True twin turbo conversion (ttc) mod

Twin Conversion

What it does:
converts the turbos from sequential operation (#1 turbo first, then #1
and #2 together), to parallel operation (both turbos spool up together at the same time).

Why would I want to
do this?

  • This mod supposedly eliminates blowing up the #2
    turbo due to shaft twist when the complex sequential operation doesn’t work properly for
    some reason, especially when you are running higher boost than stock.
  • The power delivery is smoother, there is no
    boost dip at 4000 rpm like there is with the sequential setup. This mod seems to provide
    more high rpm power (my car now easily loses traction in 2nd gear).
  • The sound of the exhaust will increase. Notice
    how your exhaust note changes at 4000 rpm when your 2nd turbo kicks in? Well, after this
    mod, your exhaust will have a similar growl throughout the entire rpm range!

What are the
Turbo lag
is increased at low rpm. The lag is probably too much unless you have a downpipe (but you
DO have a downpipe, right?!?) and a manual transmission.

2 one-way check valves (Toyota part number
90917-10049, about $5 each from Jay Marks Toyota), one foot of 1/8″ diameter vacuum
hose, several feet of picture-hanging wire, flat-blade screwdriver.

10 minutes (the temporary way),
1-2 hours (the permanent way).

read entire procedure before starting (if you want to permanently wire your actuators
open, you can skip down to that part now).


Locate the AIC actuator on the top, left side of the engine,
near the firewall.


ttc10.JPG (14087 bytes)


Remove vacuum hose from the top of the AIC actuator to the VSV,


ttc1.JPG (9371 bytes)


Cut the one foot long 1/8″ vacuum hose that you bought into
two pieces and plug into both ends of the check valve.

Cut the vacuum hoses so that the length matches the length of
the stock hose.

Keep the stock hose in case you want to put back to sequential


 ttc6.JPG (10394 bytes)


Install the check valve with the two hoses attached where the
original vacuum hose was.

The orange part of the valve faces towards the front of
the car:


ttc5.JPG (8685 bytes)


Locate the EGC actuator (about the size of a
soda can), on the lower, passenger side of the engine.
Remove the intercooler piping that is just above the air box for easier access.
The hose is just behind the wastegate VSV.
Remove the hose that goes from the top of the EGC actuator to the EGC VSV:

ttc4.JPG (8395 bytes)


As above,  cut the vacuum hose that you
bought into two pieces and plug into both ends of the check valve,
matching the length of the stock hose. Install the check valve with the two hoses attached
where the original vacuum hose was.
The orange part of the valve faces towards the front of the car:

ttc7.JPG (8564 bytes)


Take the car for a spin. Accelerate moderately
to 5000 rpm a few times to make sure everything is working properly.

If you like the new powerband, you need to
permantly wire the actuators open. Don’t run more than a few days in this configuration,
because it’s easy for the check valve hoses to pop off (you might want to use hose
clamps), closing one valve and leaving the other open, which is not good for the turbos.
You will know if this happens if your 2nd turbo doesn’t create any boost.


to wire the actuators open:

Top actuator:

Use a flat-blade screwdriver to
push down on the hinge where the bottom of the actuator rod is connected.
Notice how the rod moves downwards, away from the actuator.

ttc12.JPG (8431 bytes)


Close-ups of the rod attached to the actuator:

ttc3.JPG (6024 bytes)   
ttc2.jpg (6076 bytes)


You may want to remove the C-clip to reduce the chance of your
wire breaking under tension.

Wedge the screwdriver as shown to keep the actuator fully open
in preparation for wiring:

ttc14.JPG (5981 bytes)


Wrap the wire around the actuator and the spring-loaded bracket
as shown. Wrap several times, then tie a tight knot:


ttc13.JPG (7918 bytes)    
ttc15.JPG (9840 bytes)


Bottom actuator:

The bottom actuator is somewhat a pain in the ass to get to.
Jack up the passenger side of the car,

just behind the right front wheel. Remove four 10mm bolts than
hold the plastic passenger-side engine cover.

Pull the cover down as shown, then bend in half so that its
pointing towards the front of the car:

ttc20.JPG (9545 bytes)


Here is what the actuator looks like:

ttc21.JPG (11581 bytes)


Remove the c clip at the end of the rod by
pushing on both open ends with two screwdrivers.

ttc22.JPG (14160 bytes)


Detach the rod. Tie some wire thru the hole
where the rod was previously attached.
Wrap the other end of the wire around something towards the rear of the car, pull
tight, and secure.

ttc23.JPG (12547 bytes)


Take the car for a test drive. Enjoy!


Special thanks to Jason Tarnutzer and Jason Knippel.


Comments/suggestions? Email me


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