Cam grind opinions

[Todd Lentz]

Guys, I hope I'm not beating a dead horse, I have a hard time navagating the 63 64 site on my phone. Anyway...
80-1818

268/268

218/218

.300/.300

.480/.480

108/112

Hyd

This is the grind off of the cam card. Any master mech opinions on vacuum, brakes, idle, and valve clearance much appreciated. Im just curious as to why I have had so many problems when all mods were mild. Main problem is burning oIL since rebuild. I am going back to stock anyway. Sorry if this is a reposted subject.

[Clovis]

It's been awhile since I have read cam specs. I'll take a stab at it. 268 is the amount of degrees the intake and exhaust valves are open at .480 inches of lift and 218 is the amount open in degrees at .300 inches of lift. 108 and 112 is lobe separation between the intake and exhaust valves. The lobe separation helps lower the power band on a performance cam installed in a street engine. 268 is a little high and not really required for our cars but will give a nice lumpy sound just not to crazy. But the real number is 218 it's a much more realistic number as to the cams performance which is ok. If the was a roller cam you would probably see 268 248 at .300.

[Jason Edge]

My understanding would be a little bit different but it has been looong time since I was into performance cams and tweaking speaks.

I believe the  #'s would be
- 268 degrees duration (how long the cam holds the valve open) between start and finish for both intake and exhaust. This # was always a bit less precise as manufactures noted the start and finish at different increments of lift).
- 218 degrees duration between lifter up .05" and back down to .05" (both intake and exhaust and the more standard duration most people go by)
- .300" lobe lift (both intake and exhaust)
- .480" total valve opening lift for int and exh which is the lobe lift (.300) times the rocker ratio)
- 108 degree lobe separation angle between peak points of intake and exhaust. (The lower the # the more overlap you have.)

Looking at the shop manual the stock total exhaust lift is .466 and the intake lift is .427 so this cam has considerably more (12.4% more) total intake valve lift, which can definitely add more power. I remember on the small block chevys about .5" total lift was about the limit you would want to push them.

[Todd Lentz]

So would you both agree that this cam could be run with stock rebuilt heads, and minimal vacuum problems for power brakes etc?

[Jason Edge]

I don't see this cam having any affect on vacuum or vacuum controlled components. 108 degree lobe separation is pretty typical... and I did a quick check on other #'s and don't see anything out of the ordinary.  Very mild additional exhaust lift, a bit more aggressive intake lift...neither of which is going to significantly alter vacuum. The lobe separate, again is typical..if it was a very low # you would have a lot of overlap which can cause some loss of pressure.  Duration of lift is also pretty typical.

[Todd Lentz]

That's good to know Jason thanks! It's all pointing to those heads and valve seals i think at this point. It's getting pulled this weekend and I hope I didn't lose any friendship over it, but it's had problems from the get go. Hopefully be done around Christmas because there is a poker table waiting for me this spring in Vegas! So far, I'm 30 over on a block from Russ, cam, square bore on the manifold, and dual flow master exhaust. With 650 Edelbrock. Just have to start over. I was really wanting to be doing suspension and stearing by now.

[Jason Edge]

Hey, I found the specs from the mild HP gain cam I bought thru Kanter:

It is listed as Camcraft Performance Cams with the following specs:

Part #: 83-1818-10AZ HCR
Advertised Duration: 268 / 268
.050 Duration: 218/218
cam lift: .300 / .300
valve lift: .495 / .495
center line lobe separation  108 / 112 

The only spec I see different is the valve lift and that is a computation of the cam/rocker ratio multiplier. My card has the rocker ratio listed as 1.65, so 1.65 x .300 = .495.

So, the .300 cam lift is the constant and of course a hard #. To see which total lift is correct you can simply look at the shop manual to determine the actual cam/rocker ratio multiplier:

Intake:    .427/.258 = 1.65
Exhaust: .466/.283 = 1.65
 

That means your total valve lift is 1.65 x .300 = .495.
WE HAVE THE SAME CAM. They just miscalculated your total valve lift because they used a multiplier of 1.6 instead of the correct 1.65.

And my car runs great with that cam!!!!

[Todd Lentz]

Very cool! So that is great news! So with your cam, do you have any sucking in on the exhaust at idle? The reason I am asking is at one point I noticed that my exhaust bolts had driven out (no lock washers) and I was wondering about burnt valve and the mess that comes with it. I cant wait to see those heads! Much more my cylinders. I intentionally copied your set up with the exception of the cam which I yielded to the builder. Has a bit of a lope which I loved but wasn't sure if it was supposed to be there it and played with my head really bad. One eye on the road, one on the guages, and all ears listening through the xhaust. I started running hot 210 at The Cruise On Central, and that's when I just called it...two years later after starting... rebuild again.

[Jason Edge]

The exhaust bolts becoming loose would be a function of metal to metal heat-cooling expansion contraction, and gasket compression and it is recommended that you re-torque bolts after you run-in the engine... probably right after the initial 20 to 30 minute run-in and then say after 500 to 1000 miles. and it never hurts to check torque later. I have about 3500 since my rebuild and this is probably a good time for me to check my bolts again. I have had no issue with exhaust bolts coming loose with this manner... just a need for a slight turn in to bring back to spec.

Not sure what you mean by "sucking in on the exhaust idle?" 

[Clovis]

Hi Todd looks like Jason did a good job for you. I was going to the crane cam Web site for a better explanation but Jason beat me to it. That 108/112 lobe separation improves your idle vacuum and lowers the power band for lower rpm torque. I have a very similar cam in my boat only it's a hydraulic roller. Rollers allow a much faster opening and closing speed of the valves. The best way to explain it is if it was graphed out the roller has a flatter peak for the same amount of lift and duration.

I think your on the right track with the valves seals letting oil into the camber, let's hope so anyways. If your compression numbers are good it would be hard to believe it's gouged cylinder walls. Hoping for the best for you anyways.

[Todd Lentz]

Thanks for all your help, I'll keep you informed. Fortunately the man who built the motor is highly respected by many and is also a freind. We are going through he frustration together i think. Anyway it gave me some quiet time with the 41' lastnight...after the kids fell asleep ofcourse! Talk to ya soon.

[Tony and Ginny 429]

jason WOW - Your oattention to detail ,is always a pleasure to experience
Like the cam info

[Todd Lentz]

Well...I pulled the heads. Valve seals done improperly. Oil on intake. I also believe the head gaskets were improperly installed since water ports were blocked. A little confused why the lifter rods appear to used and not new. Possibly some were reused. Soooooo, what else can I find 5000 dollars later.