Turbo is in!

[Robb235]

a BOV is unnecessary? why?

Because it's "on throttle" surge that kills turbos, not "off throttle surge" which is what the BOV relieves. People erroneously believe things like the "turbo will spin backwards when you let off the gas, because all the boost runs back out of the turbo if you don't have a BOV".

I know this is a contentious subject for some, so I'm not going to pursue anything further regarding a BOV vs. BOV-less discussion after this post. But if you google it, you'll find loads of threads on the subject, and almost always (at least the ones I've read), the BOV-less arguments win out, because in theory, they are correct. And for people that venture to remove their BOV to see what happens in the real world, they generally find that their turbos don't magically explode or die, and that performance increases because the BOV isn't there to let out all of your boost when you get off the gas and then back on again. I don't want to de-rail the OP's thread, so I will leave it at that.

Yep you could run without one, but you do accelerate wear on the turbo. If you're a race team and get a new turbo every race go ahead, if I am paying $2200 for a turbo I am running a good BOV.

Can you post credible evidence of this? I've heard this same argument before, but I've never heard of it happening in the real world.

NINJA EDIT: Also, there's plenty of OEM turbo setups that don't run BOVs, and yet they seem to last.

 

[SmokingRocks]

First of all there is no let off the gas situations during a shift on an auto truck if its not having trans issues. I never thought the turbo would spin backwards but if you get off the gas and close the TB then the exhaust gas is less so the turbo gets less go power, and the charge side builds up insane pressure which creates resistance on the compressor wheel and slows it down faster.

So what is the benefit? Theoretically you would lose your spool faster without a BOV. If it was such an accepted practice you would see turbo cars come w/o BOV's from the factory, which you don't. In fact many of them have recirc BOV's

 

[SmokingRocks]

Let's look at a turbo like the Garrett GTX3071 boosting 30psi. It's spinning in the neighborhood of 140,000 rpm and flowing 55 lbs/min. When you let off the gas to shift/brake/play innocent near a cop or when the turbo is pushing out more air than the engine can suck up, you run into a compressor surge situation. Imagine now when the throttle plate closes quickly. The turbo isn't as quick to respond and takes longer to spool down. It continues to flow at a high rate but the air flow (which has both momentum and mass) is cut to basically nothing in no time. That compressed air has no place to go except back into the compressor wheel and thrust bearing at a destructive rate.

At this time, there is very little pressure on the exhaust side but there is a spike in charge pressure exerted on the compressor wheel's full surface area which creates a huge thrust load on the turbo bearings that could cause severe damage. A conventional journal bearing would never be able to withstand the shockwaves assaulting the compressor. A ball bearing is more resilient against this damage but the compressor surge could still generate enough force to even throw the wheel off balance, causing premature wear. Those bearings are more durable against forms of ricer monkey business without certifiable turbo failure but I'd still run a BOV.

The blow off valve (bypass valve, diverter valve) protects the turbo from these harmful shockwaves of boost pressure. It also helps to maintain boost pressure and keep the lag down. The BOV is located on the intake side of the turbo. When the throttle plate closes and the turbo continues to spin and build pressure, the intake manifold senses a vacuum and the blow off valve opens to vent the pressurized air from the intake to the atmosphere. A bypass valve accomplishes the same thing but it recirculates the pressurized air back into the intake tract instead.

Do you need one? no. should you run one? yes..

 

[Robb235]

Like I said, it's a pretty controversial subject. Let's leave it at that. No need to derail the OP's thread.

 

[alia176]

Good discussion, I'm learning.......

 

[Trux]

Both realities are correct- but >6 psi is allot different subject than 30 psi balls out- pink panties flying in the wind!

 

[Trux]

Id be more concerned about a broken china turbo fin flying into the intake pipe

 

[Trux]

And dont use a k&n type filter with methanol injection near the filter. You will have a BBQ'd 80.

 

[Robb235]

And dont use a k&n type filter with methanol injection near the filter. You will have a BBQ'd 80.

Care to explain?

 

[Heckraiser]

I would agree that a Garrett would be awesome but I would also have to deal with that quicker spooling and a stock computer trying to keep up with AFR's which could actually hurt me on my setup.
I already have to be careful if I punch it because that boost will come fast and I am watching the AFR's go lean for a second until the computer goes open loop.

This post has me a little confused. If a fast-spooling turbo is enough to lean out the AFR on spool-up, why does the computer not struggle with an instantly-spooling supercharger? Can someone shed some light on this? If I were to copy mtncruiser97's setup, I would probably go for a smaller GT35 or even a T3/T4. I hadn't considered that the quicker spool might cause trouble.

 

[Trux]

Care to explain?

The filters have oil in them. The methanol is well methane alcohol. And putting the turbo too close (like the cone filters some have attached to the turbo ) to the filter has made it catch fire.

Its in youztube i believe as well as other forums ive seen. (Sorry/ Didn't know what other face to put for mud forums?)

 

[Trux]

Oh, and ive seen the filter fail and get sucked into the turbo. the filter part came off went into the intake

 

[Trux]

This post has me a little confused. If a fast-spooling turbo is enough to lean out the AFR on spool-up, why does the computer not struggle with an instantly-spooling supercharger? Can someone shed some light on this? If I were to copy mtncruiser97's setup, I would probably go for a smaller GT35 or even a T3/T4. I hadn't considered that the quicker spool might cause trouble.

