Purpose: To create more turbo boost than stock (11psi). With this mod on a stock Toyota Supra (mkiv), expect 15-17 psi of boost, which gains you 60-70 HP!

Note: do the FFCD mod (or better yet, the Greddy BCC) before doing this mod to prevent fuel cut!

Parts Required: two 1/4"x1/4"x1/4" vacuum Ts (available at auto parts stores), knife, 2" long 1/4" diameter hose (optional).

Time Required: 5 minutes.

How it Works: By bleeding off air from the wastegate actuator, the wastegate stays closed longer, which builds more boost than stock.

Disclaimer: This modification puts additional stress on the turbos, clutch, transmission, etc. These components may wear out prematurely. Obviously this modification will void your warranty if discovered (however, it is easily reversible). A boost gauge is essential to monitor boost levels. The general consensus is that you shouldn't run the stock turbos over 18 psi on a regular basis.

Note that using a bleeder T to increase boost will produce boost spikes under certain conditions such as flooring it at 3000 rpm in 4th gear. This may cause pre-ignition or detonation as the boost can spike beyond 21psi (depending on mods to your car). If your car detonates, you can attach an adjustable valve to the end of the bleeder T to limit boost, but your car will make different boost levels depending on temperature (less boost when warmer). An electronic boost controller will eliminate boost spikes.
Note: when making this mod to a JDM Supra the boost level may be higher than a US model - pay attention to your boost gauge!

 

1. Locate the black, 6" hose that goes from the vsv to the brass actuator. Figure 1 shows the general location: front, left side of the engine bay, just above the alternator.

 

2. Figure 3 shows a close up. Cut hose 2 in half. Insert a vacuum T (fig. 2) into the two hose ends that were just created by cutting.

Note: there are two ways to insert the vacuum T:

 

Note: An alternate/better way is to disconnect hose 2 from the actuator. Connect a 2" long, 1/4" diameter hose to the actuator. Connect hose 2 to this new 2" hose via the vacuum T. This method doesn't require cutting the factory hose, making it easier to put the car back to stock condition.

 

3. If desired, attach a 12' long 1/4" diameter hose to the open end of the T (as shown if fig. 3) and run hose into the cockpit (if desired). A simple valve can be attached to this hose that can be used as a Manual Boost Controller.

 

4. To gain approx. one more psi of boost, cut hose 1 in half and insert a T (fig. 6). Note that you can't use this in conjunction with the Manual Boost Controller unless you run another hose and valve off this T as well. On my car, I just keep the T on hose 1 capped unless I go to the drag strip.

Note: some people have found that 1/4" vacuum Ts aren't tight enough. If a hose blows off the T then use a 5/16" T instead, and/or consider using hose clamps.

Note: it is normal for a small amount of oil to accumulate on the open end of the T, do not be alarmed.

Note: it is normal for the boost to spike somewhat when the 2nd turbo kicks in. The boost will then hold at a lower amount, depending on other modifications (exhaust, downpipe, etc.).

To create the maximum amount of boost (for the drag strip, etc.), simply disconnect hoses 1 and 2.