One thing I have been hearing alot here is that single pattern cams are not good choices for FE's, the 390 and 410 to be specific. My question is why? I'm not being argumentative, but rather want to understand why. I have a Comp cams 270 in my 416 and it is a single pattern cam with 224 degrees duration on both and .519 in of lift on both. It is a fairly beefy cam, it has decent lowend and an awesome top end but probably not the best cam for a pickup. Ever since I built the motor it never has run to it's potential however, it is never getting the right amount of fuel at any RPM but myself and other people have spent a lot of time trying to adjust the carb with no success. Could it be the cam? Would a dual pattern outperform a single? Right now I am looking at a couple of cams from Crower. One has an advertised duration of 280/286, with 222 intake and 228 exh. with .538 in of lift on the intake and .552 on the exhaust. Would that cam deleiver more power than my current one? The pickup is a 71 3/4 ton 4x4 and I use it for every thing. Light towing over the hills and every day driving. I usually lean toward the "bigger cams" because my CR is up around 10:1 and a 428 crank giving me the low end that i want, plus I'm low geared so I can handle a pretty lumpy cam, plus i like the sound of a lopey idle. Anyway, can anyone tell me why single patterns suck and what you think of the cam I mentioned from Crower and what other cams are out there?

 

It seems to me like you already know the answer, but I'll respond anyway.

A dual pattern cam works in that in benefits a weaker system. A longer duration on the exhaust side benefits a restricted, weak and/ or poorly designed exhaust port.

A longer intake benefits a poorly designed intake i.e. the Ford Flathead.

An FE engine has the weak exhaust hence a dual pattern cam is usually suggested for this engine. If Aftermarket heads, extensive porting has been done then yes maybe and I mean MAYBE a single pattern cam would work.

Most engines need help with the exhaust anyway, even the SBC.

In your case I think you are overcamming your engine. You are selecting cams that work in the higher midrange to high RPM power band, and you say you TOW and use this 4X4 as a daily driver. Which is low end RPM, say idle to 2000. I also assume you are also using too big of a carb, but I'll leave that alone.

If you want the RACE CAR LOPE select a cam with a tight lobe seperation such as 108 degrees and then select a cam that suits your actual intended RPM range. Most cam makers supply the ideal RPM range and the "cruise" RPM.


Josh

 

One thing to add. The best way to choose a single or dual pattern cam is by comparing flow data of the intake and exhaust. If your exhaust flows 70% or more than your intake than you should go single pattern. If it is less than you should go dual. Of course there is a gray area there around 70% and I'm sure there are exceptions out there but I think it is a very good rule of thumb. And then you have the flathead which has a very high ratio and you would get the dual pattern with the bigger intake lobe. One thing I don't really agree on above... A tighter lobe center will decrease cylinder pressure and give a rougher idle but a lot of hot street cams have 112 - 114LCA and just have bigger durations which will also decrease cylinder pressure and give a rougher idle.

 

The carb I plan on using is a Holley Truck Avenger 670. Is that a wise choice. I lean towrd the bigger cams because I do play with it sometimes and like the upper rpm power. It's not that I don't have any low end with my cam right now because I do, but not as much as i would with a torque intended cam. Thanks for he help, that answers everything I wanted to know.

 

One thing I forgot to mention. Right now i would say my operating range is more like idle to 3500rpm. When I am cruising down the highway at 60mph, I am a shade under 2500rpm and on the freeway I am close to 3000rpm so i need the power up there as well, so does that cam seem like a decent compromise or do you still think it's too much of a cam? Another thing is you can order a custom grind hydraulic cam to meet certain specifications. So what are some numbers of a true all around cam with say a 108 degreee lobe seperation? The only cams I see with 108 degree lobe seperation are top end cams, the rest have 112 or 114. What is the difference in performance between say a 108 and 112?

 

What was my point with a tighter lobe seperation?

A tighter lobe will get that race car style idle without giving up so much in the midrange. You say to just get a longer duration cam, kinda defeats the purpose 'eh?


Also, with the tighter lobe you will bleed off some compression at the lower RPM range, helping with detonation and such.

See side benefits.

Truck Avenger carb sounds pretty good. Not too big, not too small. I am a Carter AVS/AFB guy myself, but that isn't important.

Oh yeah, Comp Cams suck so I have heard. Go with Crane or Crower. Be sure to match the springs as well.

Josh

 

I definitely agree with that.

 

For 95% of our engines on here, the dual pattern is the way to go. Crower is good, but I tend to lean towards Crane. Have you looked at the "801" crane cam yet?

 

Not yet but I will, thanks guys