Cam's The Big Picture

[Zell]

Hi everyone, between different engine rebuild guides and all of the info everyone has provided on the forum in other threads I've gotten very comfortable with a lot of the language around cams (lift, duration, overlap, etc.)

I've read a lot of specific setups where people ask if a specific cam will work with certain lifters in threads on FBBO.

If I change the cam, can someone explain the big picture of what else may need to change? E.g. if the lift increases and the overlap increases, then more air is coming into the cylinder so make sure that X is adjusted. Or is this really dependent on the cam chosen?

I have a spare 440 block that came with a cam, crank, heads, and some lifters, valves, and rockers (not sure about the valve springs) in the garage that I got with a car I bought and I wanted to try doing an engine build for the first time. No time like the present to get your hands dirty

 

[66Satellite47]

If you have bigger flowing heads, more duration and lift makes more power. Duration though is tricky for best performance. Lots of performance gain from a little bowl porting on any of the stock iron heads. Again better airflow makes use of the higher lift & longer duration. Aftermarket aluminum BB heads will respond out of the box to bigger cams. For cams big is good, too big tends to break parts.

 

[dvw]

Generally speaking more duration raises the rpm range. Lift and duration are are linked due to the fact that the ramp on the cam can only be so steep. A roller wheel on the lifter will allow a steeper ramp on the cam. Thus more lift for a given duration. As the cam gets more aggressive the springs need to have more load to keep all the valve train parts in contact with each other. As more load is added the need for better components pushrods, rocker arms, spring retainers, valve locks comes into play. As for specs the better the head and intake, the larger the cam the more power it will make. Just remember to big a cam may put the RPM range beyond where you want to be. Adding compression will help crutch a larger cam. But now your out of pump gas territory. Make a honest evaluation of the intended use of the motor. Street? Track? Both? Budget? Desired power level? Then a plan can be laid out.
Doug

 

[lewtot184]

depends a lot on what you want to do. I do believe the relevance of camshafts can be overstated to the point of mythical. the valve timing and lift has to match the other components (intake/heads/exhaust). It can be a juggling act. learning camshaft math is a big help. fuel requirements will dictate timing events. intended usage; and it goes on and on. if in doubt the safest thing to do is go one step smaller.

 

[451Mopar]

The standard camshaft specs are really just a shorter way to define the valves opening and closing points.
Example: Comp XE262H big block Mopar cam specs are 262/270 @ 0.006" lobe lift, 218/224 @ 0.050" lobe lift, 110 lobe separation angle (LSA in cam degrees), 106 degree intake lobe centerline.
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=706&sb=2
All the duration numbers above are in crankshaft degrees, except the lobe separation angle (LSA). The LSA determines how much "overlap" the cam has as from the time the intake opens to when the exhaust closes.
The cams intake and exhaust duration and the lobe separation angle are ground into the cam, while the Intake Lobe Centerline (ICL) is the recommended installed position of the cam to the crankshaft.
So using the recommended 106 Intake centerline installed position, the open and closing points of the cam are:
Intake Opens: 25 Degrees Before Top Dead Center (TDC, when the piston is at its highest point, closest to the cylinder head.)
Intake Closes: 57 Degrees After Bottom Dead Center (BDC, when the piston is at its lowest point, furthest from the cylinder head.)
Because the difference from TDC to BDC is half a circle, or 180 degrees, you would add the 25+180+57 = 262 degrees intake duration.
Exhaust Opens: 69 Degrees Before Bottom Dead Center (BBDC)
Exhaust Closes: 21 After Top Dead Center (ATDC)
Again, adding the numbers together gives 69+180+21 = 270 degrees exhaust duration.
Changing the installed Intake Centerline, will not change duration or overlap, but it will change the open and closing events.
For example installing the cam with a 108 intake centerline gives these open and closing events:
Intake Opens: 23 Degrees BTDC
Intake Closes: 59 Degrees ABDC
Exhaust Opens: 67 Degrees BBDC
Exhaust Closes: 23 Degrees ATDC
In this case the overlap of where the intake opens and the exhaust closes are equal, and is referred to as "split-overlap".
Usually the installed position is slightly advanced of split-overlap to account for timing chain stretch, but often cams are also advanced to close the intake sooner to increase the compression pressure.
The intake closing point is used to calculate (estimate) the compression pressure, but that is another topic.
In very general terms, duration determines the engine RPM range where it makes best power. Lower duration makes more low RPM power, and Higher duration makes power at higher RPM levels.
Overlap, a combination of duration and lobe separation angle (LSA):
A narrow Lobe separation angle (example 106 degrees) creates more overlap. This usually has a rougher idle because the exhaust and intake are open at the same for a longer period. The torque curve may peak higher in the mid to upper RPM range.
A wide LSA (example of 112 degrees) has less overlap. Usually a smoother idle, and a flatter torque curve through the RPM range.
Again those are very general because overlap is a "Combination" of overall duration and LSA.

