240sx guys.. help me out? turbo/BOV question
08-24-2010, 05:25 PM
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240sx guys.. help me out? turbo/BOV question
Ive got a ka-t running 8lbs with a VTA blow off valve.. and ive got a few not so serious issues. Try to help me out? My turbos currently surging when i hit higher rpms. so theres insufficient exhaust from the turbo, forcing air back through the turbine. correct?
ALSO, car stumbles when quickly stepping on throttle from idle.. which is caused by not having a re-circulated blow off vlave (from what ive researched & have been told)...
Soo.. Can i kill 2 birds with one stone by getting a re-circulated BOV?
im trying to get all this done as quick and painlessly as possible.. point me in the right direction?
thanks
ALSO, car stumbles when quickly stepping on throttle from idle.. which is caused by not having a re-circulated blow off vlave (from what ive researched & have been told)...
Soo.. Can i kill 2 birds with one stone by getting a re-circulated BOV?
im trying to get all this done as quick and painlessly as possible.. point me in the right direction?
thanks
08-24-2010, 05:27 PM
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Re: 240sx guys.. help me out? turbo/BOV question
My turbo on my sr20det used to do surge but i upgraded the fuel pump and from there i never had any turbo issued. that was with the stock t25
08-24-2010, 05:45 PM
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Re: 240sx guys.. help me out? turbo/BOV question
thanks for the suggestion ill loook into it.. ive currently got a 255 fuel pump on t3/t4 turbo. Assuming we had the same problem, the only thing i dont understand is how the fuel pump would come into play if the surge is from the turbo exhaust having nowhere to go, thus being forced back through the turbo. I would think that points to the BOV being insufficient.. if that makes sense
08-24-2010, 05:49 PM
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Re: 240sx guys.. help me out? turbo/BOV question
Well when on my t25 sr20det on 7lbs, before i upgraded the fuel pump, my car would drive fine until i was in boost. the second i hit boost the turbo would surge and the car would struggle and choke. the air/fuel going towards the turbo could insufficient and cause it to surge. check vaccuum lines also.
08-24-2010, 06:02 PM
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Re: 240sx guys.. help me out? turbo/BOV question
hmm.. ill look into it.. thanks
also.. just out of curiosity, as i understand cars with MAFs arent really supposed to run VTA blow off vlaves, whereas cars with MAPs do?
also.. just out of curiosity, as i understand cars with MAFs arent really supposed to run VTA blow off vlaves, whereas cars with MAPs do?
08-24-2010, 10:15 PM
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Re: 240sx guys.. help me out? turbo/BOV question
You're seriously confused about how a BOV works.
The BOV has nothing to do with hesitation from idle. The BOV isn't venting air at idle, and because it isn't venting air it really doesn't matter where the BOV would be venting air to. Where the BOV vents air only matters when the BOV is open, so when you shift or at any other time when the BOV valve opens. The BOV should never be open at idle, and if it is open at idle you should find and fix whatever is causing it.
Cars with MAFs don't often behave very well with atmo-vent BOVs because the BOV is venting air mass that the MAF has already measured (and should be going to the engine). So there is often a hiccup right after the BOV opens when the amount of fuel and amount of air don't match up. Cars with MAP sensors don't care, because all they care about is manifold pressure (hence the MAP sensor) and air temperature.
If you're getting surging at high RPM, the turbo is out of its efficiency range and is off the left side of the compressor map. That's usually an indication that the turbo is flowing too much air for the engine, even though the boost level might be perfectly fine. If the boost rises too fast, this can happen too. Air is basically backing up against the turbo because there's too much air for the engine to handle. That loads the compressor wheel and slows the compressor wheel down, and when the flow decreases (because the wheel slows down) the load is reduced and the compressor wheel speeds back up.
If that explanation is not true for some reason, then you don't actually have surging and have another problem instead.
There are actually a few possible causes for surge depending on turbo size and some other things. But, unless the surge is occurring when you lift off the throttle (when the BOV is opening), the BOV has absolutely nothing to do with it.
