Single Pattern Cams - I'm stumped!!??

[Doug Wilson]

I've been around our hobby for a long time and have never been able to figure out why anyone would buy a single pattern cam - intake and exhaust specs the same.
Since what is happening with the intake charge before it gets to the valve is entirely different than the dynamics of the exhaust gas AFTER the valve, how could it make sense to use identical profiles on both?
If anyone has an answer, other than it's cheaper to build a cam that way (only have to set up the grinder once), I'd sure like to know the reasoning.
Thanks for your help in understanding this.

[fastback340]

because high flow heads dont allways need the extra flow

[rumblefish360]

Very good point fb340. The ideal percentage rate of exhaust to intake is a balancing act, when trying to make power. When this ideal area can not be met, dual pattern cams arrived. Also a higher rocker ratio can help in this area as well. With or without a dual pattern cam.
Good flowing heads will not allways need the extra duration in order to make good power. The best way is to compare things like this on a dyno. Check out cause and effects, pros and cons. Also, where will the benifit end if it does at all.
Cheaper to make a single pattern cam??? I think if some told me that I would have to balk at that.

[Doug Wilson]

If you are using CNC machines and spitting out a lot of identical parts, a single pattern cam would be only slightly cheaper. But, it would be cheaper, because of setup and programming time.

I STILL don't understand how intake and exhaust flow could be optimized with the same profile on intake and exhaust. I also don't think it can.

[Doug Wilson]

In addition, it's not just extra flow I'm referring to, it's optimizing the flow for the best possible effect on scavenging on the exhaust side - highest flow isn't always the best way to achieve maximum torque and horsepower at specific engine speed(s).

[sanborn]

Years ago, in pre CNC days, it was cheaper and much easier and less prone to mistakes to grind a single pattern cam. The grinder operator would grind the first lobe, index the lobe separation to grind the next lobe, etc. It required sixteen separate index changes to complete a camshaft. If dual pattern was desired, the operator would grind all eight intakes, manually change lobe profile master and grind the exhaust. The trick was getting the lobe separation correct after changing the lobe master. Of course, CNC equipment has changed all this.

Now to answer your question-Why would anyone use a single pattern cam today? They probably shouldn't. I suspect it is still somewhat cheaper to grind a single pattern cam. But with the accessability of modern flow bench capability we can easily spec a camshaft to fit the flow capability of our heads.

[rumblefish360]

Doug;

Your right as well as sanborn having a good point. But, theres nothin really wrong with a single pattern cam. A dual pattern cam is a better cam IMO. I will still recomend single pattern cams because the do work fine and I have exper. with sevral. I had 1 split cam from crane.

it's not just extra flow I'm referring to, it's optimizing the flow for the best possible effect on scavenging on the exhaust side - highest flow isn't always the best way to achieve maximum torque and horsepower

Oh, I agree that optimizing the cyl. for best combustion is the main idea. Getting a good balance from just what the head will flow is possible. However, I did leave out something in the quote.
(And this is where the can of worms come fully open I think. )

at specific engine speed(s).

I would say this sentence refers to a engine speed of....lets just say...6500rpm. This is sounding like a race engine to me. At this point, I can see a dual pattern cam for the racer tryin to eek out every last bit of power. Ya, the street guy is doin the same thing but at a different level. Not spending BoooKooo bucks in the process.
At this point if it were me, I would get a custom ground cam befitting the engine it will run in. Not just a custom from Comp thats sitting on a shelf.
Getting it perfect as to ones engine is a lot of dyno time and/or track time. That could be time and money well spent true, but few have the time and money to spend on that.

[Doug Wilson]

Thank you all. I haven't ever used a single pattern cam, at least as far back as I can remember(yesterday... 20 minutes ago... it varies). The one in the 440/452 tow motor was custom ground for me by Isky, and that's looking for peak torque as close to idle as I could get, and it's a dual pattern.
They also recommended it be installed 4 degrees advanced to help the low end. I considered proting just the exhaust side, and may yet do that.

[Doug Wilson]

That would be "porting".

[rumblefish360]

Custom ground for me by Isky? Sweet!!! Not for nothin but I do see your point in using a dual pattern cam. There main idea is to help out the cyl. head thats not up to snuff. porting should only help.
If the heads ported, the intake charge should only improve (more in) and be cleaner as well as more powerful.

[sanborn]

Most serious race engine builders say the ideal intake/exhaust flow ratio is exhaust about 80% of intake (nonsupercharged, gasoline, unrestricted intake system).

Only a very few race only heads achieve this. I don't know of any stock Mopar heads that come close-except maybe the Hemi.

