Greetings . . .

Hey Twisted, these gizmos show up on ebay every once in a while:
SF-600
I think the last one sold for north of five grand - big bucks for most. The SF website describes their 110/120 model as 'economical'
I've never seen one of them on ebay.

IGOR, I am spectator when comes to this whole topic of flow. Your comments about a 70% intake/exhaust ratio 'sweet spot' are interesting - but I am not sure I understand the magic of this ratio. It's my understanding that this ratio is part of the overall engineering of the package: port volume, valve diameters and cam timing. I read somewhere that as exhaust port flow efficiencies are increased towards 80 and above, one can then choose a symmetrically ground cam. GM engineers on the other hand crafted a dual pattern grind on the 216/235/261 because they (in effect) designed the exhaust ports around a lower efficiency - 70 and lower - but balanced it with longer duration on the exhaust lobe. Back in those days they arrrived here by trial and error - cause there where no flow benches.

The other question I have about all this flow bench data that is out there (and there is bunches):
Stan\'s Flow Bench Data

The flow bench measures CFM on the intake and exhaust under the exact same conditions (10, 20, 28 inches of water). While this seems a useful piece of information it hardly matches the operating environment of these components. In a normally aspirated engine the intake valve opens into a vacuum created by exhaust scavenging (if there is overlap) and the receding piston. While the exhaust valve opens into a cylinder that is under extreme pressures (the earlier the timing the higher pressure - plus the effect of compression ratio).

With this big difference in velocity between intake and exhaust gases - how does one interpret flow numbers based on identical velocites?

best regards,
stock49

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