Products to help with the restoration of your Turbo 4.9.

What is a PEVR?

PEVR stands for Power Enrichment Vacuum Regulator.  It was used on GM’s turbocharged Pontiac 4.9 liter V8 in 1980 Trans Am/Formula (also 1981 Canadian/Export cars) and on Buick’s turbocharged 3.8 liter V6, prior to fuel injection and Computer Command Control (CCC).
 

What is it’s purpose?

The purpose of the PEVR is to allow the primary metering rod circuit of the carburetor to provide the necessary fuel enrichment and air/fuel ratio during the various loads of the engine. 

How does it work?

The PEVR is a simple yet complex device.  First we need to understand why it is needed.  These early carbureted turbocharged engines are of a “draw through” design.  This means the carburetor is in front of the turbocharger's inlet.  The turbo is actually drawing in the air and fuel mixture from the carburetor, compressing it and forcing it down the intake manifold.

Let us look at the function of a non-turbo, Quadrajet carburetor’s primary metering rods.  The primary fuel metering circuit is controlled by engine vacuum at the base of the carburetor.  There is an opening exposed to the inside of the intake manifold.  When the engine has high manifold vacuum (idle), the primary metering rods are pulled down into the metering jets against spring pressure to close off any fuel.  When accelerating or at Wide Open Throttle (WOT) manifold vacuum starts to decrease due to engine load and the spring pressure pushes the metering rods up out of the jets to allow for fuel flow.

The draw through turbo carburetor is in a different environment from the non-turbo.  Technically, the base of the carburetor is always under a vacuum due to the inlet of the turbo always demanding air.  This would not allow the metering rods of a conventional carburetor to work properly when accelerating.  So the GM engineers invented the PEVR to help.  Instead of an opening on the bottom of the carb, an external vacuum hose port was placed at the front of the carburetor base, going to the primary metering circuit.  The PEVR regulates vacuum going to this port to control the metering rods similar to a non-turbo application.

The PEVR is screwed directly into the intake manifold.  The base of the PEVR sees manifold vacuum and boost.  The top of the PEVR has two vacuum hose ports.  The center port at the top has a constant vacuum source to it (from another port on the carburetor); the side top port connects to that special external port at the base of the carb.  When manifold vacuum is high at the base of the PEVR, it allows full vacuum flow on the top side to go to the metering rods pulling them down into the jets.  As the engine accelerates, manifold vacuum decreases at the base of the PEVR which restricts the amount of vacuum to the metering rods allowing more fuel.  The PEVR continues restricting vacuum at the metering rods even under small amounts of boost.  At 5 psi of boost and above, all vacuum has been blocked to the metering circuit allowing for full fuel enrichment.  This is the key element of the PEVR and why it is so important.  It allows some vacuum to enact on the metering circuit even when the engine is starting to make boost. Without this feature, the engine would see too much fuel too early and cause an over rich fuel mixture.  If the PEVR diaphragm fails, you end up having a lean condition and a vacuum leak causing poor performance and possibly detonation.

How to "quick test" your PEVR:

Test #1:   Remove the two top vacuum hoses and start the vehicle.  If any vacuum is felt on any (or both) of the two top vacuum ports of the PEVR, the diaphragm is ruptured internally and the PEVR has failed.  If no vacuum is felt, move on to test #2. 

Test #2:  With the engine off, attach a hand held vacuum pump to the side port of the PEVR.  Plug the center port and pump vacuum into the PEVR.  If it holds vacuum, it should be good.  If it does not hold vacuum, the PEVR has failed.  

Note: I have seen PEVRs that the diaphragm was stuck down.  Even though it held vacuum, it still was not working properly.

I have a failed PEVR now what??

If your PEVR has failed, you can send it to us to be rebuilt with a new diaphragm.  I can also repair any broken vacuum ports on the top of the PEVR. 

$75.00 (TTA-001) Core Required-you must send me your original PEVR.

Free shipping to the lower 48 state only, international shipping available. 

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 The flexible intake hose for the air cleaner of a Turbo 301 is unique

as it fits the oval shape of the air cleaner and transitions to round at

the fender duct. We now offer a replacement hose for the air cleaner.

$50.00 - (TTA-059)

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The 1980 and 1981 Turbo 4.9 Trans Ams and Formulas came equipped with Electronic Spark Control (ESC).  The ESC  module monitored engine detonation with a knock sensor placed on the engine.  When detonation was detected, the ESC module retarded the ignition timing until detonation was no longer heard, then regular ignition timing was allowed to return.

A somewhat common occurrence is for a Turbo 4.9 to experience a no start condition due to no ignition spark.  One of the causes can be from a bad ESC module.  This module can be "by passed" using our custom made by pass boards.  

Simply unplug the faulty ESC module and insert the board into the electrical connector.  This allows the ignition to function like a standard GM HEI distributor.  This board also allows the ignition timing advance to work correctly on the 1981 Turbo 4.9's with Computer Command Control (CCC) and will not cause the Check Engine Light to illuminate.

Note: After installing the by pass board, you will no longer have detonation protection.  The ESC system will be inoperable.  Make sure to always use the highest octane fuel available and listen for detonation or knock when driving your 4.9 Turbo.

$20.00 - specify 1980 or 1981 when ordering (TTA-002)

(Free shipping to the lower 48 states)

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Why mess around with a used, corroded timing cover that may not even seal properly when you can purchase this brand new timing cover for your Pontiac 301 and Turbo 4.9. Our covers have been modified to use the correct, bolt on, plastic timing tab that is exclusive to the 301.  Comes with new water pump divider plate and seals.

$255.00 (+ shipping) TTA-037 - Timing cover only (picture shown)

$285.00 (+ shipping) TTA-037G - Timing cover with gasket

$365.00 (+ shipping) TTA-037GWP - Timing cover with gasket and aluminum water pump

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The factory 1981 center console had an access door on the driver's side near the gas pedal. This was to access the engine computer. This clip keeps the door closed.

Reproduction piece. Paint to match.

$35.00 (free shipping in the US)​ TTA-048

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