Demon v. Holley

[Jack21]

Have always had love/hate things with Holleys. My first was on a '57 Fairlane with the "Big" 312 motor. Had this nasty habit of sticking in the open position at WOT, and wouldn't come back without shutting off the engine.

Holley did have the answer to Rochester Quadra-Jets that wouldn't run, but seemed like I was always tinkering with something on a Holley. Must have a sizeable investment in spare parts.

Same deal with the Cobra. Nice healthy 351W, but tinker, and tinker with the jets, power valve, idle, secondary throttle stop. 700DP (#4778).

Reading an engine buildup article in one of the rags. They decided to dyno the motor with a Demon, instead of Holley. Been seeing a lot of that lately.

Talked to Demon tech about selecting one, and the guy asks me what cam duration in my motor. I've never been asked that before, nor have I seen any references to this in Holley tech info. Demon tech guy advises not to use the Road Demon, it's calibrated for cams under 220*. Use the Speed Demon instead with the cam I'm using. Sooo, the Demons internal calibrations are more closely tailored to the rest of the engines components. Hmmm.

Sprung for the 650 DP Speed Demon. Could not believe the difference in this motor's smoothness, and responsiveness right out of the box. Like the Holley, it runs too rich out of the box because of the high vacuum hydraulic roller cams pull (15" - 16" at 850 RPM idle), but the 4 corner idle system sets right up, and no further tinkering required. So that makes me a believer.

The metering block is where the biggest difference is, and it's obvious comparing the two (Demon - Holley), that the Demon is more judiciously calibrated. It shows in the throttle bodies as well. Holleys have been around since the mid-'50's and the carb you took out of the box then is nearly identical to the one you take out of the box today. In some ways this may be good, and in others, it may not be. MHO, the Demon is worth the extra $100 - $150 over the Holley.

Also using the same K&N air filter as shown above. They're ugly, but they breathe.