Avoiding turbo lag

obi_waynne

Administrator
Staff member
Moderator
Points
1,157
Location
Deal, Kent UK
Car
A3 1.4 TFSI 150 COD
What are the best strategies to avoid turbo lag?

What are the usual causes of turbo lag?
 
First - Turbos are not designed to work from tickover so they do not produce instant power from low revs

However ways of keeping lag to a minimum. assuming there are no leaks in the boost system.

fit the right size turbo for the engine
Smaller turbo = less lag but also less power
lighter blades , usually ceramic, are easier to spin ( = less lag) but there is always a trade off . Ceramic blades break much easier at high revs and these wheels do go round very fast.

You need an the right intercooler - big enough to the cool air but not too big as the sytem has to be "charged" before real boost is reached
Efficient bearings and compressor wheel design do make a definate difference as does the exhaust design .

Its still a trade off though - more power will always mean more lag that less power.
 
Twin turbos are often set up for 1 smaller fast-spooling turbo and one bigger one that won't fall flat at high boost. There's also the twin scroll turbo like in my car. 2 cyl dump into one of the scrolls that is is smaller and spools faster but peters out in higher boost, 2 cyl dump into the bigger scrolls that can boost higher but lag worse.

I did some 0-60 MPH runs with my brother-in-law using the Torque app to time the runs. I was wondering the same thing with my own car. Even though I have little lag with the twin scroll turbo, there is still some. Could I slip the clutch while partially opening the throttle and hold it on the brakes to preload the turbo some? It'd preload the suspension sure, but would I build boost and overcome lag better this way?
 
Twin turbos are often set up for 1 smaller fast-spooling turbo and one bigger one that won't fall flat at high boost. There's also the twin scroll turbo like in my car. 2 cyl dump into one of the scrolls that is is smaller and spools faster but peters out in higher boost, 2 cyl dump into the bigger scrolls that can boost higher but lag worse.

I did some 0-60 MPH runs with my brother-in-law using the Torque app to time the runs. I was wondering the same thing with my own car. Even though I have little lag with the twin scroll turbo, there is still some. Could I slip the clutch while partially opening the throttle and hold it on the brakes to preload the turbo some? It'd preload the suspension sure, but would I build boost and overcome lag better this way?

This is the decades old problem. Getting a turbo car to give its best off the line (especially FWD ones) is very very difficult.

Preloading the turbo as you suggest will certainly improve available torque as you take off but turbos are less rev dependent than they are dependent upon exhaust gas flow. You'll certainly improve your times but you're likely to batter the life out of the clutch etc. Then again any standing start full power driving is going to do the same.

This is perhaps why many purists will go for super chargers over turbo-super chargers (to give a turbo its full name).

Turbocharging works at its best in full load constant RPM applications. Think diesel rail traction (which is diesel engine driving generator, in turn driving bogie mounted traction motors. Diesel engines are generally better disposed to turocharging than petrol engines due to their unthrottled mode of operation.
 
Yeah that would destroy your clutch LOL, that's why I didn't do it! It's not only RPM but also engine load that spools up the turbo so the timing would have to be perfect. My car is RWD, but has an open diff (for now....) so it is limited in how it gets the power down anyway. His car is FWD but he's done a lot of modding to the engine and it puts out about 300BHP from a 2.4L turbo. My car puts out about 270BHP from a 2.0L twin scroll turbo.

With our cars you can feel the difference betweeen his bigger turbo with more lag and my smaller twin scroll with less lag.
 
Quoting Guybo: "It's not only RPM but also engine load that spools up the turbo so the timing would have to be perfect."

HDi: "turbos are less rev dependent than they are dependent upon exhaust gas flow"

LSDs are not going to make the balancing act any simpler.
 
No, but it'll put the power on the ground better.

Exhaust gas flow increases as the engine load increases. I kind of reiterated what HDi said in a way.
 
I saw a video about the older WRC cars that had antilag systems in the early 2000's. The turbo is made of special materials because the heat is so intense that the metal turns translucent. The turbo went from red hot to white hot to kind of see through :confused:
 
I thought Anti lag is normally for use when changing gear.

