Turbos & intercooling

[Goldsburg]

OK, yes you can increase RPM to increase air flow, same on any engine, and I whole heartedly agree that it is more efficient and better power with the ATT, but it is the same fixed volume when that exhaust port closes. However now you could reach higher RPMs safely and efficiently, because of the lower pressure differential, boost and backpressure both.

If the scavenge process, or exhaust stroke weren't working correctly before at high RPM due to high backpressure, then that might be a way to slightly increase the volume of fresh air in the cylinder, but its not like youre gettting even a 5% increase there, not like you saying it is capable of twice the CFM at the same PSI.

And yes if you maintain lower IATs the air mass is increased, but not flow, same flow but more dense, which is also a bug imporvement. It would be better to just say you get more air mass at lower pressure.

Buddy -

You are on the right track. It is always best to think of a turbo charger in terms of a "mass flow" device. That way, all pertinent variables are taken into account. Further to that point, I never like how people talk about volumetric efficiencies "greater than 100%" when turbo or supercharging. My engineering education just prevents me from accepting that vernacular.

Beyond that, superchargers or turbochargers increase charge density (not volume). A vessel (cylinder) can NEVER be filled greater than 100%, especially when the filling process is being throttled by a poppet valve.

Regards,

 

[gmctd]

Gas flowrate is Q = PT - flow increases as Pressure increases, increases as Temperature increases

Gas Volume is V = T/P - volume increases as Temp increases, decreases as Press increases

Volume flowrate is Q = Velocity + Area

Which is why flowrate in CFM is confusing, as it is also dependent on velocity of a compressible fluid thru a system - a substance is defined as fluid when it can occupy a container of any shape without deforming the container - and don't gimme no squat about no balloons, neither - that would be any substance put in a container alters the shape of the container, such as food and yer wife, eh!

Mass is fluid density at standard barometric pressure and temperature, 14.69psia and 60*F x weight per cuft x #cuft per lb x desired unit of weight = 16 for lbs, x time in seconds per desired unit of time = 60 for min, 3600 for hour

 

[ak diesel driver]

how about some examples of these equation so I can wrap my feeble brain around them.

 

[schiker]

Would wiring in a MAF sensor after the turbo show a difference in amount of air (CFM) produced between the two turbos?....

Yes, Or you could measure at the intake and the mass flow is higher. Its higher through the intake, engine, and exhaust - measured anywhere from the inlet to the tailpipe with the ATT turbo vs the GM-X. What goes in must come out.

But if you say CFM like others have said its confussing unless you tie it back to SCFM (standard conditions cubic feet per minute).

Its actually hard to measure air flow because its compressible. Even when its not compressed it can take a lot of data points and understanding. Thats why the MAF is a honeycomb looking device its to condition the flow and get a better measurement. Then its still a calculated avg mostly.

 

[davo727]

So what kind of results do you guys think would happen with 2 GM turbos on a street 6.5 in a 92 Dually 5 speed with mechanical IP.

I realize custom headers are required to run a turbo on each bank.

 

[buddy]

Are you still trying to say you can get more CFM at a lower PSI? Now the points we are trying to make are getting confusing

I'm still sticking to its impossible to increase CFM while reducing pressure.

The reduction of backpressure is probably the greatest factor, which would explain why it might seem like the intercooler caused negative affects and Heath's landcruiser gets 30MPG. The Intercooler increased the volume and created turbulence with bends and it required the turbo to work more, build more backpressure, to create the same amount of boost pressure. Normally a good enough trade off for more dense air, but with this efficient turbo became a deteriment or at least a wash for benefit.

Whos got a pitot tube to play with?

 

[buddy]

2 GM turbos would help if you prescribe to the idea that backpressure is the efficiency killer, since you can create more boost at lower backpressure with two, like Heath's truck.

 

[Matt Bachand]

. It would be better to just say you get more air mass at lower pressure.

Exactly.

More CFM @ Less PSI. NIcely put Buddy. I think you got it!

 

[Slim Shady]

2 GM turbos would help if you prescribe to the idea that backpressure is the efficiency killer, since you can create more boost at lower backpressure with two, like Heath's truck.

Back pressure is the killer here but we can only reduce it so much with a larger A/R rating then we need to make the turbine and compressor wheel more efficient. I think the ATT is a good all around turbo but it really shines towing a load. The lower rpm band did not suffer much if any and I think less stress on the motor at lower RPM is a good thing also, no lugging the motor.

