What's the diff?

[ACAT]

I am running a 3100 f.I.roller cam in a carb engine. Speedshop guy said centerline (114?) may not be optimal. He suggested 108. What do you think? Can a cam be reground for diff centerline? I can't seem to find any cams for this engine. Thanks

[silvergtjrad]

Regrinds are available through the store here.

[geoffinbc]

What your looking for in a carb cam is a good vacuum signal and intake velocity. You need a good intake signal under the carb to get the fuel to flow out of the venturis. A wide LSA will give a good vacuum signal but there is not as much overlap (depending on duration) to provide low RPM velocity in the intake manifold. The exiting exhaust gases leaving the cylinder will create intake velocity helping suck fuel out of the carb. Cams almost have as much to do with fuel delivery as the actual carb does. You will also never see a large plenum on a carb manifold because a plenum is a place for air to sit and wait to travel down the runners. This is why EFI has so many advantages when it comes to engine performance. There is literally no restriction on cam choices if you have the ability to tune.

[torq455]

never say never. you will see large a plenum on a carburated engine. however, they are mainly used as a street/strip or strictly strip application. all depends on what powerband you are looking for and how much air the engine needs. 114 lsa is good for boost and a flat torque curve. go with a 108 and sacrifice bottom torque for top end power. yet you can have a similar effect with smaller/bigger duration too. as far as the venturi go, they have their own vacuum boosters to ensure fuel will be drawn in. it's when you start getting the high duration and narrower lsa that you begin to loose vacuum signal at idle. but that's a minor concern. the idle will be rather lopy so you'll have to raise it anyway and thus a better vacuum signal.