Pretty much all turbos road cars are prevented from producing boost whilst standing because If they produced boost in neutral there is nothing to stop them from overevving. This is why they normally don't fly off the line.

However with a decent ecu this can be controlled so you can pull away on boost - which gives zero lag off the line ( launch control )
The stagea ecu ( link G4) has a launch control function so you can dial in the revs and boost you want to pull away with.
Not for the faint hearted though - mine is set for max torque (@ 5000rpm )

So in gear , throttle to the floor , revs rise to 5k and are held there by a rev limiter . The boost builds up and when the boost gauge says 1 bar I let out the clutch. The results are quite impressive but to get the best result you need an adjustable awd system and a very good clutch and drivetrain .and of course decent tyres.

whilst lsds may not help much on a. Launch they do make quite a difference on a track. Some like quaife atb ( automatic torque bias) adjust the power split across the axle to the optimum for traction on corners. This means the power can be kept on easier so you can keep on boost
I found the difference with a quaife to standard lsd was like night and day round corners..
 
When I get the money up, I'm getting a Quaife lsd. I hear nothing but good things about them. As far as I am concerned a LSD is a safety device. When it rains here in Florida, it usually comes down in torrential rains and a RWD turbo coupe isn't the best rain car in the world.
 
Been trying to find info re fitting a Quaife or Torsen in my Starion but without any luck to date.

Yes I have em'd both of them and they don't know if any of their units will fit
 
torsen vs quaife ?

Only my opinion but i am able to drive both at the moment :)

Ive got torsen diffs in the caldina It feels very stable and surefooted and extremely safe . You dont notice it and everything is very well behaved and efficient.

The ATB feels completely different and seem almost alive in the stagea . Instead of just feeling stable it actually seems to actively pull the car round bends in a positive way, You really do notice it
 
Last edited:
Big turbos are great fun but I don't think I'll do it again. Below 80 my gt28rs was quicker but the gt3076r was insane above 90!! Silly quick.

Good fun but gets a bit tiresome after a while. I prefer something nice & quick below 80 now.
 
This is often the problem - just fitting a bigger turbo will always give more lag.
You don't just fit a bigger turbo The car needs to be professionally mapped and the rest of the set up chosen to match the characteristics of the turbo(s)
 
I'm running a diff on mine. Makes FWD very fun to drive. Pulls out of bends soo much sooner than normal. Even getting on the power before my mates Scooby. But mine is running the T25 set to high boost, so kicks in around 2750rpms and goes like the clappers, and if I change gear with high enough revs, there is hardly any lag at all.
 
i was told using a Silicon vacuum tube with a smaller diameter and of shorter length will improve turbo spooling and reduce lag ... some suggested Tifilon instead of silicon because its even more resistant to dilating under heat and pressure
 
Pedant Alert!

Silicon is much more resistant to dilating than Tifilon, because silicon is a rock! I think you mean silicone :)
 
hmmm learn something new everyday >.< didnt know a rock of such a name existed .. but thanks for correcting me
 
hmmm learn something new everyday >.< didnt know a rock of such a name existed .. but thanks for correcting me

Yes, we all do :) On checking, Silicon is actually a metalloid, not a rock.

It is used to make, among other things, computer chips hence the naming of Silicon Valley.
 
Silicon is the substrate for all VLSI electronics and has been for decades. It's also found in huge concentrations in glass :)

Glass is actually a highly viscous liquid, not a solid material.
 
Last edited:
It's not silicon based? Or are you saying that glass is solid?

Yup, as I understand it, glass is a non-crystalline amorphous solid.

Contrary to popular belief, glass doesn't slowly slide down to the bottom of the window when made into a window pane.
 
by far the easiest way to lower the boost threshold and eliminate lag is to use nitrous on a boost switch, did it on my 306, worked a treat
 
you can change the cams and modify the head which should help spool

best bet though is just to increase the cc

mine will be 3litre when it returns so should spool a tad quicker
 

Similar threads


Please watch this on my YouTube channel & Subscribe.


Back
Top