Porsche Enthusiasts Club Forum

And it produces no boost when you rev the engine in neutral. Why is that if boost is purely a function of exhaust gas flow?

Even if you are right, where does the exhaust gas escape to from the long header to turbo pipe if it doesn't go through the turbo? Or alternatively how can there be x units of volume produced at each exhaust port and less than 4x units of volume through the turbo in the same time period?

a turbo will create boost in neutral its just not prolonged because the engine hits the limit before real boost can be achieved.

if you have a short piece of tube say 1.5" dia 6" long and put an airline in the end of it and blow 100 psi direct and place your hand over one end you will feel a good strong pressure. if the same pipe/tube is 4' long the pressure has almost been lost to a minimum. its the same with exhaust gases although the open end is at the other end of the car the pressure is far greater at the front than at the rear.

a turbo is purely dependant on pressure, the exhaust side being the drive wheel while the inlet side is the compressor the greater the pressure put through the exhaust side determines how much pressure the compressor builds in the charge carrier and cylinders.

simple explanation is... pressure is lost over distance.

if a waste gate fails or the actuator fails and no longer holds the waste gate closed for boost. there is less pressure to the turbo giving little to no boost. on the other hand if it sticks shut and does not operate correctly the turbo will be on its maximum boost because all the pressure is going there and not being diverted/lessened to lower or control the boost.

Sorry, but that is almost 100% nonsense, the exception being part of the wastegate statement.

no its 100% fact. although you may hate to be wrong or admit it but you are i'm afraid.

i shouldn't have to but here is a few links to back my knowledge
http://www.turbo-kits.com/how_turbos_work.html
http://www.turbointernational.com/turbos.asp
http://conceptengine.tripod.com/conceptengine/id5.html

want more. google it.

what i wrote before is my knowledge not from any internet site.

I wouldn't say the setup was silly, I think it's been designed to last at the expense of some initial response, I've had 3 Ford turbocharged cars and they all had the turbo mounted on the exhaust manifold, they had less lag but I doubt they could have done 150k without a rebuild. The 944 engine though seems to be over designed for the sake of it.

Right, so you drive a turbo car at 4,500rpm - there is boost, yes?

Hold the same car at 4,500 with no load there is boost? No. Statement 1 debunked.

You put 100psi into one end of a open-ended 1.5" diameter tube of 18 inches long and you get good pressure out the end but you extend the tube to 48 inches and get none. Really? Not on the planet I live on. Regardless the turbo system is not open ended so even if that were true it would be largely irrelevant. Put a restriction in your 1.5" pipe at any point along its length and the rpessure between the 100psi source and the restriction will be largely unchanged. Statement 2 debunked.

Why, if the turbo is just a windmill, do people bother to lag the manifold to the turbo? It's because the heat of combustion carries a large proportion of the energy, and that is why under no load the turbo produces virtually no boost.

The wastegate works by allowing some of the gases that drive the turbine to escape. If it fails there is a leak. A leak of pressurised hot gas.

Ain't me who is wrong I'm afraid. You have a shockingly poor understanding of fluid dynamics.

there will be less heat on the porsche turbo because the heats dissipated somewhat before the turbo which is a good thing in reality

go learn something.
most lag the headers to stop things around them getting too hot and brittle

where did i mention windmills?

go back to google and come back when your talking sense

I don't want to contradict you but those links are er, over simplified to cater to a layman.

maybe pauly, but what fen fails to realise is a turbo is more efficiant when cold

What's is a turbine driven purely by pressure but a form of windmill? You're not the guy on PCGB who tried to tell us his 924 Turbo bonnet was a performance benefit because it cooled the exhaust manifold are you?

Tell you what: I don't actually care if you don't understand, because I do. I'll leave it to anyone reading this who is unsure to form their own opinion whether they choose to believe me or the guy who opened the thread by saying Porsche's turbocharging system on the 944 is "stupidly silly".

i think the 2.5S inlet is smaller than the S2 inlet but unsure if it fits the S2 head,.... maybe worth investigating

I have to admit I don't really know the dynamics of it but my understanding is the exhaust turbine requires heat and volume of flow, whereas the compressed charge is more efficient the cooler it is hence the use of an intercooler etc, whatever you seem to know what you talking about on other matters so I will leave it here.

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.