The BOV has nothing to do with hesitation from idle. The BOV isn't venting air at idle, and because it isn't venting air it really doesn't matter where the BOV would be venting air to. Where the BOV vents air only matters when the BOV is open, so when you shift or at any other time when the BOV valve opens. The BOV should never be open at idle, and if it is open at idle you should find and fix whatever is causing it.
Cars with MAFs don't often behave very well with atmo-vent BOVs because the BOV is venting air mass that the MAF has already measured (and should be going to the engine). So there is often a hiccup right after the BOV opens when the amount of fuel and amount of air don't match up. Cars with MAP sensors don't care, because all they care about is manifold pressure (hence the MAP sensor) and air temperature.
If you're getting surging at high RPM, the turbo is out of its efficiency range and is off the left side of the compressor map. That's usually an indication that the turbo is flowing too much air for the engine, even though the boost level might be perfectly fine. If the boost rises too fast, this can happen too. Air is basically backing up against the turbo because there's too much air for the engine to handle. That loads the compressor wheel and slows the compressor wheel down, and when the flow decreases (because the wheel slows down) the load is reduced and the compressor wheel speeds back up.
If that explanation is not true for some reason, then you don't actually have surging and have another problem instead.
There are actually a few possible causes for surge depending on turbo size and some other things. But, unless the surge is occurring when you lift off the throttle (when the BOV is opening), the BOV has absolutely nothing to do with it.
08-24-2010, 10:26 PM
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Re: 240sx guys.. help me out? turbo/BOV question
Well when on my t25 sr20det on 7lbs, before i upgraded the fuel pump, my car would drive fine until i was in boost. the second i hit boost the turbo would surge and the car would struggle and choke. the air/fuel going towards the turbo could insufficient and cause it to surge.
To put it another way:
You're saying the boat is rocking back and forth because the water level in the lake is low. I'm saying the boat is rocking back and forth because there's waves on the lake.
08-26-2010, 11:23 AM
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Re: 240sx guys.. help me out? turbo/BOV question
In addition to what fabrik8 posted, It would also be a good idea to check for boost leaks. They will cause the stumble, not the BOV; unless the BOV itself is leaking.
Also, what are you running for engine management?
As for the higher RPM surge, what size exhaust are you running? Are you running a cat?
Internal or external wastegate?
Also, what are you running for engine management?
As for the higher RPM surge, what size exhaust are you running? Are you running a cat?
Internal or external wastegate?
08-27-2010, 05:19 AM
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Re: 240sx guys.. help me out? turbo/BOV question
You're seriously confused about how a BOV works.
The BOV has nothing to do with hesitation from idle. The BOV isn't venting air at idle, and because it isn't venting air it really doesn't matter where the BOV would be venting air to. Where the BOV vents air only matters when the BOV is open, so when you shift or at any other time when the BOV valve opens. The BOV should never be open at idle, and if it is open at idle you should find and fix whatever is causing it.
Cars with MAFs don't often behave very well with atmo-vent BOVs because the BOV is venting air mass that the MAF has already measured (and should be going to the engine). So there is often a hiccup right after the BOV opens when the amount of fuel and amount of air don't match up. Cars with MAP sensors don't care, because all they care about is manifold pressure (hence the MAP sensor) and air temperature.
If you're getting surging at high RPM, the turbo is out of its efficiency range and is off the left side of the compressor map. That's usually an indication that the turbo is flowing too much air for the engine, even though the boost level might be perfectly fine. If the boost rises too fast, this can happen too. Air is basically backing up against the turbo because there's too much air for the engine to handle. That loads the compressor wheel and slows the compressor wheel down, and when the flow decreases (because the wheel slows down) the load is reduced and the compressor wheel speeds back up.
If that explanation is not true for some reason, then you don't actually have surging and have another problem instead.
There are actually a few possible causes for surge depending on turbo size and some other things. But, unless the surge is occurring when you lift off the throttle (when the BOV is opening), the BOV has absolutely nothing to do with it.
The BOV has nothing to do with hesitation from idle. The BOV isn't venting air at idle, and because it isn't venting air it really doesn't matter where the BOV would be venting air to. Where the BOV vents air only matters when the BOV is open, so when you shift or at any other time when the BOV valve opens. The BOV should never be open at idle, and if it is open at idle you should find and fix whatever is causing it.
