Need quick help in an arguement!

[fly89gta]

Some moron is saying that in any turbo car you can build boost in neutral and that load has nothing to do with boost.

What sparked this whole thing is that some RX7 guy said he can build 5#'s of boost in first gear with the cluth pedal pressed in all the way...I said maybe rotory engines are different because my more doesn't build boost in neutral and some tool comes in and responds with this

if you knew how a piston engine works, and how a turbo works, you would realise that anytime the engine is running, it is expelling gas, thus spinning the turbine on the turbo, thus creating boost. (well maybe not at idle or low rpms, but the turbo is still spinning, just not fast enough to produce boost.)

An engine is basically an air pump, whatever gas goes in, goes right back out. It doesnt matter if there is load on the engine or not, the air is still going to be pumping.

If an engine in gear is running at 4500 rpm and moving 280 cfm out, it will move the same ammount of air no matter if its in gear or not. This air will spin the turbo, thus creating boost. The turbo has no clue whether the car is under load.

A turbo WILL make boost in neutral, it doesnt matter if its a rotary or piston, they are both air pumps, they will both be pumping air if they are running, no matter if they are under load or not.

My best freind has a Turbo TBird, he spins up his turbo all the time at lights.

So am I right, that load is required to build boost or is he right?

 

[scottyb]

Well, any turbo will spin more if you rev the engine, but make boost?????

I suppose if you had a wacky mismatched turbo, you could do it. Suppose your turbine wheel is small along with the exhaust opening that the wheel sits in. The exhaust hasta go somewhere, so it will make it spin harder, thus possibly some boost on the other side. Obviously, this creates a huge exhaust restriction, hence my "mismatched" statement. A turbo matched correctly to the flow of the engine will not produce boost without load.

 

[fly89gta]

Originally posted by scottyb
Well, any turbo will spin more if you rev the engine, but make boost?????

I suppose if you had a wacky mismatched turbo, you could do it. Suppose your turbine wheel is small along with the exhaust opening that the wheel sits in. The exhaust hasta go somewhere, so it will make it spin harder, thus possibly some boost on the other side. Obviously, this creates a huge exhaust restriction, hence my "mismatched" statement. A turbo matched correctly to the flow of the engine will not produce boost without load.

thank you! That's what I thought

 

[Lee_Burough]

I think he's full of hot air

Insist that he demonstrate this to you. Do not accept erratic movements on the boost guage as proof that he makes boost with no load, make him show you a steady boost value. If all he can show you is an erratic needle on the boost guage, it is system hysteresis, NOT real boost.

The hole in his reasoning is that his explaination does not correctly account for the changing volume of expanding gasses in the boosted "air pump" as you consider large versus small air/fuel charges.

The exhaust wheel spins faster under load because the larger air/fuel charge in the combustion chamber produces a larger volume of exhaust gasses, which will push harder on the turbine than the exhaust gasses of a smaller air/fuel charge.

If he thinks it takes the same air/fuel charge to spin the turbine wheel with no load as it does to brake torque, then he's not understanding what happens inside that air pump as more fuel and more air are introduced into the cumbustion chamber.

My two cents

 

[Buick From Hell]

Your first two words were right on..."some MORON"! Does this clown seriously believe that simply spinning the turbo will build boost? Ask him if he's ever heard of "friction"--ya know, that "thing" the turbo impeller must overcome just to "move air"? And then there's that "pump" called an engine, does he realize just how much air it actually DOES pump? And once the turbo finally spins fast enough to overcome the friction of simply MOVING air, it must THEN spin MUCH faster to simply pump the same amount of air the engine itself is pumping? Time for a moron pop-quiz: how much boost is this? ZERO!! To make boost, the REAL work begins! Oh, I'm sure you can build SOME boost while in neutral, but it would be for a microscopicilly insignificant amount of time... The reason is simple--an engine revving under a no-load condition will reach its rev-limit long before the exhaust can spin the turbo fast enough to build measureable (or usable) boost! And just revving the engine to 7 grand an holding it there will produce manifold VACUUM, and even a moron should know you can't have boost and vacuum at the same time!


the only possible way I can think of to build 5 lbs of boost in neutral is with a rev limiter...bet THATS good on the bearings!

 

[turbo buicks]

dont know about you guys but i watched the boost gauge as my friend built 5 psi in his relatively stock GS-T Eclipse at a light with the clutch pressed all the way in. this was at redline so i think the cars RPM range affects it. an RX-7 redlines at what, 8K?

 

[fly89gta]

An engine running at a givin RPM in neutral, would move the same amount of air as the same engine running at the same RPM in park, reverse, or drive.

He keeps insisting that statement is true...

 

[turbo buicks]

it takes more power to move the car under load than not under load. more power requires more fuel and more fuel equals more exhaust gas and energy and thus more boost. ask him if he can hit full boost at redline in neutral. i bet he cant. this guy sounds like my friend who thinks his stock prelude will whoop my cars ass from a roll b/c, get this, MY TORQUE CONVERTER!!!. i told him, hahaha, you are stupid, cuz at WOT my converter locks up and transfers power better than your slippin clutch! oh well hes putting $50 on his "theory" that his car is faster from a roll. hmmmmm, what parts can i buy for $50.

 

[fly89gta]

You have no clue what you are talking about. It makes no difference if its a large turbo or a small turbo, they both operate on the same exact principle.

An engine running at a givin RPM in neutral, would move the same amount of air as the same engine running at the same RPM in park, reverse, or drive.