I think this is what youre asking- but the size of the turbo or speed doesnt really matter when the boost level is set to its limits >8psi. But a larger turbo can take longer to spool , giving more time for the computer to compensate the afr - and most have stated that under 8psi is ok for the stock AFR/ injectors (maybe bigger injectors if wanted).

And why the supercharger is run on mostly stock parts (bc it has a type ofblow off valve also), but a different MAF mass air flow sensor(?) i thought i read in the parts list.

 

[scottryana]

Nope not even close. Stock computer does zero compensation for AFR.

It has everything to do with the compressor maps. This has been covered before. I wrote several posts about it. The SC'r compresser map isn't instant boost it's a positive displacement compresser that doesn't overwhelm the engine's air needs until the ECU is almost in an open loop situation. The compresser map closely maps to the engine's needs at low rpms. You will see 0-1psi meaning is meeting engine needs but you won't see high positive manifold pressure until higher in the Rev range. That's why compresser mapping is so important if you're not doing any computer tuning. The GT35 is a decent size, in another post I also mapped a GT40 which would be safer but lose some low end which can be a good thing for longevity. Like anything it's a tradeoff.

 

[Trux]

I think you misread my post- i wasnt saying the computer compensates like a compressor mapping computer for the supercharger- not at all.

I was explaining that the size (forced air/ psi production) of the turbo or supercharger doesnt matter in the whole scheme of things - bc any extra power(forced air) that the engine couldn't handle- is completely negated by the bov (failsafe)- and the computer should never run lean (over compensate - was probably the better term) bc you arent pushing the computer past its wide open throttle fuel limits. But anything over 7-8psi will ruin your AFR at some point and cause many problems.

Youre correct that "computer compensate" part could throw someone off when i read it.

Should have said the computer will not over compensate the AFR (or change at all beyond its OEM settings) by running too lean with a big or small turbo - because you are keeping it below 8psi- which the stock sysytem can handle.

I think we say same thing different way.

My post was probably a bit confusing if someone reading thinks thestock computer could possibly "read" or compensate for a turbo- not at all what i was gettting at.

The stock computer will ONLY play
Within its settings.

 

[Trux]

Yeah its all a tradeoff. that's what best about turbo VS supercharger IMO.

You can swap small to big turbo easily- and get significant gains from low end to higj end. but supercharger is limited in its power making overall and only comes in one size.

 

[Trux]

And scotty- whats your opinion on trail gears $400 turbo j manifold for a t4? If you've seen or experienced first hand?

 

[RockJock82]

Not going to lie the turbo route has always crossed my mind. Though what has always steered me toward the v8 power plant is more power and better fuel mileage. On that note what kind of mileage do you turbo guys see? Of course it's all relative to how heavy your foot is... I may some day in the future try it out...

 

[scottryana]

But it absolutely will run too lean. It will run 14.7:1 under boost if you are boosting when the computer thinks you should be in standard closed loop operation. You hit a long Hill with low throttle input, but medium load and a small compressor will create say 3-4psi of positive manifold pressure, the stock computer will be in closed loop because you haven't satisfied the Throttle Position Sensor requirements to switch over to open loop and you are now running too lean (14.7:1) for a motor at 3-4psi on 91-93 octane fuel.

The size of the turbo or supercharger absolutely does matter. If you threw a huge SC on this motor that was able to build 8-10lbs of real boost (positive manifold pressure) off of idle, the motor wouldn't last a day. The TRD SC was sized and mapped the way it was because it doesn't create these big boost situations when the truck is in closed loop (14.7:1)

I don't know much about the trail ready manifold, I like the idea of a J-pipe better and it's what I run but I personally would go with the Treadstone manifold. I like them more as a company.

I think you misread my post- i wasnt saying the computer compensates like a compressor mapping computer for the supercharger- not at all.

I was explaining that the size (forced air/ psi production) of the turbo or supercharger doesnt matter in the whole scheme of things - bc any extra power(forced air) that the engine couldn't handle- is completely negated by the bov (failsafe)- and the computer should never run lean (over compensate - was probably the better term) bc you arent pushing the computer past its wide open throttle fuel limits. But anything over 7-8psi will ruin your AFR at some point and cause many problems.

Youre correct that "computer compensate" part could throw someone off when i read it.

Should have said the computer will not over compensate the AFR (or change at all beyond its OEM settings) by running too lean with a big or small turbo - because you are keeping it below 8psi- which the stock sysytem can handle.

I think we say same thing different way.

My post was probably a bit confusing if someone reading thinks thestock computer could possibly "read" or compensate for a turbo- not at all what i was gettting at.

The stock computer will ONLY play
Within its settings.

 

[Trux]

Hitting a long hill under low throttle input , medium load- sounds like a stretch for too lean on >8 psi boost. I highly doubt anyone would do this , especially monitoring with an AFR guage, and the point is to go up the hill with more power- not the least you can use. I understand its possible. But how is mtncruiser getting away with it with his stock TPS? Just monitoring AFR?

Like i said- its possible- but i think most will be on the gas in that type of situation going more towards open loop. Again, i havemt boosted an 80- so the TPS and all isnt my strongest knowledge in boosting an 80 vs what you have come to find the knowledge of.

"Big boost situations" are taken care of by the bov on the supercharger ? No? I know the mapping helps, but big boost situation IMO is a malfunction if your set up at >8 psi and the boost keeps rising (big boost situation)? Of course, maybe we are saying the same thing different ways