Cam Design Guide for Weber Carbs

May 14, 2009 by pikesan

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If you’ve visited MyRideisMe.com before, you know I have a 27 Ford Roadster with a fairly hot 2.3L Ford four cylinder that’s better known as a “Pinto Motor”. I’ve got a not-so-cool problem with the Weber 44 IDF induction setup right now though…

When I get into the throttle, not that I’d ever do that, I get a misting of fuel over the top of the carbs. OK, it’s less of a mist than a toxic ozone killing cloud of gas vapor. (I’ll commute tomorrow to make up for it!). I owe you a video of this, before and after.

So what I’d do? I knew Inglese Induction Systems are the experts. Inglese has been making intakes for this setup for a long time so they must know what’s happening and how to fix it. Even more cool? Inglese is now owned by the Comp Performance Group that also owns, Comp Cams. I’ve always had great success with Comp Cams in my Ford V8’s and my pops has been really happy too. Having 2 great reasons, I called over to Comp Cams.

“…should get the torque to come on sooner and make the car more fun to drive on the street; and in a more user friendly RPM range.”

I spoke to Jay over in Comp Cams tech support. Jay knows his cams and was super polite. I asked him to write down what he was thinking for my set up and this is what he said:

When doing cams for engines equipped with Weber carburetors, it’s imperative that you keep overlap of the cam reduced to that similar of what would be acceptable in an OEM injected throttle body type engine. The reason for this is the Weber carburetors are rather finicky as to what they like at idle and part throttle operation, and really prefer a strong/consistent vacuum signal.

When using long(er) duration cams, and/or tight (110 or less) lobe separation angles, the Weber carbs are bad about “vaporing” fuel out of the top of the velocity stacks, (as in your application). Reducing the length of duration, and using a quicker ramp profile on the cam lobes, naturally reduces overlap; as does widening the lobe separation. The combination herein provides a more consistent vacuum signal, flatter torque curve, and should (in your case) promote some low end throttle response and torque.

What I’ve come up with for you is a solid lifter cam that will be a 226 @ .050 duration on the intake; and 236 @ .050″ on the exhaust. More difference between the intake and exhaust durations (aka “split”) should help to burn some of the excess gaseous vapors that would otherwise continue to travel back up your intake manifold runners, and linger above the carbs. I’m going to suggest that we us a 112 lobe separation angle (as opposed to the 110) you have now. This, along with the change (reduction) in duration, should get the torque to come on sooner and make the car more fun to drive on the street; and in a more user friendly RPM range.

These cams also require nitriding (p/n 1-111-1) service as well.

So I asked, What’s with the Nitride treatment? It’s kinda pricey…

Nitriding over head cams is absolutely necessary. It’s strengthens the cam which has the constant load pressure associated with the follower/rocker and spring combination. The reason it’s become so necessary now (rather than long ago) is a two part answer:

Lobes have gotten far more aggressive (this doesn’t necessarily mean BIGGER); they have much faster ramp rates, more dwell time at max lift, etc. Secondly, the “big 3” haven’t manufactured anything with a flat tappet cam in nearly 20 years, and thus, the EPA has come down on the oil companies to reduce the good stuff in their oils such as zinc, sulfer, etc. (These are the things that help a flat tappet cam and lifter combination live) They are, however, hard on catalytic converters, and since the EPA doesn’t see the necessity in keeping it since none of the newer cars need it, well, it’s out. We have to find ways to combat this. The nitriding of the cam is a vital ingredient in the longevity of its life.