Originally Posted by TNCHEVYMAN
I have a 72 chevy pick up. It has a 355 with camel hump heads and a big solid lifter i dont know what it is,but it has a very choppy idle. It has headders a high rise dual plane with a 650 vac sec holley and hei dist. I still have the stock converter in the 700 r4 trans and i still have stock rear gear. i knoww i need a conv and gears. it runs good. but i hate the holley carb, its rich and always needs adjustments. to the floats. i found a really good deal on a edelbrock pro flo. my question is will the pro flo injection work well with the big cam. also what is the diff between pro flo and pro flo 2. there is an upgrade kit as i understand it. edelbrock,s pro flo has a in car controller so it is very tuneable, but will it work well with a big cam with low vacume.
System comes in 2 versions 2 bbl to 5500 RPM and mild cam and 4bbl to 7000 RPM with bigger cams, which are you looking at?
You will have to upgrade the 72's electrical system starting with at least a 100 amp continuous output alternator. The distributor will have to be modified or replaced as well.
The Proflo can be programmed to operate as a Speed Density (MAP) system or as a simple Apha-N where only throttle position is monitored for fuel management. For an engine that has enough cam that a Holley can't be settled down is going to run on the Alpha-N controls, while probably more stable than a carb, it'll still be fuel hungry.
Big cams need a lot of compression, often what appear to be carb problems come back to this, also, over scavenging by the exhaust, pulse transfer from the exhaust back into the intake along with insufficient plenum volume result in high reversion pulses back through the carb. The carb has a pretty low IQ it doesn't differentiate between air going in or coming out it adds fuel both ways when this fuel rich reversion cloud is sucked back in it gets another shot of fuel so the end result is an engine that has proper ratios in some RPM bands and is pig rich in others and can't be settled down.
Frankly I'd start with reversion cones where the headers bolt to the heads and a spacer under the carb. A 650 is probably too small with the cam you have (not that it canít feed the engine but an oversized carb has lower velocities through the venturies making it somewhat less sensitive to reversions upsetting the metering. Given the spacer may take some experimenting I'd buy a half sheet of good 1/2 to 3/4 inch plywood and make up a bunch of spacers that are open plenums and 4 holers so they can be mixed, matched and stacked to see what combination, if any, the motor likes before I committed hard cash to something made out of metal.
You have to consider that the stock stall converter may be keeping the idle speed lower than the engine needs. If it idles well out of gear and not very well in gear there's one of your answers as which way to go first. You also have to consider the idle tune of the carb, the air demand may be forcing you to open the butterflies to where the mid throttle transfer slot is exposed to manifold vacuum at idle, this will make for unstable fueling. If this carb is a Holley there should be a small stop screw on the secondaryís that comes up from the manifold side, this can be adjusted to admit more air to where the primary throttle can be backed off till the blades are below the transfer slot.
A big cam also kills any vacuum that can be used for advance control at idle, the lack of idle or off idle (ported vacuum) needs to be made up in the static advance. This amount, which might be considerable, needs to be subtracted from the centrifugal.
One of your first adventures should be discovering how big of a cam is in there. With this knowledge a proper decision path can be laid out as to compression, ignition, and carburetion needs. Discovering the cam timing is pretty involved follow this process: >>> Camshaft Timing - Camshaft Theory - Circle Track Magazine
The issue of getting the cam lobe measure is complicated on an assembled engine compared to what they use in this article. Given the engine's been run the lifters are probably full of oil and adjusted usually the recommendation is to pull a lifter remove the plunger, place a stack of washers into the body that can support the push rod socket, making the lifter solid and measuring from that. Actually most lifters use a wire bail to hold the pushrod socket and plunger in place, removing this bail will let you remove the plunger, set it on a clean towel, fill the body with a stack of washers set the push rod socket on and hold it down with the bail. Reassemble the push rod to rocker and adjust to zero lash, then set the dial indicator up on the rocker so the valve spring can be used to keep pressure on the lifter so that it follows the lobe for the measures to be made. When done remove the washers check with a magnet that none are left in the body, then reassemble the plunger and adjust the push rod clearance.