With an HKS SSQ BOV, and a t3/t4 (DRAG III Kit) I get a tremendous amount of compressor surge..it's not the BOV. How do I get rid of it, I already have blown the exhaust side of my first turbo out (shaft wobble, bad). What should I do to correct this once I get a new turbo?

 

What do you mean, it's not the BOV? The BOV is the ONLY thing that prevents compressor surge... so if it's surging, there's something wrong with the BOV. Period.

 

what is compressor surge?? plaes go deeper into this

 

Compressor surge is what happens when you're boosting, the turbo has built up all this pressurized air moving at high speed in your intake pipe, and then you take your foot off the gas - the throttle plate closes, and all that air has nowhere to go. If you have a BOV, the valve opens and vents the pressure all out. If you DON'T have a BOV or your BOV is not functioning correctly, all that pressure has to work its way BACKWARDS through your turbo which is still trying to push it forward. This results in very nasty sounds and damage to your turbo's bearings.

 

Maybe try adjusting the bolt on the back of the BOV all the way out as loose as you can make it.

 

ya better loosen up that adjustment screw on the bov.

 

I didn't mean the BOV wasn't the problem, I was meaning that the sound I was hearing was not the BOV. If adjust the screw on back of the BOV do I tighten it or loosen it to allow more flow, and has any one else had this problem. we believe this might have given me my shaft wobble on the hot side. But, we think the turbo could have been messed up from the beginning has anbody experienced this.

 

Stupid Q:

Don't you have to set your BOV to whatever boost you are planning on?
E.g. 8psi boost...set BOV at 8psi so anything above 8psi would be vented out. Won't loosening the BOV too much cause you to lose your boost?

 

You need to loosen the bolt in your case. It will not loose boost. The HKS design will not leak boost.

 

um u are thinking of the wastegate which is set for holding boost

 

I understand the wastegate part. About venting some exhaust energy to control the turbine speed and thus amount of boost.

I just don't get the BOV part. Don't you have to set your BOV valve to open only when it exceeds your set boost? E.g if you wastegate was set for 10 psi and your BOV was set at 8psi...won't your BOV leak the boost and cause you only be able to run 8 psi?





[Modified by xero-cool, 12:11 AM 5/2/2002]

 

u=confused

there is no psi spring rating for bovs (that I am aware of)... just a manual adjustment screw to either load or unload the pre-determined spring rate installed inside of the bov. that way you if you are leaking under boost through the bov then you can put more pressure on the spring which will keep the bov closed.

the bov isn't supposed to open under boost. It opens under vacuum. if the spring tension is too high then the bov may not open (which may be the problem) and you'll get compressor surge.

there is, I believe, a device called a pop-off valve which is configured to open on a set psi as a safety measure in the case of an overboost situation. In comparison, I'm pretty sure it isn't the same as a bov.



[Modified by Pritos, 4:28 PM 5/1/2002]

 

I dont think anyone has mentioned it yet, but there are TWO kinds of compressor surge. One of them has already been described, its when the throttle slams shut either you have NO BOV or the BOV is faulty causing the air to go back to the compressor blades and stalling ti and wearing down the thrust bearings..

The other type of surge that no one has mentioned yet, is when you have very little airflow and not enough boost, (or something like that). the oscillating air in the intake pipe causes the air to make a "snake-like" noise or a "che-che-che" sound. Even if your BOV is functioning properly, you could still get this type of surge.

I know that the definition for the compressor surge I'm describing is in the glossary for "Maximum Boost". I'm not sure if its not enough air to MUCH boost, or not enough air to LITTLE boost. I'm at work right now and I dont have my book so If someone wants too they can clarify that a little more.

 

That right there might be a result of the compressor surge I described. I think that both types of compressor surge will have the same negative effect on the turbo unit. IIRC the surging will lead to rapid deterioration of the thrust shaft, which is why your shaft wobbles so bad <- can anyone confirm this?


[Modified by BlueShadow, 3:20 AM 5/2/2002]

 

I think what you're talking is that the motor isn't flowing enough air and the turbo is making too much boost. that causes the compressed air back into the compressor causing damage. this is due to compressor mismatch with the motor. i think its when the turbo is too big for the motor. please feel free to correct me if i'm wrong, because i would love to learn.

shadow, what really confuses me is that according to some compressor maps, combinations that work in real life, don't work according to theory. ie. b18c with a t62 & 25 psi +. can you help me out here?


[Modified by SEFI8LOxCivic, 3:39 AM 5/2/2002]

 

I got the same problem. The screw is soo loose, its about to come out completly. And I still get the pigeon flutter sound. :/ Someone want to trade me and givee me a greddy type s?

 

i think that's just the way the HKS bov sound. everyone that i know with that bov has that flutter sound.

 

i've heard the hks sound before in a friends turbo type r and i heard the same thing ... not a clean 'whooooooosh' but sort of fluttery.

 

yea, i think its just the way its designed. the first stage (low boost) sounds fluttery, and the second stage (higher boost) sounds more like a swoosh. i remember watching best motoring and some of the bovs also sound like that. so maybe it is normal?

 

well like I always tell people, whenever they do their own compressor selection, there are too many variables that could offset your actual result.

say for example the airflow, to accurately determine airflow you need to know the airs temperature, and you need to have some understanding of "fluid dynamics" and also "thermodynamics".

also with things like a T62 on a B18C, a lot of the engines original qualities have been changed by things like the compression ratio, camshaft design (turbo cams), and various other things. Is the airflow for a stock NA B18C the same as a turbo prepped NA B18C? its things like that are what some people dont take into account when selecting a turbo for high PSI.

but besides that I always let people know that selecting a compressor for 18+ PSI is a lot more complicated then doing it for 8 PSI. I usually tell people to leave it to the experts when dealing with high PSI numbers.

 

true, somethings just really should be left to the experts. its just that those darn compressor maps are so perplexing/intriguing.