Lobe lift:
More lift for a given duration is generally better for power, but harder on the valve train.
With more lift, RPM, and valve train weight, you need stronger springs and pushrods.
Directly related to lift is checking for valve train binding with the valve springs, valve guides and seals, and rocker arms.

Piston to Valve clearance:
This is related to duration, overlap, and the cams installed position, not advertised max lift.

 

[threewood]

First thing is make sure your valve guides and springs can handle the additional lift without going solid and second that the extra valve lift won't bump the pistons.

 

[PRND21]

A lot of good information here. A couple of numbers not often discussed in cam comparisons, that is cubic inches and LSAs. A certain big block Chrysler cam will act very different in a 383 compared to a 440 or even bigger. As 451 wrote, a couple of degrees difference in lobe separation angles will make cams with the same lift and duration act very different. Lewtot knows from experience; expectations, engine combination, transmission type and converter, and rear end gears all have to be considered to make a well balanced set up.

 

[451Mopar]

I was just trying to cover the basic ideas of open and closing events and how they relate to cam specs, before tossing different cam specs around and how they might effect the engines power curve.
In general (again) you need to look at the entire vehicle as a system, and have parts that work together.
That is why cam makers want to know all the info about the vehicle and engine, then they can develop cam specs that will produce a type of power curve for the application.
If you have a race car with high stall converter and gearing to keep the engine at higher RPMs, the cam can have much more duration and overlap than a daily driver street car (what ever that means, since some people drive their race cars on the street too?) Anyhow, getting away from those exceptions, a street car will usually have a tight converter and gears that keep the engine operating in the low to mid RPMs which usually means less duration and less overlap.
So, post up your vehicle specs and how it will be used, and the members will have a better idea of what cams to recommend.

 

[lewtot184]

camshafts to me are like torque converters; foggy bottom. when in doubt error to the conservative side, and you just can't check and measure enough. everything above the tappet has to be considered and matched.

 

[Zell]

Thanks for the great explanations, everyone! @451Mopar, I appreciate the breakdown on LSA, opening and closing, impact on RPM (and everything else).

I was looking to build a fun driver, by this I mean it does not have to do <12s or <11s seconds at the track! (I'm read some crazy builds on this forum). 440, 4spd (A833), 3.73 gears. Looking to mod the 4spd down the road to a 5spd for 5th cruising gear. Being realistic, I would want a lower RPM power curve, so little less duration, wider LSA cam from what I'm reading. (Sorry hardcore power guys!) Is it still possible to get a cam that has enough overlap to cause that 'put-put' sound at idle for a daily? Or does that typically come with much more aggressive cams? I heard a 440 with a voodoo cam that has that sound and it's nice

1972 440 block with stock crank, remaned heads (oe spec), new valves (oe spec, I believe), rocker arms and springs are standard replacement, not sure about the pistons, 4bbl.

 

[wyrmrider]

lots of good tips Zell go back and read them again
first build
Keep it simple
Heads determine how much horsepower you can make
but too big a head (think Boss 302 Ford) as with too big a cam first the low- then the midrange and without BIG heads give you no more top end
so figure out what your goals are and car weight
and really figure out where you are going to drive and how you want to drive it
a daily commuter is a completely different street build than a Cruze the drive in Saturday night build.
figure out what kind of gas you really want to run
is mileage at all important
etc
keep those posts coming in
while thinking about it have you torn the motor down yet?

