Compressor surge. Time for a Tial 50mm bov?

[Hiitman]

I've got a forge 1g bov on my setup. 2.4, G50, methanol, 23psi. The spring that was in there was the yellow 10-12 psi spring. I put in the red 18-20 psi spring and nothing changed. I think it may have helped a little but it probably didn't. Here's a link to the forge springs Forge Motorsport

Question is, should I switch to a Tial 50mm? Next on my list is a Spearco bar and plate to replace the Godspeed tube and fin. Soon after that will be a PTE 60trim. What do you guys think?

 

[firebirdvert305]

I think you should search the difference between BOV flutter and actual compressor surge. Chances are with your 2.4L your not experiencing compressor surge, most likely bov flutter. Those bolt on mitsu turbos are prone to surging, just something you gotta deal with, if its actual comp. surge theres two ways to deal with it. One being goto a bigger hotside, the other try a port shrouded cover.

 

[Hiitman]

I ended up searching last night. Apparently most guys using forge bovs experience flutter. Also, if I was experiencing surge the car would buck in between shifts right? Not just make the fluttering noise.

 

[rich3389]

My forge BOV does not surge or flutter, I am using the yellow spring(15-23 psi) I believe...Make sure to do a boost leak test and see if its leaking where the bov meets the flange, the older forge's had that problem and can be fixed for free if you contact forge.

 

[Hiitman]

I'll check. The gasket looked good when I took it off the other day. Where did you get your bov from? When they sent mine from extremepsi they didn't note which spring set came with it. They list a valve spring tuning kit and a dump valve spring kit. Each has different spring rates for the different color springs.

 

[CanadianTSi]

When are you experiencing this "surge"?

Compressor Surge happens on initial spoolup under WOT, BOV flutter happens during shifts.

 

[Hiitman]

It's during shifts. I've got a 23psi spring in my Tial wg but my gauge only goes to 22. So during compressor surge the bov opens prematurely? What could happen if my bov has too stiff a spring in it? When I changed from the lowest rated spring to the highest the whistleing flutter noises seemed further apart inbetween shifts.

 

[CanadianTSi]

Compressor Surge happens when the turbo spools to soon and is trying to force more air into the motor than it can ingest. The air back's up in the IC pipes and slams into the spinning compressor wheel, causing a bucking and chooo choo choo sound.

 

[firebirdvert305]

I highly highly doubt your experiencing compressor surge on a 2.4L engine, most cases are only with 2.0L engines. The extra displacement is going to help curse compressor surge because it can ingest more air at lower rpms, do a boost leak check. If that checks out fine, look into the BOV. If theres a two stiff of a spring in the bov, during shifts the bov wont open or wont open enough and youd get the same "cho cho cho" noise as actual compressor surge.

 

[Hiitman]

I went from the softest spring to the stiffest and nothing changed. Bov flutter?

 

[CanadianTSi]

Check the Vacuum line going to the BOV and make sure its not split or anything.

 

[patty AT forge]

We rate the springs with the following approximations:
Green 5-15
Yellow 15-23
Blue 23-30
Red 30+

Do the "pen-test" outlined in this PDF:
http://www.forgemotorsport.com/media/valve_service(1).pdf

Also check the lock-ring on the bottom of the flange, there should be two small holes machined into it, if they pass all the way through the ring let me know and I will send you a revised part that has the holes machined only part way, the older design leaked.

And of course check for leaks elsewhere especially the reference line to the DV, also i is best to give the valve a dedicated vacuum source.

 

[DirtyBirdRacing]

Compressor Surge happens on initial spoolup under WOT, BOV flutter happens during shifts.

Compressor surge can happen anytime the throttle plate is closed while under boost, and can also happen on spool up. This includes between shifts. Not saying the OP has compressor surge, just making a comment.

