Why BOV at Throttle Body? - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-05-2008, 08:19 PM   #21
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Originally Posted by iluvspd View Post
I run the BOV before the intercooler to prevent the hot charge from flowing through the IC. Prevents heatsoaking the IC..
This statement makes it seem like you have definitive proof, which is the statement I was arguing. I can absolutely guarantee you that the miniscule volume of air if vented from the BOV before the IC will have absolutely ZERO effect on IC temps. Assume a 7200rpm/1bar/1.8litres. The engine is pumping 216litres of air per second... take the volume of the charge system and figure out the volume of air expelled during a VTA... can't be more than 2-3litres. Now assume you're on a track (the only place heatsoak matters) and spending most of your time in 3rd/4th making long pulls between corners. The volume and speed of air passed through the IC in boost over time is incredible. The volume vented during shifts or lift-throttle is insignificant.

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But for fun Ill run both sides and pull data on boost recovery time.
This statement has nothing to do with the previous and has been discussed at length on every major turbo forum on the internet. The fact that there is no conclusive evidence either way doesn't mean tests haven't been run. I assume that if there was absolute evidence to prove one way works better, we'd all know about it. OEM mounting placement is based on the most convenient place to put it... if there was a "master" technique, it would likely be employed universally.

As for testing boost recovery, laptop datalogging would be a start, but would not be accurate enough to get any useful data. I hope you didn't think you were gonna sit there and watch your boost gauge to to judge spool recovery. You'd need pressure/flow direction sensors on either side of the BOV, need a way to measure turbine RPM, be able to exactly accurately repeat shifts every time (we might be talking about machine accuracy here)... and probably some other things I'm not smart enough to talk about.

For testing heat-soak, you'd need IAT sensors on either side of the IC and probably sensors to measure the temp of the IC metal itself in several places. Simply measuring IAT's on the coldside won't provide enough data to prove anything. You'll need to actually get the car on a track with high enough ambient temps to heat-soak it beyond efficiency with both mounting options. I'd actually recommend purposely installing a small IC to assist this. Simply driving it hard on the street will never get the IC hot enough.

Unless you're willing to do the "science" to generate hard numbers that are repeatable, then you're just another guy on the internet with a story for which there are a dozen other guys with the opposite story.

So how do you propose to "pull your data"?
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Old 09-05-2008, 08:56 PM   #22
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Buy two and have one on each side, that way everyone will think you are cool.
problem solved
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Old 09-06-2008, 12:14 AM   #23
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Someone submit this to mythbusters and let them go overboard testing all scenarios.
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Old 09-06-2008, 12:59 AM   #24
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They'll get it wrong anyway. They always choose the stupidest test procedures then don't understand why people write in to say they got different results.
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Old 09-06-2008, 01:02 AM   #25
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They'll get it wrong anyway. They always choose the stupidest test procedures then don't understand why people write in to say they got different results.
qft.
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Old 09-06-2008, 04:39 PM   #26
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Someone submit this to mythbusters and let them go overboard testing all scenarios.
would they?
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Old 09-08-2008, 10:28 AM   #27
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would they?
Only if it involved a way to cause grevious bodily harm to Buster. (speaking of which, where the hell has Buster been recently?)


My thoughts on the matter, which are intuitive rather than empirical:


1- Air has mass. As a result, it also exhibits inertia.

Imagine a long tube, with air being forced into one end, and coming out the other end. The air is moving at a constant velocity.

You now close a valve at the end of he tube where the air had been coming out. As a result, two distinct things happen: the pressure inside the tube spikes and the whole column of air comes to a stop.

When you open the valve again, the column of air must once again accelerate from a standstill to its nominal velocity, and this takes time. During that period of time, the volume of air coming out of the end of the tube will be less than nominal.

Now, assume that a BOV were to be placed at the end of the tube just prior to the shutoff valve, and engineered to open when the shutoff valve was closed. By nature of the fact that the BOV is all the way at the end of the tube, the column of air is permitted to remain in constant motion. It is not forced to stop, and then required to accelerate back to nominal speed according to the state of the shutoff valve.

Having trouble with the analogy? Try picturing it with water, or guinea pigs, or cylindrical blocks of lead instead of air. Same concept.


2- Just because Mercedes does something a certain way does not mean that way is the most optimal from a performance standpoint. It may simply be the most optimal from a cost and manufacturing complexity standpoint instead. Heck, on most of their cars, Mercedes forgets to install the turbocharger altogether, and this is certainly not most optimal from a performance standpoint.
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Old 09-08-2008, 10:42 PM   #28
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Originally Posted by Joe Perez View Post
Just because Mercedes does something a certain way does not mean that way is the most optimal from a performance standpoint. It may simply be the most optimal from a cost and manufacturing complexity standpoint instead. Heck, on most of their cars, Mercedes forgets to install the turbocharger altogether, and this is certainly not most optimal from a performance standpoint.
I was wondering how many years it would take for someone to figure this out... It's cost/benefit, kids! Cold side is absolutely the better way for performance, for all the reasons of air column inertia already explained.

The heat impact on the BOV diaphragm is also an issue, as most BOVs are designed to be on the cold side. Just because it isn't hot enough to melt the rubber doesn't mean it isn't hot enough to degrade the rubber over time and eventually cause a boost leak.

But in the end (unless you get that boost leak) the performance impact of BOV placement is pretty minor, so if you're cost or complexity sensitive, it makes sense to package it on the hot side.

Example:

Neon SRT-4 is VERY cost sensitive and has the BOV integrated into compressor housing. This allows them to make a BOV with only a vacuum hose, a small stamped steel cover, three (self tapping) bolts and a diaphragm.

R32 Skyline GT-R is not cost sensitive at all, but VERY performance sensitive. the GT-R used a hot-side pipe feeding a manifold with TWO BOVs, which dumped into another manifold that collected the air, ran it into a hose, which ran into a long, convoluted plastic crossover pipe, which ran into another hose, which ran into a fabricated steel tee, which ran into two hoses, which ran into the inlets of the two turbos. FOURTEEEN hose clamps just to hold this mess together.

Boost recovery on the SRT-4 is better than the GT-R, by the way, but it's not because of the BOV.

-Dave
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