Comp Cams has recently introduced a new line of hydraulic roller cams designed to retrofit into our engines. The three cams in this new "Thumpr" sub-brand feature a range of choppy-to-very rough idle characteristics, but preserve a high degree of 'street-ability' at the same time. A combination which interests me.

My question to the engine experts here is: since our cars are so dependent on vacuum systems, would this choppy idle be likely to have a negative effect?

The specs for the mildest of the three Thumpr's are:

Duration:

Advertised: Intake 283/Exhaust 303

@.050": Intake 227/Exhaust 241

Valve lift @ 1.5:1 -- Intake .511/Exhaust .497

Lobe separation angle: 107

Comp Cams' description states that using the stock stall converter is OK; but best performance is achieved with a 2,000+ converter. And the stated operating range of this particular cam is 1,900-5,600 RPM.

I'd like to exhaust your (in)take on possibly Thumpr'ing an L-48 (which will also get new heads/roller rockers, Hooker headers, plus an Edelbrock 2101, fed by a stock Quadrajet).

Thanks for any Thumpr thoughts.

[QUOTE=SFVette]Duration:

Advertised: Intake 283/Exhaust 303 [/QUOTE]

This will effectively kill most all of your vacuum supply. The more duration a cam has, the less vacuum an engine can produce. While I love the specs, I'm not sure it would be advantageous on a heavily vacuum dependent car like our Corvettes.
Then again, there are alternative solutions to the headlight issues(electric)...

Other than having a mean sounding idle, what are the advantages of these cams?

 Ted, here are the specs for my ZZ4, I used an HEI dist and pulled the Vac from the intake manifold, Intake.525, Exhaust.525, @.050-in lift, Intake.218 and Exhaust.228 with 1:6.1 rocker/ aluminum heads, lobe centerline 112 degrees. Once I got it running with Joel's help, had trouble with timing and carb set, engine would run backwards? but, worked it out. After all was running right could not shut down the engine, Holley sent me an engine shut down solenoid and I was on my way, took her to Pigeon Forge and back home, I will start her next month and hope for the best she runs great 19 plus miles to the gallon, Idles. hard, Everybody runs over at the gas station to see what all the noise is, I'm happy with it and that what counts...

[QUOTE=Adams' Apple] [QUOTE=SFVette]Duration:

Advertised: Intake 283/Exhaust 303 [/QUOTE]

This will effectively kill most all of your vacuum supply. The more duration a cam has, the less vacuum an engine can produce. While I love the specs, I'm not sure it would be advantageous on a heavily vacuum dependent car like our Corvettes.
Then again, there are alternative solutions to the headlight issues(electric)...[/QUOTE]

Lights? what are them? Ya mean these here cars are meant ta be driven after dark too?

T