Turbo Compressor Surge!! sounds awsome

For anyone who doesnt no about turbo's the sound you are about to listen to is called Compressor surge, caused normaly when the throttle butterfly is snapped shut causing the fast flow of boost to hit the throttle and flutter backwards and forwards in the boost pipes,,,its dangerous for the turbo and the engine but the sound is amazing -

Its never been proven to be dangerous for the turbo, and is definitely not dangerous for the engine. The theory is that the sudden change in speed is bad for the bearings which have the energy of the rotating turbine/impeller transfered though them. This is certainly going to be bad for larger turbos because they have larger rotating masses, therefore more energy for the bearings to absorb. But there is no documented proof of the long term effects of this.

Many people around the world run without a BOV for many thousands of miles and no problems. Even more people have compressor surge even with a BOV fitted, either due to a massive airflow (why do rally cars have turbo chatter? something to do with running crazy boost perhaps?) or due to not adjusting the BOV properly. It also doesnt seem to affect lag between gears as much as people think either, from what ive experienced.

Heres my own car - ran it since the conversion with no BOV, now it is getting one soon though.

https://www.youtube.com/watch?v=djMOMq1z0yE

Im affriad to say but compressor surge is very harmful to most turbo's and some airflow meter equiped cars. This is one thing i learnt while doing a level 5 course in turbo tech and compressor maps at turbo techniques, The more dangerous kind of surge (on boost surge) for road cars can kill a turbo in weeks, op-erating a turbo in the area where surge (flow instablility) occours loads the bearings with forces they are not happy with which causes massilvley increased wear and thrust related damage to standard bearings hence why when propely specing up a turbo using a map its so important to make sure the engine will not run the compressor into a highly unstabe flow area, its very veruy bad for an engine in this case off on boost surge.
Literaly most modern cars have diveter valves, even the older cars like the GT turbo had one unless designed to run without, not to stop lag but to increase turbo life and prevent damge to the engine over time due to running with an airflow meter.
Engines running an airflow meter can have there life cut short by very bad fueling issues caused by the unstable air flow caused by surge, i only talk from exsperience and i was tought this turbo tech through turbotechniques,,,,who i would like to believe knows what they are doing
Good to have differnt opinions on this subject mate, but ive seen the evidence to support the fact that in most cases surge should be avoided as best as poss

thanks

jason

Ow by the way the video of your car sounds amazing, my dump valve once seized shut and it sounded exactly the same, amazing sound.

And you mensioned rally car turbo's, most rally cars use anti-lag which requirs massivley uprated thrust bearings and centrifugal bearingsin the turbo to run it with so surge cannot harm the turbo like it can on road cars and a rally car under goes a mager rebuild often, the turbo on a car is exspected to last as long as poss, also for serious road car applications the compressor housing inducer is fitted with small holes to keep surge levels stable or at bay all together.

thanks

jason

Its not really an opinion. Im certainly no expert but i am currently doing a mech eng degree and i read up loads on stuff like this, both theory and real life experiences. Your qualifications in turbo theory sound impressive and im sure you know a lot more than me about the subject overall, BUT, here is what i know to be fact.

You seem to think on-boost surge and off-boost surge are as bad as each other. Well they are not, and are caused by completely different things, as im sure you are aware.

What you say about on-boost surge being dangerous is very true, and is caused by speccing the wrong turbo and boost levels for the application. You will never suffer this unless you are running the turbo close to or at its limits.

Surge caused by coming off the throttle (is there a shorter term for this?) is not even in the same league as on-boost surge. Whilst it still puts strain on the bearings and impellers, the fact still remains is that this strain is fractional compared to on-boost surge. There is no exhaust gas to keep spinning the turbo, therefore it is freewheeling. (in fact, the momentary reversal of flow on the turbine side when the throttle snaps shut is something else to consider).

AFM equipped engines will respond differently to off-throttle surge, but think about it, when the throttle is closed there is no need for good fuelling anyways. On-boost surge - well, obviously, massive problems there.

So what are we arguing about? You seem to think off-boost surge is a turbo killer? Well i dont doubt it shortens the lifespan of the bearings. BUT, as the expert, can you tell me if this shortening is measurable?

Theory aside, in the real world people notice sod all difference in lifespan with off-throttle surge, given the number of tuned cars which suffer from it. I shouldnt have mentioned rally cars because lifespan is not important - but it still stands for many high power road cars.

Anyways, thats my tuppence. I dont mind being corrected on anything you think i have got wrong - knowlege is power and i'd rather be spouting truth than poo.

well your both up on my because i no Poo Sprinkle about it

why does this forum have a swear filter? lol

lol because its funny

munkul wrote:why does this forum have a swear filter? lol

I think it just makes the forum a better place, some people can take offence from swearing

even though we all do it......especially with fiats lol

jason

Moose Inspector Poo Sprinkle bollocks Big Sticky Hole, whatever i dont know how but it looks like this got a little heated, i may have read wrongly but thats how it came across to me, at the end of the day it seems its one of those things where in one instance something is believed true or untrue due to past experience, whereas in theory (or in other cases of this problem) it could be the complete opposite,
either way, handbags away please, no point in trying to change other peoples views/opinions as everybody has their own,
taa

nothing heated about it mate, im sure jason will say the same.

Its not like its views/opinions at all. Its what we have learnt one way or another, and when something contradicts what somone else has said its always best to talk about it until you reach a conclusion. With physical matters like engines there are a few "right" answers and plenty of wrong ones, unlike styling etc where there is no "right" answer.

I'd rather say all that i have said which is correct to the best of my knowlege, only for Jason to come along and prove me completely wrong, than not say anything at all. That way, everyone gains knowlege.

there is truth in what we both say right

everybody learns from everybody, how we learn right?

glad this is all good

lets say one thing though....surge sounds awsome

jason

yeah got to admit, sounded way better without an airfilter though! (ran it for a week with only a metal gauze over the turbo inlet lol)

i bet the sucking sound of the turbo was aggressive to then?? my T15 sounded more like a jet haha, i hope the new one sounds as good

jason