low compression for blown motors

[BurnTire]

[WildBill]

WHatever Jeff!
You're talking apples and oranges with centri and twinscrews or roots.

What part of parasitic losses don't you understand?

[BurnTire]

WHatever Jeff!
You're talking apples and oranges with centri and twinscrews or roots.

Blower Type is irrelevant. The original questions was about why a lower CR is used in Forced induction applications. If you peak at 20PSI with a centrifugal is creates the same Effective CR as a screw blower at 20 PSI. I can understand your theory on having a higher CR to help the centrifugal setup move along better at lower RPMS, but when you get into higher boost applications a lower CR and forged internals are the best choice for power and longevity.

[BurnTire]

What part of parasitic losses don't you understand?

Bill time to move on. Subject over.

[WildBill]

Blower Type is irrelevant. The original questions was about why a lower CR is used in Forced induction applications. If you peak at 20PSI with a centrifugal is creates the same Effective CR as a screw blower at 20 PSI. I can understand your theory on having a higher CR to help the centrifugal setup move along better at lower RPMS, but when you get into higher boost applications a lower CR is the best choice for power and longevity.

Wrong Jeff.

I don't know what else I can say to you for you to grasp basic concepts.
With a higher boost and lower compression combo you have the following working against the combo.
1. Higher boost pressures will result in higher parasitic losses due to spinning the SC harder.
2. With higher boost pressures, the inefficiency of the following come into play more and reduce overall efficiency.
(a) Higher boost requires the supercharger to spin at a higher rate. This raises the temperature of the air. This means less timing you're able to run.
(b) Higher boost means the air spends less time in the heat exchanger to remove the heat from the already hotter air.
(c) Higher boost will bring out further any inefficiency in the intake manifold and the heads with cylinder filling.

Bottom line is that a higher compression/lower boost combo will be quicker and more responsive on the street and when the time comes to "up the ante", all that would have to be done is up the octane of the fuel and pulley up the blower.

[silver03cobra]

I SHOULD READ ALL OF THIS BUT I AM NOT GOING TO......

having built the FASTEST 3 time or 4 time SCFCA (Southern California Funny Car Association) spelling? Funny car (chill factor) 7.272@ 160.58 only time i recall.


FOR YOU CAR!!!!!!! low comp high boost... the static loss wont matter with the boost. the d1sd would be better(over kill for street car) I REALLY DONT WANT TO START BASHING... but i have built OVER 40 Motors (still runing today..) go with 8.5:1 or 9.0:1 (with aluminum (spelling?) heads i would go with 9.0:1 and run 10-15 psi... you WILL make more safer power....) ask kieth... he tuned your car... he is a vender here and the only one I have tune my car's... and soon my diesel.... Now if the final CR 's are the same the lower CR more boost will STILL make more power it has beed proven time and time again.... end topic....... If you need you motor built i would be glad to talk to you just pm me. the real way to go is high CR's AND high BOOST... (not a street car by any means..)

[02stangGT]

im 20 years old just trying to learn a little.. thats what this is about. i am also saving for a block though too. the car will still be my DD i just wanted to know if i did get a block what compression to run and be safe for my DD.. i would like to run about 12-15 psi but this would only become when i have a new block that could handle it.

[BurnTire]

Now if the final CR 's are the same the lower CR more boost will STILL make more power it has beed proven time and time again.... end topic.....

I rest my case.

[BurnTire]

im 20 years old just trying to learn a little.. thats what this is about. i am also saving for a block though too. the car will still be my DD i just wanted to know if i did get a block what compression to run and be safe for my DD.. i would like to run about 12-15 psi but this would only become when i have a new block that could handle it.

9.0:1 as recommended by Silver03Cobra the one with Real Engine Building Experience.

[WildBill]

Yeah.......funny car.........street car.

How do you figure?
If it is the SAME effective cylinder pressure, how can the higher boost make more HP in over the curve and peak, when it has MORE LOSSES with a centri?

Please get technical as you like.