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Type-S Single Spring Mod

We get a lot of questions about the "single spring mod" for the GReddy Type-S on Evos, as well as questions regarding the Type-S possibly causing stalling problems during stopping. Below, you will find what is involved in the "single spring mod" and yes, this mod makes the Type-S work great on the Evolution. It creates a lower pressure delta necessary to open the valve, making it easier to open at low boost/low vacuum/low RPM situations, which may help with any stalling issues you may have. It also allows for an easier install since there is no need to connect the lower vacuum port.

Our first question to those mentioning stalling issues is: does the valve is recirculate into the intake pipe? The valve should be plumbed into the intake pipe just like the stock BOV to maintain accurate management. BOVs that are vented to atmosphere release air that the ECU is expecting to be in the intake and adjusting parameters for. Changing the amount of air in the intake tract without the ECU knowing it is just begging for headaches. Likewise, any leaks or flutters at idle with it vented to atmosphere, can simply equate to the biggest vacuum leaks you'll ever seen. There is absolutely no performance gain by blowing off to atmosphere, in fact, there will likely be a slight performance loss from the resulting rich conditions after shifts. There is absolutely no reason to run VTA.

Second, if the single spring mod is not done, the valve should have the lower vacuum port connected to a source still pressurized after the throttle plate closes (IC pipes) and still have a very light adjustment to allow for the easiest valve actuation possible. Look at the chart below and compare the stock BOV characteristics to the Type-S default setup and you will see why both ports should be connected or the single spring mod done....and Type-S default data is at MINIMUM spring adjustment. The valve needs the extra push from the lower port to help open it unless the mod is done. Failure to connect the lower port while keeping both springs inside will make it difficult to open on small pressure changes, and even more so if the spring is adjusted tighter.

In short, do the single spring mod as outlined here OR connect the lower vacuum port to an intake source between the turbo and throttle body if you don't. One or the other should be done for maximum drivability on the Evolution and we recommending the the single spring mod because it works very well and makes the install somewhat easier (no extra vacuum connection).

BOV Max Piston Travel Spring Configuration Adjustment Screw Begins Opening (in/Hg) Fully Open (in/Hg) NOTES
Type-S 3/4" Both Springs (GReddy default) Minimum 21 25+ Will flutter unless the lower vacuum port is used...and even then sometimes. Loud whistle without the lower port, little whistle or whoosh when using the lower port depending on throttle change and air flow.
3/4" Large Spring Only Minimum 15 21 More quiet whistle or whoosh depending on shift conditions. May flutter slightly if conditions are absolutely perfect for it. No lower vacuum port connection needed or recommended. Our recommendation for Evos with minor adjustments (generally, 2-5 full turns).
11/16" Large Spring Only 2-3 turns from first contact 16 21 This setup most closely matches the default BOV characteristics and is our recommended configuration. Adjustments should be tuned to your taste/driving habits, but this works extremely well on our Evo with cams.
3/4" Small Spring Only Minimum 9 15 Absolutely no flutter under any circumstance. Whistle or whoosh depending on throttle changes/air flow. No lower vacuum port connection needed or recommended. Increased chance of opening under high boost. We do not recommend running the small spring.
1/2" Small Spring Only 7-8 turns from first contact 11 17 Absolutely no flutter under any circumstances. Whistles on every throttle change, no matter how light (which may be annoying). No apparent premature opening up to 21psi (max. we tested), however, it does open unnecessarily during highway driving conditions. No lower vacuum port connection needed or recommended.
Stock 5/16" Stock N/A 17 21 Quiet whoosh sound only, plastic sucks, can leak, it's "stock", no flutter, very small opening distance.

Please note that vacuum readings may vary slightly and piston travel are approximates. These vacuum readings were measured using our trusty(?) hand vacuum pump. We measured vacuum by hand and drove with each of these setups on the car. Our recommendation is based on results from both. Our recommendation is based on the stock 16G turbo. Larger turbos with higher boost levels will need to evaluate their own situation and may have to retain both springs to ensure there is no unexpected opening.

We recommend retaining the larger spring to keep piston travel at a maximum (lighter adjustment screw setting) for maximum discharge. Using only the lighter spring, even with an extremely heavy adjustment (10-11 full turns), the valve opens unnecessarily (though very, very slightly) during highway driving conditions.

1. With all of the all the bolts out and the cap off, this is what you should be looking at. The two springs in question are in the middle, with the small one sitting inside the larger spring.
2. With all of the all the bolts out and the cap off, this is what you should be looking at. The two springs in question are in the middle, with the small one sitting inside the larger spring.
3. Remove the small spring from inside the larger and put it in a safe place in case you need it later for any reason. We recommend keeping the larger diameter spring since the smaller has too little tension, even with a heavy adjustment, to keep the valve closed properly during all driving conditions.
4. For those that care about their BOV sound, here's a little trick to get just a little more whistle out of the lighter tension.... Carefully push the valve up off the seat (or turn the valve upside down) until the inner section with the valve and diaphragm slides out. You will notice 4 holes around this inner section, which are used by the lower port. Line up one of the holes with the lower port and then set the inner section back in place. Don't expect any miracles, but it will help make the whistle a little more distinct.
5. Set the spring on its seat in the valve and then place the top spring perch on top of the spring with the stepped side down to fit into the top of the spring. Note the recess for the adjustment stud in the top of the spring perch. The adjustment stud needs to sit inside the recess to hold the spring(s) vertically in place.
6. Now the cap is ready to go back on. Make sure that the adjustment stud is through the cap enough to sit in the top of the spring perch (left). The stud will hold the spring centered while the cap is being pushed down.
7. Push the cap down and reinstall the six (6) allen bolts while holding the cap down. After the cap is tightened down, remove the adjustment stud and verify that the spring perch hole is visible directly under the adjustment screw. That means the spring is properly centered.
8. Wrap the lower half of the adjustment stud with Teflon tape (bottom pic) and reinstall it. A good approximate starting point is to feel when the stud first touches the spring perch and then go in another 2-3 full turns. Replace the valve in the car and do any fine tuning of the adjustment from test drives. TECH TIP: Before reinstalling the valve, we also recommend removing the top vacuum fitting in the cap, wrapping it with Teflon tape and reinstalling. Small vacuum leaks are not uncommon around the top port and the adjustment stud and while neither is enough to effect performance of the valve in a big way, a leak is a leak and every precaution should be taken to avoid them.

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