Spring Pressure February 11, 2012 10:46AM
I am building a new cylinder head right now and I am looking for some advise where to have my valve spring pressure. It is a flat tappet cam not a roller. I have been told 200 closed pressure and also have been told 350. I am nervous about taking a lobe off at 350. Just looking for some ideas. 60 lbs of boost and using Allis 426 valves.

Thanks in advance.
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Re: Spring Pressure February 11, 2012 10:47AM
Alky btw.
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Re: Spring Pressure February 11, 2012 01:05PM
I would not go over 200 seat pressure with a flat tappet cam
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Re: Spring Pressure February 11, 2012 02:25PM
With a .575 lift cam and close to 6000 rpms one AC puller I know gets by with 125-150 lbs closed and 330-350 lbs open...The spring is 2' closed and is compressed to 1.5" open...You need .050-.060 coil clearance..Excessive valve spring pressure eats up flat tappet cams..
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Re: Spring Pressure February 11, 2012 02:57PM
Is he running much boost? I am looking at a 195 closed spring from comp cams. It has a 563 open load. If you figure area of the valve minus the stem x boost I am around 140. Does that sound around the right range?

Thanks for any help.
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Re: Spring Pressure February 12, 2012 03:12AM
By running low spring pressure your cam lobes will last forever. That being said it is proven on the dyno that higher spring pressure = power. If you are having problems with the lobes on your cam shaft, are you getting them hardened correctly after grinding? Valve size, valve weight, rocker ratio, push tubes,and cam followers should all be considered. These motors were built for longevitty @ 2500rpm not a 15 second pass @ 6000rpm.
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Re: Spring Pressure February 12, 2012 04:36AM
Please enlighten me as to the correlation between higher spring pressure and more power.
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Re: Spring Pressure February 12, 2012 05:12AM
Controlling the valve, not bouncing on the seat, and making a good seal is a start.
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Re: Spring Pressure February 12, 2012 07:53AM
Perhaps I misunderstood your original post where you stated "it has been proven on the dyno that more spring pressure = more hp", as though there exists some linear and proportional correlation between spring pressure and horsepower. While it is obvious that horsepower would suffer if the spring were not doing its job of controlling the valve, spring pressure beyond what is required to do this plus a reasonable safety factor will not result in more horsepower, only accelerated valvetrain wear and increased frictional losses.
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Re: Spring Pressure February 12, 2012 12:38PM
Technically 50lbs of closed pressure will keep the valve closed enough for the motor to run even at 60lbs of boost. The cylinder pressure will close the valve but maximum hp will not be achieved. What we have learned on the dyno is the more spring pressure we ran the more top end hp we achieved. Now don't get me wrong we broke some parts but the horse power never quit increasing. It would be in my best interest if you don't believe me and you keep running your big heavy valve train with no spring pressure. Lol
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Re: Spring Pressure February 12, 2012 02:14PM
A 2" valve with 60 psi of boost would have 188 lbs of boost trying to keep it open. So you would be depending on cylinder pressure to close the valve. MACK
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Re: Spring Pressure February 13, 2012 02:25AM
You are missing or avoiding the question, so I'll simplify it. If a given engine combination has adequate spring pressure, whatever that may be, to hold the valve closed against inertia or boost or whatever forces at work, I fail to see and you have failed to explain how additional spring pressure beyond that will make more horsepower. If it really is that simple, I'll quit wasting my time with such foolishness as head porting, cam profiles, etc. and just start using Hummer coil springs to hold the valves closed. That oughtta make a ton of power, huh?
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Re: Spring Pressure February 13, 2012 03:48AM
I believe the point is that the 50 pound seat pressure mentioned above will maintain valve closure in a static (not moving) state, and that cylinder pressure against the head of the valve will help overcome boost pressure trying to open it from the port side. However it's not static in a running engine, it's being repeatedly hammered open and shut 1500-3000 times per minute. Since all of the valvetrain parts have mass and you're repeatedly accelerating and decelerating the parts, you will probably be very surprised at the amount of force required to close the valves in a TIMELY fashion. Sure, with a light spring it will close eventually, but if you want your intake valve to close at 45* after bottom dead center, but the spring is too weak and it floats it until 90* ABDC, you'll probably end up pushing your charge air backwards out of the intake valve. Horsepower will suffer.
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Re: Spring Pressure February 13, 2012 04:20AM
Thanks Arthur Good explanation. The problem is my cam isn't a roller and I wasn't really wanting to change it out till next winter when I build up a new block, it would be roller then.

The ideal for me would be between 300-350 closed seat pressure but my cam lobes I feel will not take that. Do you have any ideas where your open pressure should be?

Thanks for all the responses.
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Re: Spring Pressure February 13, 2012 04:55AM
You are getting my point Art. The math of figureing the valve size is only the beginging to the equation. To answer the question Bob, I would run as much as your valve train can handle. If your cam followers are spinning and the cam is hardened correctly, I question what will fail first, Cam lobe or an other component. If you are asking what will work, then by all means yes 180lbs. closed and 350lbs open will get the job done. But if you start looking for every last pony you cant follow in that way of thinking. There is two options in tractor pulling: lead or follow. I can guess what "wanna know" is.
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Re: Spring Pressure February 14, 2012 02:09AM
Quote
Power up
You are getting my point Art. The math of figureing the valve size is only the beginging to the equation. To answer the question Bob, I would run as much as your valve train can handle. If your cam followers are spinning and the cam is hardened correctly, I question what will fail first, Cam lobe or an other component. If you are asking what will work, then by all means yes 180lbs. closed and 350lbs open will get the job done. But if you start looking for every last pony you cant follow in that way of thinking. There is two options in tractor pulling: lead or follow. I can guess what "wanna know" is.

No need to take shots at me just because I busted you talking out your drain plug. If a particular combo requires 200, 300, or more lbs seat pressure, then that's what it requires and that's what should be used. Not arguing that point, but I am still waiting on an intelligent explanation as to the benefits of using stiffer valve springs than necessary and the intricacies of exactly how this practice produces more horsepower. If all you have to reply with is cheap shots, then I guess we know what YOU are.
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Re: Spring Pressure February 14, 2012 05:36AM
Who said anything about using stiffer springs than necessary??? Figuring the pressure needed using the area of the valve is WRONG!!! Re-read Art's post. Now, take a deep breath and answer your own question. Both Art and I have tried to explain the need for heavy springs. I have been looking on you-tube with no luck, for a video that I saw a long time ago of a valve train at high rpm's in slow motion. The video said how much spring pressure was on the valve, I dont remember particulars, but with "wanna know" 's theory, way too much. It was on a na motor, so no exterior force on valve, and yet the rocker couldnt keep up to the valve. Sorry for the cheap shot but for a highly intelligent guy, your being pretty stupid.
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Re: Spring Pressure February 13, 2012 05:59AM
What lift is your cam? How many rpms are you turning?I dont think that you need 300-350 lbs closed....To start with I'd go for 175-200 closed and 350-375 open...The cam should live..
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Re: Spring Pressure February 13, 2012 11:37AM
give me a call 270 998 0295-jeff mattingly
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Re: Spring Pressure February 14, 2012 12:52PM
Ok Guys go to You tube " High Performance valve spring testing 10k RPM" and there are several different tests showing valve float and valves moving in strange ways. Watch them all ! Crazy Horse
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