Camshaft recommendation for PMO'd 2.4S ? Options

[amallagh]

I've recently converted my 914-6 to a 2.4S spec engine with PMO 40 carbs.

The engine/heads are standard S spec but with 2.2S pistons giving about 9.3:1 compression rather and the std 8.5:1.

Can any one recommend a specific cam profile/supplier that is optimised for use on carbs with an S spec engine ?
If the std S cams from an MFI engine are considered to the the best for this application then I would be happy to hear your experiences.
I'm looking for a fast road cam to give me similar performance to the std S cams on MFI. The car is used on the road as well as for competition, so I need something smoothy and tractible at low RPM.

Regards
Andrew

[J P Stein]

The big "problem" with S cams is duration and the consequent overlap. They work fine with MFI.....tho the bottom end is nothing to shout about, but carbs & MFI are horses of a different color.
MFI delivers fuel below the butterflies and has tall stacks. Carbs deliver fuel above the butterflies...close to the top of the carb, in fact, and have shorter stacks. What this all means is fuel reversion.....a nice spray of semi-atomized sitting in layers above the carb stacks. This gets sucked into the carbs when the engine starts to efficiently scavenge....around 5K rpms for an S cam. Below there, this reversion raises hell with the tune....particularly when enclosed in your....normal K & N filter with hat.....fuel bouncing all over hell & gone. One of the main reasons to avoid long duration cams in a street motor mit carbs.

The Solex profile is less prone to this as is the E. Tuning is still a stinker. Run the idles & mains rich enuff to avoid the dreaded Weber flat spot and you foul plugs regular like. The solution here is a hot CD ignition & coil (I use MSD) with a bit fat plug gap (.045-.050)....ya prolly ought to have some hi-po plug wires to handle the voltage....to burn thru the rich mixture....a bandaid that keeps your plugs clean.

The 2.4L motors had wimpy compression. Another point or so will reward you with more hp & torque and street gas will work fine....up to about 9.5:1.

Thas about all I think I know.

Note that the dyno chart above shows 225-230 hp at the crank (figuring a 15% drive line loss)& 210 ish ft/lbs of torque The famous 2.7L RS motor was rated at 210 & 188 at the crank(Probably conservative) with MFI. OK, so I run 10:1ish compression, Solex, carbs, & race gas. It's a great AX motor where low down (relatively) torque is king. The mileage sux.

[ArtechnikA]

MFI delivers fuel below the butterflies and has tall stacks. Carbs deliver fuel above the butterflies...close to the top of the carb, in fact, and have shorter stacks.

As I know you know, the big difference here is that MFI delivers the fuel once always, in a shot calibrated to rpm and throttle position, and has no airflow sensor at all.

Carbs work by pressure differential of the passing airstream sucking in the gas.

The airstream passes the fuel delivery stuff once when 'on the cam.' When you've got reversion, as you do with big overlaps, the airstream passes the fuel delivery stuff once on intake, then again during the reversion, and the fuel metering stuff just knows pressure differential - it does not know the direction of the airstream. Finally it's sucked back in yet again, passing the fuel delivery bits a third time, picking up even more gas.

No wonder the suckers run rich...