OK this might be a stupid question but a friend asked me this and I was stumped for an answer lol. Why does a gt35/40 at 18psi go harder/faster & make more power than say a T04E running the same boost? Considering both pressures are measured in the plenum after the throttlebody so both are seeing the same amount of air forced into the engine. Any ideas? I look forward to hearing the answer...

this may also be a dum answer as i dont know about specs and diameters but is one turbo larger than the other with a bigger shaft and fins? maybe thats too obvious

its all about flow not pressure a gt35 will flow more than an older type turbo of the same size due to better designed wheels.

more likely then not the 35/40 will spool faster due to better bearings, also its probaley a much better design which results in better flow, and less heat in the air charge example my old t4/t3 compared to the 35/40 t4/t3 at 5psi was fun 35/40 at 4psi u are sideways

Duz360, i dont think your statement is correct man. If its all about flow and not pressure, than howcome a car running 20psi will make double the power of one running 7psi, regardless of "flow"? If temperature were to remain constant, than at 7psi exactly the same amount of air is going into the engine REGARDLESS of turbo size. Boyles law (1662)- "The pressure of a gas, at constant temperature, is inversely proportional to the volume of the gas." Avogadros law (1811)- "Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules" What this is saying is that at constant temperature, the number of molecules going into an engine is directly proportional to the pressure, simple. More pressure = more air (molecules) going into the engine. An engine is always going to inhale the same volume of air regardless of pressure or temperature. If you double the pressure of X amount of air molecules then they are going to occupy half the original volume. But an engine always inhales the same volume of air right, so at higher pressure the engine is inhaling more air molecules, even though they occupy the same volume. So assuming that 1 small turbo and 1 big turbo both produce 7psi throughout the rev range measured at the plenum and temperature remains constant, than exactly the same amount of air is going into the engine. The difference in power comes from other things. A bigger turbo will cause less backpressure in the exhaust and therefore more power. A bigger turbo will compress the air more efficiently and therefore will heat the air LESS than a smaller turbo. Cooler air is denser and has more molecules in it per unit of volume, so more air is going into the engine, making more power.

Quote: Originally Posted by Spool-Up Duz360, i dont think your statement is correct man. If its all about flow and not pressure, than howcome a car running 20psi will make double the power of one running 7psi, regardless of "flow"? If temperature were to remain constant, than at 7psi exactly the same amount of air is going into the engine REGARDLESS of turbo size. Boyles law (1662)- "The pressure of a gas, at constant temperature, is inversely proportional to the volume of the gas." Avogadros law (1811)- "Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules" What this is saying is that at constant temperature, the number of molecules going into an engine is directly proportional to the pressure, simple. More pressure = more air (molecules) going into the engine. An engine is always going to inhale the same volume of air regardless of pressure or temperature. If you double the pressure of X amount of air molecules then they are going to occupy half the original volume. But an engine always sucks in the same volume of air right, so at higher pressure the engine is sucking in more air molecules, even though they occupy the same volume. So assuming that 1 small turbo and 1 big turbo both produce 7psi throughout the rev range measured at the plenum and temperature remains constant, than exactly the same amount of air is going into the engine. The difference in power comes from other things. A bigger turbo will cause less backpressure in the exhaust and therefore more power. A bigger turbo will compress the air more efficiently and therefore will heat the air LESS than a smaller turbo. Cooler air is denser and has more molecules in it per unit of volume, so more air is going into the engine, making more power. you answered it yourself; bigger turbo less back pressure..to to reach the same boost level there is more air flowing though the bigger turbo so more power... boost is basicly a measurement of back pressure

answered what myself mate? If its at the same boost level then how can there be more air flowing through it??

same as my mates supercharger... he has an f1 that can flow 38 pounds and rated at like 1000hp.. but his vortech flows 30 pounds max and is rated at 1600hp Quote: Originally Posted by Spool-Up answered what myself mate? If its at the same boost level then how can there be more air flowing through it?? i think its also the actual size.. if the housising/impeller etc are all bigger.. it will have to work less to achieve the same because it has more volume.. but then the issue is getting something that big, to actually move..thats when lagg and decent power come into consideration..

Quote: Originally Posted by Spool-Up answered what myself mate? If its at the same boost level then how can there be more air flowing through it?? did u just copy and past that from somehwere else what cant you comprehind?

spoolup. no offence but you are way off. picture this,2 turbos, one is a stock t3 off a vl turbo,the other one is as big as a volkswagen beetle and is used on a oceanliner.(yes they really do make turbos that big ) they are both running 10 psi,do you really think they are flowing the same amount of air? issue if the temperature is to remain constant. a basic fact of turbocharging is that different compressor wheels flow different amounts of air at a given boost level and also at different temperature. if that wasnt true there would only be 1 size of turbocharger and it would be fitted to every turbocharged engine.

Quote: Originally Posted by MARMO. did u just copy and past that from somehwere else what cant you comprehind? copy and paste what I answered the guys original question. Quote: Originally Posted by duz360 spoolup. no offence but you are way off. picture this,2 turbos, one is a stock t3 off a vl turbo,the other one is as big as a volkswagen beetle and is used on a oceanliner.(yes they really do make turbos that big ) they are both running 10 psi,do you really think they are flowing the same amount of air? issue if the temperature is to remain constant. a basic fact of turbocharging is that different compressor wheels flow different amounts of air at a given boost level and also at different temperature. if that wasnt true there would only be 1 size of turbocharger and it would be fitted to every turbocharged engine. I know what you mean, but as i understand it an engine breaths in the same volume of air regardless of boost. A 3 litre engine is going to breath in approximately 3litres of air every 2 revolutions. How many pounds of air is that? That depends on the pressure and temperature of the air in the intake manifold. But the volume is always 3 litres every 2 rpm. If the oceanliner turbo is pushing out more air, wheres it going to go?? its going to start building up against all the other air already waiting to get into the engine, therefore the boost pressure is going to go up, so if the big turbo is flowing more air than how can boost be the same as the one flowing less air? Different compressor wheels flow different amounts of air yes, but at the same boost level? If you can find me a reliable source that states that fact ill be happy to believe it. 1 size of turbo is never fitted to all engines because 1 size of turbo isnt efficient for all sizes of engines. Some original photos have not been recovered yet.

