Choosing a cam (info)


Departed Member
There has been a lot of talk about cams lately so I decided to try to put together a bit of info on the cams that are available for the 170/200/250ci engines. Instead of listing all the choices available, I picked the ones that seem to be the most popular (between 248-290) . All are hydraulic lifter cams. I should also note that I will be adding Isky and Crow cams to my web site within the next week or two. They will be available as shafts only, shaft and lifter combo, or complete kits.

Cam specs are listed as follows: Adv.duration, .050 duration, valve lift, lobe seperation, and rpm range.
Note: Dual grinds available from Crane and Crow cams.
Note: Specs from Clifford are verbal from a phone conversation.

Crane Cams USA
256D: 256/264 - 194/202 - .398/.413 - 110* - 1000-4000
206D: 268/276 - 206/214 - .420/.435 - 112* - 1500-4500
276D: 276/284 - 214/222 - .435/.450 - 112* - 2000-5000
290D: 290/300 - 228/238 - .460/.480 - 112* - 2500-6000 (min 9.5 CR)
Clifford Perf. USA
254: 254/254 - 206/206 - .410/.410 - (not listed) - 1800-4200
264: 264/264 - 208/208 - .444/,444 - 110* (verbal) - 2000-4500
272: 272/272 - 214/214 - .449/.449 - 110* (verbal) - 2200-5000
280: 280/280 - 226/226 - .467/.467 - (not listed) - 2500-5500
Comp Cams USA
252: 252/252 - 206/206 - .425/.425 - 110* - 500-4500
260: 260/260 - 212/212 - .440/.440 - 110* - 1000-5000
Crow Cams Australia
254D: 254/264 - 194/202 - .382/.408 - (not listed) - 1000-3800
270S: 270/270 - 208/208 - .420/.420 - (not listed) - 1400-4200
270D: 270/280 - 204/214 - .420/.442 - (not listed) - 1500-4500
280S: 280/280 - 214/214 - .442/.442 - (not listed) - 1800-4800
282S: 282/282 - 222/222 - .448/.448 - (not listed) - 2100-5500
Isky Cams USA
248: 248/248 - 194/194 - .415/.415 - 109* - 1000-3800
256: 256/256 - 202/202 - .450/.450 - 112* - 1500-4800
262: 262/262 - 208/208 - .445/.445 - 109* - 2000-5000
280: 280/280 - 224/224 - .465/.465 - 112* - 2500-6500 (min 9.5 CR)
Schneider Cams Germany
248D: 248/256 - 194/204 - .400/.420 - 110* - (not listed)
256S: 256/256 - 204/204 - .420/.420 - 112* - (not listed)
262D: 262/282 - 210/220 - .435/.450 - 110* - (not listed)
280D: 280/290 - 220/230 - .465/.465 - 110* - (not listed)
300S: 300/300 - 240/240 - .480/.480 - 108* - (not listed)

NOTE: Cams above 270 duration (272,276,280,282,290) require a manual transmission or an automatic with a modified stall converter, headers, and a 3:20 minimum rear gear ratio (3.50-4.11 is preferred). Stall converter should match the lowest number of the RPM range. Cams between 260 and 270 duration will work with an automatic but a manual is suggested, rear gear ratio of 3.00-3.50 is also suggested.

So, now which one to use? A car that idles rough, stalls in gear, is a bear to drive in traffic and gets abysmal gas mileage is still cool if it rocks when you floor the gas pedal. An engine that suffers these driveability headaches and still gets blown away by a Ricer is the worst possible experience. The most prevalent reason for engines that don’t run as they should is an improper camshaft for the engine and vehicle combination.

We’d all like to have a 10-second car with a great stereo, air conditioning, 30-mpg fuel economy and 1.2g handling capability, but reality says that isn’t going to happen unless your surname is “Superman.” In the real world a street car is built for either ultimate straight-line quickness, driveability with some performance, or a combination of both, which ultimately means a compromise of both. Do you want the car to run low ETs or get you to work every day? Does the car have an automatic or manual transmission? How rough an idle can you put up with?

