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BOV question when running speed density (now with pics of new setup)

Terry Posten

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I have converted to speed density. When venting to atmosphere is it ok for the BOV to be open at idle and allowing air to blow out?

I am running the 7lb spring and I have 12 inches of vac.

Should I install a spring that will just keep the BOV closed at idle?
 
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mikus

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Aurora IL
this is an amateur answer but - since you're working off intake temp and manifold pressure, there should be no adverse effect. Your MAP would be lower, but it's consistent and reading right.
 

belize1334

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Bozeman, MT
Often the air will be sucked in through the BOV so you should put a 1.25" cone filter on there. Otherwise there should be no adverse affect. What is your new SD system?
 

Terry Posten

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Davenport, Iowa USA
ECMLink.

Will be dyno tuning it Tuesday.
 

Terry Posten

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Here are some new pics of what my car has turned into.

1st, lets show the very first picture of the engine bay I took:

This was right after I did the Keydiver 3G MAS upgrade



Here is how it sits today:




 

alansupra94

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Yeah speed density doesn't care.

I have a knock-off Greddy BOV with a authentic Greddy diaphram. If it leaks or breaks I will get a Synapse or something.
 

jepherz

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Technically, if your BOV is open at idle it's probably sucking air in, not blowing it out.

The way speed density works though, you are tuning for your actual scenario. You could drill holes in your intake tract if you wanted to, as long as you tune for it (tune with the holes there). However, unlike a stock maf setup, you also need to tune every time you change something. This means you need to tune for new exhaust, new air filter, etc. With MAF, you don't have to.

And to the comment about speed density using IAT and baro, that doesn't have anything to do with it. The stock setup uses IAT and baro as well.

A stock setup is 'more correct' in that it is actually calculating how much air is entering the combustion chamber(s). Speed density is less accurate in that it just allows you to 'tune' your ecu to equate X amount of air to Y amount of pressure from your map sensor.
 
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GSX_TC

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Dam that was well said man
 

alansupra94

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Wayne,NJ
Quoting jepherz:
Technically, if your BOV is open at idle it's probably sucking air in, not blowing it out.

The way speed density works though, you are tuning for your actual scenario. You could drill holes in your intake tract if you wanted to, as long as you tune for it (tune with the holes there). However, unlike a stock maf setup, you also need to tune every time you change something. This means you need to tune for new exhaust, new air filter, etc. With MAF, you don't have to.

And to the comment about speed density using IAT and baro, that doesn't have anything to do with it. The stock setup uses IAT and baro as well.

A stock setup is 'more correct' in that it is actually calculating how much air is entering the combustion chamber(s). Speed density is less accurate in that it just allows you to 'tune' your ecu to equate X amount of air to Y amount of pressure from your map sensor.



I think you mean MAP. I am not trying to be a dick or grammar nazi but having MAF there might confuse people.
 

alansupra94

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I am almost 100% sure it is suppose to say MAP sensor. With a MAP sensor, you don't have to re-tune anything for minor changes.
 

Terry Posten

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I have gotten word from the ECMLink guys and Chris Beran that this condition is perfectly fine.

And as I think more on it, air blowing out of the BOV at idle will allow the turbo to stay spinning more instead of the air being trapped against the throttle plate in a closed system. Should make for a shorter lag time (all be it, very small).

There will be a very short period of time that airflow may reverse and suck in during some situations and I may look for some sort of filter.

On a side note, I took it for a spin to get some gas today after work and man is the turbo smooth and absolutely zero flutter. The turbo has the coolest scream as it sings past 5 psi. I can't wait to hear it fully tuned running WOT at full boost.
 

OMFGeofffff

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Burnsville, MN
Quoting alansupra94:
I am almost 100% sure it is suppose to say MAP sensor. With a MAP sensor, you don't have to re-tune anything for minor changes.



I think he meant that when using SD you just have to retune when you change things that affect the VE tables. Depending on what changes you make you don't have to retune anything.
 
Last edited:

OMFGeofffff

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Quoting Terry Posten:
I have gotten word from the ECMLink guys and Chris Beran that this condition is perfectly fine.

And as I think more on it, air blowing out of the BOV at idle will allow the turbo to stay spinning more instead of the air being trapped against the throttle plate in a closed system. Should make for a shorter lag time (all be it, very small).

There will be a very short period of time that airflow may reverse and suck in during some situations and I may look for some sort of filter.

On a side note, I took it for a spin to get some gas today after work and man is the turbo smooth and absolutely zero flutter. The turbo has the coolest scream as it sings past 5 psi. I can't wait to hear it fully tuned running WOT at full boost.



I know for a fact that my BOV sucks IN air when at idle.
 

Terry Posten

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Davenport, Iowa USA
Don't get me wrong, it is ok either way.

The way I understand it, if you pulling air in the vent at idle, your turbo is either to small to feed enough air to the idling motor or the turbo requires more exhaust pressure to spin the impeller fast enough to supply enough air to over come the vacuum.

What size is your turbo and is it ball bearing or journal?
 

OMFGeofffff

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Burnsville, MN
Stock turbo stock bov. It should be recirc'd but I can't find a good hose configuration.
 

jepherz

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KC, Missouri
Quoting alansupra94:
Quoting jepherz:
Technically, if your BOV is open at idle it's probably sucking air in, not blowing it out.

The way speed density works though, you are tuning for your actual scenario. You could drill holes in your intake tract if you wanted to, as long as you tune for it (tune with the holes there). However, unlike a stock maf setup, you also need to tune every time you change something. This means you need to tune for new exhaust, new air filter, etc. With MAF, you don't have to.

And to the comment about speed density using IAT and baro, that doesn't have anything to do with it. The stock setup uses IAT and baro as well.

A stock setup is 'more correct' in that it is actually calculating how much air is entering the combustion chamber(s). Speed density is less accurate in that it just allows you to 'tune' your ecu to equate X amount of air to Y amount of pressure from your map sensor.



I think you mean MAP. I am not trying to be a dick or grammar nazi but having MAF there might confuse people.



No, I mean MAF.
 

alansupra94

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Oh really?

Interesting....I didn't have to re-tune when I changed minor things.
 

jepherz

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Well, if they are so minor that you don't affect your VE, I suppose you don't need to re-tune, but from my post above I was considering mods that would change VE, such as an after-market exhaust, etc. The beauty of MAF is you wouldn't have to re-tune even with major changes.
 

alansupra94

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Wayne,NJ
Ah okay I see what you are saying now.

Yeah I guess that is the upside of having a MAF. I personally love being speed density since my VE won't be changing that much until I go to a Holset VGT turbo. At that point I plan on swapping in a whole bunch of parts at one time.
 
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