Dual Pattern VS Single Pattern Cams
Burning Brakes
Joined: Nov 2000
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From: Johnston Iowa
Re: Dual Pattern VS Single Pattern Cams (blunsford)
The difference between a dual pattern cam and single pattern cam is that a single pattern cam has the same lobe profiles (i.e lift, center line, duration) on both the intake and the exhaust lobes of the cam and dual pattern cams can have different profiles on the intake and exhaust lobes of the cam. The advantage to a dual pattern cam might be if you have application where you want the exhaust valve to open a little farther on the exhaust stroke and maybe stay open for a little longer than on the intake side or vise versa. This is just a general example.
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Re: Dual Pattern VS Single Pattern Cams (Brettmc)
Basically designed for street cars running restricitve exhaust, I believe was the original intention. :D
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Re: Dual Pattern VS Single Pattern Cams (blunsford)
Remember...just 'cause it's new...it's not necessarily better!
Many old style cams are still exactly what your motor may require. You just have to do some homework to figure out what you need.
Brett is correct...the dual pattern usually is used in a situation where the exhaust flow needs to be increased. Like poor exhaust port design (small block Fords), stock type restrictive pipes, nitrous, extremely high rpm etc etc.
If you have decent heads, often a single pattern cam can be the best choice, but it's tough to tell without lots of testing.
I usually err to the dual pattern design (longer exhaust event) for most stuff that will run on the street through any kind of muffler. But once again, you have to watch out for the rpm range you are playing in..often smaller "restrictive" exhaust setups have fantastic scavenging ability in certain ranges and can "overscavenge" a little. This is really true if overlap increased much when you made the ex. lobe longer.
The tendency these days with all the killer heads out there, is to open the intake further either by lobe design or with increased rocker ratios, and if the intake/exhaust flow ratio is up above 80% or so, typically they move back closer to a single pattern cam. Once again..the better the ex. flows, the more likely it will like a single pattern.
But in 90% of the cases, I believe a dual pattern will "hang on" longer. The single may make more "peak" power in a few instances, but the dual will really help the top end. Especially if you are limited with exhaust in any way as compared to open header dyno testing. Even "X" pipes sometimes require different cams for optimum results.
When you start looking at cam catalogs and comparing specs you will find amazing differences in lobes with similar duration and lift numbers. The "rate" of opening has a huge effect. That's what makes roller cams run so well. They can "slam" the valve open and close faster without float or wear.
You will typically find the intake lobes are more "aggressive" than the exhaust. But many folks will grind the cam with two intake lobes to make a particular characteristic. That's where experience pays off. That's exactly what Joe Sherman did in that Engine Masters Dyno challenge in the magazines last year. It works!
But once again, don't fall for the advertising hype...lots of "new" stuff they talk about is in some old Ed Iskendarian books I have from the 50's!! In fact most of it! He was designing cams back then that utilized much of what is hyped today. Engines still have 4 strokes and they have worked for years optimizing the events. As SWC Duke says often on here...the factory engineers did a pretty decent job designing cams in the old days based on what parameters they were given. Throw in some new heads etc, of course the whole picture changes, but overall, engines haven't changed that much.
When I was working on my newest cam, we actually looked at some old Pro Stock grinds that were considered radical in their day. But these days with increased valvetrain ability (springs are drastically better) they would make excellent serious street cams!
JIM
Many old style cams are still exactly what your motor may require. You just have to do some homework to figure out what you need.
Brett is correct...the dual pattern usually is used in a situation where the exhaust flow needs to be increased. Like poor exhaust port design (small block Fords), stock type restrictive pipes, nitrous, extremely high rpm etc etc.
If you have decent heads, often a single pattern cam can be the best choice, but it's tough to tell without lots of testing.
I usually err to the dual pattern design (longer exhaust event) for most stuff that will run on the street through any kind of muffler. But once again, you have to watch out for the rpm range you are playing in..often smaller "restrictive" exhaust setups have fantastic scavenging ability in certain ranges and can "overscavenge" a little. This is really true if overlap increased much when you made the ex. lobe longer.
The tendency these days with all the killer heads out there, is to open the intake further either by lobe design or with increased rocker ratios, and if the intake/exhaust flow ratio is up above 80% or so, typically they move back closer to a single pattern cam. Once again..the better the ex. flows, the more likely it will like a single pattern.
But in 90% of the cases, I believe a dual pattern will "hang on" longer. The single may make more "peak" power in a few instances, but the dual will really help the top end. Especially if you are limited with exhaust in any way as compared to open header dyno testing. Even "X" pipes sometimes require different cams for optimum results.
When you start looking at cam catalogs and comparing specs you will find amazing differences in lobes with similar duration and lift numbers. The "rate" of opening has a huge effect. That's what makes roller cams run so well. They can "slam" the valve open and close faster without float or wear.
You will typically find the intake lobes are more "aggressive" than the exhaust. But many folks will grind the cam with two intake lobes to make a particular characteristic. That's where experience pays off. That's exactly what Joe Sherman did in that Engine Masters Dyno challenge in the magazines last year. It works!
But once again, don't fall for the advertising hype...lots of "new" stuff they talk about is in some old Ed Iskendarian books I have from the 50's!! In fact most of it! He was designing cams back then that utilized much of what is hyped today. Engines still have 4 strokes and they have worked for years optimizing the events. As SWC Duke says often on here...the factory engineers did a pretty decent job designing cams in the old days based on what parameters they were given. Throw in some new heads etc, of course the whole picture changes, but overall, engines haven't changed that much.
When I was working on my newest cam, we actually looked at some old Pro Stock grinds that were considered radical in their day. But these days with increased valvetrain ability (springs are drastically better) they would make excellent serious street cams!
JIM
