Turbo Lag

[Inline6Merc]

I've heard of turbo lag before and ive heard of it in the forums. What is it caused by, besides being turbocharged. Can there be anyway to overcome turbo lag? Don't you want to get off the line as quick as possible?

Thanks

Curtis
Inline6Merc

 

[66Sprint6]

Lag can be caused by alot of things, and Im sure someone will elaborate more later, but Ill tell you what I know. Too big of a turbo=lag, too big of a compressor housing, too long of piping to the intake, from exhaust to the turbo, etc.= lag. Best thing to do is get a good matching turbo (using turbo maps) and keep the piping as short and simple as possible
Matt

 

[Anonymous]

Along with the plumbing aspect, the most important key to reducing turbo lag is the size of the turbine (exhaust side of the turbo). Lag is never desireable, but sometimes you have to live with it if you want REALLY big HP numbers where you have to run high rpms. Otherwise, lag can be completely non-existant in a mild application.

A turbo's compressor has different efficiency levels at different flow rates and pressures. The trick is to get your to find a suitable match for how you want your engine to behave. Compressor maps (and knowing how to read them) are an invaluable tool in this aspect.

For a street engine, you can use a small turbine. This will minimize lag and get you up on boost quick. The downside is that by 5,000 rpms, you will be putting a lot of heat into the engine because you are out of the compressors efficency range. You will also be spinning the turbo at a very high rpm.

Race engines use larger turbines. You will typically have very little boost until 3000 rpms or even higher in order to have the compressor in a peak efficiency at 6,000+ rpms. That's where the big HP numbers develop. They often use tall gear ratios, hi-stall converters, trans-brakes, or even nitrous to overcome the lag and get the engine up on boost right after launch.

VATN (Variable Area Turbine Nozzle) turbocharges are on the market now as well. The A/R of the turbine changes with rpm and allows minimal lag, with impressive top end performance. In effect, the turbine gets bigger with rpm - stabilizing the turbine rpm and keeping the compressor in acceptable efficiency ranges.

 

[Anonymous]

Lag can be (a little bit) your friend at the drags. You'll be slower out of the hole, but you're not planting all the HP to the track right away. It gives your tires a little more time to hook up. The power surge kicks in and you're on a rocket ride.

This can (and probably will be) debunked, but it's something I've heard from time to time.

I second the other stuff already posted here about lag and it's causes. It's basically the time it takes the turbo system to get spooled up and pumping out boost.

--mikey

 

[Anonymous]

What Mikey says also applies. If your budget doesn't allow for a trick 4 link suspension, a super HD rearend, or huge drag slicks (and the tubbing that goes with them), then a little lag would be desireable to get you moving in a straight line before torque curves begins to rise.

 

[XFlow_Fairlane]

yeah my old tbird was fast off the line because of this. I would dump the clutch at 4500 and get a little tire spin as it came out (helped kept it from booging) and once it started rolling out the boost would come up. lag is more noticable basicly at lover rpms (like off idle) when the turbo needs to be spooled up still.

 

[CobraSix]

Inliner hit most of the basic important parts.

I think Lag is mostly a myth propogated by supercharger enthusiasts. Does it exist, yes. Is it noticable? Not if the turbo system is designed right and the turbo is sized properly. I think people put turbos too large on their cars (not here on FSP, but import guys, unknowledgable domestics).

I know my Turbo Volvo has virtually no lag. It does lag in 1st gear, but that's a computer issue as it opens the wastegate more in 1st gear as to help with traction control. It also limits the boost to 8psi for the same reason. After that, I can get the full 16psi at any RPM in less then 1 sec (quicker that I can push the pedal down and look at my boost gauge).

Slade

 

[Anonymous]

electronic boost controllers help the lag problems, as do camshafts i think. but as mentioned earlier, when you make big power the lag goes up. however no matter how good the setup, lag will shed its face as the power begins to rise. ball bearing turbos also spool faster, as do mitsubishi turbos which should suite our low rpm engines well. just dont go crazy on tthe boost pessure because that also increases lag. if yor running 10-12 psi you shouldnt have any problems though as long as the setup includes quality parts and design.

 

[xctasy]

Just go for a way too big turbo, with way to much wheel for the engine, and then add a bottle of nitrous to operate from 3000 rpm to just below maximum boost. That way, there will be virtually no lag, and absolutely the best boost you can get.

I remember reading up on spool times for standard T03, T04 turbos at 9 psi from stall to maximum boost. The t03 was about 0.6 seconds, the to4 about 1.2 secs. A bigger T66 or T72 would take even longer. A nitrous bottle reduces that lag by more than half, as the nitrous is 1.5 times the power you had at any rpm.

Oh, to have the oportunity to try both!