Spool up, So if you compare a large turbo against a small turbo both at the same boost levels the performance will be the same? provided both turbos have no issues of producing the set level efficiently throughout the rev range? EG: T03 will show the same performance as a GT35/40 if both are set at 10psi? I'd of thought the same but it doesn't. From dyno sheets I have seen the larger turbos show higher horsepower even at lower boost. I understand a larger turbo will flow more air but I thought measuring boost pressure is how we determin how much air we enter into an engine. So I dont understand how 10psi can be different between the turbos. Obviously it does but I am too confused to comprehend it lol. I take it the below statement is the answer to my question then? Quote: Originally Posted by Spool-Up The difference in power comes from other things. A bigger turbo will cause less backpressure in the exhaust and therefore more power. A bigger turbo will compress the air more efficiently and therefore will heat the air LESS than a smaller turbo. Cooler air is denser and has more molecules in it per unit of volume, so more air is going into the engine, making more power.

Quote: Originally Posted by Spool-Up 1 size of turbo is never fitted to all engines because 1 size of turbo isnt efficient for all sizes of engines. tell me the reason behind that statement and you will have the answer your dilemma

spool up i suggest u stop trying to sound educated for a minute and have a think about what your saying... just because the 2 turbos are running the same PSI, they are not going to make the same power...

Quote: Originally Posted by INMATE Spool up, So if you compare a large turbo against a small turbo both at the same boost levels the performance will be the same? provided both turbos have no issues of producing the set level efficiently throughout the rev range? EG: T03 will show the same performance as a GT35/40 if both are set at 10psi? I'd of thought the same but it doesn't. From dyno sheets I have seen the larger turbos show higher horsepower even at lower boost. I understand a larger turbo will flow more air but I thought measuring boost pressure is how we determin how much air we enter into an engine. So I dont understand how 10psi can be different between the turbos. Obviously it does but I am too confused to comprehend it lol. I take it the below statement is the answer to my question then? No, 2 different turbos both set at 10psi will not give the same performance. Boost pressure AND boost temperature are how we work out how much air is going into an engine. What im saying is that assuming boost temperature was constant, yes a gt35/40 set at 10psi will give more power than a to3 set at 10psi but its NOT because more air is going into the engine because the exact same amount of air is going in. For example, say i had a stock vlt running 7psi and i then upgrade to a bigger turbo but still running 7psi, if the intake temperature stays the same then the same amount of air is still going into the cylinder each intake stroke, and i dont have to get it tuned etc, but its still probably going to make more power. DUZ-360 theres probably a hundred reasons why different turbos are more efficient than others for a given application, how much air flow its capable of is just one of them. And no [SLY.747] im not saying that if 2 turbos are running the same PSI, they are going to make the same power... I know this... The debate is about the reason why 2 different turbos at same boost level make different power. DUZ-360 is saying its because a bigger turbo is pumping more air into the engine at a given boost level, and im saying its not, assuming intake temps remain constant.

no im saying at the same boost they will both have different temps and therefore different air density. the point you make about the same amount of air going in is incorrect because of this.

spool-up, i think what duz is trying to say is it is dependant on how much air can actually be forced into the motor as the intake is opened ie the flow of the air, which is measured in units of volume/time. picture this, 2 large groups of people trying to fit through 2 doors that open and close every 10 seconds (ie a constant time like the intake valve for this case). both groups of people have the same density (pressure), however the people in group 1 are walking (low flow) while the people in group 2 are running (high flow). in that ten second interval, which situation is going to result in more people making it through the door, the group with larger flow or the group with lower flow? so pretty much, a larger turbo will be forcing the air in at a greater velocity than a smaller turbo, and at the same pressures, the bigger turbo will result in a larger volume of air passing a point per unit time.

Quote: Originally Posted by duz360 no im saying at the same boost they will both have different temps and therefore different air density. the point you make about the same amount of air going in is incorrect because of this. Well then ud be correct Im really anal and rely on hard facts and when you say stuff like "more flow" it makes me wonder what you actually mean by that. Look what nukz had just said, thats exactly what im arguing against. Sorry Nukz, but your wrong. The same volume of air goes into an engine, you cant force in more "volume" but you can force in more mass, (i.e pounds) I suggest reading some info on this link. http://www.gnttype.org/techarea/turbo/turboflow.html Oh and when i made the point about same amount of air going in i said at constant temperature. Some original photos have not been recovered yet.

the facts are the turbo x and turbo y (both of different size) will never run the same psi at the same outlet temps and therefore will never make the same power at the same boost levels

but wouldnt a larger compressor wheel have a higher compression ratio of the air than a smaller one, therefore more mass per unit volume, therefore more air particles getting into the motor the reason a bigger turbo will produce higher outlet temps is due to the fact that it has a higher air compression ratio, which obviously generates more heat as there is greater friction between particles