Twins-low EGT's, single-high EGT's
11-16-2006, 04:08 PM
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Because you are pushing more air and burning more fuel. Also some guys will make let say 55 psi of boost with twins and I can make 45 to 50 with my 66, but this is can be tricky because he is shoving a barrel of air through while I am shoving a milk jug.
11-17-2006, 09:41 PM
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So even if the boost was the same, for a single vs a twin, there is more actual air in the cylinder with the twins? And more ari means cooler EGT's?
Is that right?
Thanx.
Is that right?
Thanx.
11-17-2006, 10:14 PM
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Because you are pushing more air and burning more fuel. Also some guys will make let say 55 psi of boost with twins and I can make 45 to 50 with my 66, but this is can be tricky because he is shoving a barrel of air through while I am shoving a milk jug
Twin turbo's often produce lower egt's do to the fact that you are working within the two turbo's efficiency ranges. Single Turbo's typically are working harder with higher shaft speeds to produce the same amount of boost. -----Which will result in higher charge air temperatures resulting in a less efficient combustion event.
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11-18-2006, 12:05 AM
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It kind of seems like 50lbs of boost is 50lbs of boost, no matter how you get it. But is it the single turbo is making twice as much heat, with one spinning shaft at a certain boost than twins would with two shafts making that same amount of total boost? Does the one shaft between impellers (right term?) get so hot, it heats up the the metal on the intake impeller, which heats up the air?
Thanx.
Thanx.
11-18-2006, 03:06 AM
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Heat of Compression
A centrifical compressor that is operating inside it's ideal operating range, does so without adding more energy to the air then what the air already has in it. (in theory of course, friction is always at play.) The further outside this range the unit is run, the more friction there is between the impeller and the air. Simply put, 50 psi boost at 125 degrees f from twins versus 50 psi boost at 200 degrees f from a single running at the edge of it's operating range, the first has a larger mass due to lower temperature. Thus when it comes to the EGT end of it think of it as trying to heat 5lbs of air with 2cc's of fuel verses heating 2lbs of air with 2cc's of fuel. (assuming you've made no changes in Fuel flow) The temperature won't climb as high, but you will get a larger pressure increase in the cylinder's. Another option is to install a bigger/more efficient intercooler to drop the temperature from your fatshaft 62 or what have you, but you would also see a subsiquent drop in the boost pressure because you will then be thermally compressing the discharge flow of the turbo, thus lowering the backpressure in it, but it would help to increase the mass flow and lower the egt's. My question awhile ago was why they don't intercool between and after the twins, but I guess fitting a 2nd intercooler would be no small task.
11-18-2006, 01:37 PM
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A centrifical compressor that is operating inside it's ideal operating range, does so without adding more energy to the air then what the air already has in it. (in theory of course, friction is always at play.) The further outside this range the unit is run, the more friction there is between the impeller and the air. Simply put, 50 psi boost at 125 degrees f from twins versus 50 psi boost at 200 degrees f from a single running at the edge of it's operating range, the first has a larger mass due to lower temperature. Thus when it comes to the EGT end of it think of it as trying to heat 5lbs of air with 2cc's of fuel verses heating 2lbs of air with 2cc's of fuel. (assuming you've made no changes in Fuel flow) The temperature won't climb as high, but you will get a larger pressure increase in the cylinder's. Another option is to install a bigger/more efficient intercooler to drop the temperature from your fatshaft 62 or what have you, but you would also see a subsiquent drop in the boost pressure because you will then be thermally compressing the discharge flow of the turbo, thus lowering the backpressure in it, but it would help to increase the mass flow and lower the egt's. My question awhile ago was why they don't intercool between and after the twins, but I guess fitting a 2nd intercooler would be no small task.
Thanx.
11-19-2006, 12:12 AM
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A centrifical compressor that is operating inside it's ideal operating range, does so without adding more energy to the air then what the air already has in it. (in theory of course, friction is always at play.) The further outside this range the unit is run, the more friction there is between the impeller and the air. Simply put, 50 psi boost at 125 degrees f from twins versus 50 psi boost at 200 degrees f from a single running at the edge of it's operating range, the first has a larger mass due to lower temperature. Thus when it comes to the EGT end of it think of it as trying to heat 5lbs of air with 2cc's of fuel verses heating 2lbs of air with 2cc's of fuel. (assuming you've made no changes in Fuel flow) The temperature won't climb as high, but you will get a larger pressure increase in the cylinder's. Another option is to install a bigger/more efficient intercooler to drop the temperature from your fatshaft 62 or what have you, but you would also see a subsiquent drop in the boost pressure because you will then be thermally compressing the discharge flow of the turbo, thus lowering the backpressure in it, but it would help to increase the mass flow and lower the egt's. My question awhile ago was why they don't intercool between and after the twins, but I guess fitting a 2nd intercooler would be no small task.
That's one of the better explanations I've heard in a long time. You rock. 
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