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Performance related tech question...

P

poptopjr

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It is my understanding that the waste gate on a turbo helps control how much boost is applied (please correct me if i'm wrong). That being said, if the A-Team Turbo has no waste gate how is boost controled?
 
boost on the a team is merely a large enough drive turbine that the 6.5 can't produce enough heat to overdrive it.
 
A wastegate dumps drive pressure that bypasses the turbo. This is how a wastegate controls boost, by limiting the turbo's drive energy to prevent overboost on a small turbine sized to spool quickly. As AK said, the turbine size on the ATT is so large that the 6.5 can only generate about enough drive energy to spin the ATT to 20psi of boost, and most people don't hit that.
 
Yes turbine drive pressure is the exhaust gas coming out of the engine. Drive pressure is variable on RPM, fuel and boost. You can measure drive pressure just like you measure boost pressure. The more efficient turbos will have a low ratio of drive pressure to boost, so that 1:1 ratio is 100% efficiency, but the GM4 that I measure seems to be about 1.5:1 at 12psi, so like 65% efficient at that boost. The ATT I measure is more like 1.2:1 ratio at 12psi, so like 85% efficient at the same boost.

Turbo works off of pressure differentials. the turbine spins faster as drive pressure increases over turbo exhaust pressure. So lower exhaust pressure from larger exhaust pipe after the turbo helps the turbo spool faster and boost more efficiently by increasing the pressure ratio on the two sides of the turbine.

Edit for clarity: thats two differet ratios I was talking about. One is a boost pressure to exhaust drive pressure for determing efficiency; that is the compressor side vs the turbine side of the turbo. The other is exhaust drive pressure to exhaust backpressure only across the turbine of the turbo.
 
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Thanks for taking the time to explain all of this. Very interesting. So, if I understand this, we (6.5 owners) simply can't put enough fuel and air into our engine to create enough drive pressure to turn the turbine fast enough to over boost, thus no waste gate needed. Pretty cool.
 
And it is not that are engines are weak, or can't generate a lot of drive energy by burning lots of fuel. The thing is the turbine and housing is just large on the ATT. The DMax and Cummins guys use a variable geometry turbo that makes its turbine smaller to make it boost faster and higher, but the turbine still enlargens to make it efficient when not accelerating.
 
DZZ71 said:
On an ATT that is. Different story on other turbos
Click to expand...

????

There are countless numbers of combinations that can be had / made. Most 6.5 engines will not live with a high boost situation for a long time. Cummings are 17.5 to one compression, 5.9 liters and direct injected. The 6.5 is 20.1 or higher,6.5 liters and indirect injected.

Two totally different turbos meant for two totally different motors. You are raising the mean compression ratio on the 6.5 at lower rpm with the smaller turbo, this in my opinion is what causes the engine stress on the crank and lower block. This is just my opinion though. :skep:
 
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