F40 BOV Replacement (long)

Lack of boost in your F40?? Get turbo chatter and lousy turbo re-spin up during shifts, read on.

Short story: I was being robbed of boost and thus horsepower by faulty air recirculation valves (recirculation BOVs). I replaced them (x2) for $62 and my car got a new lease on life! It’s never run this good since I’ve owned it! Wow!

Longer story:

There are lots of threads about the F40 wastegate, but very few on the air recirculation valves.

Ferrari nomenclature:

F40 Owner’s Manual C11:
Bypass Valve refers to the wastegate
(Charge) Air recirculation valve refers to what people call a Blow Off Valve (BOV). I guess a proper term might be “recirculation BOV”. I’ll use simply “BOV” for short.

Air recirculation valve description (BOV): “When a depression occurs in the inlet manifold, it activates a diaphragm which opens a recirculation route between the delivery side and intake side of the compressor (turbo).”

This equalizes the intake pressure before and after the turbo and essentially nullifies the turbo effect.

For fun, I composited 2 parts drawings so you can see the BOV (#35) connections. NOTE: I used the *left* air intake and the *right* intercooler in the composite due to how the drawings were laid out. So, don’t take it as gospel. However, the basic connections are correct.

You can see how the input (horizontal pipe) to the BOV comes from the output of the turbo charger after the intercooler, and how the BOV output (vertical pipe) vents back into the input tract after the air box and before the turbo input.

I also added the vacuum line placement to the BOV in the lower right corner. You can see how the BOV vacuum line connects to after the butterfly valves. When the butterfly valves close, a vacuum is created, thus pulling up on an internal BOV diaphragm thus opening the passage to vent the high pressure turbo output back into the pre-turbo air stream.

“So what?”, you ask! Well, if one of your BOVs is STUCK OPEN, like one of mine, it essentially nullifies that turbo’s boost. E.g., Your boost gauge shows crappy boost (<6-10 or so) and your car turns into a slow shopping cart. If your BOV is stuck closed, also like one was, you’ll get boost but will also lose a lot of it with “turbo chatter” when you let off the gas to shift because the turbo back pressure waves slow down the turbo instead of the excess pressure getting vented back to the inlet which allows the turbos to keep spinning (equalized pressure before and after the turbos).

Everyone concentrates on the wastegate as the central boost related problem. However, with the stiff wastegate return spring, it’s not probable that it will stick open. Possible, yes, probable, no. A wastegate failure more likely results in over boost because it doesn’t open to bleed off the exhaust from getting to the turbos.

Lack of boost more likely points to one of both or the BOVs. The picture below shows the right hand BOV.

With the car off, and thus no BOV vacuum applied, the BOV diaphragm should be closed. I popped off the BOV vacuum hose from the top of it and hooked up a small vacuum hand pump. As I created a vacuum, nothing happened. No popping, no clicking, nada. I then applied some positive pressure and sure enough, I heard a “thunk” as the BOV valve closed. Argh! There was my missing boost!

I pulled the BOV off the car and inspected it.

What I found was:
1) It’s totally made out of (cheap) plastic.
2) The cheap plastic, including the diaphragm, had the texture of 355/550 *sticky* window switches!!! It would stick either in the open or closed position until it was dislodged. Junk.
3) Both BOVs needed to be replaced.

The following shows what the BOVs look like closed and full open.

The BOVs were standard 1990s era Bosch P/N 0280142102.

The Ferrari priced replacements were between $200 and $250 *each*! I found an online store that sold the same OEM BOVs for – ready?, $30 each. I ordered two.

I replaced both of them and took the car for a test drive. WOW!!!!!!!!! I now have apparently full boost for the first time since I’ve owned the car! I thought the car was fast before (when both BOVs were semi working). Now, it’s a rocketship!! The boost gauge approaches 20 or so (hard to read when driving) whereas before it would hit about 15 or so.

You can tell the BOVs work when:
1) the boost approaches 20 (or so).
2) the turbos continue spinning when shifting gears (letting off the throttle) making for rapid re-boost response. Cool.

So, if you’re having a loss of boost (from stuck open BOVs), or if you get turbo chatter (from stuck closed BOVs) or if you’ve never changed your $30 BOVs, change them!!

Tim

P.S. How do you interleave pictures and text in threads?
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I looked at that web site too! Good info. I decided to stay with the OEM P/N and actually had to find a retailer that would give me the 102 and not automatically give me the 110.

I'm trying to stay with original P/Ns if at all possible for some reason. Maybe it's a concours thing...

Tim