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Old 11-08-2007, 10:10 AM
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Comp Cams Valve Spring Questions - Selection

I have a BBC (468) with iron oval port heads with spring pockets as part of the casting. I am running a comp cams 11-250-3 hyd FT cam. I want to change the valve springs to something different. currently have the comp cams 911's, even though Comp recommends the 924's (long story).

I've had a few guys who are very knowledgeable tell me to try different springs from Comp such as the 928's and 930's. Those have higher pressures than the 924's and will fit my application so it appears. I took measurements of the head and valves and valve guides, etc, and it looks like those will all work.

So I have at least 3 choices at this point. The 924's, 928's and 930's. All are "dual" spring types. How do i know which to choose? Very confusing for me.

Question: is it common to run springs other than those recommended by the cam manufacturer or should you always run what they recommend?

Although I am not "drag racing" my car, I do want the most performance I can get out of it from 2500 to 6500 rpm. It's basically a street car. Right now my motor falls "flat on it's face" at about 5300-5500 rpm.

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Old 11-08-2007, 11:06 AM
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There is a limit as to how much spring pressure a hyd lifter will take before it tends to collapse. That exact pressure is dependant on a few variables such as oil viscosity and oil pressure at idle as well as lifter internal clearances.
The break point tends to be around 130-140 lbs seat pressure . The 928 and 930 springs are meant for a solid lifter or street roller motor.
Did you check the actual installed height of your springs? You can shim them a bit to increase the spring pressure. (within limits.)

BBC's with their heavy weight valvetrain are notorious for lifter pump up at high rpm where the heavy valve train goes in a harmonic resonance at a specific rpm. At that point a hyd lifter will "pump up" and power goes away. "falls on its face"
A solid lifter will tend to pass thru this narrow harmonic band of unstable rpm and rev higher where a hyd lifter cannot recover. One thing that may help is to reset the lash preload (rocker adjustment) right up to the top of the lifter plunger travel or even dial in a slight bit (.001-.002") of valve lash. Now the hyd lifter acts more like a solid lifter and will rev higher up to the valve lift point.
I prefer using a solid lifter camshaft on a BB chev motor that will see more than 5200-5500rpm. its just a lot more stable at high rpm. A SBC with its lighter valvetrain can rev higher with a hyd cam than a BBC can. Often more spring pressure will not help because the spring is the part that is "in resonance" at the specific rpm. (natural vibration). This is where a dual spring #924 or beehive spring helps with its more dampened natural resonance caused by either the counter wound dual springs with damper or by the beehive shape of the spring and smaller-lighter retainer.
So a #924 dual spring will help. A beehive spring/retainer set will help. Adjusting the valvetrain for 0 preload or a very slight lash (.001-.002") will help. But, if your really want to rev it, swap to a solid lifter cam with the recomended springs.
A properly selected solid lifter set up is not a excessively noisy at idle and is not a pain to maintain.
A comp cams #11-219-4 CB294s-10 magnum or a comp cams CB280S-10 #11-551-5 are my choices for ya. Both use a 924 or better spring. Both are very good street cams that will make more power and rev higher than you present cam.
They both idle and drive very similar to your present hyd cam. You'll like either of 'em.

Contact comp cams tech for premium spring choices and other details about these cams. You will notice and like the difference these solid lifter cams will make on you BiG BloCk. Any BBC regardless of hyd solid or roller cam requires a premium valve spring because the valve train is so big and heavy. A heavier valve train mass has a low(er) natural resonance frequency (critical rpm) making it much harder to control at high rpm.

isky #8005-A is another good spring choice.

Last edited by F-BIRD'88; 11-08-2007 at 11:20 AM.
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Old 11-08-2007, 11:25 AM
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springs

Why do you want to change the springs????


Keith
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Old 11-08-2007, 11:40 AM
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Quote:
Originally Posted by k-star
Why do you want to change the springs????


Keith
I have no power beyond 5200 rpm. that's fine I guess for the street, but.......other guys agree with me that even though I have a BBC I can easily get 6000 out of that motor if the cam/valvetrain is setup correctly (and everything else - carb, fuel line/pump, ignition, etc) The springs in there now are the 911's. Supposed to be the 924's. that all got me started on this whole mess. Thinking that for $125 I can try new springs and see what happens. but, like every other "adventure" I go on with my "ride" it takes on a life of it's own and grows to something much bigger.

