More blower psi vs same + ported heads
More blower psi vs same + ported heads
(OP)
Okay, here's an engine with hypereutectic AL pistons traditionally said to be limited to 5psi from a DIY blower kit using a Whipple blower.
Setting that aside for the moment, but keeping that limitation in mind, what's the difference between adding ported heads to that 5 psi s/c engine, or just changing to a smaller 7psi rated pulley with unported heads?
Net operational psi is a function of backpressure/restriction in the head isn't it?
I haven't heard any objections to adding ported heads to a 5psi s/c setup, but that would have to raise cylinder pressure wouldn't it? - At the same time lowering measured blower (back)pressure.
Yet a '7psi' pulley blowing through un-ported heads isn't putting as much volume into the cylinder perhaps. Depends on whether the s/c vendor has designated that 7psi pulley from testing on an engine with ported heads or not I guess eh?
How different is a psi pulley on ported heads from a 7psi pulley in unported heads??
:)
Setting that aside for the moment, but keeping that limitation in mind, what's the difference between adding ported heads to that 5 psi s/c engine, or just changing to a smaller 7psi rated pulley with unported heads?
Net operational psi is a function of backpressure/restriction in the head isn't it?
I haven't heard any objections to adding ported heads to a 5psi s/c setup, but that would have to raise cylinder pressure wouldn't it? - At the same time lowering measured blower (back)pressure.
Yet a '7psi' pulley blowing through un-ported heads isn't putting as much volume into the cylinder perhaps. Depends on whether the s/c vendor has designated that 7psi pulley from testing on an engine with ported heads or not I guess eh?
How different is a psi pulley on ported heads from a 7psi pulley in unported heads??
:)





RE: More blower psi vs same + ported heads
The qualifiers on this are:-
The blower rotors do not seal perfectly, so there is some leakage. This increases at higher boost, so there is marginally more air flowing into the cylinder.
the blower absorbs more power to drive it at the same volume and higher pressure.
The higher pressure generates more heat in the manifold, but less in the cylinder to give the same final heat at the same final cylinder pressure with small deviations for leakage etc
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: More blower psi vs same + ported heads
That aside, I'm still wondering what the difference is in the end for this example between a 7psi rated blower atop unported heads vs a 5psi rated blower atop ported heads.
Is there any? The tuners didn't reply much, I think they want to sell $2500-$4400 heads more then $125 pulleys..
RE: More blower psi vs same + ported heads
Increasing blower speed will increase airflow, power, and physical/thermal loading of pistons.
methinks if you want to make lots of power, an intercooler, more blower drive, and better pistons would be the way to go...
Jay Maechtlen
RE: More blower psi vs same + ported heads
Quite likely there will be a small power increase, but it will reduce the stresses on all the various parts. What you can then do is to increase blower drive speed to get the boost back to where it originally was. That will definitely increase airflow and power.
.
RE: More blower psi vs same + ported heads
RE: More blower psi vs same + ported heads
JayMaechtlen and Warpspeed have interpreted it correctly.
If you leave the blower drive the same, you will get slightly more power at slightly lower boost and at lower stress on the engine and with less chance of detonation.
If you port the heads and up the overdrive to maintain the boost, you will get a bigger increase in power, but with more stress and more chance of detonation.
If you run the original heads, but more boost to equal the HP of the ported heads and original blower over drive, you will put more stress on the engine.
As Warpspeed says, supercharged engines really respond to big exhaust systems. They also like strong valve springs on the inlet valve and wide lobe centre cams.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: More blower psi vs same + ported heads
RE: More blower psi vs same + ported heads
A higher cylinder inlet charge temperature mostly because the air's heated up more by the increased blower speed, or by increased compression in the intake after the blower?
As designed, this particular blower setup is picking up just tons of radiant heat as inlet air travels the 2.5 feet or so from throttle bodies to s/c inlet at the back of the blower. The 3"OD or so metal tubes are at the most 1/2" away from the 150deg valve covers all the way.
RE: More blower psi vs same + ported heads
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.