Dumb Question

[2lazy]

Hi,

I have searched but couldn't find a straight answer.

when a rd26dett us pushing 1bar at the manifold does that mean that each turbo is making 0.5bar or

each turbo is making 1bar per 3 cylinders which gives 1bar total at the manifold?

[lachlanw]

do a search . there was a massive argument about this 2 months ago

both turbos make 1 bar

[2lazy]

I search, could someone give me the link?

[NXTIME]

If the turbos are running parrallel (like the RB26) then the boost is the same for each turbo ie 1 bar each.

[2lazy]

so that means that in total your boost guage will show 2 or 1bar?

[Guilt-Toy]

it makes me smile every time someone asks me this question. yes i have been asked this question a few times in the last 6 months.

[SiR_RB]

i would like to read the old topic about this also, anyone got the link lol

[PM-R33]

Here's one of the threads about it:

http://www.skylinesaustralia.com/forums/Gt...turbo+boost+add

Any logical person that knows a bit about physics realises that each pressure can not combine the way people are thinking.

Edited April 25, 2010 by PM-R33

[2lazy]

Thanks for the link, so 2 turbos are more efficient than one, great.

[Thelen]

The real question is, if you run a turbo + supercharge setup, what will the boost be

Forgot to say too, it isn't so much about how much boost the turbos make, it is more about how hard they WORK to make that. All things being equal, 2 turbos will only have roughly half as much work done on them to make the same boost, since the air FLOW is higher even though boost is the same.

Edited April 25, 2010 by Thelen

[2lazy]

^^^ well if the super is receiving air from the turbo it will be compressing compressed and pressurised air therefore e.g 2.5psia from the turbo compressor outlet into super inlet will give 5psia.... It would be like compound turbocharging, 40psi anyone?

If the super and turbo are receiving atmosphere air then if both run 12psi then manifold pressure should be 12psi??? not too sure on this one.

Edit: Let me make sure that im perfectly clear on this subject, if my sr20det made 200rwk at 1bar from a t28 will that mean that two t28's will make 400rwk at 1bar total?

Edited April 25, 2010 by 2lazy

[Adriano]

If 1 t28 on an sr20 makes 200rwkw, then 2 t28's on 2 sr20's make 400rwkw, now that'll do your head in

[D_Stirls]

in an ideal system they can flow 400kw of air together but whether the head will let them flow 400kw of air at 1 BAR is another story.

[paulr33]

manifold prussure, is exactly that, pressure in the manifold, or what we call "boost" when its past positive pressure or absolute pressure

where the pressure comes from is irrelevant, ie 1 turbo, 2 turbos, 3 turbos, supercharger and turbocharger etc

and pressure does not equal volume

this why 15psi on a stock turbo vs 15psi on a GT35R make different levels of power

[2lazy]

I understand that but on that link there are two arguments, one is that:-

two turbos making both 1bar will make half has much air as one turbo making 1bar(same turbo model as the twin), so they flow the same both twin or single. You will see 1bar on your boost gauge with both set ups but they make ruffly the same amount of hp.

The other argument:-

twin turbos both at 1bar will make 1bar of pressure at the manifold BUT it will flow twice as much air.

[MBS206]

I understand that but on that link there are two arguments, one is that:-

two turbos making both 1bar will make half has much air as one turbo making 1bar(same turbo model as the twin), so they flow the same both twin or single. You will see 1bar on your boost gauge with both set ups but they make ruffly the same amount of hp.

The other argument:-

twin turbos both at 1bar will make 1bar of pressure at the manifold BUT it will flow twice as much air.

You need to remember boost is a measure of restriction to air flow.

Keep everything at the same efficiency, increase air flow, boost will increase...

Hence two turbos at one bar combined flow as much air as one turbo at 1bar, making the same power...

[PM-R33]

Exactly, boost is a measure of restriction. It means the turbo(s) are pushing that much air, that the engine can't keep up taking it all in so it builds up and increases in pressure. (Think of blowing up a balloon). It is all about volume of airflow! Turbo(s) technically do not create "boost", they create heaps of airflow that as a result of being in an engine environment ends up being pressurised which is what we call "boost". Hence if you pop an intercooler pipe, no restriction, no boost in the intercooler pipes (theres a lot more that comes into play here but in general that's an easy way to think about it).

Edited April 26, 2010 by PM-R33

[Kwyjibo]

Exactly, boost is a measure of restriction. It means the turbo(s) are pushing that much air, that the engine can't keep up taking it all in so it builds up and increases in pressure. (Think of blowing up a balloon). It is all about volume of airflow! Turbo(s) technically do not create "boost", they create heaps of airflow that as a result of being in an engine environment ends up being pressurised which is what we call "boost". Hence if you pop an intercooler pipe, no restriction, no boost in the intercooler pipes (theres a lot more that comes into play here but in general that's an easy way to think about it).

That is the best way I've heard someone describe it and should assist people in understanding.

[sickr33]

pressure is constant but the flow/ volume of air doubles

[mad082]

pressure is constant but the flow/ volume of air doubles

not exactly. the possible volume of air doubles (free air delivery). once you put them into an enclosed system such as they are on an engine, and have the boost regulated by a wastegate measuring pressure (aka resistance), then you won't get double the airflow. your total airflow won't really change much because the things that are causing the restriction will still cause the same level of restriction whether you compress the air via 1 million mice blowing through straws or the worlds biggest turbo. there is a limit to how much extra air you can flow through the intake before you are going to hit the same restriction and i would guess that it isn't much more than with anything else.

"but people make more power with bigger turbos at the same pressure" is a common reply to that line of thinking, and i understand that, but how much of that is down to the bigger compressor on the turbo and how much is down to the fact that the exhaust flow is much higher and there is much less restriction on the exhaust side of the turbo? i'd say that a fair bit is on the exhaust side and not that much has to do with the bigger compressor (not saying that it doesn't play any part in it, but just not as much as people think).