Did you see the previous response from that FBird guy? Can't argue with what he said. Sounds correct. I've been thinking of going to a solid cam anyway - maybe it's time. I've got the motor 50% apart anyway. Maybe I should pull the radiator, remove the timing cover and chain, and pull the cam while she's already 50% apart.

I'll go check the cost for a solid cam/lifter/spring setup. If it's affordable I may just change the whole dam thing and be done with it.
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Old 11-08-2007, 11:46 AM
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Quote:
Originally Posted by F-BIRD'88
There is a limit as to how much spring pressure a hyd lifter will take before it tends to collapse. That exact pressure is dependant on a few variables such as oil viscosity and oil pressure at idle as well as lifter internal clearances.
The break point tends to be around 130-140 lbs seat pressure . The 928 and 930 springs are meant for a solid lifter or street roller motor.
Did you check the actual installed height of your springs? You can shim them a bit to increase the spring pressure. (within limits.)

BBC's with their heavy weight valvetrain are notorious for lifter pump up at high rpm where the heavy valve train goes in a harmonic resonance at a specific rpm. At that point a hyd lifter will "pump up" and power goes away. "falls on its face"
A solid lifter will tend to pass thru this narrow harmonic band of unstable rpm and rev higher where a hyd lifter cannot recover. One thing that may help is to reset the lash preload (rocker adjustment) right up to the top of the lifter plunger travel or even dial in a slight bit (.001-.002") of valve lash. Now the hyd lifter acts more like a solid lifter and will rev higher up to the valve lift point.
I prefer using a solid lifter camshaft on a BB chev motor that will see more than 5200-5500rpm. its just a lot more stable at high rpm. A SBC with its lighter valvetrain can rev higher with a hyd cam than a BBC can. Often more spring pressure will not help because the spring is the part that is "in resonance" at the specific rpm. (natural vibration). This is where a dual spring #924 or beehive spring helps with its more dampened natural resonance caused by either the counter wound dual springs with damper or by the beehive shape of the spring and smaller-lighter retainer.
So a #924 dual spring will help. A beehive spring/retainer set will help. Adjusting the valvetrain for 0 preload or a very slight lash (.001-.002") will help. But, if your really want to rev it, swap to a solid lifter cam with the recomended springs.
A properly selected solid lifter set up is not a excessively noisy at idle and is not a pain to maintain.
A comp cams #11-219-4 CB294s-10 magnum or a comp cams CB280S-10 #11-551-5 are my choices for ya. Both use a 924 or better spring. Both are very good street cams that will make more power and rev higher than you present cam.
They both idle and drive very similar to your present hyd cam. You'll like either of 'em.

Contact comp cams tech for premium spring choices and other details about these cams. You will notice and like the difference these solid lifter cams will make on you BiG BloCk. Any BBC regardless of hyd solid or roller cam requires a premium valve spring because the valve train is so big and heavy. A heavier valve train mass has a low(er) natural resonance frequency (critical rpm) making it much harder to control at high rpm.

isky #8005-A is another good spring choice.
Hmmmmmmmmm.........

interesting stuff. you really got my juices flowing now. Here I go again an another adventure. That solid cam setup sounds interesting - very interesting. I've been thinking about that anyway.

and thanks for all the theory about hydraulic vs solid valvetrain setups. That was very helpful.
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Old 11-08-2007, 11:50 AM
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Are you using a mechanical fuel pump?
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Old 11-08-2007, 11:55 AM
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Quote:
Originally Posted by F-BIRD'88
Are you using a mechanical fuel pump?
Hi FBird Dude.........thanks for all your help . appreciate it.

Yes, I am using a mechanical high volume 3/8" Holley fuel pump. And yes I have the "stock" heavy pump rod. I will order a lightweight one as others have suggested me to do.

Lee
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Old 11-08-2007, 12:10 PM
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woops double post.
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Old 11-08-2007, 12:10 PM
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Quote:
Originally Posted by leejoy
Hi FBird Dude.........thanks for all your help . appreciate it.

