Ways to get rid of turbo lag 1

[inultus]

I was wondering if this would be feasible:

We all know that turbo "lag" is due to the process of waiting for the turbo(s) to spin up via the exhaust gases flowing through them.

Why couldn't you simply hook electric motors up to the turbos to spin them forcefully, in compliance with the amount which the gas pedal was depressed.

It seems to me that this would get rid of turbo lag. Of course, it would take some tuning and such...

 

[NickE]

Because the energy required to spin the turbine and create boost is too much to use a physical device to spin-up.

(IE you cant get something for nothing.)

Heres the idea: In my car a 4cyl 2.0L Boxer I can see full boost at 2500-2750rpm in 5th gear. At that point the turbo is spinning roughly 100,000rpm and producing approx 14.5psi boost at btw 415 and 475 cfm.

There really isnt an easy way to produce this kind of pressure and flow w/o using lots of HP. (I dont know all about it but a company I worked with used a 100HP Roots blower (watercooled motor and compressor) to simulate exaust flow (cold) of 500cfm and 12" H2O.

The reason a turbocharger is effective is that it recovers HP lost through the cooling and slowing of exaust gas. This HP would normally be lost out the tailpipe (or changed to heat by the mufflers, resonators, adn cats.



Nick
I love materials science!

 

[Majik]

garret researched this and found the amount of electric motor required... deamed a 42v system in the car... it was lame...


nitrous will help spool.. um.. shooting CO2 onto the blades of the intake will as well... or into the exhaust turbine but there's a temp shock on that one so expect shorter turbine life. these are all things that you can stick into a incar fire extinquisher and cheat at your local drag strip as well.... of course these are one time solutions instead of a permanent fix for lag... sorry if I did find a permanent fix for it then I would pattent it and sell it to the supra crowd for thousands..... you could always do a two step launch or learn to downshift to pass.

 

[CESSNA1]

INULTUS:There is a company called "TURBODYNE" in southern California and other areas, that has just what you are seeking. Do a search on TURBODYNE and check it out.

Regards
Dave

 

[patprimmer]

This has been done at length previously. Do a site search, then ask any questions you still have.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[sreid]

In Professional auto racing the technique used to try to keep the turbo spooled up was through a servo controlled waste gate. Besides controlling spark and injectors, the motor control system controlled the waste gate for optimum performance. Twin turbos also help enormously due to their considerably lower rotational inertia. And a Silicon Nitride turbine and a magnesium compressor.

 

[tbuelna]

inultus:

there are lots of ways to reduce "turbo lag", and they've all been tried:

1. electric assist- Caterpiller, Garrett and Turbodyne are all experimenting with electrically compounded turbos.

2. hydraulic assist- Garrett produced a "3 wheel" turbo for a Hino diesel truck. It was a standard turbocharger with a hydraulic "pelton wheel" built into the center housing of the turbo. I also have seen a similar concept hydraulic supercharger that was being developed by a guy named Dave Kapich. Do a search on the patent files.

3. throttling the turbo inlet- check out the throttle arrangement on a Champ car, a centrifugal compressor spinning in a vacuum will maintain its momentum fairly well.

4. If fuel consumption is not an issue, I remember seeing a turbo F1 car (Ferrari?)that gave an extra squirt of fuel into the exhaust turbine to keep the turbo spun up (kinda like an afterburner).

Regards,
Terry

 

[guvs]

there is a cure for turbo-lag, it's called anti-lag.
Try searching for GEMS or MOTEC.
Basically, they remap the ECU and alter fueling. Basically, raw fuel is thrown into the exhaust cycle, this raw un-burnt fuel ignites with-in the turbo (as turbo is runnning at red hot temps), expansion of igniting the fuel, spools up the turbo. This is the way I explain it to people when they ask what the POPS & Bangs are from my car. Am running a GEMS ECU with a full anti-lag system. Not good for turbo life, amazing for acceleration and sounds !

 

[microhenry]

Similar to Tbuelna's #2, is compressed air assist.
There's an accumulator and small compressor that's
clutched to the drivetrain when braking. The air
is directed into the compressor fan. Has the additional
benefit that the air is cold.

 

[patprimmer]

If the laws in your region or class rules allow, a very short shot of nitrous oxide will give enough power to overcome lag, while increasing exhaust gas volume and temperature which then accelerates the spool up rate. This was in the PM thread.

This wastes very little fuel and creates no undue wear nor noise. Of course a NO2 bottle is not a nice thing to be around in case of leaks or traffic accident.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Warpspeed]

Another very effective way is to compound the turbo compressor with a positive displacement roots supercharger.

The extra exhaust flow on throttle opening really makes a very big difference.

While antilag and nitrous do work, they can have problems of their own.

By adjusting blower drive ratio and turbine a/r, the engine can be given a fairly wide range of boost characteristics that can be tailored to suit the application.

Another advantage is that boost pressure can be easily kept above exhaust back pressure which really aids exhaust scavenging and this has many advantages especially when choosing valve timing. Expect a higher detonation threshold too at any given boost level.

Probably too expensive for wide scale production, but Lancia did it, and so have Nissan.

A lot of two stroke diesel trucks now run turbos compounded with a roots scavenge blower. Nothing new there either.

Speaking from my own practical experience, it makes for a very potent and tractable package on a small capacity gasoline engine.

 

[rmw]

I thought that a roots blower, since it is fixed flow device, impeded a turbocharger once the turbocharger was spooled up and it's output exceeded the capacity of the blower.

I have a Detroit two cycle engine manual that mentions a blower bypass that is simply a spring loaded flapper damper device that opens into the air box to relieve turbo boost around the blower when the blower is the bottle neck (flow limited).

The bad part is that I operate a vehicle with at two cycle Detroit (6V-92 TA) that doesn't have that feature. It is called a "freight truck bypass" as I remember it.

