Solid roller valve spring pressure?

[blueovalz]

I've just installed my one and only roller cam (solid) in my engine. After speaking with CC techs, and then with the cam manufacturer, along with several racecar mechanics, I'm somewhat confused on how much spring pressure I need. I planned on using 200#/525# pressures, but after talking with the CC tech, he indicated my 175#/475# pressure springs would be adequate up to 7K. As far as solid rollers go, this one is fairly benign (.593" lift with 60 degrees overlap). My goal is to go with the mininum needed to safely operate the motor to 7K with a little extra insurance for missed shifts. Any comments or experiences? This is only a weekend street/strip car. No serious racing any more.

[Mike C]

My Comp mechanical street roller 280 advertised/236@.050 and .550 lift has only 145# seat pressure. (Comp 950 spring) Actually, they recommend more pressure now than when I bought the cam circa 1988. I have had no troubles however, but only turn it about 6500 max. I do have titanium retainers and Manley Pro Flo valves with undercut stems which are a little lighter then most, and Crane Gold TR series rockers. I'd be tempted to stay with the 175's for street driving.

[Kevin Shasteen]

Terry,

 

This is one concern of mine. Of all the books I've read, I've not found one that discusses what seat pressure is required for any one cam's profile in relation to maximum rpm's desired. For starters, the machinery for doing this is expensive and beyond the auto enthusiest's budget. This implies that the enthusiest's will have to concede knowing this data and blindly accepting what a cam's tech line tells us.

 

This concession leaves the enthusiest with the only other option, which is determining a spring's "Rate" within the seat pressures -vs- installed/compressed height figures the cam mfg's actually do give us.

 

Determining a "Rate" of a spring is all good and fine. But what if you've determined your Rate for your given choice of components; does this mean you can now relax? What if you've chosen incorrectly. Its my concern that one ("One" being yourself or the person on the cam's tech line) could possibly choose an incorrect spring but still properly determine that incorrectly chosen spring's rate; but what good does this do us(?) as we've properly determined its rate however we've chosen a spring that doesnt compliment our cam profile to begin with: AKA, JUNK IN=JUNK OUT.

 

How I understand the issue and how I would approach seat pressures is this way. Look at your cam catalogues in the valve spring listings. First go to the column listing Installed Height...this is what you need to know first. Then deduct your lift measurement (lift at the valve) and then take that number and compare it to the cam catalogue's number in the "Coil Bind" column to ensure you had reasonable "Over the Nose" tolerances once the spring has been broken in.

 

From what I've read an engine's valve tolerance between compressed height and coil bind should be at:

 

1) Street Engine = .060"

2) Race Engine = .100"

 

Now, let us look at your cam. If I remember correctly you're running a Ford. In the Comp.Cam's Catalogue their 953 spring lists a 185/475lbs spring for Installed/Compressed Seat Pressure on a mechanical roller. Its Installed Height/Compressed Height is 1.890/1.280 with a Coil Bind measurement at 1.100.

 

How to determine your spring's "Rate" is you either look at the column in the catalogue if you know where your valve springs came from. If you dont know where your valve springs came from then you'ld have to put your spring in a valve spring compressor measuring tool & mark down their readings.

 

Take the Comp.Cam's 953 Spring I mentioned along with your cam's valve lift of .593", like so:

 

A) Installed Height - Compressed Height = Total Valve Lift

 

Compressed Seat Pressure - Installed Seat Pressure = Actual Applied Pressure

 

C) Actual Applied Pressure/Total Valve Lift = "Rate of your Spring"

 

Now using the above formula but applying our 953 Spring & your cam's lift at the valve:

 

1) 1.890" - 1.297" = .593" Total Valve Lift

2) 475#'s - 185#'s = 290#'s Applied Pressure

3) 290/.593" = 489 lbs/in Rated Spring

 

This rate is actually 6lbs higher than the catalogue. This is why its so important to check the spring values yourself. A cam mfg will always have a few dozen springs which are used on many different occasions; now, 6lbs isnt really a biggy, but what if it was 50lbs and you didnt check it prior to running the engine: UH-OH!

 

In other words, one spring, rated at [X] lbs/inch on one engine may have a different rating on another engine w/a cam of a different profile altogether.

 

This presents two problems with our previously given example. First, I dont really know your installed/conmpressed height nor do we really know the lbs of seat pressure at your installed/compressed height. The only true way of knowing is by measuring your installed/compressed height and then measuring the spring's pressure's on a valve spring measuring tool.

 

Secondly, if this valve spring were actually installed on your engine w/the installed height/compressed height as advertised; then your .593" Valve Lift compresses the valve to 1.297; whereas Comp.Cam claims a coil bind exists at 1.100"; that leaves you with .197" of free play. According to the books I've read; only .100" are needed for a race endurance engine; so that would put us .097" too much free travel.

 

Who, what & how is that fine balance between too much seat pressure -vs- valve float determined(?), because I'ld really like to know: this is something where our "Faith" in the cam & valve spring mfg's come in to play.

 

It appears our dilemma still arises in that no one can tell me what the actual "Seat Pressures" are required at any one particular valve lift for a particular desired maximum RPM. It appears this info is something that the cam mfg's and auto mfg's think would be too confusing for the hobbyist as no one has come forward in any of the perf.books I've purchased and offered an "AVERAGE" seat pressure for [x] amount of cam lift.

 

If I was revving to 7000 or more I'ld definately want a rev kit installed.

 

So the two questions that are within our control are:

 

1) What tolerance is required between compressed height and coil bind when a peak rpm is desired:

 

a) .060" for a Street Engine

.100" for an Endurance Engine

 

2) What valve stem length/rocker arm ratio are you using, as this determines what your installed height and compressed height will be. Then you can determine your "RATE" in lbs/inch of your spring....but this is totally dependent upon the installed height/compressed height of the cam mfg's whims. What to do, What to do?

 

I hope this helped somewhat. and didnt add to the confusion.

 

Kevin,

(Yea,Still an Inliner)

[blueovalz]

CC was the ONLY entity to say that the lower spring pressures would be fine. All others strongly recommended the higher spring rates. The primary concern was not whether the valve would close at the correct time, but also to prevent the valve from bouncing open again. This particular situation is harder on the valve train that if the stronger springs are used in the first place. I went ahead and went with a stronger spring. The extra pressure was also added insurance being I do not have a rev limiter.