want to overtake something, if I floor the throttle there is a distinct pause as the boost builds. After a second or so the car is on boost and starts to fly. Are you proposing that I shift to second (with the baulky gear shift) and then floor it. I could shift down in anticipation, but it is not very smooth or pleasnat to drive around in second gear.

I am being very picky, if I am in the car on my own and wanting to have fun it is easy to keep the car on boost or within a blink of full boost. I had thought that a forum about performance and modifications would have been more prepared to discuss the merits of reducing turbo lag - not commenting on the driving technique of someone you haven't met. I am pleased that the lag for you is not a problem, or that you are happy to drive around it. My approach is to not have to drive around it.

My car on boost feels to have a much bigger engine than a 2 litre. If I could get that feeling from say 1600 rpm rather than over 2000 rpm, then so much the better.

Thanks again, I'll post if I make progress.

colombo
11th December 2005, 07:55 AM
The Subaru way isn't necessarily the way to go. There we are talking serious lag, like in "99 Turbo lag"... I think the only way to overcome this on a high output turbo engine is 2 turbos, similar to the what BMW is using in their 535d engine.

johnc_22
11th December 2005, 09:36 AM
For example, if I am driving in town at 25mph in third gear and I want to overtake something, if I floor the throttle there is a distinct pause as the boost builds. After a second or so the car is on boost and starts to fly. Are you proposing that I shift to second (with the baulky gear shift) and then floor it. I could shift down in anticipation, but it is not very smooth or pleasnat to drive around in second gear.

The sweet spot in 3rd gear occurs at around or just under 2500rpms. If you are in 3rd a 25mph you are probably well below that and so 3rd gear is going to give you a long lag as it slowly climbs to the sweet spot. I can't speak to the balky gearshift but this is a case where downshifting to second with a bit of throttle can be achieved pretty smoothly, and flooring it is not necessary unless you really need to take off that fast - yes, that will be like a carnival ride! :p

boenka
13th December 2005, 04:55 AM
Adam,

if flexibility at low ranges is your thing, take a tuned up 2,0t or a V6 , the first will spool quicker for the smaller turbo and the second has the power especially in the low revs due to the extra cilinders.
I mean, there are physical limitations to everything and in our case only more or less expensive workovers if your driving style is the one you describe. No problem with me but i would recommend a 6 or 8 cylinder car to satisfy your need, honestly.
Go for a testdrive and have some fun!:cool:

Deli-Llama
5th January 2006, 07:03 PM
Have you had a look at:

http://www.3barracing.com/product_6.htm

How it works: The Hybrid Boost Controller mounts in-line between the intake manifold (or turbo nipple) and the wastegate. The controller holds the signal from the wastegate until the desired boost level is reached. By conditioning the boost signal this way, the following results occur:

a) Time to Peak Boost is dramatically improved

b) More boost "area under the curve" for increased mid-range torque!

c) Boost limit is raised to the point that you, not the ECU, desire!

I know everyone is worried about the T8 software but for US$43 is might be worth a go.