I overcome turbo lag in my diesel pick up truck which has an aftermarket add on, non waste gated turbo that is bad about turbo lag, by a certain driving technique.

If I am about to pass, for example, before actually fully initiating the pass, I put my foot into it just a little, not enough to bump into the back of the vehicle in front of me, but enough to start gaining on it some so that at the moment I need to initiate the pass, and "mash on it" the turbo is already spooled up to some extent, and the extra fuel I add when I "mash on it" is easily handled without any turbo lag.

If I don't drive it that way, and just "mash on it" without spooling it up, then all I produce for the first few seconds of such a passing maneuver is a lot of black smoke.

And, by the way, I drive the bus with the two cycle Detroit the same way, and train younger drivers in this technique, calling it "building a fire in it".

rmw

 

[patprimmer]

rmw

I even use that technique with NA cars, just to get a bit of momentum up to make the pass easier.

I learnt it driving old 1200cc air cooled beetles. You needed all the help you could get to overtake someone if you were in an old beetle.

To compound the superchargers, you must have the turbo blowing into the roots blower.

This way, the roots blower can suck through the lazy "fan" blades of the turbo before it spools, but when the turbo spools, it pumps boost pressure into the roots blower. The roots blower still only pumps the same volume, but at higher density.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Warpspeed]

Pat is right, the roots blower sucks air through the turbo compressor while it is spooling, and can just about totally eliminate compressor stall problems.

Compressor stall is where the compressor spins in its own wake and no (or very little) new air is drawn into the intake. The symptoms are, that usual expected surge of acceleration just fails to occur sometimes. With a roots blower behind the turbo creating a depression, fresh non turbulent air is drawn into the compressor eliminating any tendency to stall. That is another big advantage of the system.

The roots blower must have a greater displacement than the engine in order to create boost. Pressurising the intake of the roots blower with a turbo does not change that relationship. It will never be a restriction to the turbo if the blower has a positive pressure differential. I can assure you that it sure will have.

The other point is that you reference your turbo wastegate pressure to the combined total boost, so you reach and hold a fixed boost level controlled by the wastegate.

A bypass around the supercharger is an excellent idea too. All the factory supercharged cars use a bypass of some sort. It is used to completely unload the supercharger during idle and light throttle operation. It reduces blower noise and heat buildup, and improves fuel economy.

AS you progressively apply throttle the bypass closes causing boost pressure to rise to maximum at wide open throttle.

 

[VinceA]

what if you just increase the compression ratio, wouldnt this decrease lag?

 

[patprimmer]

The limitation is knock or detonation. Once the compression ratio and boost get high enough to cause detonation, it will soon blow the tops out of the pistons.

You can increase compression ratio if you either reduce boost or run higher octane fuel, unless you started with good fuel, low boost and low compression.



Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[VinceA]

yeah, i knew that the detonation/ octane rating on the fuel would be the limiting factor. i just remember that my old roomate had like 11:1 compression and he was boosting slightly uner 10 lbs. on 100+ octane and there negligable lag, but having that said, there are a lot of factors that would affect this

 

[rmw]

Pat,

One of those 1200CC air cooled VW's put me through college.

It basically had two fuel positions, idle and floored.

Great little cars, overall, especially in light of the abuse I gave it.

The throttle response on the motorcoach bus is a lot like the VW, now that you mention it.

If you keep the boost above 5 psi, the bus will do OK without smoking. The '92 series two strokes have a lot better torque rise characteristic than the older '71 series did. Now those were exactly like driving the older VW's. You had to keep them wound out to get anything at all out of them.

The turbo on my pickup truck is not waste gated, and I have the fuel turned to it quite a little bit, so I have to watch the rpm, and keep them above 2K, or it is guaranteed to smoke.

rmw

 

[Artsi]

Why not duplicate OEM solutions?
Let's say Toyota Supra twin turbo model from mid -90's. That has 2 turbo's, which step in sequentally.
Only one charger receives all of the exhaust flow the engine is capable of producing below e certain pre-determined rpm point. At this point engine is quite happy to receive compressed aircharge from one turbo only.
As engine reaches that rpm point (approxiamately at around 4000rpm), the flaps and valves open up to guide exhaust flow into adjacent turbo charger. In higher engine rpm's these two turbochargers work in unison. Please do not mistake this arrangement to staged (or stacked) turbocharging. Boost pressures in this OEM Toyota solution are kept at normal approx. 10-15psi/0.7-1.0bar levels.

BMW 535d diesel engine has a clever turbocharging arrangement. It has similar function to Toyota's, but this has an added feature of controlled staged charging. They call it "Variable Twin Turbo technology". More of it here:

http://www.germancarfans.com/news.cfm/newsid/2040718.001/page/9/lang/eng/bmw/1.html

Modern diesel engines enjoy use of the variable geometry turbochargers. Garrett and Holset have these models out on the market. This makes a single charger to act in a very flexible manner. It will kick in very early, and also will allow engine to extend useable rpm band reasonably high.

 

[Warpspeed]

I have a Garrett VNT turbo fitted to my gasoline road car at the moment, and it is not a happy conversion.

While the very low boost threshold and much reduced lag are excellent, the top end power is a total disappointment. The problem being that all the exhaust has to pass through the relatively small turbine, there being no wastegate. Exhaust back pressure rises far too high for good top end power.

A larger turbine would fix it, but then the response would not be so crisp. VNTs seem to work wonderfully well on diesels, but people that have tried them on gasoline engines usually end up removing them.

The usual reason given is that the higher EGT of gasoline is not good for the vane mechanism reliability, but I have had no difficulty with that.

There are no production gasoline engines running Garrett VNTs that I am aware of, and that should tell you something.