Compressor Surge-Does it Really Matter

[SMB315]

do u reckon it makes a baig difference in power, besides it being laggy till the surge is over, the power rush when it's over is pretty sweet. rekon u can screw the turbo up?

[DoughBoy]

Yeah it can snap the shaft and bend compressor blades. So not really any problem, just sit through the jolting and bob's ya uncle. She'll be right.

[BHDave]

Yep, it's a problem.

Best bet is to fit a turbo that is matched to your engine or to mask the problem get a boost controller that can reference boost against revs so you aren't trying to stuff too much air into the engine at low revs.

[hayes_666]

Sorry for being a bit stupid, but, What do you mean by compressor surge?, can you explain with a little more detail for me?.

Thanks

Nathan

[Mandingo]

its when the engine cant swallow the air the turbo is pushing in basically

[hayes_666]

Sorry to still seem slow, but how do you mean cant swallow you mean that the turbo is so large that the boost goes so high the turbo stalls untill it gets enough exhaust gas to get going again?, Would have to be one hell of a efficiant turbo to do that?,

Nathan

[DoughBoy]

It's more airflow levels rather than extreme presure ratio i.e. the turbo's producing 100 squares of air at 5psi and the engine can only "swallow" 30 squares, so air comes back out the intake system via the turbo. The main reason for it is the exhaust housing is too small - if you go up a size (or two) in exhaust size it should sort the problem out by bringing on the turbo later, when the engine can make use of the airflow.

[Lithium]

Sorry to still seem slow, but how do you mean cant swallow you mean that the turbo is so large that the boost goes so high the turbo stalls untill it gets enough exhaust gas to get going again?,  Would have to be one hell of a efficiant turbo to do that?,

Actually the opposite, it takes a badly matched turbo to do that - at least one that is badly matched to the engine it is bolted on to. This is the reason you can just leave the same exhaust wheel on a turbo and bolt on bigger and bigger compressors to move more and more air into the engine. A very efficient turbo strictly speaking would be PERFECTLY matched to the engine, shoving just the right amount of air for the engine into it over a wide rpm range.

[sweetr33]

how can u tell if ur car is surging? What would happen to the boost gauge?

[Warpspeed]

The needle might turn into a blur, and you will hear the dreadful noise, the engine might not not be terribly happy either abut the rapid pressure fluctuations. The effects can vary quite a lot from hardly noticeable to turbo end engine shattering violence. It all depends on how bad the surge is.

All turbos can surge if the compressor flow drops below a certain value. As lithium says bigger and bigger compressors surge at higher airflows. There is a myth that huge compressors will force more air through the engine. It simply is not true.

If the engine has 10psi boost with a small compressor, and you fit a humongous compressor wheel that also makes 10psi boost. The engine just sees 10psi and flows EXACTLY the same amount of air. It might be more efficient at the top end, but if you have a decent intercooler, that does not matter either.

Suppose the air going into the intercooler is 120C and 50C coming out. You fit the monster compressor wheel and the air going into the intercooler drops to 90C, and the air coming out of the intercooler to 47C. Hardly worthwhile doing. If it also now surges, you have wasted your money on that "hi Flow"compressor wheel.

[tang0]

so are you saying that hitting my 0.80 bar at 2800 rpm with a standard turbo is not good, i mean, it hits that, the the car seems to be pulling pretty hard, still going faily slow, but uphill, in 3rd, doing 40kmh at 0.80 bar seems the turbo is spooling up v fast for under load ...

just wondering ..

[Coxy_]

I was getting some compressor surge in my car when I was running the boost too high- the boost needle would hit the right amount of boost straight away but it would take the car a second or two for you to feel the take off- you're better off lowering it down a little until it stops doing it or you could do some damage eventually- my turbo has got a small leak because of it........@##$$#%$#!!! hehe

[DoughBoy]

Oh yeah and it hammers bearings too.

[hayes_666]

My car runs, from 2800rpm 5psi boost then at 3800rpm she reaches full boost (10psi) the needle is steady, she pulls well but not really hard untill 4300rpm, i just assume that the engine is just more efficient at those revs, as on the standard turbo it didnt get going till the same revs but came on boost earlier????.

Nathan

[sweetr33]

i think my stock turbo used to reach full bost (1bar) at about 3300rpm. But of a difference in spool up time. But willbe interesting to see how the hiflow goes with the other nik naks i got done too

[tang0]

mine also feels a bit lumpy under hard load / wot type conditions ...

powerfc is on the way, so hopefully hould be able to iron out some of the holes in the fuel maps ...