Compressor Surge on Turbo MX5s

[pixola]

Hey guys,

Just wondering how many SP or other MX5 owners experience compressor surge (that fluttering noise) when not on full boost (ie. 2-3000 rpm, low throttle gearshifts).

I've had it ever since I built my car, and even with a new BOV, it seems like I'll never get rid of it.

The volume of the surge depends on how much air volume is in your pipework (eg. large IC, large dia. pipes, large air intake) and apparently isn't too damaging to your turbo at low revs (as opposed to at full boost).

Cheers,
Andrew

[Sean]

Yes.

I get compressor surge just teh same, It was significantly reduced by moving the BOV considerably closer to the throttle body.

[Sheck]

i thought surge was a different thing, ie turbo providing too much air for engine (which cant take it all in) - this makes a weird noise - but can only be heard while foot flat and low in revs.

That fluttering noise on shift is just the air comming back and hitting the compressor wheel. A fix would be to loosen up your bov - which may lead to leaks, or to put up with it cause it doesnt really damage the turbo.

Dave

[pixola]

Nah no matter how loose the BOV is.. now I've tried 2.. the only time it goes away is when the BOV is so loose that it's open at idle.. not right..

From reading a few other forums .. some Silvia owners with modded cars get it too..

It's just low boost surge vs high boost surge..

[4sfed5]

no surge with my VF10 turbo on a 1600...also running a stock subaru plastic bosch bov recirc'd

[rjr666]

just keep the compressor surge... Thorpey said its fully sick

http://www.youtube.com/watch?v=L5V01zH3KEg

[nfs13b]

I dont notice any compressor surge on mine, but I probably wouldnt hear it over all the other noises and the wastegate....

[The Pupat]

i thought surge was a different thing, ie turbo providing too much air for engine (which cant take it all in) - this makes a weird noise - but can only be heard while foot flat and low in revs.

Compressor surge is definitively a bad thing (far far more so than what happens when you back off without a BOV which would be pretty much harmless). Compressor surge is when a compressor tries to raise the fluid to a pressure ratio that is too high for it to hand at the current flow rate. IE 2:1 pressure ratio at 100 CFM of air flow when the compressor is designed to work around the 2:1 pressure ratio at 200CFM of air flow. If you've seen the pretty lined graphs showing compressor maps then it's the area to the left with the hard line. The hard line is refered to as the surge line and anywhere where you push to the left of that is bad. Basically the turbo compressor starts pulling skids in the air.

[Sean]

i thought surge was a different thing, ie turbo providing too much air for engine (which cant take it all in) - this makes a weird noise - but can only be heard while foot flat and low in revs.

Compressor surge is definitively a bad thing (far far more so than what happens when you back off without a BOV which would be pretty much harmless). Compressor surge is when a compressor tries to raise the fluid to a pressure ratio that is too high for it to hand at the current flow rate. IE 2:1 pressure ratio at 100 CFM of air flow when the compressor is designed to work around the 2:1 pressure ratio at 200CFM of air flow. If you've seen the pretty lined graphs showing compressor maps then it's the area to the left with the hard line. The hard line is refered to as the surge line and anywhere where you push to the left of that is bad. Basically the turbo compressor starts pulling skids in the air.

Yep that's the way I understood it too, the BOV is to vent the air to minimise the ffect of the surge if I'm not mistaken.

[The Pupat]

i thought surge was a different thing, ie turbo providing too much air for engine (which cant take it all in) - this makes a weird noise - but can only be heard while foot flat and low in revs.

Compressor surge is definitively a bad thing (far far more so than what happens when you back off without a BOV which would be pretty much harmless). Compressor surge is when a compressor tries to raise the fluid to a pressure ratio that is too high for it to hand at the current flow rate. IE 2:1 pressure ratio at 100 CFM of air flow when the compressor is designed to work around the 2:1 pressure ratio at 200CFM of air flow. If you've seen the pretty lined graphs showing compressor maps then it's the area to the left with the hard line. The hard line is refered to as the surge line and anywhere where you push to the left of that is bad. Basically the turbo compressor starts pulling skids in the air.

Yep that's the way I understood it too, the BOV is to vent the air to minimise the ffect of the surge if I'm not mistaken.

Except that when the BOV is supposed to work is when you back off the throttle and cut off the power to the turbine so it starts to slow down. The damage to the compressor comes from overspeeding it from what I understand. EI when the compressor reaches aerodynamic stall (goes to the left of the surge line) the turbine is still spinning it hard but the compressor can't use all the power so it speeds up and up and up.

It was defined as spinning the rear wheels up to 100kph (so very light throttle load) on a jack then releasing the car to the ground, IE the car will most likely stall and do nothing. Compared to dropping the accelerator and getting the car to full load on the ground (IE overspeed/overload the drivetrain), and this is why BOV are there to meet emissions and to make cars STFU. Well it makes sense to me so believe what you will.