dual and single pattern cams [Archive] - Chevy Nova Forum

: dual and single pattern cams


69NovaSS
6th-August-2006, 08:52 AM
Some cams are duel pattern(intake & exhaust have different lift & duration numbers) and some cams are single pattern(intake & exhaust have the same lift & duration) Cam makers like Isky seem to like the single pattern cams while most other cam makers really seem to like the duel pattern cams (of course I'm positive you can get both from all cam makers if you want)


I am looking at two different cams at the moment. One is single pattern and one is duel pattern. So whats the scoop is one better then the other or is it an application issue (depends on the application/combo) or it really makes no difference?

NOVACA1N
6th-August-2006, 10:21 AM
Dual pattern...I saw a tech article in a magazine not to long ago ( I forgot the magazine) and the dual pattern made more power...plus they love nitrous!!:rolleyes:

69NovaSS
6th-August-2006, 10:28 AM
Dual pattern...I saw a tech article in a magazine not to long ago ( I forgot the magazine) and the dual pattern made more power...plus they love nitrous!!:rolleyes:

Duel pattern might make more power at the top end but from what I have read single pattern cams will make more torque here is a quote form the Isky site

Longer Exhaust Duration: Is this really necessary?

Most stock camshafts from American production V8, V6 and 4 cylinder engines manufactured today are ground with the longer exhaust lobe duration. Or, another way of looking at this is that they are ground with shorter intake durations! The former embraces the viewpoint that either the Exhaust Ports or Exhaust Pipe system is somewhat restrictive, and is in need of an assist. The latter suggests that the intake system is rather efficient and cam timing can be trimmed back a bit with out much sacrifice in power, in order to maximize throttle response and cruising efficiency.

Take your pick here. There is no absolutely correct viewpoint - because both are probably true! In a stock engine running at conservative RPM levels, for the sake of overall efficiency, fuel economy and a quiet smooth running engine, this staggering of intake and exhaust duration is quite common and appropriate.

However, High Performance is another thing entirely. Change one factor, let's say in this case, the exhaust system (installing headers and larger pipes) and you have just negated in most cases, the need for that longer exhaust lobe. Now couple this change with a different intake system and camshaft and you have really scrambled the equation. But, wait just a moment. Why is it that so many people (racers & cam grinders alike) insist on running a cam with longer exhaust duration regardless of what equipment is employed? The answer is "habit". Most of them have been somewhat successful in doing it their way and will probably never change unless virtually forced by circumstances to do so.

Before we go any further however let's review what it actually is we are trying to do with an engine when we attempt to make more power. Our best result comes when we are cognizant of the fact that an engine is basically an air pump. We pump it in and out (although in a different form) and we have problems when one side or the other is restricted. Balance or the equilibrium or flow should be our objective, unless of course we are not trying to make more horsepower!

Example #1 (Oval track racing) Here, I have often observed that the most experienced drivers are those who are most likely to run a single pattern (equal on intake and exhaust duration) cam. Why? Because such cams always, I repeat always make more torque! These veterans have a more educated foot and greater experience in feathering the throttle in the corners. They can therefore, utilize the benefit of added torque, in the lower to mid RPM range, to their advantage.

Their counterparts, the younger drivers on the circuit, generally are not as experienced and may at times actually get "crossed up" in the corners especially with a lighter car or when they are learning the ropes. In their case, a longer exhaust duration is often the more appropriate choice. It will often help them to drive better, more "flat footed" if you will, without consequence. But please for the sake of accuracy, let us be truthful. The benefit comes from an actual bleeding off of low to mid range torque, which is always what happens when Exh. Duration is lengthened, not from any improvement. The improvement, (if any) would come because of an improvement in scavenging at the extreme upper end of the power curve and would usually be marginal at best. Yet the so-called "extra power" potential of a longer Exh. Duration cam is most often why they are touted - power most people are backing away from at the end of the strait away!

Example #2 (Drag Racing) At the drag strip it's a little different and I feel more honest. Here, racers have long enjoyed longer exhaust and longer durations across the board (If I may add specifically for the purpose of "killing" low-end torque) to keep the tires from too easily breaking lose. This has been successful and sometimes actually results in a slight increase in top end power - something you can actually use in drag racing since it is a full throttle endeavor through the lights. Keep in mind here though, it's quite possible that a longer duration cam overall would have done just as well or better. In other words if you needed that longer exhaust for top end, perhaps the intake could have benefited from such a lengthening as well.

One of my favorite expressions is how "The Drag Racing mentality has infiltrated the ranks of Oval Track". Many have crossed over and made the switch in the past 10-15 years and some have brought their preconceived notions about how to cam an engine with them. A few may actually read these concepts and if they do so will at least come away with a better understanding of what they are doing. On the other hand they also could find that this information might actually help their cars to run just a bit faster!



http://www.iskycams.com/techtips.php#2003

novaboy009
6th-August-2006, 11:25 AM
If the exhaust port approaches 75-80% or the intake port, the single pattern cams tend to work better. The dual cams are a crutch for the weak exhaust ports of a SBC. That ones out of David Vizards book.

Kev

69NovaSS
6th-August-2006, 12:14 PM
If the exhaust port approaches 75-80% or the intake port, the single pattern cams tend to work better. The dual cams are a crutch for the weak exhaust ports of a SBC. That ones out of David Vizards book.

