i figured that "lift" is how much the valve opens. I didn't know what duration meant but now it makes sense. I just needed the 101 on cams. Thanks guys. I guess I have a pretty decent cam then..

Say I don't beat on my car too much. I do not track it or street race, how long should a cam last? Could I go another 180-200k?

 

List all the timing numbers

Just as shown on cam card.

IVO, IVC, EVO, EVC.
Let me know if stated at .006. .020, or .050" lifts.

If your Corvette thumps hard, & goes sideways on the 1-2 shift where you have to crank the steering wheel 180 degrees opposite to keep it straight , and pulls hard to at least 6K,
Its a good Non - race camshaft to me.
Its a decent street grind then to me.

 

I agree your cam is medium-sized though the lift is slightly more than medium. You have more lift and more duration than a hotcam -- which was considered GM's mecca for the C4.

1963SS: A 3/4 cam referred to the advertised duration meeting/exceeding 270-degrees of duration. IOW, the cam was off the base circle for 3/4th of one revolution. (Of course, there could be variance for a 3/4 cam's performance since the .020 and .050 events show how fast it opens/closes. We call this ramp speed.)

The overlap determines how much additional scavenging affect the exhaust has -- in pulling air thru the motor. When the overlap is happening, air can pass all the way from the intake, thru the piston, and out the exhaust. As Vizzard's Exhaust Science points out, scavenging has a much greater affect at moving air thru a motor than the pull from piston suction.

The reason duration (especially larger duration) matters is how it relates to engine speed. As the motor turns faster and faster, it gets harder and harder for the air to actually get INTO the pistons. At lower rpms, less duration holds compression longer and gives more power (often called torque). At higher rpms, more duration creates more top-end horsepower.

The other thing worth knowing is that the cam can't open/close the valve instantaneously. Because it's an oval lobe, valves open and close more gradually. For sucking in air/fuel, that leaves two options. If you set the cam so it closed the valve at the bottom of the strock, the piston would be losing it's ability to pull air/fuel as the valve was closing -- before it finally closed. If you set the cam (like most motors do) where the cam is still holding the valve open as the piston finishes sucking air/fuel in, you've pulled a bigger charge. The problem is the charge gets pushed right back out of the intake until the valve finishes closing. In a way, you lose what you gained. This is called intake reversion. And, it leads to the tuned port terminology associated with our cars.

As that reverted air is pushed back up into the intake, air (like a siphon) still hasn't lost its momentum INTO the cylinder. So, the incoming and reverted air crash into each other and pressurize. Longer tubed intakes capture this pressure easier. (But, they are harder to pull air thru as rpms get higher.) Shorter tubes are easy to get air at higher rpms and also build some reversion as a higher rpm. This is what's called the tuning of the motor.

Again, that tuning is effected by all of the cam events and scavenging of the air/fumes/exhaust.

For passenger car function, your cam is pretty big. That's why it can create much more power than your family sedan. Compared to a race car, it's fairly small. But, they concentrate on making power in rpms much higher than we normally drive.

 

3/4 cam was jargon used to describe the couple grinds that were out there for the flatheads.

Derek, lobe lift x 1.5 or 1.6 gives you gross valve lift.

Say your cam lobe is only .300
Your rocker, 1.5 will make the valve open .450 if that makes sense.

 

these are the rest of the numbers...
valve timing open @.006

Int: 28 BTDC 68 ABDC
EXH: 83 BBDC 27 ATDC

GRIND number LT1 276HR-14
part number # 07-305-8

here is the website that has my cam listed

http://www.compcams.com/Company/CC/c...csid=1102&sb=0

 

Well that makes perfect sense now. 270 degrees is 3/4 of a revolution. I'd of never thunk it. Thanks Gregg

 

Nice reliable, safe & easy on valve train camshaft grind.
Make nice streetable torque & decent HP too.

Sure you know that already because its in your LT-1 car.

Camshaft you chose takes advantage of long tube headers & LT-1 short runner induction system.

5th cycle effect.

BR

 

And here I was thinking I had a 3/4 cam when I wiped 4 lobes!

 

That would be 3/4 OF a cam.

 

so does anyone know what a cam like I have lifes span might be? Like I said I dont race or anything, just get on it once in a while.