Bill

 

[Black_Bullet]

When using my Dodge garage modded 1g bov my car likes to compressor surge in 5th gear only.
It repeatedly does it at high way speeds when im cruising and building up boost while under partial modulated throttle. It wont ever make any sounds but it will start briefly bucking. It doesnt do it in any of the other gears, i suppose from the higher load in 5th gear the turbo spools the fastest and throws the most air then, and thats why i manage to "backup" my intake air at that point when the throttle plate is only partial opened while im feathering the gas.
So i try not to let it build any boost in fifth, or i normally just be sure to be careful about it. I dont want to prematurely kill my turbo.

I had the lock ring problem with my Forge bov so I took it off, but when i had it on the compressor surge in 5th went from a 6 out of 10 with the modded 1g to a 4 or 3 out of 10 with the forge w/ yellow spring.

Patrick straightened me out with a new revised forge bov that i just got in the mail, so i will put that on this weekend and see how it does as far as compressor surge.

I know the yellow spring is rated at 23 psi max, but i actually plan on running more like 24-25 psi once i get meth injection/E85, but i dont want to switch to a stiffer spring that would worsen my surging in 5th gear.

So i was wondering if I just put one shim on the yellow spring would this affect surging any while allowing it to hold at least another 2 psi tops?

 

[turboglenn]

Black Bullit, i don't think what your feeling while cruising is surge, or at least in the way i've experienced it and that was only under WOT high boost. You could be hearing BOV flutter and the bucking could be from AFR or timing

There's a video posted on here with a 240/silvia ( not sure cause it was in a foreign language) but you can hear the BOV fluttering like crazy. Light fluttering isn't going to hurt anything, you just don't want to shut the throttle and not have a blow off valve period and hear that surging (or surging under WOT that's almost as bad as no BOV). I saw a grand national break it's compressor wheel off the turbine shaft from shutting down hard at the end of the drag strip at Norwalk Raceway Park the conclusion came that it was from the massive surging when he would let out and get on the brakes and not having a blow off valve at all. While it is a form of surge, i've not seen too many cars that make high boost on a regular basis and have a BOV that doesn't flutter under light boosts and throttle changes... That one in the video on here is horibbly loud, but you hear them like that all the time at the import drag and drifting events from the high power cars

 

[daren_p]

Check to see if you have the new revised lock ring, as mentioned above & of course check for leaks. Does the BOV have a direct source from the intake mani? From what I've experienced, the flutter usually gets worse with stronger springs, so I'd go to the lightest one you can run without it leaking. Also as the link shows above, make sure the piston/orings are lubed properly. When I had a Forge the greeen spring (lightest) was able to hold 20 psi no problem with a boost leak test....

 

[Black_Bullet]

Check to see if you have the new revised lock ring, as mentioned above & of course check for leaks. Does the BOV have a direct source from the intake mani? From what I've experienced, the flutter usually gets worse with stronger springs, so I'd go to the lightest one you can run without it leaking. Also as the link shows above, make sure the piston/orings are lubed properly. When I had a Forge the greeen spring (lightest) was able to hold 20 psi no problem with a boost leak test....

Daren reread my last post.

And to TurboGlenn, no i think its surge, it only does it in 5th if im at light throttle building boost but modulating the throttle... My 16g spools pretty face with this Fp mani, and theres been occasions were ill be cruising 90mph on the highway and look over and notice im on 10psi even though only being on partial throttle.
It doesnt flutter at all, i dont have that problem, it either blows off really loud, or it hardly blows off at all, depending how much psi was in the intake track as i let off.
( This is with the stock one and the forge bov, its just worse with my modded stock one. )

Honestly im not worried about it as it only happens in 5th and I can change my driving style in that gear.

 

[daren_p]

Daren reread my last post.

Okay, & why am I doing this

 

[patty AT forge]

Black Bullet,

Since you observed a difference between the stock and the Forge valve one of two things is happening: either the Forge is "holding" better than the mod'ed stocker or it is leaking more. Either of these can be a benefit when we are talking about odd-ball driving situations. My guess would be that ours is "holding" better...

