Quote:
Originally Posted by racprops
Two “out there” ideas were Rhoads Lifters, and Power Valves, a special pressure control add on to the intake valves that closes very early, building higher pressure for real low rpm power.
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Rhoads Lifters are not "out there" at all. I've used them on two different cams in the 350 that's in my '57 Chevy and they work great. Right now, the cam is a Comp 268H with Rhoads and it made 400 ft-lb of torque at 2,500 RPM on an eddy-current dyno. The version I have is the "original" and will bleed down overnight and cause rough starts, but they now have anti-bleed-down versions. I've found the owner of Rhoads to be very responsive, so I'd contact him to see if the cam you're considering is already too small to use with the lifters (you don't want to create excessive dynamic compression).
The specs of the engine that made 400 ft-lb are:
Quote:
-Built in late 1993
- 355 (350 w/ 0.030" overbore)
- Melling high-volume oil pump
- ARP rod bolts
- Keith Black hypereutectic 17cc dish pistons
- Childs & Albert "Zero Gap Second" rings
- Ed Hamburger roller timing chain with needle thrust bearing
- Comp Cams 268H cam (218° @ 0.050" lift, 0.454" lift at valve)
- Rhoads lifters
- "882" iron heads, 76cc, 1.94"/1.5" Manley Pro-Flow undercut valves, DIY porting
- Edelbrock Performer 2101 intake
- Edelbrock (Carter) 600 cfm 4-bbl
- Mallory Unilite distributor
- Edelbrock Victor aluminum water pump
- Doug Thorley tri-y headers
- 2.25" dual exhaust w/ h-pipe and Borla mufflers
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If they had been available back then, I would have used iron Vortec heads, which are widely regarded to be the best (best ports, best chamber) OE iron heads ever made for the SBC. They make more power and torque than the vaunted "Double Hump" heads, even though they have smaller valves.
FWIW, I just got 17.8 MPG on a 400-mile trip in the '57, and I was not trying for max mileage. All windows were down and I was doing 60-75 MPH most of the time. This is with a close-ratio 5-speed with a 0.82 5th and a 3.55 diff ratio (so a 2.91 final ratio).
The
Power Valves concept is iffy, at best. Implementing them will not be inexpensive, and I bet they will not be reliable. This falls into the "hairbrained idea" category, IMO.
I might have missed it if you mentioned them earlier, but if you don't already have headers, they are a must for this, IMO. NOT large-tube headers, but Tri-Y or small-diameter long-tube headers. I know there are 1-1/2" primary long-tube headers available for your application, which are a great match for the RPM range you are trying to optimize.