Turbo compressor sizing
Discussion
Pros/con... thoughts. 2 liter turbo engine, MPFI.
Choice between; T04E w/2.75" inlet... 2" outlet or same compressor w/4" inlet... 2" outlet.
How does the TO4S compressor, w/4" inlet... 2.5" outlet, compare against the above?
These are to be used with a turbine a/r of .64.
Thanks for your thoughts/ideas.
Alan
Choice between; T04E w/2.75" inlet... 2" outlet or same compressor w/4" inlet... 2" outlet.
How does the TO4S compressor, w/4" inlet... 2.5" outlet, compare against the above?
These are to be used with a turbine a/r of .64.
Thanks for your thoughts/ideas.
Alan
Stevieturbo... yes i'm aware of this.I wondered if there was/is any relationship between a turbos ability to draw air, with more velocity thru the smaller inlet, at the expense of some topend power loss. Would seem that as the engine takes its "gulp of air', it would be easier thru the smaller inlet.
Of course at the upper rpm range(s) the larger would be more efficient, but the engine doesn't run in that range for prolonged periods of time.
Kind of like airboxes that are very small, and offer there own form of restriction/ power loss.
Alan
Of course at the upper rpm range(s) the larger would be more efficient, but the engine doesn't run in that range for prolonged periods of time.
Kind of like airboxes that are very small, and offer there own form of restriction/ power loss.
Alan
Actually what i'm trying to determine is wether the different size inlet(s) of the compressors, has any adverse effect on the actual air supply to the compressor. I know the compressor has enough flow to support the required hp necessary, but was concerned that the ductwork might be lacking. Realizing of course that the air in the ductwork can only be replaced at atmos pressure.
Thanks Alan
Thanks Alan
I would doubt the size of ducting has much effect.
You could find a turbo with a 4 inch inlet that flowed less than one with a 3" inlet.
The 4" one will probably reduce down to a smaller compressor wheel anyway, so the 4" bit is irrelevant. its just how it was cast, and the same casting probably does a few turbos.
I recently helped build a Subaru engine, with a 3" inlet, and 2" outlet, yet its rated at 680bhp.
So far its working quite well, although maybe only making about 500bhp.
You could find a turbo with a 4 inch inlet that flowed less than one with a 3" inlet.
The 4" one will probably reduce down to a smaller compressor wheel anyway, so the 4" bit is irrelevant. its just how it was cast, and the same casting probably does a few turbos.
I recently helped build a Subaru engine, with a 3" inlet, and 2" outlet, yet its rated at 680bhp.
So far its working quite well, although maybe only making about 500bhp.
so why has nobody even talked about the diffuser,because as you all know the compressor impeller does NOT on its own increase pressure,it's half and half,the math's involved WILL fill a phone book so i shake the hand of the man who knows fluid mechanics this well,ive been building and runing model jet engines using centrifugal compressors and radial inflow turbines for 12-13 years and still havent scratched the surface of it yet,the turbo charger is an engine,thats why we get an increase in power you have two engines under the bonnet,
T03-T01 is the stagnation temperature rise across the whole compressor,so we do have a pressure increase here due to the diffuser basically cloging up the comp wheel,now the hot compressed air will enter the diffuser which will increase velocity and lower pressure,upon exiting the diffuser an even higher pressure will be obtained in diff housing,we havent talked about the torque required to drive the compressor and thats another story and can go way back to cam timing and design before we get to the turbine.
T03-T01 is the stagnation temperature rise across the whole compressor,so we do have a pressure increase here due to the diffuser basically cloging up the comp wheel,now the hot compressed air will enter the diffuser which will increase velocity and lower pressure,upon exiting the diffuser an even higher pressure will be obtained in diff housing,we havent talked about the torque required to drive the compressor and thats another story and can go way back to cam timing and design before we get to the turbine.
If you are using a T04 on a 2.0 litre engine then you are clearly after big power. A T3 will run an engine up to around 350 bhp, then be restricted in the air it can flow.
If you want to make big power on a T4 you need to remove restrictions. But with a lower A/R you get reduced lag if you are in a no power zone transitioning into a high power one.
Bottom line is this - if you want ultimate power then bigger is better. A T4 with an A/R of 1.0 can make a 2.0 engine deliver 600 bhp based on what people manage with Cosworth YB series engines.
If you want driveability then you need to come down on the A/R and then desize it.
The only way to really understand the effect is to speak to some tuners who have tried all the iterations and then decide what you are after. Broadly speaking it is better to sacrifice a small amount of top end power if you can avoid having to wait for the turbo to spool up.
You also want to invest in an anti lag system.
