Everybody knows that to prevent compressor surge you need a blow-off/recirculation valve that efficiently vents boost to atmosphere (BOV) or dumps it back into the intake upstream of the blower (RCV).

Surge is your mortal enemy. It places tremendous stress on your impeller and input shaft causing premature bearing wear or even blower death. The sound you hear is the blades of the impeller chopping air moving in the opposite direction it's supposed to. The impeller never turns backwards even though it probably wishes it could lol.

I've tried different BOVs/RCVs. The one thing they all have in common is a 1.0 in. or 1.25 in. inlet and outlet. Some were diaphragm and some were piston type. I've been able to detect compressor surge in (most) of mine and my friend’s cars.

Why? Inadequate air flow through the BOV and/or the rubber plumbing if it's a RCV. Disconnect your recirc hose from the blower intake and place a rubber expansion plug in the bung you removed the hose from. If during a test drive you hear an f t t t t t t t t noise as you shift gears you've got compressor surge.

I recently located a large diameter RCV that can be used as a BOV on the Forge Motorsports site. It's got a (50mm) internal piston and a (1.625 inch) inlet and outlet. It's a "life time" part and with some discounts only $140.

My only concern was- could my S2000 produce enough manifold vacuum to actuate the "supersize" valve. The valve is "tunable" in that it comes with four different internal springs rated from about 10 to 30 lbs.

I was hoping to be able to use the (red) 30lb spring for eliminating lost boost (to a partially open valve) as I went through the gears. The 50mm diameter piston housing and the 1 5/8 in. inlet/outlet orfices and hose should provide ample flow to eliminate compressor surge as long as the valve opens completely with each shift!


Forge Supersize Valve (FSV) with the green (lightest) spring about to be installed.


FSV with the green spring involved. This spring which comes with many of the smaller piston valves was not even able to entirely close the FSV. This worried me for second or two.


FSV with the yellow (medium) spring about to be installed.


FSV with the yellow spring installed under vacuum idle. Opens and closes fully.


FSV with the blue (heavy) spring about to be installed.


FSV with the blue spring installed under vacuum idle. Opens and closes fully- and it shuts hard!


FSV with the red (heaviest) spring about to be installed.


FSV with the red spring installed under vacuum idle. Snaps shut hard and fast but only opens about 85% at idle. This concerned me for second or two.


Here's where the piston is at idle with the red spring. This is the one I really wanted to use to eliminate lost boost running through the gears to WOT.


Here is where the piston needs to be every time I shift gears. I concluded that it didn't matter if the valve only opens 85% at idle- that "passage" would allow more than enough flow to prevent surge at idle.


The S2k in good working condition produces 22.5 in. HG of vaccum at idle.


However every time you let off the gas to change gears there is an instantaneous vacuum surge to 26 in. which causes the Forge Super Valve with the "red" spring to open FULLY. Then with accelleration it slams shut like the mouth on a thirty pound snapping turtle. No compressor surge. No lost boost.

Happy New Year,

Louis

 

I'm not the smartest guy in the world, but I think its pretty obvious that when you unhook the vacuum source to the BOV, you will get surge. I don't get your test you're telling us to perform.

This almost seems like an advertisement to me for that blow off valve, but then again, I've had a couple of drinks and might not be thinking clearly.

 

i believe he was speaking of the blower guys, and telling them to disconnect their recirculating hose from their blowers intake pipe but still actually functioning, basically eliminating the RCV and making it a BOV of sorts. i have a hks SSQ ver.3 and still get surge from time to time but RED Star uses the same one on their 7.75 race car with no problems? subscribed

 

Exactly. Simply disconnect the approximately 1.0 in. "return" hose from the blower's intake bung and listen for surge. The sound will readily come out the end of that hose.

The HKS SSQV l, ll, or lll are excellent BOVs. Versions l and ll come with 19mm (0.75 in.) and 29mm (1.125 in.) recirculation fittings (outlets) for running a return line as above. Version lll is a BOV only. The inlet on all three is 21 mm (0.875 in.) and the valve body is 40mm in diameter.

Both the Forge and HKS products are piston type vavles and function in essentially the same manner. Both can be quickly and fully actuated by the manifold vacuum produced by the S2K.

The difference is which will pass more air through the valve and thereby totally eliminate surge.

HKS: 0.875 in. inlet to 40 mm valve body to 0.75-1.125 in. outlet OR
Forge: 1.625 in. inlet to 50 mm vavle body to 1.625 in. outlet

Remember the cross sectional area of a 1.0 in circle =.785 sq in. is about 1/3 the cross sectional area of a 1.625 in. circle = 2.07 sq in. Area (cir) = Pi X r2.

Disclaimer: I don't rep for Forge products and own and have owned several different BOV/RCVs. I think I've found the best for my purposes and I'm just sharing what little I've learned lol.

P.S. Don't presume race teams are teaming with guys who know everything about their cars.

 

what do you think of the tial 50mm bov. From what i'm told it should be one of the best in the market

 

[QUOTE=riceball777,Jan 1 2011, 12:23 PM] what do you think of the tial 50mm bov.

 

[QUOTE=riceball777,Jan 1 2011, 12:23 PM]what do you think of the tial 50mm bov.

 

My bad. Carry on.

 

are you sure the pink spring is the stiffest and the one best suited for preventing surge and maximum dump? looking into getting a tial

 

Naturally you want to use the stiffest spring in the set that will open the valve completely in between shifts. Peak manifold vacuum (during shifts) for an S2000 in good running condition is about 26 in HG. That should open even the stiffest spring in a blow-off or recirc valve set. It's easy enough to test this as well before you install a valve with a particular spring.