I'm not talking about the leak past piston that your valve had, something like that seems extremely bad but is a pretty insignificant volume of air all things considered. I could overcome the leak with a hand-pump so to an engine this leak is inconsequential really (so long as it is recirc'ed). The way in which a valve leaks that is an enormous problem is by opening, this is what happens with softly sprung valves and is usually a problem with OEM valves.

A bench test won't really show this problem, it will usually manifest itself due to pressure drop and latency. For example, a car is losing ~2psi through the intercooler and there is a .05 second delay from when the bottom of the valve sees pressure and when the top of the valve is pressurized from the intake manifold.

So lets say the valve in question is a Bosch 25mm unit found on a VW (I'm using this 'cause I know what the cracking pressure is), the cracking pressure of the valve with boost applied just to the bottom of the diaphragm is about 3 psi, so it opens and begins to leak. Also since it is open the area available to the pressurized air to act open is greater than the 25mm when it is closed so even after the pressure on the top and bottom of the valve equalizes (or as close as it is possible to come due to the pressure drop) it will take a little longer than usual for the valve to close fully.

Now in the same example if we are running a valve with a cracking pressure of 6 psi. Nothing will happen. That is to say, the valve will remain closed and the car will build boost normally.

Now I am greatly simplifying this, ignoring the fact that the valves are already open due to vacuum, just to illustrate my point.

And my point is this: Both of these valves will impact greatly where the turbo is on its compressor map. So in Black Bullets example of cruising speed in 5th, lets say 3000rpm and 10psi. The soflty sprung valve is forcing the turbo to spin much faster to produce the same amount of boost. This can place it to the left of the compressor map, which is the surge line. And the valve that remains closed will not, even if it leaks during a boost leak test or a bench test. I think that this is the case with the Forge valve that you had.

Now the trade off here is that the valve will need to open during vacuum so you can't just throw a super stiff spring in the valve. The figures we give for the valves are really just approximations and are culled from data that mostly applies to VW/Audis so don't be that concerned with that figure of 23psi. Give the shims a try or move up to the blue spring. And it is more complex than the amount of boost that you are running, the amount of vacuum will play a part as will how quickly your car makes boost (latency). The data that we have compiled from the VWs assumes a turbo that will make full boost nearly instantly, step on it at 2000rpm and you will have 20-25 psi by 2500rpm, springs in a situation like this need to be very stiff to keep the valve closed against that enormous boost spike...

Hope this helps. And sorry to be so long winded...

 

[Black_Bullet]

Okay, & why am I doing this

Oh i just thought you didnt read the whole post because i mentioned clearly that I know that I "didnt" have the revised lock ring, and thats why i put the stock modded 1g bov back on, and that Pat at Forge sent me a new bov that i havent put on yet.

Right now the forge i am about to put on has the revised lock ring, and it has the yellow spring in it.... I added one shim to it to see if it holds 25psi since its only "rated" at 23.
Maybe it will actually get away with 25 though without needing the shim which would be better because the tighter i go the more prone it is to surge/buck.

 

[Black_Bullet]

Black Bullet,

Since you observed a difference between the stock and the Forge valve one of two things is happening: either the Forge is "holding" better than the mod'ed stocker or it is leaking more. Either of these can be a benefit when we are talking about odd-ball driving situations. My guess would be that ours is "holding" better...

I'm not talking about the leak past piston that your valve had, something like that seems extremely bad but is a pretty insignificant volume of air all things considered. I could overcome the leak with a hand-pump so to an engine this leak is inconsequential really (so long as it is recirc'ed). The way in which a valve leaks that is an enormous problem is by opening, this is what happens with softly sprung valves and is usually a problem with OEM valves.

A bench test won't really show this problem, it will usually manifest itself due to pressure drop and latency. For example, a car is losing ~2psi through the intercooler and there is a .05 second delay from when the bottom of the valve sees pressure and when the top of the valve is pressurized from the intake manifold.

