roller cam spring pressure

[RedRacer]

We dyno'd an engine for another shop, a 454 Big Block Chev that had a Comp Cams mechanical roller cam part numb: 11-770-8. Listed in the catalog as 2200 to 6200, 236/242 at .050, .639/.646. Engine has decent ported 781 heads, with a performer rpm air gap and a 950 holley it made 535HP(6000rpm) and 560 torq. (3800rpm). Problem is at 6500 it hits a wall and the torque goes in the crapper. I am thinking the springs are not enough pressure. They put in what the comp book says (929 - 150 seat/440 open). Any comments on this, such as what spring pressure you would reccomend? Thanks - Red

[SupStk]

Without knowing the whole combination, it seems light on power along with spring pressure. Do you see any other indications on your other data that it is going into valve float? How much RPM do you figure this thing will go before it runs out of cam? Seems to me it is almost there.

[k-star]

I think with that cam and those heads you about at the end with 6500rpms, not sure springs would bring it around much, but those pressures do sound low to me..

What is the static compression on this engine.

Keith

[RedRacer]

Yes you are right on the fact that it is almost out of wind... but what bugs me is the torque absolutely drops straight down at 6500 and I was thinking that it could use some spring and it will at least stop the thing from tossing the valves so badly at the top RPM, even though it will not see much time at that rpm.

The engine is 9:1, pump gas street car, from their reaction to the HP numbers they were happy. That is thru mufflers with full exhaust on a very conservative dyno.

We are going to put a 943 comp cams spring in it, which is 240 seat and around 578 max lift along with changing to a titanium retainer.

I did not see the flow sheets on the heads, but it was a street port that picked up something around 13% through the flow curve from what they say. Thanks, Red

[DOTracer]

Is this a cast core Xtreme Energy street roller grind?

Looking at the specs, it appears to be.

if it's on a cast core, do not use that much spring pressure. You'll eventually track the rollers into the lobes.

I ran a XR286 grind and wound up having to use a Comp 933 spring which seemed like just enough spring to control the valves to 7000 rpm. I had the spec'd comp titanium retainers and 11/32" stem valves.

The recommended springs by Comp 929 + 939 are too light for the heavy bbc valvetrain IMO. maybe OK for 5000-5500, but not enough for 6500 rpm.

[RedRacer]

Good Point DOTracer. I talked to the engine shop and they indicated it was a cast core so we will pull back on the spring pressure and go with the Comp 933 set. They told me that the engine has the heavy 3/8 stem valve so that is another thing against it.

The pressures will be up about 80 on the seat and 75 on the nose with the 933 spring, so we are hoping it will at least pull to 6500 without problems that will be an improvement over what it is doing now. Red

[Wolfplace]

Good Point DOTracer. I talked to the engine shop and they indicated it was a cast core so we will pull back on the spring pressure and go with the Comp 933 set. They told me that the engine has the heavy 3/8 stem valve so that is another thing against it.

The pressures will be up about 80 on the seat and 75 on the nose with the 933 spring, so we are hoping it will at least pull to 6500 without problems that will be an improvement over what it is doing now. Red

=

You can try more spring but I wouldn't leave them on there,,,
The -8 cam is a cast core roller which is in my opinion about the dumbest thing Comp has come up with.
If you run the recommended spring it will not control the valve train.
If you put a decent spring on it, it will usually kill the cam.
I personally will not run a cast core roller of any type, solid or hyd.

In my opinion too little spring is the single worst thing you can do to a roller.
I prefer to err a little on the high side with rollers because of the damage that can be done if they don't follow the cam. If the lifter comes off the lobe it will beat the crap out of stuff.
Same deal with valves. A lot of spring isn't what kills valves it is usually the opposite.
I see people posting things like they don't want to pull the top off the valve with heavy springs????
What causes the tip to remove itself is usually the valve floating & crashing back to the seat.
The loads when this happen are tremendous. Kinda like dropping a sledge hammer on your car from the roof of your house