do automatics need to run a bov?

[big_zop]

You guys havent seen this yet?

Garrett Turbocharger Speed Sensor

[JustenGT8]

i think most people are missing one critical point, STANDARD blow off valves are of a plumb back nature and take the air out of the turbo to throttle side of the intake and put it before the charger... BOV's are needed in some cars so the turbo doesnt throw "regurgitated" air back thru the air flow meter making it run rich or shit during gearshifts or coming off the throttle...

Yup, maybe overstating it a bit but that's the emissions aspect i referred to earlier.

[trdee]

for all the warnings i've read about needing a BOV, this statement has held true throughout- i've seen no evidence of any turbo that has failed from a lack of BOV.

......................


i do believe that the ceramic turbos on the 3SGTE are more sensitive to any sort of weird forces on the impeller shaft, which is why the MR2 came with a factory BOV. an inconel turbine wheel turbo will have no issues running without one.

lol you just contradicted yourself.

[MWP]

for all the warnings i've read about needing a BOV, this statement has held true throughout- i've seen no evidence of any turbo that has failed from a lack of BOV.

But this is the question.... how do you know??
Is there something you know to look for that would show that the turbo did fail early due to a lack of BOV?
I cant see how this is possible, especially when it comes to the wear of the bearings and thrust plates.

[peanutsfmx]

none of these cars have done 100,000kms on the turbo though

actually i doubt any of these cars have even done 20,000kms

Pm adsport about his ihi running on his ke corolla

[KENut]

This topic is the best.

Flutter.
Ever had pipe hammer? As in if you shut off a house tap fast, you will hear a bang bang bang noise. Clearly the water isnt being forced backwards, its just been shut off with nowhere to go. The banging noise is the pressure wave, which when shut off travels back up and down the pipe rapidly. This can cause burst piping.

Same situation with turbos when the throttle is shut off suddenly with high velocity air (high rpm/high boost) forced towards it. Albeit a little different being a gas, ie compressable.

[trdee]

we've already discussed that and yes it is one factor. however that in itself is not compressor surge. for one, you can also get compressor surge at full throttle........

[KENut]

I know it was previously discussed, I thought it might be a useful explaination for people to understand 'dose' etc.
I know its not compressor surge, I did not refer to surge at all.

[trdee]

what im saying is that those pressure wave things are only one of the factors that happen when you quickly close the throttle. you can also get compressor surge.

this has all been established anyway. the current point of contention is whether the surge/pressure waves actually cause any significant damage over the life of a turbo

[grue0038]

lol you just contradicted yourself.

not at all. i believe toyota put them on because they might have been concerned about it, but that part is pure speculation and is certainly the exception rather than the rule.

as i said though, i've never heard of a turbo failing from lack of a BOV, that includes MR2 turbos. all the failures i've seen were due to FOD, overspeed, contaminated/lack of/clogged oil supply, etc.

But this is the question.... how do you know??
Is there something you know to look for that would show that the turbo did fail early due to a lack of BOV?
I cant see how this is possible, especially when it comes to the wear of the bearings and thrust plates.

i guess that is the question, isn't it? while i dislike the practice of using absence of evidence as evidence of absence, the distinct lack of evidence in this case at least downplays the hooting and hollering that goes on about the dangers of not using one. in fact, there are quite a few 1980's t-birds and volvos and saabs here in the states that are still on the original turbo and have never had BOVs fitted- many of which are running higher than stock boost levels. i checked the shaft play on a volvo turbo in the u-pull last time i was there just out of curiosity and there was nothing remarkable about it *shrugs*. thus far, it seems that there is more evidence to dispell the BOV argument (in the form of OE turbos on cars never fitted with BOVs still on the road today) than there is to support it (in the form of documented turbo failures with lift-off compressor surge as the cause). i'm merely going by what the evidence suggests. honestly, i wish there were some solid data to swing the argument one way or the other. i'm certainly not averse to changing my mind if the right data came along.

either way i intend to run a pre-turbo throttle just as soon as i can figure out where the hell to put it. my intake pipe layout is a bit of a necessary clusterfuck. until then, it's sans BOV for me.

[trdee]

i agree that there is not enough info. the theory suggests that damage could be possible. but the severity and whether it would be something significant over the life of a car is not documented anywhere that i know of.

[senn]

I would have thought, even if you aren't 100% sure, that for the cost of a BOV (what's a good one worth nowadays, a couple hundred bucks for a street setup up to 20psi?)
For peace of mind, it'd be worth having.

The people who are saying this car and that car don't run a BOV and their turbo's are fine, seem to be using cars with unknown, or fairly low km usage, but having seen cars with factory setups do 100,000km + with aftermarket boost controllers (ie increased over factory boost), and factory BOV, i know which i'd be doing if it was my choice. But it would be a quiet BOV, plumb back or not. So weigh it up i spose, cost of a BOV, vs cost of a (possible) turbo rebuild or replacement. Also if Garrett reccomend it (yes i know they probably want to sell you a BOV) i'd say they know a bit more than anyone else here

[Z2TT]

Yeah it was my thinking too, but does Garrett recommend them because it is more of an issue when running larger turbos or an issue even with stock turbos running stock or increased boost a bit?

[grue0038]

i agree that there is not enough info. the theory suggests that damage could be possible. but the severity and whether it would be something significant over the life of a car is not documented anywhere that i know of.

right. my contention is that something like FOD or oil contamination will kill the majority of turbos long before compressor surge does.

also, i run an MHI turbo, and at least for MHI, things like bearings and compressor wheels are so easy to replace that i have no issue considering them wear items to be changed out every couple of years anyway- long before any signs of damage from lift-off compressor surge would ever rear their ugly head.

if i were really concerned about trying to get 200k out of a set of journal bearings, maybe i'd change my mind. for the way i push my car though, the turbocharger is definitely considered a maintenance item anyway. i would say that most performance-minded folks also don't expect a turbo to last as if it were an OEM item on an unmodified car.

[river]

Hi,

I'm sure a plumb-back BOV is more cop friendly, which is a good thing.

Even with the PB BOV my turbo can still make some loud sounds, but no where like it used to. I just don't need the attention from the cops. From a visual perspective I think Trini would get some cop interest, and with a noticable flutter on each gear change she'd really be begging for it.

seeyuzz
river