InfamyOffroad

Ok, lets take a detroit 6v71t for example. So you have the turbo sitting on top of the roots blower, i understand everything about it this is strictly a boost question.
Just for example that turbos pushing 20 pounds of boost into the blower, which is then simultaneously pushing lets say 7 pounds boost itself. What is the total amount of boost this setup is making? 27? or does the blower multiply the boost from the turbo a bit?

Tate

Its all about multiplication. If the turbo is pushing 20 psig, that is 34.7 psia. Atmosphere is 14.7 psia. Divide the first by the second, and you get 2.36:1 pressure ratio. The blower is at 21.7 psia, which would be 1.46:1 PR. Multiply those and you get a total of 3.48:1 PR. That would be a total of 36.5 psig.

pind

when in reality, the blower is used to pressure the airbox up to approximately 7 psi, if I recall right.

Then when the boost from the turbo surpasses that of the blower, the blower essentially bypasses, and the forced air induction is supplied strictly by the turbo.

That is an over-simplified explanation of how the 2 stroke blower/turbo detroits worked.

With a simple blower on them, they are considered to be a naturally aspirated engine.

Bluedually4x4

Pind is correct. After the turbo pressure exceeds that of the blower, a valve opens and the blower is bypassed. So there is no multiplication of boost, the blower only really pushes enough air to force the exhaust out the exhaust ports and push clean air into the cylinders. Because the way air enters and exits the engine it would not work as well with out the blower.

As another interesting fact if a hot rod guy tells you he has a 6-71 blower on his small block or big block you know know where those gas burners got the idea for supercharging a car engine

Number47

if i remember correctly the blower is only there to start the engine(due to the lack of intake stroke) but i'm sure it helps low end grunting power

InfamyOffroad

Well yes thats true, i guess that was a poor example, i was speaking in reference of a 4 stroke engine where the blower isn't required to run. But i'm pickin up what your puttin down tatedefinately answers my question
Thanks