colt45_gto wrote:
i've worked with turbo's for a long time i have a great understanding of how they work.
a turbo will spin up faster when cold its why real tuners don't use bleed off valves instead they use boost controllers. the exhaust side of the turbo will glow red then white hot under extreme use on cars that are fitted with turbo's on or close to the manifold.its the sheer heat of the hot gasses that cause this ( this bit isn't rocket science)
when the turbo is cold things are a little looser so it spins at a fair old rate and normal 14 psi@ 4,500 rpm on a hot run would be 16 psi on cold this coupled with the cold air its pushing is creating a boost spike. if you could keep the turbo exhaust body cold the turbo would work very efficiently. but this will not happen because of the blow torch effect from the burnt gases. when the engine reaches temperature the body and bearings of the turbo expand and different levels (cast iron body, phosphor bronze bearings, steel shaft) these will all act differently at temperature. thus the turbo runs a lower boost than it does on cold.
the engine blows out what it sucks in so its blowing the turbo impeller (turbine wheel) round, that is making the compressor wheel create pressure in the induction forcing air into the engine (forced induction) which passes through a cooler (intercooler) to cool the air slightly to try to achieve cool enough forced air so it doesn't evaporate the fuel before ignition.
now fen if you read this part congratulations you just learned something.
Did I. What was that? That you don't
really know what you're talking about? Oh no, I knew that already. Actually you're right though - I learned that as well as not understanding how a turbocharger produces boost you
also don't know what an intercooler is used for, nor I suspect how a bleed valve or boost controller works.
In order:
Paragraph 1.Wrong. You have at best a sketchy understanding how turbochargers work.
Paragraph 2.I don't even know what you're saying here. Bleed valves vs. boost controllers? You're right; real tuners don't use bleed valves as they are rough as you like (a small step up from vice-grips on the control line; very small), but even if you did use one you'd still need a boost controller of some sort or the boost level would keep rising until something fails. A bleed valve is employed only to bleed off some of the boost pressure that the boost controller (be that a mechanical actuator or electronic device) "sees" to fool it into allowing a higher boost level than it has been set to allow. Regardless the controller still has to be there and functional.
The turbo hot side still glows very brightly even on a 944 when it's oh-so-far away from the exhaust ports.
Paragraph 3.Your figures for boost and rpm are meaningless as every application is different and the actual figures are set by the boost conroller, so I'll ignore them.
The turbocharger is designed and optimised to run hot; there's no avoiding heat. It's true that the various materials and components have different thermal properties, hence the unit is designed to have ideal working tolerances when it's
hot, so it's not correct to say it performs better when cold. Why on earth would you design something that spends its working life at hundreds of degrees C to perform optimally at 20 degrees C?
What you refuse to understand is that the heat of the exhaust gasses is required as that holds the bulk of the energy that the turbocharger converts to induction pressure, and for that reason you actually
want the manifold and hotside of the turbo unit to hold as much of the exhuast port heat as possible.
Paragraph 4.If it were true that the engine blows out what it sucks in and that turns the impeller, and that was the end of the story then it simply wouldn't work. Are you honestly saying that if you were to pump the piston up and down in the cylinder and displace air throught he exhaust valve and header then on through the turbo exhaust impeller that you believe the induction impeller would create positive boost through the inlet and back into the cylinder? If so it would start to run itself and you'd have a perpetual motion machine. In fact you'd be creating energy, but as the first law of thermodynamics states "energy cannot be created nor destroyed, only changed in form" it's sadly not possible.
Lastly the intercooler is
not designed to stop the fuel evapourating. You actually want the fuel to be a mist, so if you could get it to evapourate (which means it would turn to gas or effectively boil) it would probably be a good thing - I don't even know the boiling point of petrol, but I'm pretty sure it's higher than the temperature of the induction charge. Regardless in a closed system like the intake after the turbo impeller where would such evapourated fuel go but into the cylinder?
The
actual purpose of the intercooler is to drop the temperature of the compressed induction charge to increase its density, or in other words so more air fits in the cylinder, air being the bulk of the fuel the engine runs on, hence more of it meaning more energy is released. Incidentally the heat in the induction charge comes from the temperature increase associated with compressing gas, not through being in close proximity to the hot side of the turbocharger for a brief part of a second as I suspect you may believe.
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