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Compressor Surge

iz32

By iz32,
in Engines & Forced Induction

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iz32 Community Regular

iz32

Posted
Posted

I have just been reading up on compressor surge all afternoon particularly in relation to low rpm on an RB20. i have dug up some stuff on sau regarding this topic when incorrect wheel configurations in highflows can cause a compressor surge at low rpm, what im unclear about is would this only occur at full boost or can it also occur whilst building boost? and how?

as i understand from what i have read is that the compressor wheel will push x amount of air out and if the pressure between the turbo and engine is greater then what its pushing then it will be forced back thru the compressor causing surge.

now how would this occur in a low rpm situation when the boost pressure isnt that high?

what causes the engine to restrict this compressed air entering the combustion chamber?

could an incorrectly setup engine cause surge or is it all to do with a spiking turbo?

i have theories on incorrect inlet cam lift duration or timing....but im not a qualified mechanic or an engineer and could totally be off the mark so opinions would be great!

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InterCooL Rising Star

InterCooL

Posted
Posted (edited)

surge typically occurs when you start to build boost, the blow off valve is not going to vent at low pressures, so the air gets pushed out the compressor. can happen at 0psi, can happen at 20psi, pending if u how tight / if u even have a blow off valve

does that help?

Edited by InterCooL
iz32 Community Regular

iz32

Posted
  • Author
Posted
surge typically occurs when you start to build boost, the blow off valve is not going to vent at low pressures, so the air gets pushed out the compressor. can happen at 0psi, can happen at 20psi, pending if u how tight / if u even have a blow off valve

does that help?

it does clarify that point but im also trying to figure out where the problem occurs in the engine. as positive boost builds it should be drawn/forced into the chambers so what would cause it to bank up and surge?

in my particular case the turbo is a constant and 2 different engines are the variables...

edit: i should add that im refering to during the spool phase... not off the throttle BOV type scenario.

InterCooL Rising Star

InterCooL

Posted
Posted
edit: i should add that im refering to during the spool phase... not off the throttle BOV type scenario.

you're getting surge when you are spooling up? :)

you cannot be doing that. you must be mixing 'surge' with something else. but i cant imagine what

iz32 Community Regular

iz32

Posted
  • Author
Posted

yer im really confused...

I just cant understand how 2 RB20's can behave soooo extremely different with the same tune and mods hanging off em.

just relating everything i can find to the situation.... SAU is killing my brain cells

--END THREAD--

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
you're getting surge when you are spooling up? :)

you cannot be doing that. you must be mixing 'surge' with something else. but i cant imagine what

Yes you can have that.

You can have compressor surge as you build boost.

Generally due to a comp wheel that's too large to the rear. Can happen in low RPM definitely as boost is created.

Basically the comp wheel is flowing more air that the motor wants at that stage, once you overcome this its ok usually

bazr33 Mentor

bazr33

Posted
Posted

i notice compressor surge on my r33 with a plain bearing hiflow, Front wheel was off a isuzu truck. Old skool design To4

what appeared to be happening, is that the turbo was generating way too much air that what it should of, at start of spool phase.

This was at 5psi, and then we believe the bov started to pulsate, pushing air through the plumb back pipe into the intake, then too my afm.

The afm recognised more amount of air, getting pushed through, so it dumped more fuel into the engine. I didn't notice this surging when i have the standard airbox on with my standard afm, as it mighten of not of been as sensitive as the z32afm, and the apexi pod filter being able to suck ???

I didn't get around to fix this problem, but i believe it was either relocating the afm to another position, change the bov to atmo, or putting a stronger spring in my BOV.

Then again these ideas could not of worked either.

I have now changed turbo setup, so see what happens. (also going to put a sharp bend in for my intake pipe)

Slim Mat Collaborator

Slim Mat

Posted
Posted

Yo, IZ32

Please visit Garrett's website:

http://www.turbobygarrett.com/turbobygarre...bo_tech103.html

This is all pretty advanced stuff, just read through and filter out most off it and learn what you need to know about Surge. There is a few paragraphs about a 1/3 down the page.

This should help explain it a lot.

Slim

InterCooL Rising Star

InterCooL

Posted
Posted
Yes you can have that.

You can have compressor surge as you build boost.

Generally due to a comp wheel that's too large to the rear. Can happen in low RPM definitely as boost is created.

Basically the comp wheel is flowing more air that the motor wants at that stage, once you overcome this its ok usually

i had a gt2876r 0.86.

massively oversized compressor relative to the exhaust wheel. renown for it. i hated the setup. but i never had any strange induction / surge noises

not saying its not possible, but if a gt2876r doesnt give you it, then you're not going to be getting it with a hks2530 that iz32 is using?

Hardman69 Collaborator

Hardman69

Posted
Posted

Happens with big (relatively speaking) boost, at low rpm. If you look at a compressor map for a turbo, you'll usually see a dotted "Surge line" running up the L.H.S. of the map. This is where the compressor can't push any more pressure at that flow-rate, and stalls (like an aeroplane wing stalling, or a boat propeller cavitating). It stops pumping & sheds a tonne of boost pressure and (turbo)rpm, until it can re-establish compressor flow & start building shaft rpm & boost again.

If U keep the clog in, this keeps happening in a cycle, and U get compressor surge. Wind down the boost at low rpm, or back off the throttle when U hear it hissing REAL loud just before it stalls (and makes the ssssSSSSSCCHHEEW sound as it stalls the compressor). Good luck :D

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