Cars with MAFs don't often behave very well with atmo-vent BOVs because the BOV is venting air mass that the MAF has already measured (and should be going to the engine). So there is often a hiccup right after the BOV opens when the amount of fuel and amount of air don't match up. Cars with MAP sensors don't care, because all they care about is manifold pressure (hence the MAP sensor) and air temperature.
If you're getting surging at high RPM, the turbo is out of its efficiency range and is off the left side of the compressor map. That's usually an indication that the turbo is flowing too much air for the engine, even though the boost level might be perfectly fine. If the boost rises too fast, this can happen too. Air is basically backing up against the turbo because there's too much air for the engine to handle. That loads the compressor wheel and slows the compressor wheel down, and when the flow decreases (because the wheel slows down) the load is reduced and the compressor wheel speeds back up.
If that explanation is not true for some reason, then you don't actually have surging and have another problem instead.
There are actually a few possible causes for surge depending on turbo size and some other things. But, unless the surge is occurring when you lift off the throttle (when the BOV is opening), the BOV has absolutely nothing to do with it.
Originally Posted by hottscennessey
In addition to what fabrik8 posted, It would also be a good idea to check for boost leaks. They will cause the stumble, not the BOV; unless the BOV itself is leaking.
08-27-2010, 05:30 AM
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Re: 240sx guys.. help me out? turbo/BOV question
You're seriously confused about how a BOV works.
The BOV has nothing to do with hesitation from idle. The BOV isn't venting air at idle, and because it isn't venting air it really doesn't matter where the BOV would be venting air to. Where the BOV vents air only matters when the BOV is open, so when you shift or at any other time when the BOV valve opens. The BOV should never be open at idle, and if it is open at idle you should find and fix whatever is causing it.
Cars with MAFs don't often behave very well with atmo-vent BOVs because the BOV is venting air mass that the MAF has already measured (and should be going to the engine). So there is often a hiccup right after the BOV opens when the amount of fuel and amount of air don't match up. Cars with MAP sensors don't care, because all they care about is manifold pressure (hence the MAP sensor) and air temperature.
If you're getting surging at high RPM, the turbo is out of its efficiency range and is off the left side of the compressor map. That's usually an indication that the turbo is flowing too much air for the engine, even though the boost level might be perfectly fine. If the boost rises too fast, this can happen too. Air is basically backing up against the turbo because there's too much air for the engine to handle. That loads the compressor wheel and slows the compressor wheel down, and when the flow decreases (because the wheel slows down) the load is reduced and the compressor wheel speeds back up.
If that explanation is not true for some reason, then you don't actually have surging and have another problem instead.
There are actually a few possible causes for surge depending on turbo size and some other things. But, unless the surge is occurring when you lift off the throttle (when the BOV is opening), the BOV has absolutely nothing to do with it.
The BOV has nothing to do with hesitation from idle. The BOV isn't venting air at idle, and because it isn't venting air it really doesn't matter where the BOV would be venting air to. Where the BOV vents air only matters when the BOV is open, so when you shift or at any other time when the BOV valve opens. The BOV should never be open at idle, and if it is open at idle you should find and fix whatever is causing it.
Cars with MAFs don't often behave very well with atmo-vent BOVs because the BOV is venting air mass that the MAF has already measured (and should be going to the engine). So there is often a hiccup right after the BOV opens when the amount of fuel and amount of air don't match up. Cars with MAP sensors don't care, because all they care about is manifold pressure (hence the MAP sensor) and air temperature.
If you're getting surging at high RPM, the turbo is out of its efficiency range and is off the left side of the compressor map. That's usually an indication that the turbo is flowing too much air for the engine, even though the boost level might be perfectly fine. If the boost rises too fast, this can happen too. Air is basically backing up against the turbo because there's too much air for the engine to handle. That loads the compressor wheel and slows the compressor wheel down, and when the flow decreases (because the wheel slows down) the load is reduced and the compressor wheel speeds back up.
If that explanation is not true for some reason, then you don't actually have surging and have another problem instead.
There are actually a few possible causes for surge depending on turbo size and some other things. But, unless the surge is occurring when you lift off the throttle (when the BOV is opening), the BOV has absolutely nothing to do with it.