In cars with sticks, you dont lose boost when you press the clutch, you lose boost WHEN YOU LET OFF THE GAS. (you press both at the same time)

And spinning the turbo = making boost. It depends on how fast the turbo is spinning for you to actually notice the boost. When the turbo is spinning slowly, it is still moving air, its just moving very little, so you dont even notice it.

Like i said before, the turbo has absolutly no clue on how much load is on the engine, there is NOTHING hooked up to the turbo that tells it if the car is in gear or not. The turbo will spin the same, regardless of if its in gear or not.

Thats like saying that if you were towing a boat on the back of a turbo diesel, the turbo would make more boost.

And, BTW, on an automatic tranny, there is always a load on the engine, its called the torque converter.

He's making himself look REALLY bad lol

 

[FlyinGN]

Ill bet hes thinkin he making boost IN gear in an automatic. Ask him if the car is in Park or in drive. I have NEVER seen a car build boost out of gear unless there is a stutterbox or something to create backpressure.

 

[Randy Greenoe]

Originally posted by FlyinGN
Ill bet hes thinkin he making boost IN gear in an automatic. Ask him if the car is in Park or in drive. I have NEVER seen a car build boost out of gear unless there is a stutterbox or something to create backpressure.

Exactly! My son's Talon can make 7# when it is on the two step . Prior to the two step it made zero boost.

 

[fly89gta]

Originally posted by FlyinGN
Ill bet hes thinkin he making boost IN gear in an automatic. Ask him if the car is in Park or in drive. I have NEVER seen a car build boost out of gear unless there is a stutterbox or something to create backpressure.

whoah, you're alive lol I haven't seen you post much

 

[FlyinGN]

hey Tony. I post.. a couple a day usually. Actually I have only been on here a few months longer then u and I have 300 more posts.. So I post at least as much as you

 

[tjthorson]

OK guys. TECHNICALLY he is right. The turbo spins when air moves across it. Then his train falls off the tracks. I skimmed the posts and nobody mentioned the deciding factor - vacuum. The reason you don't build boost in neutral is because you do not have zero vacuum long enough to make the wastegate shut. While sitting at idle in neutral and stomp on the gas, the freewheeling engine will rev to redline faster then the turbo can build boost, hence you won't see a net boost gain.

If he holds his foot to the floor long enough, it will build boost. But you won't hear turbo whine over the sound of the valves floating and the rods banging.

You guys equate "load" with lack of vacuum. You stomp the gas, the engine loads up against the torque converter, you have zero vacuum and the wastegate shuts and you then build boost.

Make sense? So, he is a moron thinking he can build boost in neutral (unless he wires the wastegate shut!) and revs his motor to scatterpoint.

But, now you know the mechanics of WHY.

 

[tjthorson]

Oops, I just read Kevin's post. He and I are on the same page - the RIGHT one.

Great minds think alike!

 

[BLACK6PACK]

I agree with what the guru's say on here. I have an eagle talon tsi with a stick. The only way I can launch under boost (100% stock car) is to slip the clutch a little with my foot on the brake and gas. Then you get that nice burnt clutch smell!

One question though. I can build a little boost with the car out of gear, and was wondering if this is just a hair trigger guage or what. If I stab the gas and let off, the boost guage will show a pound or two of boost and go back down. If I stab the gas and hold it, it will do that same, climb to a pound or two and drop. Is it actually building boost for a fraction of a second due to the weight of the rotating assembly creating a load or not?

 

[gn85]

You're both right..

I read this thread earlier and started thinking of how I can say this and have it make sense with my analogy. So try to follow me.

Think of a balloon. You blow air in a balloon, you get resistance from the rubber of the balloon as you inflate. What you feel in your mouth is pressure or what we think of as "boost". Now, here is where fly89GTA is correct... because in OUR cars the rubber of the balloon (resistance) is the drivetrain fighting against the pistons. The pistons can't move air as fast, air builds up from the turbo and you get boost. (Hopefully a lot of boost ) No, imagine you put a 1/2 inch hole in the balloon. All of the sudden that pressure in your mouth is greatly reduced or hardly there because the air is quickly escaping out of the hole in the balloon. The only way you could build pressure is if your lungs could push out A LOT more air to get backed up. That's just like if you didn't have your car in gear... the pistons don't offer any resistance and allow the air to move right outta the engine.

Now for where HE'S right. Still using our analogy, his car has the 1/2 hole in the balloon. But unlike our cars which will only see 5k rpms, his will keep RIGHT on going 7k... 8k... 9k??? At this rate, even with no resistance from the drivetrain, the pistons movement will offer resistance because they just CAN'T move any faster yet the air wants to keep coming. Just like our balloon.. if we KEEP adding air, our 1/2 hole isn't getting any bigger but the air volume keeps increasing. You get out your superman lungs and start filling that balloon, you'll start to get pressure in your mouth because the balloon is filling up and your meeting resistance again from the rubber in the balloon.

OK.. that's my analogy. I hope everyone followed along.

Please feel free to tweak this analogy for explainations.

 

[fly89gta]

perhaps in some cars you can build boost in neutral. The problem I have is that he insists that at any given RPM the boost levels will be the same no matter if you're in park,neutral or in gear...which is wrong in my mind

 

[turbo buicks]

yes, if his boost is the same at redline in park and drive tell him he needs to run more than a pound or two.

 

[Turtle TR]

I would say it's harder for a turbo'd car to build boost in neutral. I remember reading something about WRX w/ manual trans, building boost on the line while reving the engine on an off, to create more exhaust heat and which causes more velocity to drive the spool. I've also heard of guys using sometihng called a two step to build boost in neutral on cars with manual transmiussion. I dont have any documented proof of what I'm writing about. I'm just too lazy to look for them.