Single Pattern vs. Dual Pattern Cams

[AmericanPie]

Originally posted by Excaliber


Dual pattern cams were the "in" thing a few years ago because head/valve flow cfm on the exhaust side of things was not up to the head flow standards commonly used today. The dual pattern typically has higher lift/duration on the exhaust side to help the out flow where it WAS needed most. RV and Truck use were common applications (torque and gas mileage).

But todays heads flow pretty well on the exhaust side so the TREND is going back to single pattern cams. BUT this assumes your talking MODERN stuff, AFR, Twisted Wedge, possibly some Edelbrocks, etc!

As far as the FE is concerned: Keith Craft recently posted the old medium riser iron heads flow just about the same as a Shelby/Edelbrock head "out of the box". I've noticed that among the FE heads, in general, the exhaust ports SEEM to be pretty close to the same size. It's the INTAKE ports that very a LOT from the typical medium riser to the HUGE (in comparison) High Riser ports. But even on the high riser heads the exhaust ports aren't "that big".

We need some flow numbers here! DO the iron medium riser, Shelby and Edelbrock heads (out of the box) flow ENOUGH on the exhaust side or would they flow more with a dual pattern cam? Amazing to me that a 1964 High Riser Iron head "out of the box" is about as good as it gets unless your doing some serious port work to modern heads! And an old iron medium riser is right up there with todays best! Could they be even better with a dual pattern? Or would the money be better spent on "port" work instead? Without hard core flow numbers I doubt we will find a definitive answer.

Comp Cam 282S single pattern is what I'm running. Good to 6000-6200 and then falls off sharply. I kind of miss my old roller cam good to 6500 and beyond (but the low end wasn't so good).

I've always assumed that generally, most engines need some help on the exhaust side and therefore benefit from a dual-pattern cam (with more exhaust duration/lift). However, single pattern cams seem to be very popular on some motors, plus I do see some exceptions to this rule; some cams actually feature more INTAKE duration/lift than on the exhaust side. It sometimes makes me wonder if cam manufacturers often jump on the dual-pattern cam "bandwagon" because they think that's what sells. Then there's also the possibility this is such an inexact science, that nobody really knows what the h*ll they're doing.

If the Shelby or Edelbrock heads don't flow all that well, are there alternatives? You mentioned AFR; does AFR make an FE head? As you can tell I'm still learning about FE's but I do know AFR makes some great flowing Chevy (whoops!) LS1/LS-6 heads.