What's a generally good accel pump cam to use?

[sum_weirdo]

I know it varies but for the amount I normally drive the truck it would take a while to get to it by trial and error. The carb is a Holley 750 CFM 4160 sitting atop a largely stock 78 460, besides the carb the only real modification is a 2.5" single exhaust and glasspack. What pump cam would you expect to work best? Thanks.

[PatsPOS]

Well, you're probably not going to want to hear this, but a 750 CFM is too much carb for a "largely stock" 460. In stock form, they're not high-revvers...they're built for bottom-end torque. A stock 460 doesn't have the compression AND the cam profile to be a high-revving engine. The factory-issue 600 CFM will be plenty enough for 99% of the 460s out there. Now if you get into internal engine mods, then the 750 might come into play.

Having said that, and if you still want to keep the 4160 on there...if your truck takes off well, then bogs, then takes off again, you'll want to look for a pump cam with a more aggressive profile...one that ramps up fast, then trails off slow. There are a variety of pump cams in a pack...you'll most likely have to experiment.

Now, if your truck bogs at the hit of the throttle, it's likely that you'll need a bigger accelerator pump...50cc vs 30cc. On some manifolds, it's possible that you'll need to run a small spacer between the intake manifold and the carb.

All said, I think you'll be happier with a 600 or 650 CFM carb...years ago I actually picked up .4 seconds in the quarter-mile by "downgrading" to a 600.

HTH,
Pat

[sum_weirdo]

I know it probably can't use all of it but it's as much planning for the future as anything. With the current secondary spring it's not likely to fully open up anyway.

[mark a.]

Is the timing set right ? Vacuum leak ? I'd find it hard to believe that such a big carb could be lean anywhere with a stock motor. With a stock camshaft & stock spring in the pot they are opening you just can't feel it. You shouldn't be able to feel it if it's working right. Bigger cams produce less vacuum making it sometimes necessary to put a lighter spring in.

[sum_weirdo]

There's not actually a specific problem I'm troubleshooting, the truck's operation is adequate, that's why I haven't bothered much with excessive tuning before now. I'm just sure there's a better pump cam to use than the orange one.