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The mkiv Supra Owners Club

What BOV?


FOSTA

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IIRC below is something A Wise Man had to say on the subject of the use of BOVs.

 

There's a vast amount of rubbish talked about blow off valves. They were designed to stop customers complaining of "funny noises" on early turbo cars, they do nothing to aid spool, can be unreliable, add weight and complexity, and are now used to do the exact opposite of their original purpose. That is they are now used to make silly noises, a mechanical means of shouting "I have a big one" from under the engine cover of the car. (IMHO). To say they stop shock loadings is also incorrect. If they aided spool and added turbo reliability every turbo charged 24 hour Le Mans prototype, and every F1 engine in the turbo era would have had one. The fact is, none did.... Maybe all the drivers were supremely endowed?

 

In the F1 era turbos often didn't last a single race, so if a simple BOV would help them live longer, what do you reckon they'd have fitted?

 

Le Mans is won or lost on reliability, to a large extent. Again, a simple BOV would be fitted if it gained reliability. Honestly, a lot of the stuff on the net is garbage on this subject.

 

If I/C's are splitting and pipes blowing off it's more down to unsuitable I/C's and piping systems being used than no blow off valves, per se. If you DO choose to believe they help spool then you would certainly need a recirculating BOV achieve any hope of this. A proper intercooler designed for the higher boost pressures will not split, nor will pipework joined by proper Adel Wiggins fittings blow off.

Edited by Frank Bullitt (see edit history)
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The chance of damaging your turbo without a BOV is pretty low, but can occasionally happen The main reason I run one is for speed of boost recovery on gear changes. When drag racing, with the plain bearing turbos I run, it makes a huge difference to how fast the boost recovers. With ball bearing turbos it is probably needed less, but would still help. On the street you would be hard pressed to tell the difference.

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Since I sold my Supra I usually just lurk here but. I was on the don't need a BOV side.

 

Until recently My FD had a GT4088 Turbo without a BOV. Started to have compression issue and found both rotarys were low on compression. When it went to be rebuilt the turbo was inspected an there was a large amount of play in the shaft. It was possible to move the compressor wheel about 5mm back and forth in the housing so the wheel was hitting the housing.

 

Once the turbo was off and the housing removed both compressor wheel was missing about 1mm of metal and the housing had 1/2mm of metal missing. There were tiny shards of metal in the intercooler and pipes all the way to the throttle. So as the engine had only done 4500 miles since it was rebuilt it appears as if the compression had been lost due to the sharks getting into the engine

 

The Compressor wheel had unscrewed itself, I was running 1.4Bar and the only way for it to unscrew would be compressor surge.

 

So now I'm in the need a BOV camp

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Since I sold my Supra I usually just lurk here but. I was on the don't need a BOV side.

 

Until recently My FD had a GT4088 Turbo without a BOV. Started to have compression issue and found both rotarys were low on compression. When it went to be rebuilt the turbo was inspected an there was a large amount of play in the shaft. It was possible to move the compressor wheel about 5mm back and forth in the housing so the wheel was hitting the housing.

 

Once the turbo was off and the housing removed both compressor wheel was missing about 1mm of metal and the housing had 1/2mm of metal missing. There were tiny shards of metal in the intercooler and pipes all the way to the throttle. So as the engine had only done 4500 miles since it was rebuilt it appears as if the compression had been lost due to the sharks getting into the engine

 

The Compressor wheel had unscrewed itself, I was running 1.4Bar and the only way for it to unscrew would be compressor surge.

 

So now I'm in the need a BOV camp

 

Ill bet that was down to poor assembly/fitting rather than anything to do with a dump valve.

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