Question, if boost is based on resistance to fill a cylinder, you have twin 70mm and 10lbs. say flowing 1000 cfm each at 5k. Boost guage says 10lbs. if you shut one turbo off will boost drop to 5 pounds, stay the same, or will second turbo have to spin twice as fast to make the 10 pounds of boost? Will twins that flow 2000 cfm total make more average power than a single that flows 2000 cfm due to less heat build up and less back pressure plus spool faster? Does the flow have to be the same before the power is the same? People say they run into trouble running pump gas around 16-18 pounds, if you have a single 75mm making 16lbs. and this is the limit could you make more power with twins at 10lbs. and not have detnation, just more flow. Trying to figure out when one will outperform two with the same cfm. If you got a s480 making 15lbs boost flowing 1500cfm vs. say twin 70mm making 12lbs. flowing 1600cfm total which is going to produce more hp and why?

 

My head hurts.

 

First if you shut one turbo "off" that bank would choke from backpressure and kill the power... Or if you freespun it, it would kill the turbo. if you didnt recirculate the exhaust gasses back onto the other turbo, yuo would only get half the energy, and might not have enough energy to spin the turbo to make that set boost pressure. but in a hypothetical world that you bypassed the turbo in question, and recirculate the exhaust pressure to the other turbo the system would equalize and the turbo would try to spin faster, to achieve set boost pressure.

But it wont so NO

Average... that relative to the RPM. Heat is energy, if backpressure is the same and output is the same... both systems are equal

WHA????

People say they run into trouble running pump gas around 16-18 pounds, if you have a single 75mm making 16lbs. and this is the limit could you make more power with twins at 10lbs. and not have detnation, just more flow. Trying to figure out when one will outperform two with the same cfm.

The twins in this equation is more efficient... and will flow more, however I dont see that much change happening on the same engine, as boost is just a measure of resistance, or what the engine will ingest... Same engine should have the same boost numbers for same CFM... I might be wrong on that but seems correct?

 

Sorry Disney, I guess what I'm trying to say 05 stang is that twins at say 10lbs. will make more power than a single of the same size at 15lbs. because of the volume of air going thru the twins vs. whats going thru the single, and the air going thru into the intake is not heated up as much as with the single which means more power correct? Plus less back pressure. Anyone understand what i'm asking?

 

Correct me if I'm wrong somebody but your intake air temps aren't relevant to having single or twins.

 

All else equal... total flow capabilities on a single vs twins, the only advantage twins have is the ability to mount the turbos close to the exhaust ports. The closer the turbine is to the exhaust ports the more responsive the turbos will be. (quicker spool)

 

Don't the twins also spool faster (with same flow capabilities and at same psi as the single) do to the smaller turbine housings, or is that negated since it has half the exhaust flow?
Interested since I'm debating twin ebay 57s vs one gt45.

 

It is negated since twins receive half the exhaust flow.

If you debating between twins and a single, consider upgrading in the future. Two turbos to sell two to buy and the maintenance, 2 wastegates...

 

Let me say it another way, when air is compressed more it is heated up more correct? (single at 15lbs. to make the same power twins will at 10lbs.) the colder the air going in the more power and less detenation prone correct? This is why I say you can get away with more on pump gas with twins if its not heating the intake charge as much as with a single to make the same power. All three turbos are the same size.

 

I don't understand why you keep comparing twins to single and changing the boost number. To keep it consistent for this discussion you would need to say 15# for both single or twins.

Now, that being said, the differences in efficiency of the two systems is highly dependent on the parts being used. I would say a very good and properly sized single at 15# would be better than over or under sized twins at the same 15#. The key here is to match the turbo to the combo it is feeding. If you have twins that are going to be way off the map to make the boost, then you're going to lose the power too.

I don't think you can absolutely state single > twins or vice versa.

 

Will 2 turbos at 10 lbs make the same power 1 will at 15lbs because of the VOLUME? All three being the same size. Like fuel injection and carb, on fuel injection you can run a smaller fuel line at higher pressure and make the same power as a carb with larger fuel line and less pressure.

 

"Mass Flow Rate". That is what were are debating here.

Andy Dorsett make a great post about this.:

This same principal works in this discussion. Once you get the air to the intake manifold, you have a constant system. Thus, the single at 15# > twins at 10# assuming both systems are sized to produce the same MASS FLOW.

 

OOOH AHHH!

 

Don't assume. Both systems are not sized to produce the same mass flow. 3 turbos all the same size. Will 2 of them at a lesser pressure make the same power as 1 of them at a higher pressure? Like if you had three fuel pumps all same size and same hose size and pumped two of them into one bucket with 10 pounds of fuel pressure and pumped the 3rd pump into a seperate bucket you would have to turn up the pressure of the 3rd pump higher than 10lbs. to fill the second bucket at the same rate as the first bucket which in turn heats up the fuel.

 

The point you seem to be missing is that the engine determines it's own volume flow rate. This doesn't change no matter how many turbos you throw at it, or what size, or what boost pressure. Boost pressure is simply a result of air molecules getting crammed in closer together, or in other words, the density rises.

The fuel pump analogy doesn't work because liquids are non-compressible fluids. The fuel molecules can't be crammed closer together.

 

So what your saying is 15lbs of boost wheither its a 58mm turbo or a 101mm turbo is 15lbs of boost and they will run the same? Will the compressed air coming out of both be of the same temperture? Still learning.

 

That's kind of what I'm saying, yes. There will be two other factors that can affect the way the engine would run in this instance, and the temperature is one of them. The answer to that can't be stated without knowing the full specifics of the turbos and engine in question. It would depend on where the engine falls on the respective compressor maps.

However the relevant point here is that if both turbos could make 15lbs on the same engine and the charge was intercooled down to the same temp before entering the engine, then yes, the mass flow will be very, very close with either turbo.

The other factor would be back pressure. The 101 would almost certainly have a much larger, free-er flowing turbine section and thus would show less back pressure than the 58. It would make more power due to this.

 

Now were getting somewhere, the charge coming out of the big boy is going to be cooler which is more dense which in turn doesnt take as much pressure to make the same power as with the pee wee., and as with twins you do not have heat on the incoming charge or the backpressure issue you would with one. Right? Take out the intercooler I'm talking blow thru without intercooler.

 

Which weights more a ton of feathers or a ton of lead? According to the post above by Mr Dorsett BOOST is BOOST. Regulardless of how its produced, OR regulardless of WHAT is producing it.
The fuel does not care what is going to make it detonate. It the equipment is wrong and you have super hot intake charge a 10psi (large turbo) and that is the limit of the fuel it will detonate.

 

That is what I'm saying with two the intake charge will not be as hot or as restrictive as one. Therefore you can run more boost before the intake charge reaches the det. point. Is 10 pounds of boost at 100 degrees equal to 10 pounds of boost at 32 degrees going into the engine?