I happened across this post by Big Joe on another thread:

Tunnel ram, fact or fiction for a 351W?
A tunnelram is only for an engine that can rev well above 7000 RPM. The bigger the engine, the sooner it will catchup and pull away fron a single plane. On a 427 SB Chevy. It would equal the single victor at 5300 and pull away to the tune of a 45 HP gain up at 7500 RPM. On a 355 size engine, it would not catchup untill 6000 RPM, then pull away by 40 HP at 8000 RPM. On a big BB Chevy (545 ci ) You gain an unbeliveable 100 HORSEPOWER at 7500 RPM. JOE SHERMAN RACING

The guys I knew with tunnel rams back in the day definately did not have engines set up to rev above 7000 rpm. They were red-lining before the tunnel ram could even catch up!
I guess if I ever mess with a car that has a tunnel ram sticking out of the hood at a red light one day and I hear him dump the clutch at 6000, I'll know I'm in trouble!!!

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'67 Mustang coupe
425W-KB Forged 10.2:1-AFR 205's-Victor Jr.-Mighty Demon 825-Joe Sherman spec'd Comp Cams HR -Miller rockers-Hooker Super Comps-3" exhaust-Gene Hughes AOD-3.55 Posi-4wheel disc brakes- 423RWHP @5600/ 448RWTQ @4400