Kev


Ya I've read the same thing before however not specificly from Vissard. The quote from Isky sort of addresses that issue. I dont know which is right to be honest. Maybe they both are depending on the setup/situation.

Isky does say it will make slightly more power up top with duel pattern cams but at a sacrifice of low and midrange torque. Which as they point out would be good for drag racing. In other motor sports where low and mid range torque would be an advantage a single pattern cam always makes more torque. I would suspect too that a single pattern cam might be a better cam for the street where low and mid range torque are more important then all out high rpm power is.

I dunno cause you read so much info that seems to contradict each other that its hard to decide which is best or who is right. One thing I will say is that Isky cam has been around a very long time and I suspect they have a lot of dyno time behind them with their various cam designs to be able to see the certian trends. Not saying their right just pointing out I suspect they have a lot of first hand knowledge. Just like Vissard does too. Like I said its hard to decide who you believe and who you dont;) :)

Paul Wright
7th-August-2006, 12:28 AM
It comes down to port flow AND what kind of exhaust system you have. The worse the exhaust is the more it will benefit from a dual pattern cam.
On some engines the intake is poor so the dual pattern could favor the intake.

69NovaSS
7th-August-2006, 07:53 AM
However, High Performance is another thing entirely. Change one factor, let's say in this case, the exhaust system (installing headers and larger pipes) and you have just negated in most cases, the need for that longer exhaust lobe. Now couple this change with a different intake system and camshaft and you have really scrambled the equation. But, wait just a moment. Why is it that so many people (racers & cam grinders alike) insist on running a cam with longer exhaust duration regardless of what equipment is employed? The answer is "habit". Most of them have been somewhat successful in doing it their way and will probably never change unless virtually forced by circumstances to do so.


http://www.iskycams.com/techtips.php#2003

It comes down to port flow AND what kind of exhaust system you have. The worse the exhaust is the more it will benefit from a dual pattern cam.
On some engines the intake is poor so the dual pattern could favor the intake.

Paul; your comments sorta support what Isky said in their tech tips. thanks for your input:)

askgene
12th-December-2008, 07:16 PM
Duel pattern might make more power at the top end but from what I have read single pattern cams will make more torque here is a quote form the Isky site


http://www.iskycams.com/techtips.php#2003
I dont think thats the reason at all its because that most stock heads flow much better on the intake side and not so good on the exhaust side.The ideal ratio of intake to exhhaust is 75-80% to get this ideal ratio most heads require a dual pattern to make up for the poor exhaust flow,Now my heads are Dart Iron platinums which flow 76-78% of the intake so a Single pattern was for me, if it was 71-72 % like RHS,proline,edlebrock rpms HDS,a dual pattern would make more power as the cam will make the exhaust side stay open longer,making up 4 the low % So u guys runnin Darts or AFR heads should try the 246/246 510/510 Lunati bracket master Hyd,or the 248/248 520/520 solid Comp cams u might be pleased......:yes:

bowtie0069
12th-December-2008, 08:10 PM
The ideal ratio of intake to exhhaust is 75-80%

That depends on who you're talking to. I know a story of a Super Stock racer who had some porting guru get his exhaust to flow 75% and the car was slower than ever. He was told by a another guru to fix the heads and the car would pick up--with the heads flowing 61% (which some feel is the ideal number) the car was much faster and responded to tuning changes a lot better than before. Mine flow over 83% which is probably why it responds so well to nitrous; or boost, and why it doesn't run any better uncorked.

tnblkc230wz
12th-December-2008, 09:24 PM
Isky's statement about stock exhaust systems needing a assist makes sense.

levisnteeshirt
12th-December-2008, 11:34 PM
in Grumpy Jenkins book ,, ( kinda old ,, but its still good reading ) , he descibes using a split pattern ( 10 degree split ) in his full race tunnel ram engines , because the intakes work so well . On his nascar engines of the period ,, he recommended 4-6 degree split. I love reading his stuff. This is a guy that wasn't scared of some cam timing ,,LOL ,, he ran 282/286 at .050 in his nascar engines for long tracks ,, a 354 drag engine got 290/300 at .050 , a 330 in engine got 282/292. He liked to twist the 354's to about 8000, and the 330 to 9500 and liked 109 LSA until cubic inches started going up

71SS454
13th-December-2008, 12:48 AM
As for the torque thing, I don't get how a single pattern cam will always make more torque. If your dual pattern is lacking some bottom end, you can grind a cam, with a dual pattern, with a different LSA and intake centerline and pick up the torque while maintaining the top end. It all has to work together. Now the exhaust port will flow the same unless you report it. Now the dual pattern cam will help the poor exhaust tract to flow better, so you have to look at the entire engine package to decide which is better. Then once you decide single v. dual pattern, then you need to figure out duration numbers, what LSA you're going to need, and where to grind the intake (what center line).

whitelightning
13th-December-2008, 10:37 AM
Its probably worth your money to get a custom cam grinder to either tell you which aftermarket cam would suite your needs or make you a custom cam. Whether its single or dual is a byproduct of what was considered ideal based on a certain formulation, not because one works better than the other.

69NovaSS
13th-December-2008, 11:24 AM
holy old threads Batman, how do these things come back to life after two years on the back shelf:confused::)

Mike Goble
13th-December-2008, 11:34 AM
Sort of a duel of the duals?

Maybe it'll be the new signature line -

Four bolt fuel bowls and a dual pattern cam...