Originally Posted by CHEVILLAC
Cam specs are in my original post but it is a summit cam, k1108. This is setup as a race motor and has very little vacuum at idle but the previous owner was able to drive it on the street. This motor was in an all steel 41 willy's 4 door and clocked 10 flat on the strip with a 150 shot of NOS, several times. I know vacuum secondaries are generally better for vehicles less than 3000lbs or so with automatic transmissions and mechanical secondaries are generally better suited for heavier ace vehicles. I want to take this truck to the track but be able to drive it to a cruise-in or car show too, hopefully without changing anything except MAYBE the distributor and the stall converter for now and add my posi later. Which brings me here asking which carb to run. It looks like a 750cfm is the consensus and I'm guessing mech secondaries since I have very little vacuum. Unless a vacuum secondary carb can be tuned to operate correctly with little vacuum, So because I'm also reading that vac sec carbs are more street friendly and pretty good at the track when a person is not so into racing that they're trying to shave tenths off their et. So I'll put the 600 eddy on there so I can get a vacuum number because the previous owner doesn't remember how much the motor had because he didn't care since he ran with fuel injection. From there maybe I'll have a better idea which carb to use. I do the fab and body work part of building custom cars and truck. This is my personal ride and I want it to be fricken fast and track worthy. I'll upload some pics and maybe that will help some of you understand my perspective a little better, if you don't already. I've never had more than 300hp and never been the driver at the strip but I drive my truck like I stole it.
The idle vacuum doesn't matter as to whether to use a vacuum secondary or DP carb. When you floor it, either way the vacuum drops off to nearly nothing, regardless if it has a small or big cam.
Heavier vehicles and/or higher (lower number) rear gear ratio equipped vehicles are generally easier to drive w/a vacuum secondary carb. Light vehicles w/low rear gears take to a DP like a duck to water and aren't as likely to bog on you.
Either will work (the DP requires a learning curve- think of it as the difference between an AT and a stick shift). But for the street most guys tend to like a vacuum secondary-type carb better than a DP, and the mileage will tend to be better as well.
There's a lot of trickery that goes into a race engine. Glad you know the cam in this engine. I guess it's the heads that nothing is known about and I confused the two. My mistake.