BigDogJonx

iTrader: (7)

This is something that has boggled me for the longest time. I cannot understand this at all. Maybe Im thick in the head.

But why on a turbo (dont know about s/c) it only boosts while in gear? Why cant I get the boost gauge to show 5psi in neutral? I mean technially the turbo is being spooled up once I rev it upto 5k rpm in neutral. Shouldnt I be seeing boost then?

What am I missing here?

BippuBenji

iTrader: (4)

I always wondered that as well. When in neutral, I always like hearing the Greddy BOV, but it would never boost, even at redline, maybe nothing is going to the crank? I don't know.

Craig Mack

Your SC doesn't boost in nuetral? I revv all the time in nuetral and I get boost and BOV feedback.

BippuBenji

iTrader: (4)

Nope, never. It would sometimes get right in the middle where theres no vaccuum or boost.

Stephen Max

iTrader: (59)

When you rev it in neutral, are you pushing the gas pedal all the way to the floor? If not, then maybe your BOV isn't staying closed because your manifold vacuum never really gets to zero.

BippuBenji

iTrader: (4)

Ahh, maybe that's why sometimes it goes to zero. Well, I really didn't have to step on it all the way to get the BOV whistle, it was there as long as I let the needle drop from anywhere 3K rpms and up. I'll try it later today, I just hope I don't overrev and then break something. Honestly, I pretty much have more fun hearing the BOV when I drive or in neutral than actually going superfast by boosting.

Craig Mack

It doesn't matter how hard I push down the peddle, if it's above 2000rpm, you hear the bov go PSSHHHH and hear the crickets whine.

This isn't an issue of the auto transmission is it?

Craig Mack

Ok, I just went outside and revved it several times. I didn't go past 2800rpm becuase neighbors were outside, but my boost always stayed in vacuum. This could be becuase I wouldn't be in boost anyways, but it wasn't close to zero.

But the BOV still pshhhed like mad and you could hear the compressor's loud whine.

BigDogJonx

iTrader: (7)

That is my issue, still trying to figure out why it cant boost in Neutral. It never goes past 0.

Dixit

nismo2020

iTrader: (1)

there is no load on the engine... think of it as you jump higher when you have something to jump over...

resistance is the name of the game i.e. dynoing on a roller for resistance.

Nealoc187

iTrader: (23)

Exactly. Turbo boost is dependent upon engine load, you aren't loading the engine when you blip the throttle in neutral. Centrifugal supercharger boost is dependent upon RPM.

Bags

iTrader: (3)

BY far one of the best posts you have ever made on the .orgy



HI CARL

BTW project ... DELAYED.. details on AIM next time

BigDogJonx

iTrader: (7)

I still dont understand how a turbo knows wheather the engine is on load or not. Better yet, it cant tell when the engine or tranny is on load. All it knows how much exhaust gas is coming through. From that is spins the turbine and increases boost to the throttle body. To me that is flat out boost.

I need of a technical answer.

Dixit

LatinMax

iTrader: (1)

I have the same question. Where does all the boost go. It has to be in the engine somewhere. It doesn't just disapear. So there should be some kind of reading.

BigDogJonx

iTrader: (7)

Where are the boost gurus when you need them?

turbomax97

iTrader: (6)

agreed, and I understand how the engine is not under load while in neutral... but I think where these guys are getting confused is, even if you hold rpm's @ redline, you don't make say 6 psi wiht a 3.60 inch pulley, u make maybe 1 psi. I believe this is partially due tot he fact that since the motor is under no load, it is still in vaccum, causing the bov to remain open and vent the air into the atmosphere.

Anyone else wanna shed some light?

BigDogJonx

iTrader: (7)

Cant be on my turbo setup for sure, reason being is that I have an HKS Racing BOV, I can see straight into the outlet and see the valve, it is open during idle, and as soon as it detects boost, it shuts FULLY. So at 4000rpm I should be making 5psi of boost. Which I dont see.

Dixit

BippuBenji

iTrader: (4)

Hmm, I tightened my BOV so that it doesn't vent any air at idle, and it doesn't open until I let off the throttle. I would no if it is open because my BOV is crazy loud and noticeable from inside the cabin. But anyway, I don't know what to tell you.

turbomax97

iTrader: (6)

well the bov opening is vacuum dependant, so it should be open at idle, and close under boost, then opening when you let off...hmm..

turbomax97

iTrader: (6)

well the bov opening is vacuum dependant, so it should be open at idle, and close under boost, then opening when you let off...hmm..