 

[Zell]

Wyrmrider I would like to build a daily driver that doesnt need to be reliable. (There's always a truck in the driveway! So it's not the end of the world if there's an issue.) I've been rereading this thread- as you said, lots of good info on here.

Looking to upgrade to disc brakes, power steerig, stiffen up the frame, upgrade suspension. I would like to get away with premium pump gas (or as little additive possible). Didn't even think of gas until you mentioned it.

The 440 I am referring to was disassembled when I got it, down to the bare block.

 

[451Mopar]

I was looking to build a fun driver, by this I mean it does not have to do <12s or <11s seconds at the track! (I'm read some crazy builds on this forum). 440, 4spd (A833), 3.73 gears. Looking to mod the 4spd down the road to a 5spd for 5th cruising gear. Being realistic, I would want a lower RPM power curve, so little less duration, wider LSA cam from what I'm reading. (Sorry hardcore power guys!) Is it still possible to get a cam that has enough overlap to cause that 'put-put' sound at idle for a daily? Or does that typically come with much more aggressive cams? I heard a 440 with a voodoo cam that has that sound and it's nice

1972 440 block with stock crank, remaned heads (oe spec), new valves (oe spec, I believe), rocker arms and springs are standard replacement, not sure about the pistons, 4bbl.

The Lunati voodoo cams are a good cam, be aware that they use a 3-bolt timing set which is not standard for a stock 440. I think the 3 bolt timing set was used on the 426 Hemi, and 440 6-pack, but a good upgrade on any big block if buying both cam and timing set. I think the Voodoo cams are like the Comp cams XE series of cams which have the standard single bolt for the timing chain sprocket. A dual exhaust with performance mufflers can make a mild engine sound really good.

If this is your first build, do you have someone helping you, and access to the specialized tools?
To calculate compression ratio, you will need to cc the cylinder head combustion chamber(s), and know how far the piston sits below the block deck when it is at TDC. We could figure a rough estimate of compression if you know the part number of the piston, or a rough idea how low the piston sits at TDC in the engine block?
You will also need more information on the valve spring pressures to check if they will work with the cam?
You may need to change the valve springs to match the cam you choose. Unless you have the special tools (valve spring compressor, spring pressure tester, install height micrometer, and valve spring shims), you may want to work with an engine shop or engine builder to test and set up the valve spring package.

If you like the Voodoo cams, look at the 10230703LK 268/276 cam if you have at least 9:1 to 10:1 compression.
http://www.lunatipower.com/Product.aspx?id=2337&gid=362
If your compression is under 9:1, you may want the next size smaller cam.

 

[Zell]

451mopar my neighbor that has built a number of engines is really into helping me. Strangely enough, has always worked on Chevy motors (327, 350, 454, etc.) and knows them like the back of his hand. However, since I brought home a giant pile of car parts and RR to put them in, he's bought a new Challanger with Hemi and has confessed to secretly loving MOPAR his whole life.

I'm very fortunate, he's going to help and teach me, and he has all the specialty tools that are typically used with an engine build (or at least from what I've read), e.g., dial bore gauge, ring compressor, filer for piston rings, square, feeler gauge, on and on. This will be my first engine build- VERY EXCITED!

 

[rumblefish360]

Hi everyone, between different engine rebuild guides and all of the info everyone has provided on the forum in other threads I've gotten very comfortable with a lot of the language around cams (lift, duration, overlap, etc.)

I've read a lot of specific setups where people ask if a specific cam will work with certain lifters in threads on FBBO.

If I change the cam, can someone explain the big picture of what else may need to change? E.g. if the lift increases and the overlap increases, then more air is coming into the cylinder so make sure that X is adjusted. Or is this really dependent on the cam chosen?

I have a spare 440 block that came with a cam, crank, heads, and some lifters, valves, and rockers (not sure about the valve springs) in the garage that I got with a car I bought and I wanted to try doing an engine build for the first time. No time like the present to get your hands dirty

Zell, the first thing is make a plan and then stick to it.
Next step is explain what you want. More detail the better and yes I understand there is a lot of unknowns about that. A lot of grey area.

You mentioned overdrive? Always a good idea if you can!

