Well im in the process of building a new engine in both my 67 Dart 408 stroker and 34 Rat rod 440 .30 over and other goodies. Anyways ive been reading and reading and reading about cams, and my head is about to explode. But ive learned a lot about cams and cam choices but i still am wanting to understand more about them and what makes them tick. For example what makes the chop in an idle? is it the lobe separation and lobe center-line? I understand to that rocker ratio and Cam lift is what determines valve lift. I just wanna understand more about cams cause it seams to me that the cam choice is the biggest effect on an engine. Thanks for the advice.
help me to understand cams
- Thread starter HOOCH
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Mo-Par
Well-Known Member
Cams are like women , will never figure them out 100 %.
Read every article you can on them.
Read every article you can on them.
Mrmopartech
Well-Known Member
Dude,i am going on 40+ years dealing with motors and cams,guess what,still learning every day and will in 20 years,mrmopartech
67Dart273
Well-Known Member
I don't think there "is" an easy answer. One is to ask here, post as exact as you can what the combo will be..........
Car, model, weight
axle ratio, transmission
intended use.....
"What you want" if street, IE mild street, radical as hell, etc.
You have to remember that the factory OEM combos came about after millions of dollars of testing and EVEN THEN sometimes they got it wrong
And........nowadays, many cam profiles are much improved over older, and sometimes, they are AFU.
We just went through this on a friend's car........had an MP cam that turns out was a dog unless advance "a bunch" from advertised.
Car, model, weight
axle ratio, transmission
intended use.....
"What you want" if street, IE mild street, radical as hell, etc.
You have to remember that the factory OEM combos came about after millions of dollars of testing and EVEN THEN sometimes they got it wrong
And........nowadays, many cam profiles are much improved over older, and sometimes, they are AFU.
We just went through this on a friend's car........had an MP cam that turns out was a dog unless advance "a bunch" from advertised.
Coronet 500
Well-Known Member
A smaller LSA Lobe Seperation Angle, which gives more overlap is what makes the chop.
As an example look at some of the Thumpr type cams out there now, even if the advertised duration is not that big it will have more overlap than a similar one that is not advertised as "with that muscle car sound".
As an example look at some of the Thumpr type cams out there now, even if the advertised duration is not that big it will have more overlap than a similar one that is not advertised as "with that muscle car sound".
Isky's catalog's,have some really good basic information as well.Above all,be honest about what you actually wan I it to do. And patience in degreeing & installing it. Slapping stock rockers, push rods,& valve springs,guarantees it won't perform/last like it should.
fishy68
Tyr Fryr's Inc.
What causes a engine to lope/chop at idle is really a combination of several things, including the engines size. Tighter lobe separation, duration (total and at .050" lift) and valve lift and engine size are the 4 factors that affect it most. A cam that idles pretty choppy in a 273 might idle perfectly smooth in a 408 stroker because larger engines "eat up" duration. That only answers part of your question. Reading the Comp cams info will answer a lot of other questions.
In any case your always best off having a cam custom ground for your particular application by a reputable cam grinder rather than try guessing what might work, unless you have a lot of experience with engines and cams. I have used both Racer Brown and Bullet cams with real good results and there are several others out there that are good. Maybe some others will chime in on who they like.
In any case your always best off having a cam custom ground for your particular application by a reputable cam grinder rather than try guessing what might work, unless you have a lot of experience with engines and cams. I have used both Racer Brown and Bullet cams with real good results and there are several others out there that are good. Maybe some others will chime in on who they like.
67Dart273
Well-Known Member
^^As well as the intake manifold, for another^^
But I've never been one to buy a cam "just because" it makes a lot of rump-rump in an otherwise mild engine. Do you want to be first down the road, or "first" to sit there and impress the onlookers who are NOT paying to build your car?
But I've never been one to buy a cam "just because" it makes a lot of rump-rump in an otherwise mild engine. Do you want to be first down the road, or "first" to sit there and impress the onlookers who are NOT paying to build your car?
Thanks for all the reply's fellas and the links too. I understand its going to take a long time to understand it all but im young so i got time to learn. Ive spent a lot of time talking with delta camshaft choosing the right custom grind for my build. Ive been very particular with choosing my parts to make sure they all work together. Im just searching for info so i figured asking here would help me on my path to enlightenment.
moper
Well-Known Member
The biggest problem with cam theory is they are the heart of the engine, and an engine is very individualistic. You can have two 408s, with every part exactly the same, but have different cams, and they will be totally different personalities. Conversly you can have the exact same camshaft in a 360, and a 408, and again - they will be entirely different.
In terms of "short and sweet" hints...
The longer the stroke, and the higher the static compression ratio, the smoother the idle and lower rpms the power will occur at for any given camshaft.
The wider the Lobe Seperation Angle, and/or the higher numerically the Intake Center Line, the smoother the idle and the flatter the power peaks will be.
A solid flat tappet cam and a hydraulic flat tappet cam that are "identical" on paper are not identical and the hydraulic will have the more raspy idle and a more peaky power curves.
In terms of "short and sweet" hints...
The longer the stroke, and the higher the static compression ratio, the smoother the idle and lower rpms the power will occur at for any given camshaft.
The wider the Lobe Seperation Angle, and/or the higher numerically the Intake Center Line, the smoother the idle and the flatter the power peaks will be.
