Same boost different turbo\'s...

[Archbish]

The twins heat up the incoming air more than the larger single does

That suggests Water Injection, or a nitrous spray onto the intercooler would result in similar hp??  but even Yorkies most powerful stock twin UK car is struggling at 400hp with daft low temps, whereas single turbo\'s are breaching this with ease at similar or lower boost.  Surely this must be a result of \'post-engine\' items, as the boost forced into the engine is at an identical level, with very similar boost temps?

[Glenn Butcher]

Originally posted by Carl
Hi All,
If the single and twins are on an identical  highish boost,say 12 psi, then answer is simple.(This is just for the sake of argument)

Carl - you are talking standard FD Twins I\'m assuming?

The exhaust housing must play a huge part in this also, as Bish has mentioned above?  On that theory Carl - having a VERY large compressor housing and a standard exhaust housing may make you a little more power.  But large of both with make a stack more...

Would this comment following be correct?...

The smaller the exhaust housing on a turbo, the more back pressure in the engine as the turbine housing/wheel cannot extract the gasses fast enough.  Therefore the harder it is to force more air through from the intake side, and as the turbine wheel in the exhaust housing is driving the compressor - it wouldn\'t be able to do this efficiently because of the exhaust restriction.

[Cycaduk]

PV=nRT

R here is the gas constant.
Reynolds number is a fudge factor used by chemical engineers to determine when fluid flow will change from laminar to turbulent.

[Carl]

Hi Glenn,
Of course the compressors are not the only complete factor,and the turbines and their sizing has much to answer for in this discussion.
But as you will see from my words quoted below I was trying to simplify the point and not go in to the other factors too much.
If we were then fueling,intercooler,intercooler piping,water injection,air temp ambient,type of fuel,porting,state of the engine int terms of condition like is it fresh or tired,and much much more come into the picture,I just did not want to go there.
Kind regards
Carl

Originally posted by Carl
Hi All,


There are many other parameters, such as compressor maps, that come in to it but that is the simple answer as to why the right single turbo can make more power at the same or sometimes even less boost.

Kind regards
Carl;)

[BlitzBoy]

My Brain is fried reading this lol:D

[scooby_si]

tell me bout it http://www.smileycentral.com/?partner=ZSzeb008\' target=\'_blank\'>http://smileys.smileycentral.com/cat/3/3_3_103.gif\' border=0> but is good stuff....:god
Si

[Schtoo]

I kinda thunk that using a bigger single turbo over stock twins (on anything) would have the following benefits.

1. That the plumbing for a single will not be the same as an OEM setup, and the OEM setup has to allow for such niggling things as reliability, economy (hah!), emissions, and packaging. An aftermarket setup can be as big and bad as the clown paying for it wants it to be. The \'clown\' just wants neddies and is not overly concerned with other things, are they? So all those things that a factory setup must attain in some way can be altered or removed for best performance. Short version: OEM\'s are always like a garden hose, good stuff is like a sewer pipe. Big pipe flows better (most of the time).

2. The smaller turbos will spool up quickly, and as such can\'t keep spinning up for as long as a larger turbo could at a given RPM/gas flow. For example, the twins may be at max RPM at say, 5500 engine RPM, where the bigger single is only at 2/3 of max RPM at the same engine rpm. They are both flowing about the same amount of gas, the single just has more ability to move it in and out. It\'s why an undersized turbo will spin up fast, but the thing will run out of boost pressure at higher engine RPMs. It just can\'t keep spinning forever.

3. And while we are talking about spinning turbos, those smaller turbos are going to make the air turn lots of corners through small pipes, the smaller compressors are going to chop the air up a heck of alot and the impellors are going to do the same trick on the way out. All that bending, chopping and squeezing reduces possible flow, raises temperatures and generally make a pest of itself. A larger turbo won\'t smash and bash the air so much and it will have larger pipes to send it\'s gas through so it\'s doing about the same work but it\'s being kinder to the gas. Good things happen to kind folks.