 

Roller cams are very, very long life devices. They will last virtually forever if there are no oiling problems. I've pulled LT1's apart with 1/4 million miles on them and the cam looked as new.

 

what would be an oiling problem? timing cover? rear seal? bad gaskets? I just had the motor rebuilt and I want to make sure it lasts so my children can beat the hell out of it like I did.

I told the shop to put good parts in it to gve me more power to play with the newer cars but yet live a long life.

 

You won't have an oiling problem if the motor was built correctly. Don't panic. Valve springs are the best thing to check (periodically) with a performance cam. Opinions will vary about how often.

As mentioned, roller cams were a huge jump in longevity and technology. It should run forever. Since they compress springs more than a stock lobe, that can shorten life of a spring. That's why it's good to check...or just replace valve springs within say....5 yrs.

Might go more if you don't drive it much. (Lloyd Elliot would say 50-80k miles with dual coil springs...single springs not as long.)

Having springs within spec just guarantees your valves and pistons don't kiss at higher rpms.

 

If Ryan did your tune you are making all you can.

 

With no disrespect to Lloyd, the Patriot Gold springs that I put in 12000 miles ago are toast. I just checked them and when installed they were 380# at .650. Installed height was 1.790 or within .010 of what's recommended. Now they are 145#'s at the installed height and 245#'s at .650. That was running a Comp XFI 280 cam.

So yes, be sure to check your springs. They can be an issue. Now I know why at 6000 miles a lifter flew apart on a 6800 RPM burst. I didn't check the springs then because I just knew they still had to be good. Thatt's what you get when you know everything

 

One big key to longer valvespring life I have found for myself,

Is to allow about .080" to .100" between valvespring coils before valvespring coil bind ax Max lift at the valvespring retainer.

Often that requires longer valves than stock.

More parts to purchase just make sure.

Why you see +.100, +.250, + .300 valves listed.

Performance cams require very high load valvesprings.
Tremendous heat is generated.

At 7K crankshaft RPM's,
an intake & exhaust valve opens & closes 40 times per second.

So valve springs do work very hard.

Anything you can do to prolong their life is to your own benefit.

Also why I just refuse to use any china origin parts.

To each their own.

 

Should last 80 K to 100 K miles easy.

 

I think the Patriot Gold are Chinese made....is that right? That could explain their crappy lifespan. I just pulled the K-Motion's off my solid roller and they were 1.985 Installed height and with a ton of miles on them were very close to their original settings. They were 155 on the seat and 445 @ .600 and 475#'s at .700.

What brand springs would you recommend for my Impala engine? Lift is going to be around .600 and RPM's around 6500. A forum member recently had trouble with Comps also. I'd like to stay at my 1.8 installed height or thereabouts.

 

I used the Comp 987's for many years on my Pontiac cars.

I always ran them super hard just like You.

When it comes down to the bottom line & $$ to win..........

You have to wind them out till no tomorrow.

Rev limiter chips went in the garbage can right away.
Fick those things. LOL

The quality has gone everywhere,
including our standard of living here in the USA.
Pisses me off.

Isky Tool Room Gold springs are the best.

Pacalloy is good stuff too. .......Comp Cams trade name I believe still.

Standard Iskendarien Chrome Vandium Steel is very good too.

Will not go wrong with Crower's too.

Maybe the grandkids will get a little less this year come Christmas?

Grandpa Needs Very Good Valve Springs.

Take them for a ride each,
They will understand.

 

K- Motion's are very good too.

One of my bud's Steve S. is about 48 now.

He build's a ton of SBC every year for dirt track racers & drag racers.

He tried using the china stuff too.

Every single engine came back with connecting rods broken in 2 and big windows knocked out in the cylinder block, broken crankshafts in 2,
dropped engine valves, broken valvesprings, hydraulic & solid roller lifters flew apart and shot those tiny needle bearings everyhwere.
Camshafts broken in 2.
Timing Chains snapped in 2.
List goes on.

All china sourced parts.

I told my bud Steve that china chit would not last.

He called me every known god damn swear word known.

I called him a ficken dummy when I got mad.........

Guess what, I was right.................

He is back using all made in the USA.

BR