Justy

From what I understand single pattern cams produce more torque throughout the powerband but don't have the top end like a dual pattern. Is this correct? What other differences are there? Thanks.

RB83L69

That is not a correct generalization. What dual pattern cams do is to help compensate for the poorer flow on the exhaust side which virtually all SBC heads have a problem with, due to bolt hole placement etc. Other factors about cam design have alot more influence on the power band than that. A dual pattern cam properly designed and matched to the rest of the engine combo will produce more power at every RPM than a single pattern one can with most heads because it improves the engine's overall efficiency.

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"So many Mustangs, so little time..."
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ede

not to disagree with RB, but i've built several 355s with the lunati bracket master series cams (single pattern) and they make great power and seem to work well through out the power band. now maybe a duel pattern would make better power, but these single pattern cams work good too. not having time, money or a dyno to play around with cam selection i'm stuck always making an educated guess.

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ICON Motorsports

1st & 3rd

Justy

Well, here's the deal... I have an '84Z28 with a 305, T5, headers, catback, accel supercoil, and a recurved HEI. I want to port my heads and install an intake and new cam at the same time. I live in a small town and it's not often that I see 4500 rpm before hitting the brakes - so I'm trying to figure out what cam will give me more low and midrange power. I was thinking of Comp Cams 252 high energy --> 206/206 @ .05 w/ .425 lift. Is this any good or does it suck? Any suggestions for a cam? BTW I'm probably going to go for an Edelbrock Performer intake. Thanks

87RS402

RB, ede, your both right. While single pattern cams do make excellent power, split or dual pattern cams make up for the poor exhuast flow by allowing extra time for scavanging to take place. There will always be those who say they are one is no better (someone will be along shortly ) and in a some cases they aren't. I don't think they really work well untill your cam is trying to push the limits of flow for the application and/or high rpm's. At the higer rpm's they help to increase the cylinders abilty to expell the burnt gases allowing for a more efficent intake charge

There are many other factors that affect powerband and torque range like lobe separation.

I'm just starting to get into cam design and theory myself so I can only speak from my experience, but I have always used the dual pattern cams and had excellent results.

I just looked and all of the cams in edelbrock's performer kits are dual patterns in case you are wondering.

[This message has been edited by 87RS402 (edited January 21, 2001).]

Jester

As much as I hate to rain on all your guys overly verbose parades it's simple IMO. Unless you have high dollar aftermarket heads, you're better off with a dual pattern. If you do have good heads, ask the manufacturer. and it has been my experience that ede is never wrong.

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[This message has been edited by ede (edited January 21, 2001).]

BadSS

My experience,,, you can make good power from a single pattern,, it's just you can make more with a split pattern (ALL other things remaining constant). And I've installed / tested cams from 8.5:1 "stock" smoggers to 13.8:1 fully CNC ported heads.

Box of Rocks

Justy,

The engine builders' rule of thumb for ideal exhaust/intake flow ratio is 80%

So, if you have 200 CFM intake flow, you need 160 CFM exhaust flow. As RB stated (and I find he is very,very rarely off-base), most stock Chevy heads will not flow anywhere near 80%. Most flow from 58-70%.

This is why every major cam manufacturer offers dual pattern cams. If you have a good aftermarket set of heads that already flows 80% (such as AFR's and the new Gen 2 TFS) then a single pattern cam works best.

As previously stated, overlap has a major effect on exhaust scavenging, as well as pull-thru of the intake charge. A single-pattern cam with more overlap (all else being constant), will generally act more like a dual-pattern cam. This is generally achieved by grinding the cam on a tighter LSA.

Sorry for the "more than 30 seconds" response, but camshaft science is not understood by most people overnite; nor is the person asking the question served very well by skipping the gory details.

Good luck.

BOR

Justy

My heads are stock so I guess I'll be looking at some dual patterns. Thanks to all for shedding some light on the darkness. Later!

Grim Reaper

Good discussion. I think RB's comment that "it depends on your combo" is bang on.

Good flowing heads with a 1 3/4" full length headers don't need any compensation on the exhaust, as lesser heads or lesser exhaust; or someone with a power-adder.

Regardless of cam selection, with mixing 1.5 and 1.6 rockers, you can tailor either to effectively work like the other to find the combo that works best for your setup.

For the typical street engine with full muffler, cats and shorty headers; I'd lean to dual pattern.