I do beileve very strongly in a simple book titled “How to rebuild my big block Mopar “ as an excellent source with pictures and step by step instructions.

I have the small block version and follow it since it is an excellent set of steps that cover the engine and then some.

Pump gas engines are an easy thing. Limit your static ratio to 9.0-1. 9.5-1 is a maximum!

Also, don’t be afraid to “Copy Cat” an engine build. You only flatter the original builder.

 

[Zell]

Yes it is!! I read a similar (could be the same) book every morning for a month on the train while on my way to work! I bought "How to Rebuild Big Block Mopar Engines" and "High Performance Manual Transmissions" so I could get the down and dirty on the A833.

 

[451Mopar]

That is great that you have someone to help you and has the tools.
Way back when I was 14 years old, I tried to rebuild a 318 engine for my '67 Coronet that I bought from my aunt (for $175)
All I had was basic hand tools and some books (no internet back in 1978.)
I made a bunch of mistakes, but met some older kids in high school who were in auto shop class that helped me.
I got the engine back together and running before I got my drivers license, and learned alot (mostly cussing and patients.)

 

[Ranger16]

Is it still possible to get a cam that has enough overlap to cause that 'put-put' sound at idle for a daily?

A good muffler can go a long way in that respect.

I was looking to build a fun driver, by this I mean it does not have to do <12s or <11s seconds at the track!

I am far from a cam expert and had to do a lot of research as well before changing mine. I can speak camese, though not fluently. What I can tell you is that when I bought my '69 Road Runner (383), it was idling at somewhere around 2000 RPM (no tach at that time so that is an estimate by sound). First thing I did was to drop the idle to 1000. I soon realized why it was there. I noticed that it would bog when I started from a stop unless I got the RPM up to about 2000. I too wanted a driver, not a racer and found it was not fun to drive and decided to change it. Not knowing exactly what cam I wanted, I called Comp and talked to someone explaining what I had and did not like about it. He said, "with a car like that, I'm sure you want a little lope" and recommended a cam that I went with and am happy with. It idles n ice with a great sound (Flowmaster 40 series). The point of all this is note the operating range. I don't think you want one with a low end at 2500 for a "fun driver". At least that was my experience. I'm sure some of the more knowledgeable guys here can comment on this.

Also understand LOBE SEPARATION ANGLE
From what I understand, based on what you said, you'll want to stay below 110. The one I removed was 110 and the one I installed is 108. As usual, Google is your friend and once again, some of the more knowledgeable guys can touch on this.

Here are a few thing I found to consider.

"LOBE SEPARATION ANGLE: This is the relationship between the centerlines of the intake and exhaust lobes. A 110-degree lobe separation angle means that the peak opening points of the intake and exhaust lobes are 110 degrees apart. This is ground into the cam and can’t be changed without changing cams. Lobe separation angle is another way of expressing overlap, which is the term formerly used by cam manufacturers. Overlap is the amount of time that both valves are open in the same cylinder. When both valves are open at the same time, cylinder pressure drops. A cam with 106 degrees of lobe separation angle will have more overlap and a rougher idle than one with 112 degrees, but it’ll usually make more midrange power.

What does it do?
At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality."

"Idle Quality" would be your "put put", but there is a price to be paid for that as I see it.

 

[wyrmrider]

Ranger do you remember what cam you removed and ended up with?

Remember that squeezing the lobe centers depends on lots of factors- it should be the result not the input
it changes both the overlap and intake close point (unless you also change the Intake Centerline- Intake Close point)
Nice Post- thanks

 

[Ranger16]

I was afraid some one would ask that.
I'm pretty sure the one I removed was a Mopar Purple cam.
I recall the lift was .509 and the lobe separation was 110. Can't recall any other spec's.

The cam I installed was a Comp #21-223-4
Xtreme Energy 268H Hydraulic Flat Tappet Camshaft Only
Lift: .477''/.480''
Duration: 268°/280°
RPM Range: 1600-5800

I stand corrected on the lobe separation. The new one is 110 as well.

I might have confused lobe separation with center line.

http://www.compcams.com/(S(4x2m03vf...mpany/CC/cam-specs/Details.aspx?csid=707&sb=0