4. Finally, the factory setup will try to meet the needs of all owners as best as it can. Some will want lotsa bottom end, some will want a healthy top end, some prefer a well rounded package. The factory will attempt to keep everyone happy to some extent. With something aftermarket, you can choose what to sacrifice and by how much. Those nutters running 1,000bhp Skylines think they have anything resembling driveability? Of course they don\'t, their engines are all top end and who gives a rodents bottom about the, well, bottom end. Of course, you could squeeze 1,000bhp out of a 13b with the factory turbos but you would need some pretty interesting things to make it happen. Like a track on Antarctica, prolly neat Toluene for fuel and liquid nitrogen as coolant. And deep pockets because the thing would pop PDQ. :p

I hope that\'s readable AND understandable.

The whole turbo thing is a mixture of science, art and black magic, all doing the high wire act above a crocodile infested desert. It\'s also why guys with no official training get good results, and why folks with a bazillion letters after their name still can\'t get it right.

Oh yeah, if you want big power, lock the wastegate shut. Works really REALLY well and makes great smoke clouds soon afterwards...

[MONSTER]

Basically, a larger turbo doesn\'t have to work as hard to produce say 0.9BAR as a couple of smaller ones do.

The flow is far better through the bigger turbo due to the exhaust gases being able to escape more easily from the engine, which as mentioned already cuts down operating temperatures in the engine and improves efficiency - this is why we fit free flow exhausts.

The maximum power produced by an engine is totally dependant on how easily (or efficiently is probably better) air can be drawn in and expelled.  The more air (& fuel) you can process per minute = the more power that will be produced.

Since the single turbo can flow a much greater mass of air  more easily it doesn\'t heat up the gases as much - which is effectively what Ross said - at the same pressure the air is denser from the big turbo giving you a bigger bang and the exhaust gases can get away more quickly as there isn\'t the same bottle-neck as with the twins.

Efficiency is the key!!!!!:D

[Cycaduk]

Please explain why the two smaller turbos heat the air up more than one large one?  all the sensible heat is going to come from the compression, plus a small amount conducted over by the turbo from the exhaust gases. Also note that in the PV=nRT equation, T is in absolute units, K, thus air at 27 Deg C will be about 300K; air at 87 Deg C will be at 360 K, representing a 20% reduction in mass for the higher temperature if pressure and volume are the same.


I believe the opinions expressed along the lines of single turbos having bigger exhaust pipes/bigger inlets are correct. Physics/chemical engineering shows that mass flow of a gas through a pipe is dependent on the fourth power of the radius of the pipe (ie a 2inch pipe will flow 16 times the amount of gas  as a 1 inch pipe.)  However, bends, especially sharp ones restrict the flow much more than a slightly smaller diameter.

[MONSTER]

Physics/chemical engineering shows that mass flow of a gas through a pipe is dependent on the fourth power of the radius of the pipe (ie a 2inch pipe will flow 16 times the amount of gas as a 1 inch pipe.)

Exactly,  so say the outlet of the large turbo is 2 inches and each of the small turbo\'s is 1 inch - does this not mean that the large one is capable of flowing that much more gas?
As a result the compression of the gas in each of the smaller turbos is that much greater and  the temperature of that gas is increased proportionally.

Also, I may be wide of the mark here, but I would assume that two turbos working near their peak efficiency would generate a lot more heat mechanically than one that is well within its limits and easily flowing the same mass of gases.

[Carl]

The smaller turbo(Taking one individualy) when pushed outside of its optimum range(Compressor map) to make higher than stock boost does the following..............
The compressor starts to agitate the air more creating more turbulance than at lower boost settings and as a result it becomes less efficient.The compressor thus starts to heat up the air more instead of moving it smoothly through itself.
A larger single turbo compressor can maintain a smoother air delivery for higher boost settings by virtue of its not having to work so hard which means less heating up of the air,of course when the turbo is asked to work outside of it\'s optimum compressor map range then it too starts to agitate the air creating turbulance and heats it up more(Albeit at higher boost than smaller turbo\'s).
Kind regards
Carl

[bobster]

Originally posted by Archbish
OK - this is where I look even dumber than usual...

How can 0.7 bar of boost on a T78 produce more horsepower than 0.9 bar of boost on sequentials.  The manifold pressure is higher in the second case, yet considerably more power seems to be available from the first.  Surely pressure is pressure, irrespective of source?

This has been confusing me for ages...

Cheers

OJ

Okay ignore all the technical explanations.....In terms you understand

It costs more so it must be better.

[Andyp]

I was gonna suggets it was magic