Most stock SB and BB heads I have worked with on the flow bench show the exhaust about 68% of intake. W2s are the exception. Most of our performance work should be with the exhaust but yet most of us start on the intake which is backwards.

Dual pattern camshafts ( and multiple ratio rockers) enter the picture. We can use longer duration/higher lift on the exhaust to make up for a poor flowing exhaust port (remember this is for race only). I have found that up to 10 degree longer exhaust on stock heads helps a great deal at higher RPM (7000 up) and up to 6 degree on W2s. Higher lifts don't seem to help much except on W2s.

Have also done some work with dual plane intakes. Same thought applies but reduce the split back to about 4-5 degrees.

If any of you ever get into restricted intakes ( 2 barrel carbs, restrictor plates, etc.) you will find probably the best performance is obtained with exhaust durations shorter than intake. A good example of this is Nascar Busch engines. They use a Holley 390 four barrel carb. Most of their roller cams use exhaust 2-5 degrees shorter than intake (but their exhaust is .030" higher). And they use longer lobe centerlines as well but that gets into another can of worms.

Hope I didn't confuse everyone.

[djswwg]

generally the rule of thumb is split duration cams for street type engines looking for mid-range tork and running full exhaust systems; single dur. cams for wide open throttle/max power applications. again, this is just a general guide line. go to isky cam's website for an in depth explanation about why the differences and how they work. you will notice that Isky prefers single pattern cams, and they explain why....djs

[jelsr]

Best reason I can come up with is they work very well. However, I was wrong once years ago! Actually turned out to be a mistake.

[fastback340]

i think the saying is i thought i was wrong once ,turns out i was mistaken i love that saying

[Mopar_Mudder]

Originally posted by Doug Wilson
The one in the 440/452 tow motor was custom ground for me by Isky, ..... They also recommended it be installed 4 degrees advanced to help the low end.

Just a question here, but if it is custom ground why would they want you to install it 4 deg advance? Why did they not grind the cam that way to start with if it is going to be better? Make no sence to me........

[Tarrbabe]

Cam talk always gets my attention due to the mysteries of flow enhancements. To hear most people talk about cams, they are straight forward, almost cookie cutter technology. There is more than simple tech. involved from my past experience. Here's the bad part so dont start throwing rocks. A number of years ago, about 20, I traded my 68 Polara for a 66 Nova. The 327 ran like crap and used oil baddly and backed up with a stock powerglide and 3.07 gears. This car wouldnt get out of its own way. After I traded I rebuilt it to stop the oil problem and found out it had a solid cam, big block oil pump and Hooker Headers. The rest of the short block was stock down to the cast pistons. The cam had the lifters set at 0 lash when I got it and found out by trial that .028 worked best for lash. Don't know what cam it was but sounded nice and was a dog until tach hit 2800 and the right rear tire would break loose and start spinning. Best running chevy I ever had. But the best part was it had that Super Stock sound, you know that WaaaaaammPaaaaaaaaa sound from the headers. My question is what matches the cam and exaust so perfectly that you can actually hear the scavaging? Anyone that wont throw rocks want to take a shot at that?

[Doug Wilson]

The Isky guy told me that, even though the cam was ground for my application, Installing it advanced would still improve the bottom end. Basically, he told me that ANY grind can get more low end by installing it advanced. I did not then, nor do I now, believe that.

[djswwg]

Doug-he's right, and if you retard it 4 it''ll lose bottom end power but have a harder top end charge. But don't believe me, try it yourself.......djs PS, check out the explanations on the Isky cam site, it's well worth reading

[Doug Wilson]

Thanks for the info. I will check their website. Also, I did install the cam 4 degrees advanced. I'd have to undo that to get an "as ground" baseline. Not gonna happen. Like the engine fine. Any comments on my other post today "Offenhauser manifold"?

[Tarrbabe]

that was strange, i guess the moderator didnt like the timing of my post. maybe i will have to look elsewhere.

[hey-you]

Every cam manufacturer has different ideas and thoughts about there particular product.
Hustle stuff, Direct Connection, Mopar performance has been selling single pattern cams for many years, and have quite successful in doing so.
I guess this is a topic that is very controversial and i'm curious on it's end result, like politics.
But in the long run, it's all a question of, if it works, why fix-it.

I think it's getting late...Time for bed.

[sanborn]

Let me add a little more wood to this fire.

Several have asked the question, why do the cam mfgs. grind a 106 intake c/l cam and tell you to install it 4 degrees advanced.

Think about this for a minute. When you degree in a camshaft (degree wheel, dial indicators, etc.) there is no resistance to rotating the camshaft. When you bolt on the heads (springs, rockers,etc.) you have a great deal of resistance to rotation. When the engine is running you have more resistance to camshaft rotation. In other words you have timing chain stretch.