MAXIN

iTrader: (5)

Im no boost guru at all but I would guess it goes back to simple physics. Energy cannot be created nor distroyed. Turbos run off of waisted energy, since the engine is effectively using very little energy to rev in neutral, very little 'usable' waiste is exerted for the turbo to use thus very little (ideally no) boost.

I guess what im saying is the engine uses MUCH less engery to get to 5k rpm in neutral. Once you put the tranny in gear, the engine now has to 'work' to get to the same rpm since it now has resistance working against it; generating much more waisted energy for the turbo to 'use.'

uh, sorry if this doesn't make any sense, im sleepy...

BigDogJonx

iTrader: (7)

Cant be that MAXIN, even though that is a good theory, but the turbo truly runs off straight waste gas pushing the fins of the turbine. That gets full out exhaust regardless of wheather it is on load or not. You can spin the turbo upto full boost in idle for sure.

Just need to know why the boost gauge dont read that. Must have something to do with the way the vacuum/boost lines are run and how it is hooked up to the car.

Where the hell the Boost Gurus?

BippuBenji

iTrader: (4)

Who are the boost gurus?

BigDogJonx

iTrader: (7)

People like MardisGrasMax, Delio, .....

MAXIN

iTrader: (5)

Ok scratch my physics 'theory' as I did a little surfing (cant sleep), I believe that since the engine is at vaccuum, no load, you cannot 'read' positive boost on a boost/vac gauge (since vacuum is a common measurer of negative boost). "Boost" is the positive manifold pressure (compressed air) created by the turbo-charger and/or super-charger. Revving the engine in neutral will not create positive boost.

Credit 1

Credit 2

sorry if im talking out my rear again, i have nothing else better to do

ejj

iTrader: (5)

I'm no boost expert...but...

My impression is that the boost you create is highly dependant on throttle position. My understanding is that you could get to the red line without opening the throttle much, and you wouldn't see much boost.

So, holding the RPM at a given number with just enough throttle to do so wouldn't create much (if any) boost, would it?

I would think to see boost in neutral, you'd have to hold the car WOT, and that could cause all kinds of problems. Even if you did this, you'd hit the limiter so quick, fuel would cut, and you'd loose power (in either case I would think).

Someone please correct me if I'm wrong.

MacGyver265

Ok...

When you have the engine under no load conditions because you just let off the throttle, all that boost pressure is still in the manifold between the compressor of the turbo or S/C and the intake valves.

For a turbo, what do you think would happen if you have 7 or 8 PSI boost and the BOV doesn't open?

Well, if there aren't enough exahaust gasses flowing through the turbo, and there is pressure in the manifold, where do you think that pressurized gas is going to want to go? (BOV is still closed). Its going to want to go back out the way it came. What's the only way that's going to happen? The turbo or S/C spins backwards. Now for a turbo, this will kill your power at idle and cause major problems because it will keep exhaust gasses from flowing freely past the turbo unless the wastegate is open. If the turbo is spinning backwards, what do you think will happen when you get on the throttle again? Talk about turbo lag!!! Not only will the turbo have to spool up from a stop, it will have to spool up from spinning backwards! What a waste of power!

For an S/C, all that pressurized air in the manifold will kill your power at idle as well (engine stalls) because the S/C will continue to try to compress the already boosted air and bleed off considerable power off the crankshaft.

Pressure X Volume = Energy

This means the more pressure you generate in a volume of air, the more energy it will take to continue to pressurize. This is pretty intuitive. So why pressurize air you don't need using power you don't have? The answer is a BOV to let off the pressure and work needed to be done by the compressors at zero load.

MardiGrasMax

iTrader: (14)

Manifold pressure past the TB plate is what controls this. Part throttle reving requires very little TB plate opening so manifold pressure past the TB will not see boost or low vacume. On a SC set up the vacume in the manifold is pulling the BOV valve open, only when you open the TB plate open enough that the manifold pressure changes to less vacume than your bov spring is adjusted to , or pure boost, so it will close will you see boost. On a turbo car i think the same applies, but with the waste gate.

MAXimumHP

iTrader: (7)

I'm no turbo expert either, so take my theory with a grain of salt.

One of the largest sources of energy that spins the turbos turbine is the expansion of gasses, This is because the exhaust gas cools so fast (cause its d@mn hot when it comes out). When the engine is under heavy loads, the combustion chamber temperatures are much higher, thus meaning more cooling necessary, more expansion, more boost.

hlh0501

iTrader: (1)

Here is the answer:

Energy consumption.

Measure the exhaust coming out of your car when you rev in neutral verse revving it to redline say, on a dyno.

It takes FAR less from the engine to rev in neutral, say 10hp (just a number..), compared to flooring it, in gear creates the max hp, also creating SO much more exhaust...