Intake center line.

[texas69bee]

I am finally to the point of putting together my motor. I am double checking everything on the cam card. One of the first things I checked was the intake center line. I came up with 108 degr. but the card calls for 106 degr. If I advance the crank 2 degr I should end up at 106. Is this correct? Is this necessary? How does the 4 degr built into the cam affect this? It is currently installed dot to dot at tdc

 

[jason lewis]

If the card calls for 106 then,my assumption would be that the cam with 4 degrees built in then it would have been 110.As you advance the cam,the valve events start sooner.It will increase cylinder pressure,the idle will get choppier,and it will make more low end at the expense of top end.Even if you don't change it,it is still beneficial to know the number for reference.

 

[lewtot184]

advance the cam 1 degree to get 2 degrees at the crank. advancing the crank 2 degrees will have the effect of retarding the cam,... clear as mud? the truth is the 2 degrees your looking for may or may not make a significant difference. what are the cam specs? some shorter duration cams in larger engines will benefit from no advance and vice-versa for smaller engines.

 

[texas69bee]

Its for a 383

 

[lewtot184]

just my opinion, but if that cam is going in a big block i'd install it straight-up; 110centerline. comp makes a magnum replacement cam that is just a little shorter than the 268xe. I used it in a 440 one time installed at 106. made gobs of low end but ran out of steam below 5000rpm. those short cams with tight lobe centers and 4 degrees of advance ground into them make a bunch of cylinder pressure that may effect running on pump gas.

 

[texas69bee]

My overall compression is 9-9.5. Shouldn't pump gas be fine?

 

[383man]

Whats the use for this eng ? I mean is it for basically a cruiser or are you looking for every ounce of performance. If its just basically a cruiser that you dont plan to race then I would just go with it as it is. Ron

 

[texas69bee]

90% cruiser 10 % to play around with. Not intended to be a racer. I haven't rebuilt a motor in 30 yrs. and that one was with my dad. Was just trying to dial everything in according to the card. If I can get better performance from what's there than I would rather go that route.

 

[jason lewis]

All true,and at your altitude the power band listed for the cam will be close depending on where you install the cam.At my altitude we loose about 500 rpm right off,so cam choice changes for us.Since it's for a cruiser makes some noise and enjoy.

 

[lewtot184]

when i used the comp magnum cam i had 195psi cranking compression with 9.3:1 static compression. thats probably a little much for iron heads and pump gas and i was using a quench dome piston. i'd install at 110 centerline to be safe. those cams close the intake valve very early.

 

[Meep-Meep]

Agreed that 9-9.5:1 should be fine on pump 91 with about 175 PSI of cylinder pressure. Also agree that changing the ILC 2 degrees may not even be noticed. The 4 degree advance built into cams is to deal with timing chain stretch.

 

[texas69bee]

Ok, I will take everyone's advice on leaving it but in checking other stuff on the card I noticed that at .006 I am at 24 degr. Is this do the intake centerline being at 108degr?

 

[mentor70]

i ran that cam in a 9.5 to 1 440, 2.14 1.81 valves, ported 452 heads, stock magnum manifolds and six pack, stuck it in straight up, didnt ck ****.

pretty much the best running street engine ive EVER had!

lots of torque!

 

[opus65]

Let's remember the engine he is using this in is a 383 and not a 440 as everyone here has referenced in their favorable response to the use of this cam. Stroke makes a big difference when it comes to torque.

 

[Cranky]

Ok, I will take everyone's advice on leaving it but in checking other stuff on the card I noticed that at .006 I am at 24 degr. Is this do the intake centerline being at 108degr?

Things don't start happening until around .050 and not much is happening at .006. Looks to me like that cam will build a good deal of cylinder pressure. You could do a PSI check before finishing up the build and you can plot your readings using .050 valve lift as it is more of a real world check. I hate cams that give 'advertising' specs at .005 or .006 because it makes them look bigger than what they really are. And usually cams with late intake valve open and closing events build a good deal of cylinder pressure. The higher your static compression is, the higher the cylinder pressure (PSI) will be with a given cam. It's possible to run pump gas in an engine with 11-1 compression where as it's possible to make an engine with 8-1 ping it's *** off with the right cam.

 

[texas69bee]

So I have it sitting at TDC. How do I do the math to figure out the duration if the intake lobe has already risen past .050. If I go counterclockwise so the lifter is on the heel, 0 the indicator then go clockwise I end up with.050 4 degrees after TDC.

 

[texas69bee]

65+152=217/2=108.5 for Intake center line
63+149=212/2=106 for Intake center line

Valve timing open at .006 I had to back it off(counter clockwise) to the heel of the cam.When the dial indicator read .006 while rotating clockwise, the 21degr and 25 degr is where it stopped. Is that the correct procedure?

Duration How can this be figured out if the intake lobe has already risen to .060 while sitting at TDC?

 

[texas69bee]

You ever stare at something long enough, reread something over and over and then realize the process you were doing wasn't correct to begin with. For the duration I wasn't taking the reading off the base even though I was told to. I was taking it off the lobe. Got it now!!! Thanks to everyone. I'm sure there will be more dumb ?? to follow.

 

[Cranky]

Anything new on this?

 

[texas69bee]

Sorry Cranky that its been so long to respond. Ive been back in Wisconsin for a while. Pretty sure I have it dialed in.