If you want to make big power on a T4 you need to remove restrictions. But with a lower A/R you get reduced lag if you are in a no power zone transitioning into a high power one.
Bottom line is this - if you want ultimate power then bigger is better. A T4 with an A/R of 1.0 can make a 2.0 engine deliver 600 bhp based on what people manage with Cosworth YB series engines.
If you want driveability then you need to come down on the A/R and then desize it.
The only way to really understand the effect is to speak to some tuners who have tried all the iterations and then decide what you are after. Broadly speaking it is better to sacrifice a small amount of top end power if you can avoid having to wait for the turbo to spool up.
You also want to invest in an anti lag system.
Unless you are in competition, and have loads of money to replace turbos, you do not want anti-lag.
The precision turbos GT35 rated at 680 to the 2.33 Subaru isnt that laggy. It makes full boost by 4000, but makes very usable power and boost from 3000rpm, and thats a big blower.
Its also fairly compact as I said, with a 3" inlet and 2" outlet. Smaller in general than some similar rated turbos.
The days are gone, where a big turbo means big lag. With modern turbos you really can have your cake and eat it.
The precision turbos GT35 rated at 680 to the 2.33 Subaru isnt that laggy. It makes full boost by 4000, but makes very usable power and boost from 3000rpm, and thats a big blower.
Its also fairly compact as I said, with a 3" inlet and 2" outlet. Smaller in general than some similar rated turbos.
The days are gone, where a big turbo means big lag. With modern turbos you really can have your cake and eat it.
dilbert said:Hi dilbert, I’m not exactly a self-proclaimed expert on fluid dynamics but here it goes.
Surely this is about two factors......
Absolute flow rate, and turbine "gain".
I know nothing really, but I'd start by working out the required flow rate, and required potential boost pressure at the rev limit.
No?
He wants the maximum boost the car produces to be made at the lowest possible engine speed while not allowing the turbocharger to spin to fast when running the engine at a high crankshaft rotational speeds. Over boosting the engine will not be a problem because he undoubtedly has a valve that releases pressure in the manifold. This would be easy enough except that he also wants the geometrically smallest, most efficient, turbine available because he wants the kinetic energy in the turbine to be minimal (KE = ½ Moment of inertia * Angular speed^2) – We are talking about a sophisticated windmill that runs up to 150,000 RPM (No error with the zeros). I think you will find that a turbocharger would turn at quite a low speed using just ordinary exhaust gas at air temperature to turn it, most of the energy is gained through the thermal gradient that exists between the engine and the outside world.
His main problem of the restriction he places on the inlet/outlet to his turbocharger is one that really needs to be analysed using sophisticated computer programs. If the inlet is to small it will allow a build up of backpressure between the engine and the turbocharger, particularly at high engine speeds, which will cause poor running. On the other hand if the turbine inlet is too large he will not be extracting all the potential energy in the exhaust gasses (particularly problematic at low engine speeds) and he will not gain full “boost” until he revs the engine (The infamous turbocharger lag). Additional problems he will encounter are things like making sure the turbocharger is not subjected to excessive temperatures (beyond manufacturers specifications – usually around 1100 degrees centigrade, often turbocharged engines are left to “run off” after use so that oil cools the turbocharger, rapid changes in temperature often cause thermal stress/strain which would damage his turbocharger, if not immediately then over time with use), the fit of the housing compared to the turbine blades as to bigger gap will allow exhaust gasses to escape and to smaller gap may allow the turbine to rotate to fast, the volume of the intake/exhaust manifolds as both the intake air and exhaust gasses are readily compressible he wants the minimum volume (reducing lag) while not adversely effecting the flow characteristics of his intake manifold as to cause turbulent flow and he will want to place the turbine as close to the inlet and exhaust as possible (to reduce the intake volume) without allowing the heat of the turbocharger housing to penetrate the intake manifold as this will heat the air inside leading to earlier detonation and hence less power produced at high RPM.
To avoid the said problem about running the turbine above it’s designed rotational speed most cars are equipped with a bypass that allows excess gas volume out of the section of pipe before it gets to the turbocharger reducing the volume of air passing through the turbocharger when the control system (now largely computer controlled, older models used more crude methods) senses the exhaust gas pressure/flow rate/temperature will exceed that of the turbocharger design.
He has probably had extensive modification to his oil system to allow for the turbocharger as it creates sensational amounts of heat, some people have a completely separate system for this alone. It’s taken as standard now I think that the turbocharger has an electric oil pump that continues to pump oil through the turbocharger so that the oil inside the turbocharger does not go stagnant and “coke” which will reduce turbine performance.
