This page hosted courtesy of Regan Rotary Racing. December 2009.

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Boost Limitation and Sequential/Non-Sequential Switches

Below are to types of switches you can install to modify your 93+ RX-7's boost pattern. You can use them individually or in conjunction with one another to further enhance/modify boost.

1. Boost Limitation Switch

This modification is intended for those who have sufficiently modified their car such that boost exceeds that of the factory levels and for those who have stock or non-PFS piggy-back ECUs.

What? Limit boost you say? Read on.

This modification reduces the signal from the factory or piggy-backed ECU to the wastegate control solenoid. The signal is reduced so that it does not operate the solenoid, but sufficient current to is allowed to flow from the ECU to the solenoid to eliminate ECU error codes. The switch is a 2 position toggle that allows one to run standard boost and (relatively) low boost, approximately 8 pounds on the first turbo and 6 on the second (see results below). This modification is also used in conjunction with a switch for the double throttle control solenoid that some have deemed the "valet-mode mod". I was not concerned about valets parking the car. Rather, I wanted a switch that would reduce the strain on the engine when desired, such as driving to and from work, in extreme cold when boost spikes are very common, and when learning at the track.

This modification is very easy to do and should require less than 1.5 hours to accomplish. With the exception of the soldering iron, all of the parts can be had for less than ten dollars, including the price of the solder and wire. If you'd like to install a very high quality switch (with silver internals) and resistor, using high silver content solder, check Welborne Labs and Aircraft Spruce for parts.

Parts/Tools:

  • 18 gauge wire. Get as much as is required to mount the switch wherever you desire.

  • One 1K Ohm 1/2 watt resistor, RadioShack PN. 271-1118. Sold in quantities of five for very little money. 

  • Insulated butt connectors (optional). For splicing into the ECU to wastegate solenoid wire. RS PN. 64-3037.

  • Electronic solder. I like RadioShack clear flux solder in .063 diameter, PN 64-018C. Only a few bucks.

  • SPDT Toggle switch. I prefer the RadioShack micromini as it is relatively unobtrusive. PN 275-625A.

  • Soldering iron. Your choice, but do not use very high wattage (>40).

  • Wire strippers and crimpers (optional)

Schematic:

Instructions:

 

You may approach this one of two ways: 1). build the switch as above using extra wire and connect this assembly to the ECU wires using insulated butt connectors; or 2). cut and solder the existing ECU wire to the toggle switch along with the resistor. I wanted a remote switch under the radio, so there is not enough factory wire for option number 2. Additionally, it's easier to solder the assembly and extra wire on your work bench and connect this to your ECU lead using insulated butt connectors, avoiding dripping solder and carpet burns in your interior.

 

Now, identify the blue and white wire leading to the ECU on the largest connector. This is the top connector and the wire is among the 3rd pair from the top of that connector. Look at the ECU diagram at the bottom of this page for reference. Connect this wire to the common (middle) connector (or extra length of wire you've already soldered) on the SPDT toggle switch. Decide the orientation of your switch and whether you want the high setting on top or bottom. Given the image above, the contacts within the switch are arranged such that this switch is depicted closing the circuit between the ECU and the wastegate solenoid (high or normal setting). Connect/solder  the wastegate solenoid wire to the desired contact (left as depicted above) and the resistor to the other (above right). Remove the shielding from a very small portion of the wastegate solenoid wire and solder the resistor into this area. Thus, when the switch is toggled in the opposite direction, the circuit is closed between the ECU and the wastegate via the resistor. 

That's all there is to it!

Optional:

A carbon fiber or other custom switch mount. 

Use your imagination.

Results:

With intake, intercooler, M2 ECU, cat-back, DP, and high flow cat mods, my boost pattern is 13-10-13. My boost has been a bit higher due to the recent cold weather. With the switch activated, my boost is reduced to 7-9-9, and this was in 18 degree weather. Very nice.  Similar tests in warm weather yield approximately 7-8-7!

 

2. Non-Sequential Switch (designed and conceived by Michael Smith, Andrew Ghali and Aaron). 

This is a very easy to do mod that allows one to choose from the stock sequential boost pattern to non-sequential (i.e., parallel) boost. This mod is not as effective as the full non-sequential mod (where the wastegate is wired open, midpipe is used, and vacuum hoses spliced), but still offers some advantages, primarily no boost spiking at turbo transition.  Below is a table comparing advantages and disadvantages of both configurations.

Position

Advantage(s)

Disadvantage(s)

Stock (sequential)

Higher boost at lower RPMs.

Good for autocrossing.

Boost spiking at transition, particularly with extensive aftermarket modifications.

Dangerous boost when balancing a car through a turn at or near transition point.

Non-sequential

Consistent, reliable boost without spiking

Good for track events.

Lack of high boost at low RPM resulting in loss of around-town driveability.

More lag than the true non-seq. mod 

The switch changes the way three solenoids/actuators work: charge control; turbo control;, and charge relief. Charge control is on during sequential, and gets turned off for non-sequential.  Turbo control and charge relief operate at different times determined by the ECU. These are both turned fully on during non-sequential.

Parts/Tools:

  • To configure this switch, you'll need a three pole, dual throw switch (3PDT or TPDT- where the first "T" stands for "Triple") with an "On-On" position. Do not use "On-Off-On" or a switch with "(On)" listed in its designation (parentheses stand for temporary). Surprisingly, Radio Shack does not have these switches. I found a nice aircraft-quality unit with silver contacts for $15 at Aircraft Spruce

  • 18 gauge wire. Get as much as is required to mount the switch wherever you desire.

  • Insulated butt connectors (optional). For splicing into the ECU to wastegate solenoid wire. RS PN. 64-3037.

  • Electronic solder. I like RadioShack clear flux solder in .063 diameter, PN 64-018C. Only a few bucks.

  • Soldering iron. Your choice, but do not use very high wattage (>40).

  • Wire strippers and crimpers (optional)

The idea is to splice the switch between the wires going from the solenoids to the ECU.  Use the locations from the ECU diagram at the bottom of this page.  Make your cuts and wire the switch accordingly. 

The rear of the switch is to be wired as follows:

 

ECU Diagram:

4R - yellow & blue wire w/silver stripe

4S - pink wire w/silver stripe

4T - blue& black wire w/silver stripe

Update 12/29/01

Installed both switches (WG again) in combination with a hallman/grainger-type boost valve. Boost control is very nice. I should have done this mod years ago. Honestly, I notice only a subtle difference in responsiveness between sequential and non-sequential under full throttle after 3500 RPMs. Running non-sequential at the track is a must!!  Around town, however, is a different story. Under non-seq. the lag is appreciable, but manageable.