A solid flat tappet cam and a hydraulic flat tappet cam that are "identical" on paper are not identical and the hydraulic will have the more raspy idle and a more peaky power curves.
Fisher
Old Guy with a Cool car.
I look at Lift and duration as Time and opportunity. You want to fill the cylinder with as much air fuel mixture as you can, and you need to be able to evacuate that cylinder as well. A certain amount of overlap is good, the exhast valve open will help draw in your intake charge. Its a fine line. When you call a cam grinder, ask what the duration numbers are at.050 as well as .0200 that will tell you how fast the ramps are on the cam. The Lunati Voodoo cam i have now has fast acting ramps, but in the same breath its not going to beat the **** out of the valvetrain.
Your best bet is to sit down with your engine builder who should have a good grasp on this. Mine is awesome, we have sat down on every build i have done, and determined what the GOAL was to start??? Street car, race car, pump gas, race gas? How much HP would you like to have. Then pick all the parts accordingly.
Sorry but asking people on the internet what cam should i use wont really get you the answer you need. People can tell you their combo and what worked and what didnt work? But why throw good money after bad.
Your best bet is to sit down with your engine builder who should have a good grasp on this. Mine is awesome, we have sat down on every build i have done, and determined what the GOAL was to start??? Street car, race car, pump gas, race gas? How much HP would you like to have. Then pick all the parts accordingly.
Sorry but asking people on the internet what cam should i use wont really get you the answer you need. People can tell you their combo and what worked and what didnt work? But why throw good money after bad.
oh i completely agree with you on this. i just like picking the brains of folks on here, and ive picked up a ton of good info. Plus i know a lot of you guys have had lots of trial and error in the motor building department. But sitting down with my engine builder will be kinda difficult seeing as he is 4hrs from me, the 2 builders here are junk and wouldn't use them if i was paid for it.
At least you took the time,to find a good one.
Cams have bumps that open and close the valves.
Ya he was recommended to me by a friend and was told his shop is surgically clean, said you can eat off the floor, an he wasn't lying this guy is quite anal about cleanliness and organization. So it made me feel like I made the right choice. Plus my buddy's LS1 goes 8's in the quarter, so I think the guy knows his stuff.
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omahamoparguy
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I've been messing around with these things for over 30 years and yes I too am still learning.
There is a book that I have bought just recently by a guy by the name of David Vizard. The book "how to build horsepower" has a complete chapter (and more) just on cam function and theory. Some of my long held beliefs on cam selection have now been changed due to the information revealed in this book. If you can set up the overlap to work with a scavenging of the exhaust setup, you can reap great advantages in efficiency and power. I recommend the book for gaining knowledge in cam theory.
There is a book that I have bought just recently by a guy by the name of David Vizard. The book "how to build horsepower" has a complete chapter (and more) just on cam function and theory. Some of my long held beliefs on cam selection have now been changed due to the information revealed in this book. If you can set up the overlap to work with a scavenging of the exhaust setup, you can reap great advantages in efficiency and power. I recommend the book for gaining knowledge in cam theory.
I love Vizard's work. He thinks out of the box.(applied physics, like Smokey Yunick..). It happens,and an explained reason behind it.
Cam selection can be critical or general. It all depends on what your after. The 440 Rat Rod, just by the title of it, sounds like cam selection is less critical.
The s/b 408, what are you doing with it?
The s/b 408, what are you doing with it?
Idaho
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I fried my brain doing the reading and reading thing too. :violent2::violent2:
Rusty's quip tickled my funny bone but in fact says a lot.
Many newer engines have variable valve timing. In a way the benefits of it explain why an engine that runs strong at high rpm has the crappy idle we are so fond of
This is merely a random observation not intended to be of any real value whatsoever from a fellow member of the fried brain club.
the 408 is just going to be toy, hit the streets, and track i doubt if the car will see 2000 miles a year Im looking for a very healthy very nasty sounding sb. the car is a 4spd and im not too worried about street manners as most of my cars dont have much for those. I love th sound of the thumpr cams but there performance is terrible, id like to have my cake and eat it too.
moper
Well-Known Member
Smokey's speed secrets bookis great too...
fishy68
Tyr Fryr's Inc.
A tighter lobe separation (106) will produce a nastier idle. Power is a little "peakier" and drops off a little sooner than a wider lobe separation so you may have to run some more duration to make it spin up more rpm's and that'll also add to the nasty idle your wanting. If you go this route make sure the heads and compression can support it or you'll just have a nasty idling pig
To try to simplify how I think about cams:
Duration determines the power band (sweet spot).
Mild engine use 240° - 260° duration
Street/strip use 260° - 280° duration
Race uses 290° and up.
Lobe separation is how far apart the lobe centers are. A larger separation means the lobes are farther apart and reduces overlap. A smaller separation means the lobes are closer together and increases overlap. Larger cams need more overlap than smaller cams.
Lift is how far off the seat that the valve opens. More lift = more flow.
This is just basic simplified explaination.
Duration determines the power band (sweet spot).
Mild engine use 240° - 260° duration
Street/strip use 260° - 280° duration
Race uses 290° and up.
Lobe separation is how far apart the lobe centers are. A larger separation means the lobes are farther apart and reduces overlap. A smaller separation means the lobes are closer together and increases overlap. Larger cams need more overlap than smaller cams.
Lift is how far off the seat that the valve opens. More lift = more flow.
This is just basic simplified explaination.
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