Baseline 858 head air flow test results

[Clem Z.]

Re: Baseline 858 head air flow test results

Since the pressure ratio at exhaust blowdown is less than critical what amounts to a converging-diverging nozzle as used on rocket engines will allow the flow to achieve greater than Mach 1 for a brief length beyond the curtain area at low valve lift. Such will improve blowdown efficiency and reduce exhaust pumping work.

It will also create a very sharp exhaust note.

...but you need to be a "rocket scientist" to understand...

Duke

a friend who was a GM employee working down at "smokeys" put me on to this idea,he even sent me a sketch of how to do it which i still have somewhere. we made them out of HRS and shrunk fit them into the heads. i miss those good old days.

[John C.]

Re: Baseline 858 head air flow test results

Duke

The listing in the first line is the calibrated maximum flow for the test plate orifice they were using to do the flow check. 150 x 39% = 58.5

John

[Duke W.]

Re: Baseline 858 head air flow test results

Got it, thanks. As you can see from computing the E/I ratio, even with the 1.88" valve it's only in the low 0.6 range at higher lifts.

As lift approaches and exceeds 0.25 of valve diameter, the port geometry, rather than the valve itself becomes the limiting factor in flow, so it's clear why GM needed to do some work to improve port flow in addition to the larger valve.

The current LS7 exhibits a similar low E/I ratio and it was intentional in order to fit the largest inlet port and valve possible. Then the restrictive exhaust side was compensated with a camshaft with 19 degrees more exhaust duration than on the inlet side, with all the extra duration in the form of a very early opening exhaust valve.

Duke