The next time you degree in a camshaft, after you have the advance set where you want it, go back and record the degrees where the lifter is up .050" from the back side of the lobe. Write that degree down. Then install the heads, rockers, adjust valve lash on all but that one lifter. Recheck the degrees at that same .050" on the same lifter. I bet you will find the camshaft has retarded about 2 degrees. I have done this several times (even with all springs, rockers, etc.) and have found this to be true.

I'm sure not all chains stretch equally, gear drives are also different and I understand belts are far different (never used a belt system but I understand even the Jesel stretches far more than chain).

Don't know if this answers your question totally but I bet it accounts for most of the advance recommendation.

[sanborn]

Sorry, can't leave this subject alone.

For a particular engine there isn't ever a ideal camshaft. As the requirements on the engine change so does the ideal camshaft requirements. If you are a street runner, the engine has one ideal configuration, if you drag race there is another ideal configuration, etc. If you oval track race (as we do) the requirements vary according to the length of track, tacky or slick, flat track or high banked, etc. So choosing a camshaft is at best a compromise, sometimes a guess and often times trial and error. Go into any serious racers shop (who builds their own engines) and you will see a half dozen camshafts in boxes. They are the result of trial and error or are used at various tracks. Heck, I am trying to decide on the profile of a new cam for my flathead Ford engine. I got two already and I may change to another. Why? Because it doesn't hit the "Lick" I want. Sound crazy? Yeh, but for "geezers" that's what makes the world go round (in addition to old dogs, smooth whiskey and pretty women)!

If I can digress a little (for you young guys who are bored, turn me off) back in the early 50s There was a guy in Nashville who owned an Indy Champ car. And I would ride my bicycle over to their shop and watch them work on that USAC champ car. There I learned about genuine Meyer-Drake Offenhauser engines. They were double overhead camshaft engines. One cam for the intake valves the other for the exhaust. You could change one cam at a time. There I learned(although I really didn't know what I was learning) about the effect of camshaft timing on performance. The head mechanic (Johnny Albright) was an old guy (maybe 40) but he had the patience (and time) to teach a kid about engines. He would show use how to change camshaft timing to meet track conditions, etc. Unfortunately, I don't remember 1/10 of what he told us but I still have the memory of it. Sigh, I try to carry on the legacy today when I can. Don't know as much as Johnny but I try to pass on what I know.

Sorry I'm so wordy.

[Doug Wilson]

I think you should be ashamed of being a geezer. Youth is good. Old people are embarrassing. Who would want to hear anything YOU have to say. Go down to the VFW and drink whiskey with the other Civil War Vets, where you belong. Experience in the world is meaningless, and certainly, anything you learned in the '50s could have no value in the 21st century. You should be replaced at work with a 23 year old MBA.

Ooops... that's what they say to me.

I'll be 58 in May.

I hate it.

Young mind, old body. Sob...

Thank you for your thoughts, and keep 'em coming!

[sanborn]

Doug, we are the same age. Not old, just "high mileage". Wonder if we could have our own section "For Geezers Only"?

[Doug Wilson]

Sounds good to me! We could chat about things like when they changed over from wooden wheels, flying machines, Nesbit's Orange, wild trout, whether or not 8 cylinder engines would ever make it, computers you could walk through... stuff like that.

[moeflo]

Doug, listen to Sanborn. He'll deny it, but he knows his $hit. I've down-loaded a complete piece he did on small-block oiling modifications, just in case I ever do one.(and I don't build motors)

As far as the single pattern cams, I'd have to add, that every motor, if worked out, will want something different, depending on the arena it is to play in. Fact is(and this is what I do) you can totally change the way a specific cam acts, by how the heads you use have been done. If you have big low-lift numbers, you'll pay a price at hi lifts. Is this bad?, depends on your cam. A rule of thumb is strong "off-the-seat" flow will be much like having more duration in your cam. And what's best is a matter of the relationship between your stick, and your heads/intake/headers. And one reason them guys whats got the money run better than us guys whats don't got the money, is they can beat these combinations to death, on their dynos. Gives you a hell of a lot better 1st shot at the track.

but the magazine "wizards" don't know how your induction and exh system is set up. They are selling parts. And you can bet the farm, after you attempt to provide all the info you can , about your motor, they'll have just what you need. And in stock!
About the best you can do is pick one, study the results, and make a more educated 2nd choice, based off your results.

[Doug Wilson]

Your comment about magazines being in the business of selling parts is right on the money. That's why I try to learn as much theory as I can, and watch what happens at the track. It's still a crapshoot!

[sanborn]

Moeflo, I appreciate the kind words. I try to help where I can. Sometimes I get get too wordy, especially with my old stuff.