RB30 (VL) Throttle Body Upgrade

The VL throttle body upgrade has been around for a while now, however it’s an extremely good modification to the E15ET engine based on the “bang for buck” concept. Although you will only feel a slight increase in power from a standard e15et, the biggest benefit of the VL TB upgrade is after air flow upgrades such as larger exhausts, high flow air filters, or head work having been carried out.

You should be able to pick up a RB30 TB for around $20 – $50 from nearly any wreckers. I would advise not to pay any more than $50 otherwise the wrecker is just trying to rip you off as they really aren’t worth anything more. Shop around because there are quite a lot of them available.

There are two different versions of the RB30 TB. The difference between them is that one is a TB that came of a VL with cruise control. It will have a 2nd plug coming out of the throttle position sensor (TPS) which is the black box on the side of the TB.

The Following article will try and explain more clearly some of the “myths” involved in correctly installing the VL TB to the E15ET engine.

Things you will need:

  • RB30 Throttle body
  • File or Die grinder
  • 1/2 inch longer TB bolts ( x 4 )
  • Larger inlet pipe connector hose (To fit over VL TB flange)

Step 1. Removing the standard throttle body.

  • Disconnect the inlet pipe off the TB.
  • Unplug the TPS plug and Vacuum hose.
  • Disconnect the throttle cable from the cam.
  • Undo the 4 allen key bolts holding the TB onto the plenum. If they are still std bolts it should require a 6mm allen key.

With all of these things disconnected and undone, the TB should now be ready to take off. It may require some gentle tapping with a rubber mallet/hammer to break the gasket bond.

Step 2. Removing the Top half of the plenum.

In this step we must remove the top half of the plenum to grind a small proportion of the plenum/TB face to ensure a smooth transition of air between the 2 parts. You can get away without doing this step, but personally I would not recommend putting the VL TB on unless you carry out this part of the installation. Without grinding away some of the plenum there is a 2-3 mm overlap between the TB which will no doubt cause a big disruption of air flow into the inlet manifold. In my opinion without filing/grinding the plenum you would be best to retain the original TB.

After reading this I here you say “Lets grind the plenum”.. Good! then lets keep going.

I have heard of some people grinding the plenum face while still on the car. They have done this  by shoving a rag down the throat of the plenum to catch all the shavings. This may have worked fine, but I would recommend taking the plenum off to reduce the chance of shavings entering the engine.

Now to remove the top half of the plenum there are 6 bolts that need to be undone. 4 of these bolts are located around the edge of the plenum and are relatively easy to remove. There is also a 5th bolt that is situated just in from the edge of the plenum and is relatively easy to reach from the top of the engine bay, however there is a 6th bolt that goes up through the center of the manifold from underneath the car. This is the bolt that usually causes the most grief when trying to remove the plenum normally due to the fact they don’t realise its there! All of these bolts are a 10mm hex head and their locations are shown in the picture on the left.

Access to the 5th bolt in the middle is best achieved by going up from under the car.

Once these 5 bolts are removed the plenum should come off. However if this is the first time it has been removed from the car in it’s lifetime it may need some persuasion in the way of a rubber hammer to crack the gasket lock.

Step 3. Grinding/Filing of the Plenum Inlet.

Now that you have the plenum off, it’s time to grind the inlet to allow smooth air flow due to the increased size of the new TB. This step can be achieved by using a circular file, or the use of a die grinding tool. Both work equaly well, but the die grinder will save you a lot of time and energy.

Approximately 3mm of metal must be removed from the edge of the circular inlet on the plenum. The best way I found to get the correct ammount removed from the inlet is to keep matching up the VL TB and cross checking with the butterfly open (as shown in pic on left) to check how much more metal is required to be filed to achieve a smooth flow, ie. no lip of protruding edge.

Once the required ammount has been shaved off it is advisable to wash the plenum out with water to ensure that no shavings are left for the engine to suck in.

Step 4. Refit the plenum.

Refitting of the plenum is basically the same as it came off. Although you should check the condition of the gasket inbetween the plenum and bottom half of the inlet maifold. If this gasket appears to be damaged you will need to make/buy a new gasket otherwise you will no doubt experience air leaks mainly under boost.

Step 5. Bolting up the RB30 TB.

With the Plenum back in it’s place, it’s now time to bolt up the new TB. Once again check the condition of the gasket between the TB and plenum and replace if damamged. Here is where you will require the new longer bolts. These are required due to the VL TB having thicker castings where the bolts go through and will need the exta 1/2 inch to thread into the plenum.

Once tightly bolted up, you can now re-connect the vacuum hose and TPS plug. The TPS box will most likely need some tweaking, but we’ll deal with that later.

Step 6. Making the Throttle Cable fit.

On the Aussie Spec inlet manifolds (as shown in these pictures) you will need to slightly modify the throttle cable mount to allow the cable to have sufficient slack. This is most effectively done my gently hitting the bracket with a rubber hammer to slightly bend it forward towards the TB. It is ductile enough to bend this small ammount yet still retain its strength required for throttle movement.  I would also suggest doing this with the throttle calbe inplace and connected to the throttle cam so you can gauge when the tension has been removed from the cable.

Step 7. Refitting the inlet pipe.

Due to the increased size of the VL TB the standard E15ET connecting hose that used to be between the TB and inlet pipe will no longer fit. Therefore a larger size hose must be sourced. From memory the hose must be 60mm to fit over the VL TB flange.

Step 8. Testing.

With the VL TB now bolted up and in place, it’s time to check all the connections one more time, and take it for a drive.

A common problem that people have after installing the TB is the appearance of a big “flat spot” inbetween gear changes. I have found this to be the result of the TPS being set incorrectly from the VL. This makes the switch inside the TPS turn on to late (or to early) which has an effect on timing set my the ECU.

To fix this problem, the TPS has rotational adjustment via 2 small bolts (phillips head). After loosening the TPS, it’s a matter of moving it to a new position and taking it for another test drive. For me I was experiencing this problem when the TPS was in such a postion that the plug was facing upwards in the air. I moved it to a horizontal position and the flat spot was gone.

I hope this article has shed some light on the steps required to correctly install the RB30 throttle body. Please let me know if you feel something in this article is incorrect or mistaken.

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