Any way I’m probably boring the socks off you all now so I’ll leave it at this, turbochargers are extremely complex with many dynamic variables that need to be considered in order for you to get the best power output per $ and to avoid extensive damage to the engine and turbocharger. It’s 75% science, 20% luck and 5% an art. If any one has any corrections, questions or comments feel free to ask.
Boosted LS1 said:
Good post Speedy. Turbocharger matching needn't be to complicated, so long as you do a few simple calcs you will be in the right ball park.
Boosted.
thong said:I know one (possibly two) people who could, but they work at a very high rate of pay. Some of those fancy new CAD programs can do all the hard work for you (Pro-Engineer, Solid works etc) which would probably be the best option.
math's involved WILL fill a phone book so i shake the hand of the man who knows fluid mechanics this well
Best bet is do the flow calcs for your engine and power goals, learn to read compressor maps (easy, dont be intimidated) and then select your turbo accordingly - try to find others that have done similar setups on your engine and follow that design IF it worked.
Ive just fitted a pair of T34's to a 5.7 V8 recently, and the design seems to be working SO FAR, but there's still a long way to go. Mainly getting a gearbox to survive is proving more difficult right now.
Read the Great Ape Racing Paper, link on my site:
www.mez.co.uk/turbo1.html
Hope that helps,
Eliot.
Ive just fitted a pair of T34's to a 5.7 V8 recently, and the design seems to be working SO FAR, but there's still a long way to go. Mainly getting a gearbox to survive is proving more difficult right now.
Read the Great Ape Racing Paper, link on my site:
www.mez.co.uk/turbo1.html
Hope that helps,
Eliot.
speedy_thrills said:
Surely this is about two factors......
Absolute flow rate, and turbine "gain".
I know nothing really, but I'd start by working out the required flow rate, and required potential boost pressure at the rev limit.
No?
Hi dilbert, I’m not exactly a self-proclaimed expert on fluid dynamics but here it goes.
He wants the maximum boost the car produces to be made at the lowest possible engine speed while not allowing the turbocharger to spin to fast when running the engine at a high crankshaft rotational speeds. Over boosting the engine will not be a problem because he undoubtedly has a valve that releases pressure in the manifold. This would be easy enough except that he also wants the geometrically smallest, most efficient, turbine available because he wants the kinetic energy in the turbine to be minimal (KE = ½ Moment of inertia * Angular speed^2) – We are talking about a sophisticated windmill that runs up to 150,000 RPM (No error with the zeros). I think you will find that a turbocharger would turn at quite a low speed using just ordinary exhaust gas at air temperature to turn it, most of the energy is gained through the thermal gradient that exists between the engine and the outside world.
His main problem of the restriction he places on the inlet/outlet to his turbocharger is one that really needs to be analysed using sophisticated computer programs. If the inlet is to small it will allow a build up of backpressure between the engine and the turbocharger, particularly at high engine speeds, which will cause poor running. On the other hand if the turbine inlet is too large he will not be extracting all the potential energy in the exhaust gasses (particularly problematic at low engine speeds) and he will not gain full “boost” until he revs the engine (The infamous turbocharger lag). Additional problems he will encounter are things like making sure the turbocharger is not subjected to excessive temperatures (beyond manufacturers specifications – usually around 1100 degrees centigrade, often turbocharged engines are left to “run off” after use so that oil cools the turbocharger, rapid changes in temperature often cause thermal stress/strain which would damage his turbocharger, if not immediately then over time with use), the fit of the housing compared to the turbine blades as to bigger gap will allow exhaust gasses to escape and to smaller gap may allow the turbine to rotate to fast, the volume of the intake/exhaust manifolds as both the intake air and exhaust gasses are readily compressible he wants the minimum volume (reducing lag) while not adversely effecting the flow characteristics of his intake manifold as to cause turbulent flow and he will want to place the turbine as close to the inlet and exhaust as possible (to reduce the intake volume) without allowing the heat of the turbocharger housing to penetrate the intake manifold as this will heat the air inside leading to earlier detonation and hence less power produced at high RPM.
To avoid the said problem about running the turbine above it’s designed rotational speed most cars are equipped with a bypass that allows excess gas volume out of the section of pipe before it gets to the turbocharger reducing the volume of air passing through the turbocharger when the control system (now largely computer controlled, older models used more crude methods) senses the exhaust gas pressure/flow rate/temperature will exceed that of the turbocharger design.
He has probably had extensive modification to his oil system to allow for the turbocharger as it creates sensational amounts of heat, some people have a completely separate system for this alone. It’s taken as standard now I think that the turbocharger has an electric oil pump that continues to pump oil through the turbocharger so that the oil inside the turbocharger does not go stagnant and “coke” which will reduce turbine performance.