Everything about the car combination and intended function must be decided upon before choosing the cam. Once this is determined, the following important details must be taken into account to get exactly the right camshaft: the engine’s compression ratio, the basic power range of the heads/intake manifold/carb/headers combination, the car’s weight, the transmission type (and/or torque converter stall speed), the rear gear ratio and the rear tire size. Once you’ve decided how you want the car to behave, you must build the entire engine and drivetrain to fit.

The problem is that there are many things to consider when choosing a cam, and it involves much more than just the other engine parts. The entire vehicle and the sum of its parts are just as important. Below is an outline of what all those specs and numbers mean and a general explanation of how they affect performance, followed by a rundown of the areas that must be addressed at cam selection time.

UNDERSTANDING CAMSHAFT SPECIFICATIONS There are many numbers and terms used when describing a camshaft’s design that must be understood when choosing a cam. It’s good to know exactly how each of these specs affects the engine’s performance, but one of the most important is duration, so pay special attention to that one.

LIFT: The cam’s basic function is to open the valves. Lift refers to how far the valve is opened (or lifted) off its seat. A street performance cam will usually have between .450- and .550-inch lift. More lift can increase power, and increased lift without changing duration increases power without affecting the point of peak power on the rpm band. The rocker arms have a direct effect on lift because they don’t have a 1:1 lever ratio. A cam that has .318 inch of lobe lift (that’s how far it lifts the lifter) will open the valve .477 inch with 1.5:1 rocker arms (.318 x 1.5 = .477) and .508 inch with 1.6:1 rockers. Generally, a stock engine will tolerate .500-inch lift before the valves hit the pistons or the valvesprings hit coil bind, but any time lift is increased, these clearances should be checked.

DURATION: Duration is how long the cam holds the valves open. It’s expressed in degrees of crankshaft rotation (remember, the cam rotates at half the speed of the crank). A 280-degree-duration cam holds the valves open longer than a 260-degree-duration cam. Holding the valves open longer allows more air and fuel into the engine and also allows more to get out through the exhaust. Longer duration (higher number) improves top-end power but almost always sacrifices low-end torque. Lower duration improves low-end torque and makes the car idle better, but it limits top-end power, and you can get only so much valve lift with a short duration cam due to the rate-of-lift limitations of the lifter. Roller cams have the advantage of allowing high rates of lift with relatively short duration, but are not available for our sixes.

The confusing thing about duration is the difference between “advertised” and “at .050-lift” duration. At .050-lift duration is measured from the point where the cam moves the lifter up .050 inch until .050 inch before the lifter is all the way back down. Most cam manufacturers differ in where they start and finish measuring for advertised duration. Some start at .004-inch lift, some at .008-inch and some measure it somewhere in between. That’s why the .050-lift numbers are the best to go by. A 280 cam (advertised duration) from one manufacturer could actually have less at–.050 duration than a 278 cam from another, due to the different points at which the companies measure advertised duration.

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.

DUAL-PATTERN CAMS: A dual-pattern cam is one that has different duration and/or lift specs for the intake and exhaust. Usually, the exhaust lobes have more duration and lift than the intakes. Depending on the engine, this can be beneficial for engines with poor exhaust-port flow or otherwise-restricted exhaust systems.

TYPE OF LIFTER: A hydraulic-lifter cam is the best choice if the car is to be a daily driver, because it doesn’t need periodic lash adjustments. A solid-lifter cam is beneficial in high-rpm applications (6500 rpm and higher), but it requires a lash adjustment every few months. Hydraulic and solid, nonroller cams are also called “flat-tappet” cams. Also, you can’t mix and match cams and lifters. Because they’re ground differently, a solid-lifter cam must use solid lifters and a hydraulic cam must use hydraulic lifters.

