I just got my comp cams cam installed and there seems to be a lack of compression. When I installed it, I put it in 4* adv. Becuase it has a LSA of 114 and the card said it was suppose to be installed at 110 Intake centerline. Is that logic correc or is the 4* adv. ground into the cam and I was suppose to install it striaght up? Thanks again guys.

Jim

 

CG99,

Most HE and Magnum cams from Comp have a 4° advance at the provided dowel position. Not ALL of their cams are advanced, but most of them are, since that is a good compromise for street use. If you want a little more high RPM power, take the timing back to dead center or even a couple of degrees retarded from the centerline.

XE and racing cams are often doweled at 0° from centerline. As always, it's best to degree the cam when it is installed to be sure.

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Later,
Vader
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Justice and Freedom will Prevail

 

Are the valves adjusted properly?

 

When I adjusted the valves I did it per cranes instructions (gold race rockers) I turned the engine over until the exhaust (I believe) was just starting to open then I adjusted the intake vlave to 0 lash. Then turned the engine a little more until the intake was mostly closed and then adjusted the exhaust.

Vader,

thanks again for the reply that makes sense, although I have it 4 * adv and I have a lack of torque. The top end seams better as it starts to pull around 3500-4000. It seems that I have little or no torque. So following your logic In order to gain more torque I would want to advance it more?

If I had some valve overlap would retarding the cam back to 0* make that worse or might that solve the problem? Thanks again, I'm having a hard time grasping how all this works. Please be patient

[This message has been edited by camaroguy99 (edited September 25, 2001).]

 

The LSA (lobe separation angle) is the number of degrees between the centers of the intake lobe and exhaust lobe. The other number (110° in your case) is the position of the center of the intake lobe, in degrees of crank rotation after TDC. Those are 2 completely different specs. The cam isn't "supposed to be installed" at any particular centerline "because" of the LSA. You don't change valve overlap by altering the cam's timing with respect to the crank (what you do with a "degree kit").

I'd suggest you put the cam back to "0°" and try it there, and then make a decision as to whether it needs to be changed. Without detailed knowledge of the exact engine combo you have and prior experience with an identical combo and cam, it is completely impossible to predict that the engine will run better with the cam's timing altered from its design value.

How does it seem to have a lack of compression? That is, what's the real problem?

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"So many Mustangs, so little time..."
ICON Motorsports

 

I did a compression check on it and, granted it was cold I was only getting about 90 psi after about 25-30 strokes. after about 5 strokes it wasn't higher then 40 psi . Thanks again guys

 

Your particular cam, if it's the one I beleive it is, has 4* of advance ground into it from the factory, just like Vader says. The cam card says to install it on a 110* intake centerline. That's where it will (or should, in a perfect world) install if you use the 0* install keyway on your timing chain. If you used the 4* advanced setting on the timing chain you are over-advanced. You'll be on a 106* intake centerline and that's not where you want to be.

HOWEVER, being off by 4* should not cause such a complete lack of power. I'd suspect the valves are adjusted wrong. You're hanging one or more valves off the seat when they should be fully closed. You should be getting full cranking compression within 3-4 compression strokes. Needing 20-30 to get up to 90PSI is not good. If the car is also idling like a top fuel machine I'll almost guarantee that you're hanging a few valves slightly open.

 

There's no way that the cam timing can cause that. Either: there's no rings on the pistons; or the valves are the wrong size; or the rockers are several turns too tight; or, most likely of all, the compression test is being done wrong.

Did you have the throttles blocked wide open?

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"So many Mustangs, so little time..."
ICON Motorsports

 

All right guys heres the deal. The cam is a comp cams XE 262H-14

GVL. .464 / .470
Dur. 218 / 224
LSA 114

Specs for cam installed @ 110 Intake center line.

As far as the valves being adjusted wrong I did it by spinning the pushrod while tightening the nut untill it wouldn't spin anymore. If you have a better way please tell me.

The compression check was done by just cranking the engine with the throttle closed. Is that wrong?

I'll try it again with the throttle open... well that didn't do much. It's still about the same. There are rings in the engine and the valves are the right size. I inspected the heads before I put them on. I guess I could readjust the valves.

The car isn't idling too badly. Accually it's kinda smooth. It's not really torquing from side to side as each cylinder fires.

I'll readjust the valves tommarow and get back to you guys. Thanks again.

Jim

 

running the valves by spinning the push rod works reat but you have to watch the lifter doesn't start spinning. did that happen?

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

When you're adjusting hydraulic lifters, the idea is to find the point at which you just barely take up all the clearance between the little spring-loaded plunger that the push rod sits in, and the rocker arm. Once you reach that point, further tightening of the rocker depresses the lifter's plunger into the lifter body. Then if you continue to tighten the rocker, when the plunger reaches the bottom of its travel, the rocker begins to be forced to open the valve even when the valve is supposed to remain closed.

A good way to adjust the valves is to position the motor as you described for each valve; then tighten the rocker until the push rod can no longer be moved up and down between the lifter and the rocker; then tighten it a little more. ½ to ¾ turn past "zero lash" is typical.

Try adjusting them that way, and re-check your compression. It might be a whole lot better. You should end up with something in the 150-180 psi neighborhood.

It's important to prop the throttle wide open during the test because if you don't, the cylinder can't fill up with air due to the throttle's restriction (after all, that is its job); and if the cyl is not completely full of air, the readings will be way low.

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"So many Mustangs, so little time..."
ICON Motorsports

 

ede, I did not check to see if the lifter was spinning. I did have oil on my hands so it didn't take much for my finger to start slipping.

Thanks again for your help. I can never say that enough. I would have never learned as much as I have nor been able to get this far without everyone on this board. I will adjust them from your instructions tommarrow.

 

Update:

Well, I just readjusted the #1 cylinder and got the same readings. I just barly turned them past snug to make sure I wasn't compressing the spring.

Next I will pull the timing cover off and reset the cam to 0*. Wish me luck .

 

Well I reset the cam to 0* and that did it, I went from 35 PSI on 6 strokes to around 185-200 PSI in 4!! That will do very nicely. Thanks for all the help guys. Hopefully this will solve all my problems.

 

Good that fixed it. I find it surprising that a 4 degree advance (8 total) would change cranking compression that much. Advancing the cam timing should improve lowend (up to a point) as opposed to reducing it.
strange.

[This message has been edited by jcb999 (edited October 02, 2001).]