So lets say the valve in question is a Bosch 25mm unit found on a VW (I'm using this 'cause I know what the cracking pressure is), the cracking pressure of the valve with boost applied just to the bottom of the diaphragm is about 3 psi, so it opens and begins to leak. Also since it is open the area available to the pressurized air to act open is greater than the 25mm when it is closed so even after the pressure on the top and bottom of the valve equalizes (or as close as it is possible to come due to the pressure drop) it will take a little longer than usual for the valve to close fully.

Now in the same example if we are running a valve with a cracking pressure of 6 psi. Nothing will happen. That is to say, the valve will remain closed and the car will build boost normally.

Now I am greatly simplifying this, ignoring the fact that the valves are already open due to vacuum, just to illustrate my point.

And my point is this: Both of these valves will impact greatly where the turbo is on its compressor map. So in Black Bullets example of cruising speed in 5th, lets say 3000rpm and 10psi. The soflty sprung valve is forcing the turbo to spin much faster to produce the same amount of boost. This can place it to the left of the compressor map, which is the surge line. And the valve that remains closed will not, even if it leaks during a boost leak test or a bench test. I think that this is the case with the Forge valve that you had.

Now the trade off here is that the valve will need to open during vacuum so you can't just throw a super stiff spring in the valve. The figures we give for the valves are really just approximations and are culled from data that mostly applies to VW/Audis so don't be that concerned with that figure of 23psi. Give the shims a try or move up to the blue spring. And it is more complex than the amount of boost that you are running, the amount of vacuum will play a part as will how quickly your car makes boost (latency). The data that we have compiled from the VWs assumes a turbo that will make full boost nearly instantly, step on it at 2000rpm and you will have 20-25 psi by 2500rpm, springs in a situation like this need to be very stiff to keep the valve closed against that enormous boost spike...

Hope this helps. And sorry to be so long winded...

I get with your saying. Thanks for the post.

But i think you think im referring to compressor surge from straight up building boost to fast for the engine to digest while i start to get into it....

No, This is happening when i modulate throttle 5th gear while the bov is in a mixed position of whether it should be blowing off fully or just cracking open some.
( i.e. cruising and going 40%-20% then back to 40% throttle simutaneously.)

My stock 1g bov is modded and has proven to hold 25psi so far with no problems and seems to take a certain amount of boost to open.
( and no the stocker isnt not crushed, it has the dodge garage mod done to it.)

My stock one wont even make the blow off noise unless more than 10psi has been built while the forge only took 5-6 psi to make the noise.

So what im saying is that the stock one was stiff enough to not like to blow off spontaneously while the forge seemed to like to allow boost out easier when relieveing pressure was needed. And thats why im assuming it surged worse on the stock one than the forge when i feathered the throttle in 5th cruising.

Its like i start building boost ( roughly 10 psi cruising feathering throttle ) by letting off the gas slightly then back on it simutaniously i dont think the valve was cracking open quick enough to allow the boost to exit and i think that is why i was getting slight surge/bucking in 5th when the turbo is spooling its fastest.
Meaning there was too much air being thrusted back into the intake pipe as soon as i touch the gas again in 5th while there was already a lot of air still sitting in the pipe from before i let off due to it not relieveing enough pressure.

Make any sense?

 

[Black_Bullet]

This is my new issue with my new forge, which was the issue i discovered with the old forge i had after i had self fixed the lock ring problem by welding.

Forge Bov Review!! - DSMtalk Forums

Pat I know in your post above you mentioned that the slight air lose out the recirculated valve is inconsequential but i feel it is still "enough" to feel uncomfortable...
On a car that is under high boost and the turbo is already climbing towards its peak efficiency, I take everything into consideration, and the amount of air lose im feeling thru the valve hole ( as described in that link.) is notable.