Thread: Forge BOV spring question

they adjust the BOV for different boost levels. So for instance, you modded the ECU and now make 22PSI WOT, you'd use the corrisponding spring for that boost pressure. They don't increase your boost in any way, but set your BOV for when you do.

Ah ok. I get it now, thanks. Basically it would be pointless to have the engine and computer tuned for 22 PSI if the blowoff valve is adjusted to vent any pressure exceding say 15 PSI. So the BOV spring is just to let the boost build up to the desired level and get rid of the rest.

welll... uhh. sort of. The spring prevents cracking, which is when boost pressure exceeds spring tension and opens the BOV to vent air. So you're right in saying that if your BOV is set to 15psi and you're running 22 psi it's pretty pointless, you're damaging your BOV.
When you release the throttle it causes the BOV to open and vent the intake pressure preventing damage to your compressor (aka intake side of the turbo) and throttle plate.

This is typically when I go into some long winded explaination of things but I'm trying to stop doing that. If you'd like more detailed info I'll provide it but otherwise just know that if you have a stock turbo and stock ECU settings and no boost controller, use the spring Forge put in the BOV.
But I'm told pictures say a thousand words, so here's two.



Thanks Wikipedia for your pics!

Hope this explains things, and it's better to ask questions than to guess wrong.

Actually I'm a very technical minded person who loves to understand the intricacies and technicalities of how stuff works. I love details. Blame my computer tech/geek side for that one. So I would love to read that long winded explanation :P.

Unless you'd rather not, in which case I would understand. But yeah I get the basics. I can picture the whole shebang in my head. the BOV is just a pressure release valve to release turbo pressure when the foot is off the throttle. I'm guessing something along the throttle body is closed so the engine isnt taking as much air as the turbo is pushing in, the excess pressure could damage the throttle plate of the throttle body as you said and/or backup and hit the compressor, carnage ensues?

Sweet, saw the picture after I posted. Very nice. So that's the hose that goes from the engine to the BOV/Recirc. It's a vacuume line.

My guess is when the throttle body is closed the action of the piston going down creates a vacuum because it cant suck in as much air from the intake. The BOV would use the vacuume to pull the piston which is normally held closed by the spring. Also explains to me the whole concept of vacuum in an engine.

So the springs will seemingly decide how far up the piston opens during vacuum. That's my guess. And a higher boost spring will open the piston more(is softer) than a low boost spring(firmer)??

I've decided to use more pictures just to help in the explaination. Typically I wouldn't mind writing paragraphs of detailed information but it's been a long day and I think the pictures really show what I mean.
Again, thank wikipedia for the base pictures but these three I modified to show what I mean.

I'm a locomotive mechanic by day, a computer technician by night and a scientist on the weekends so I'm fairly apt for research and trial and error.

You're right about the piston going down creates vacuum, thats why if you have a boost gauge and are idling you read inHg (inches of mercury), the turbo isn't generating enough pressure to counter the vacuum being created by the engine, or in the case of the Genesis Coupe, the ECU holds the wastegate open and dumps all exaust until it detects a throttle response, ie. you push down on the gas pedal. Doing this reduces heat transfer from the exhaust turbine to the intake compressor allowing cooler air for idle which improves economy and emmisions.
The vacuum however is through the whole intake so it won't open the BOV at this point because the spring for one holds it shut and there is no difference between pressure on one side of the BOV piston and the other.

The spring counters the positive pressure on the intake side of the BOV and the vacuum on the back side of the BOV, so yes, it does decide how far up the piston goes during release of throttle, but it also decides how quickly it shuts once pressure is restored. Thats key in building boost again quickly.
A high boost spring is typically firmer to counter more positive pressure and vacuum during open throttle.





I hope my notations on the pictures help explain my additional or modified doodles.

Wow, thanks for all the info it really helped!

I now consider myself way more informed. I also understand the concept. thanks.

I was wondering, I have the Forge BoV and the 20 lbs PA tune. Should I be using a different spring that the one that was initially in it? Also, I may be switching to the 18 lbs tune what is the suggested spring for that?

I have the yellow and blue springs as well as the 2 shims. I am not sure of the color of the one that is in the bov.

Whaever, hope this helps I got it right from Forge's site, but I'd ask the sponser here before modding just to be safe:

Valve Spring color coding


Green - 5-15 PSI


Yellow - 15-23 PSI


Blue - 23-30 PSI


Red - 30 + PSI


The above figures are estimates only and should only be considered as a guideline

Please note - fitting a stronger spring into a valve will not increase boost pressure unless existing pressure is being lost. Failure to allow the valve to operate by installing a spring which is to strong may cause damage to the turbocharger.

Please note - the red coded springs should not be installed in the DVR or DV007 diaphragm valves

I'd say go with the yellow spring because it suits all your current and potiential ranges. I'd say the green is in there now because apparently stocker boost is only suppose to be 14-18 PSI.

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