Sources: Mustang Monthly Tech Article, Crane Cams, Comp Cams, Crow Cams, Clifford Performance, Isky Racing Cams.
Howdy All:

Well said Mike! If you and Jack are willing, this ought to be kept and posted as a response to a "Frequently Asked Question", Which cam is best for my__________(feel free to fill in the blank)?

Tell me more about the Crow cam product? It seems like I recall that name from the early days. Where are they located? How do they compare, price wise to the others?

Adios, David

The Crow cams are manufactured in, where else, Australia. :LOL:

I e-mailed them last week asking if I could list/sell them on my web site and for pricing. Received the response this morning along with some tentative pricing, but am still negotiating quantity pricing. They should be comparable to US prices if I can get them down just a bit more.

They offer two different grades, street and race, although I am still uncertain as to the differences. Once I find out, I'll post the info. I like the fact that they offer shelf and custom dual grinds.

I got some good prices from Isky too.
Some damn great info. I printed it.

Heres another cam grind

Manufacturer: ISKY
Part#: 321262
Grind No./Type: 262-SUPERCAM HYDRAULIC Low/Mid-Range performance cam. 9.5:1 compr. 3.08-3.70 axle ratio. Passenger cars & trucks. Up to 625 CFM Carb. RPM-Range: 2000-5500 Valve Lift - INT: .445 EXT: .445 Valve Lash Hot - INT: .000 EXT: .000 ADV Duration - INT: 262° EXT: 262° .050 Duration - INT: 208° EXT: 208° Lobe Center: 109°
View timing chart data (details on this part)

Retail Price: $248.00
Your Price: $136.40

CompCams also makes custom grinds upon request...I bought a 310M cam from them.
One overlooked fact about cams is that two cams with the same card may have different details between the spec'd points.

It may rise quickly after the 50 thou index point, to a flattish curve on the tip, or more slowly, to a sharper "point". Both cams having the same duration and lift. Yet one will be more suited to an engine than the other.

That's why talking about a "260" or "252" or other size, is a nominal indicator only. The more aggressive profiles (generally for performance and race intentions), require more valve springing than the "softer" equivalent lifts. It's a good reason to consult the cam maker about your specific situation for spring info, and temper their conservatism with as much nihilistic glee as suits.

"Custom" cams are usually ground off generic masters. The situation desribed above becomes more critical, the more you ask of the engine. That is why a cam is best designed using flow figures. Having the flow in 50 or 100 thou increments will enable the best profile to be chosen and scaled for the cam.

Masterless grinding - a true custom cam - is slowly coming in. This is probably "overtech" in a pushrod six-potter, but nice to know it's out there. Crow have been trialling this process over the last year - and at one stage had a good deal to say about it on their website; no doubt some other companies mentioned here have such technology if they have to use it. (Make 'em sweat for your money!)

Still, there's something appealing about a lumpy old-tech grind with all its approximations and inefficiencies; maybe the sound is the key! Or is it the cool stickers?

As the "movers and shakers" on the board get dyno'd in, take stock of their flow numbers, and generally keep tabs on what's actually happening, it may well be possible to shoot closer to the target with an off-the-shelf grind. Martín's plans to bench test an Argentinian head will help there.

Regards, Adam.
Nice work, good info. Here's another... Schneider cams. They list seven grinds both hyd. and solid $119

so what would be the highest cam i'd be able to get away with on a 78motor with headers and sometime soon a different carburator, prolly a 2bbl, it was rebuilt so it has the thicker gasket so we're looking at a low compression ration, i've got a manual and 3.20 gears out back

i have no problem with a rough idle if i'd even be able to get a cam high enough to create one
Rule of thumb that I use is that 210-212 @ .050 is about the limit for duration for a stock auto converter and gears. Up to about 218-220 @ .050 is probably ok for a manual with stock gears. Anything bigger and you need to look at more gear.

Bear in mind, I sometimes tend to be on the conservative side, but I build drivers. I can live with a lumpy idle, but I hate it when all the power is concentrated between 2500-5000 rpms. It's like driving a car with a light switch instead of a throttle and you spend a lot of time rowing thru the gears.