 

[dirtfarmer629]

So what kind of results do you guys think would happen with 2 GM turbos on a street 6.5 in a 92 Dually 5 speed with mechanical IP.

I realize custom headers are required to run a turbo on each bank.

This is what i was thinking off doing when i got out of school running a twin turbo setup. Would two GM 8 turbos have alot of lag?

 

[buddy]

Exactly.

More CFM @ Less PSI. NIcely put Buddy. I think you got it!

Now youre just being facetious

 

[ercaduceus]

Bill did not share names, but did say several folks have asked about it, not sure from which site where the ATT has been discussed, some folks got downrite unpleasant. :nono:

That is unfortunate. I'm anxiously waiting to hear news but that is completely uncalled for.

 

[DennisG01]

Whos got a pitot tube to play with?

How would you plumb it into the system - sort of an odd shape, you know?

On the other hand, if you think you have a good idea I'll mail you one. I think I can find one sitting around the shop - if not, my cost on them is probably less than $5 - no biggie.

The ones I would have access to at the marina would look like this:

http://www.go2marine.com/product.do?no=65293F

 

[gmctd]

A pitot tube is easily accomplished - a straight tube inserted into ducting at 90* to the flowing plane gives static pressure indication - a pitot tube is inserted at 0* facing against flow direction to measure flowing pressure, so you would use a section of tubing with a 90* bend, inserted to occupy the direct center of the aluminum intake duct - or the exhaust pipe, if you're interested in exhaust pressure - or the radiator hose if you're interested in coolant pressure - or about a foot ahead of the nose of the vehicle (pressure wave) if you're interested in pressure vs velocity in mph - or the etc, etc

 

[ak diesel driver]

How do you guys think a belt driven supercharger would work. Some are just a belt driven turbo. I wonder if it would be an even tradeoff on efficency?

 

[tracy]

Superchargers/blowers are very inefficient, they can suck up to 1/3 of the total hp an engine can produce. Example: if a supercharged 6.5 put out 300hp at the flywheel the super charger can be robbing 130hp but stressing the engine like it was producing 430hp. In the case of the 6.5 with a relatively week bottom end, ouch!

 

[96TD]

One thing that seems to be somewhat left out of this discussion is air temperature. A couple of people have made reference to it, but then it hasn't gone anywhere.

You can get alot more air into the same space, with higher air pressure, or lower temperature.

A 1 liter container is going to contain exactly 1 liter of air. If the air is ice cold, you are going to have alot more air in that container than if the air was say at 500 degrees. (Still 1 liter, but more air molecules.)

Also, if you have that same container and the air in it is at 1# pressure, you are going to have alot more air in that same container if the air is at 100# pressure, but is at the same temperature.

So, on a turbocharged engine, air is getting pumped into the cylinders. You are getting more air into the engine because it is at a higher pressure.
If you run an intercooler, you are getting more air into that same cylinder at the same boost pressure, because it is cooler.

A more efficient turbo may not need an intercooler to achieve better results at the same boost pressure as a less efficient turbo. Because it can create this same boost pressure without heating the air up as much.

The reason that the ATT turbo does this is that it is obviously must be much more efficient than the GMX turbos, and generates alot less heat when making boost. That is why it doesn't need an intercooler.
An intercooler would help cram even more air into the cylinder, but it also is adding more piping into the system, creating lag, which is counter productive.

Now if I could only get the rest of my projects completed so that I could upgrade!!!!

 

[buddy]

:iagree:

Thank You I think you restated everything I have previously said, but in a single post

 

[96TD]

Yup, I did notice you were one of the few that brought temp into it. I just didn't see enough of it all put together, and I'm just waiting to leave work so I had time.

 

[ak diesel driver]

Superchargers/blowers are very inefficient, they can suck up to 1/3 of the total hp an engine can produce. Example: if a supercharged 6.5 put out 300hp at the flywheel the super charger can be robbing 130hp but stressing the engine like it was producing 430hp. In the case of the 6.5 with a relatively week bottom end, ouch!

I talked with a supercharger company (ATI) and told them about my idea about the belt driven superchager and the gentleman I talked with said that the losses from both turbos and superchargers was about the same until about the 350-400 hp range he said after that there was no ? that turbos started to become more efficient with the trade off being lag time.