Any way I’m probably boring the socks off you all now so I’ll leave it at this, turbochargers are extremely complex with many dynamic variables that need to be considered in order for you to get the best power output per $ and to avoid extensive damage to the engine and turbocharger. It’s 75% science, 20% luck and 5% an art. If any one has any corrections, questions or comments feel free to ask.
Surely a considerable number of these issues are tied up in the manufacture of the of the turbo compressor it's self.
Most people, I'd have thought, wouldn't make their own, they'd likely buy COTS. I'd guess that a sizable issue is the difficulty of fabricating decent blisks, let alone the issues of calculating out all of the environmental, and functional concerns.
You talk much of restrictions, but is it not the case that the inlet (turbine or compressor) is always going to be larger than the outlet? Presumably this allows the pressure/velocity ratio to remain approximately constant in a dynamic fluid?
Maybe not?
dilbert said:Yes but there need not be an aversion to modification of off-the-shelf products to better suit engine characteristics, a practice widely carried out I believe by companies that build engines.
Surely a considerable number of these issues are tied up in the manufacture of the of the turbo compressor it's self. Most people, I'd have thought, wouldn't make their own, they'd likely buy COTS.
dilbert said:Absolutely, building turbines is well beyond the capability of most people. It would cost millions to acquire the equipment to make it possible and much knowledge of CNC machines.
I'd guess that a sizable issue is the difficulty of fabricating decent blisks, let alone the issues of calculating out all of the environmental, and functional concerns.
I think it’s important to distinguish between the two types of people who install turbochargers in their cars (these are extreme gross over simplifications and highly stereotypical):
Type 1. Install turbochargers because they like the little bit of kick at the end of the rev range, the hissing sound of the blow off valve and watching the pressure gauge fly through the roof. These people are most likely to be seen with a bean can stuck on the end of the exhaust and radio on full blast in town centers.
Type 2. People who actually want performance from their engines. They are often found on back roads having fun or at a racetrack. They will usually drive in quite a sedate and sensible manner while in town, rather like most PHers I suspect.
Type 1. People really would not care less about selecting correct turbocharger size or modification or existing turbine to suit their driving characteristics. Type 2. People value their machines and want to get every bit of performance from them so they can enjoy the thrills of fast but largely sensible driving.
When I talk about turbocharger modification therefore I refer to Type 2. people because I assume this is most relevant to PHers.
dilbert said:You are correct. Generally a fluid traveling through a contracting pipe will travel at a higher velocity and a fluid traveling through a pipe of expanding diameter will have a decreased fluid velocity (Q=Velocity*Area - for an ideal fluid). However to translate that to the actual motion of a turbine (or blisk as you refer to it) is slightly more complicated. In very general terms the turbine extracts kinetic energy from the gas. This is done through the pressure being exerted on the blades, indeed the average pressure acting upon each blade. Not just the overall pressure however but the effective center the pressure acts upon. To explain that better if the center of pressure is acting upon the outside geometry (furthest from the axis the turbocharger revolves around) of series of turbocharger blades the force will be better able accelerate the turbine – we can prove this using moments (torque as it’s often referred to around a movable axis) about the turbine center – however if we consider the velocity of the fluid to be a constant the turbine will accelerate well but not reach a very high velocity, I suppose this is best described as the fluid having most the best mechanical leverage around the axis of the turbine. However the reverse of this situation where the center of pressure acts at a point on the turbine blades that is very close to the axis of rotation the gas will no longer be able to accelerate the turbine as well, however the velocity of the turbine will be much higher.
You talk much of restrictions, but is it not the case that the inlet (turbine or compressor) is always going to be larger than the outlet? Presumably this allows the pressure/velocity ratio to remain approximately constant in a dynamic fluid?
Maybe not?
To put this in simple terms imagine the center of pressure is you winding a handle on a sailing yacht to raise a sail. If you have a very long handle you will easily raise the sail but it will take a lot of time as your hand will have to travel a large distance and there is only so fast you can wind (In fluid terms Q is set as a constant). However if the handle is shortened you will be able to wind much faster but you will not have the same amount of mechanical leverage over the sail so you will have to push harder to move the sail upwards.
Incidentally as we are on the subject this is how variable geometry turbochargers work, they have a nozzle that can vary the effective center of pressure over the blade to an optimum value so your turbocharger works optimally throughout the range of velocities it has to operate.
In general terms you are correct that having a larger inlet than exit port on a turbocharger will increase the velocity. However we do not live in an ideal world and in fact inlet size will make quite a lot of difference due to the dynamic effects some of which are described above.
If I’m wrong on any of the above feel free to correct me. I’m still a student and by no means know it all.
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