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Cam Change Issues
I am helping a friend with a 427 that has a radical 250s @ .050 duration solid lifter roller cam. He would like to change to a more streetable Compcam, similar to a 33-432-9 with 330-336 dur. @ .050. We are evaluating just having his Comp solid roller cam reground to the smaller cam.
So here is the question. This engine has 2.25 and 1.75 valves with 495 lb. springs. The recommemded spring pressure for the new cam is 377 lbs. With a roller cam does it really matter that you have more spring pressure than required. Could we just run the existing springs that are in the heads? I can't seem to find springs that are the same diameter as the big springs with the less pressure. Thanks. |
I normally just buy the springs and the retainers for the cam. if there are spring cups/seats on the heads you may need to get those too.
but with that being said, in a perfect world,.........i have also in the past just used what i had and with that type of cam a higher spring pressure would certainly work, it would just place un-needed stress on the valvetrain |
That is what I was thinking. In this case because of the size of the valves and installed height of the springs, putting the recomended springs in looks like it is not possible. When I talked to Compcams they recommended lighter springs but didn't seem to have a solution.
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why is it not possible? or should you be saying it's not possible to do it without removing the heads.
if it was me, in seeing all of the issues with solid rollers, and i just lost a roller lifter in my engine, i would certainly lean towards using the lightest spring pressure i could with the cam, in fact i am not going back to a roller with my motor, i'm switching over to a solid flat tappet. i got 7k miles out of it before the lifter let go....... |
Sorry, the engine is out and all apart. I say not possible because with the large valves and longer stem length, matching the installed height of the softer springs to the valve is the challenge. They are about .090 different. Years ago you use to be able to buy all different widths and depths of retainers. Maybe someone knows who still does.
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are there spring cups on the head now? you could add them and a shim to make up the 90 thou.
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I just checked and no they don't. I'm going to check that out.
Good idea. |
check Isky's catalog, if i remember the springs come in two installed height flavors
cups are around .05 or .06 or spring locators are around .04.....it'll get ya close. |
If you're going from a solid roller to a hydraulic roller, then yes I would change springs.
A 495lb open pressure is too much for a street oriented hydraulic roller lifter. Most of my hydraulic roller stuff gets about 160-170 seat and 385-400 open. I personally would not listen to any Comp Cams phone tech. Their recommended springs don't always work because every engine is not a SBC. The last time I relied on them to recommend a valve spring for a hydraulic roller, the valves were floating at 5400. With as many engine builders as there are on the forums, you can directly ask what works and what doesn't. Lighter spring pressures on solid rollers do not help....they hurt as it allows more of an opportunity for valve control loss. |
We are staying with the solid roller that it has. At this point it looks like we may just be getting a slightly milder cam. Compcams says they can do a custom grind on one that will calm it down and make it more reasonable for the street. They say we can still use the springs we have. I am waiting to see what the specs are.
Compcams checked the serial number on the cam today and found out it has been reground once already. So it's a new cam. |
If you're staying with a solid roller, then the spring pressures are just fine.
How much is Comp wanting to charge you for a cam? |
The 495 pound springs are already on the light side for a solid roller. You'd be fine. You really don't want to go too light - solid rollers don't like bounce. You'd get a trench pounded into the cam face on the backside of the lobe. Things get uglier from there...
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