school me on cams

GotWood

GotWood

Sayer of Fact
Joined
Jan 12, 2007
Location
Maiden, NC
I'm rebuilding a 351 and need a cam. Just going stockish,and low budget. I hear folks refer to a rv cam for more torque. What am I looking for and what r the differences.
 
If you have some gear in it and you want it to be snappy, go with a Comp Cam 268H. It will come on strong arround 2000 rpms. If you just dont want any chop in your idle, go with the 260H comp Cam. You will think it grew 50 cubic inches.
Both cams are best sellers for street and trail trucks. I have a 268H in my 57 chevy, 63 Impala, Dad's 68 chevy truck, My old 72 Blazer. All with 350's . The 268 has a great sounding choppy idle, but not enough to mess with the idle or off idle performance. Be sure and splurge on the break in additive and break it in at 2000 rpms for 20 minutes.

With that being said... The right gear to tire ratio is very important to this equation. No cam can operate properly if you are lugging it.

Just my .02... Hope it helps.
 
351 what? All of the cam companies are pretty great to work with and know a good bit about what you need. Calling them would be my first step.
 
351, I assume Ford. An RV cam is how the old folks referred to a cam a little better than stock. Something that didn't affect drive-ability at all, but offered better response and more torque. You say low budget, so unless you've changed heads, you need to stay around stock cause of the springs. The costs are all relatively the same, so if you are putting new valve springs in anyway, skys pretty much the limit. You will be looking for a hydraulic flat tappet, something in the range of 250-260 ADV duration, around .500 lift, and a LSA of around 110-114 degrees. A quick search on Summit will give you an idea, and I see they have a filter for off-road 4wd. But like said above, I'd give Comp a call and tell them what parts you are using, and they will have the best idea to get you something that works together.
 
351 m. It is going into a yj. New bearings, rings and seals, that's it. Cam has a bad lobe so must b replaced. I'm not looking for high HP but more torque would be nice. I'll b using the stock gearing and axles (44hp, 9", 350 gears, np435 4spd) from a fsb. I know most will say go a different direction but have the parts and too deep now to stop.
 
Duration 262/272, Lift .484/.510

What exactly is each number? I'm assuming duration is degree and the lift is max lobe lift in inches. Which number is intake and which is exhaust.
 
I drag race and the word among engine builders is... Stay away from the Summit cams. Lots of recent complaints concerning break in quality. They were ok before the changes in motor oil came arround. The lack of Phosphates in the new generation motor oils is killing flat tappet cams left and right. (Especially the cheap ones). Go get a comp cam 260H if you are box stock or 268H if you have headers and a 4bbl or plenty of gear. You will hug my neck next time you see me for saving you a hard learning curve. Put the comp cams break in additive. Use Rotella 15/40 wt. to break it in. Diesel oil still has the propper lubricity you need to break in a new cam properly. There are no negative long term side effects. A lot of people are using it to gain the extra protection it offers.
 
GotWood said:
Duration 262/272, Lift .484/.510

What exactly is each number? I'm assuming duration is degree and the lift is max lobe lift in inches. Which number is intake and which is exhaust.
Click to expand...


Lift measures how far the valve is opened, duration tells us how long the open cycle lasts. How long here is given in degrees of crankshaft rotation, fundamentally measured from when the lobe starts raising the lifter, until the same lobe finishes by dropping the lifter back down to the start position. There is one complication, and that's just what procedure to use for making the measurement. The procedure here refers to the checking height, which is the tappet position at the start and finish of the measurement.


Unfortunately, when calculating advertised or gross duration, not all camshaft manufacturers use the same checking height, and that makes it difficult to directly compare advertised duration numbers from one company to another. For instance, some manufacturers measure advertised duration starting when the tappet moves up 0.006 inch from the base circle, and finish at 0.006 inch up on the closing side. Another company may use a tappet rise spec of 0.008 inch to calculate advertised duration. In this case, the measurement starts later (waiting for the tappet to rise another 0.002 inch before starting to measure duration), and finishes sooner (stopping the measurement 0.002-inch earlier), so the advertised duration ends up being shorter, even if the exact same lobe is being measured.


For the advertised duration numbers to be truly meaningful, the checking tappet rise used to calculate the duration needs to be known. Most cam manufacturers will provide this information in the specification section of their catalogs. Decades ago, most camshaft companies agreed to list the duration specification at 0.050-inch tappet rise. With "duration @ .050-inch," the checking tappet rise is given at 0.050 inch, so all of the companies are using the same yardstick for calculating their specs. These numbers provide a good basis for comparison when considering different camshafts.
 
Best thing you can do for those motors is to get rid of the retarded timing. Whatever you get, make sure the cam and timing chain are either straight-up, or adjustable to zero.

Putting 400 rotating parts in it wouldn't be a terrible idea, either.
 
I'd do the 400 but don't want to spend any extra cash. This thing should have plenty of power for a dd and weekend wheeler. I'll probably run headers but the stock 2 barrel. Hoping to get a 4spd from a member on the board. Stock 350 gears for now and maybe next year gear down depending on how she feels.
 
I'm fixing to put an Edelbrock cam and intake on my 351M. I'm using a cam with the same specs listed above. 204/214 duration at .050, 262/272 advertized duration. .484/.510 lift. You WILL have to change valve spring on a 351M/400 to run any cam with more lift than .480 too by the way, or you'll have spring bind and bend push rods. Get an aftermarket adjustable timing chain like mentioned also and install it at 0 degrees. I'm using an Edelbrock double roller chain as well, the stock replacement chains you can buy at the local parts stores have the timing retarded 6-8 degrees like stock, so stay away from them.
 
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