Yes, I am using a mechanical high volume 3/8" Holley fuel pump. And yes I have the "stock" heavy pump rod. I will order a lightweight one as others have suggested me to do.

Lee
There is a small spring on the pump arm and another within the pump body above the diapharam. If either are broke or missing the pump will give up way too soon in the rpm band. How is your fuel pressure in 2nd and high gear at hi rpm? You're probabily at the point of needing a larger fuel line to feed your hungry BBC at high rpm anyway. My vortec headed 400SB runs out of gas in the top end with a mechanical pump and 3/8" fuel line. I run the same XE284H-10 hyd cam grind in my SB 406, as you have in your BBC.
Other than the top gear fuel flow issue, it will rpm well past 6000rpm with just a high pressure 1.26" single spring, but the valve train is much much lighter.
I built and raced many BBC's for street use and drag racing before and always prefered a solid lifter cam over a hyd in any BBC that revs over 5500rpm.
Even on a street motor. It's only money.... you'll get more
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Old 11-08-2007, 12:28 PM
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Quote:
Originally Posted by F-BIRD'88
There is a small spring on the pump arm and another within the pump body above the diapharam. If either are broke or missing the pump will give up way too soon in the rpm band. How is your fuel pressure in 2nd and high gear at hi rpm? You're probabily at the point of needing a larger fuel line to feed your hungry BBC at high rpm anyway. My vortec headed 400SB runs out of gas in the top end with a mechanical pump and 3/8" fuel line. I run the same XE284H-10 hyd cam grind in my SB 406, as you have in your BBC.
Other than the top gear fuel flow issue, it will rpm well past 6000rpm with just a high pressure 1.26" single spring, but the valve train is much much lighter.
I built and raced many BBC's for street use and drag racing before and always prefered a solid lifter cam over a hyd in any BBC that revs over 5500rpm.
Even on a street motor. It's only money.... you'll get more
I'm embarrassed to say that I don't know my fuel pressure at high rpm. I know I'm supposed to have tested that and I havent yet (no time). but I can say this......even in 1st gear when I step on it, and before shifting to 2nd, the motor falls flat above 5000. I find it hard to believe that in about "2 seconds" my huge Demon 850 dual fuel bowls and my Holley High Flow 3/8 pump and line are lacking fuel already. I can understand that if I'm racing through the gears for 8-10 seconds, but how can it be starving of fuel in 2 seconds? I personally still think it's a valvetrain issue. don't mean to be a stubborn "know it all". Just a hunch it's the valvetrain.

Lee
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Old 11-08-2007, 12:48 PM
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Well I'm 100% sure you'll like either of the comp solids I pointed out to ya.....But won't make a bit of difference if the thing is just simply running out of gas at high rpm.

I like using a mechanical fuel pump in a street motor but....
Mechanical pumps can be a bit fussy. The pick up/feed side is critical. Because the fuel in the feed side line is under no pressure (partial vacuum) it tends to boil in the line very easily. Especially near the exhaust system especially where there is a change in internal diameter (fuel fittings etc). Any rubber connecting hoses tend to collapse/kink easily from vacuum and heat while the motor is running hot. A common spot is the rubber hose that connects the pump inlet to the fuel line on the frame. it tends to collapse/kink when hot and fuel demand is highest.
The engine mounted pump adds a lot of heat to the fuel also. The pump cannot tolerate any boiling/bubbles in the feed side of the fuel system. It cannot move fuel that has bubbles in it.
A electric pusher pump at the back pressureizes the fuel line to the mechanical pump helping a lot lot lot. 3/8" fuel line becomes marginal with more than 375BHP reguardless of the fuel pump used. A healthy BBC needs a 1/2" fuel line or dual 3/8" fuel lines and pumps.
A pressure gauge is a must.

i have the big federal mogul 6 valve mechanical pump on my car and it cannot keep up with the fuel demands of my 406 SB. It's around 460hp.
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Old 11-10-2007, 06:42 AM
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By looking at the pictures from your other posts I can see where your fuel system will definatly not be able to feed a BBC like yours. Look at the brass barb fitting on the fuel pump inlet. remove it and measure the inside diameter of that fitting. (a drill bit works good as a guage) Ain't no 3/8" is it. More like 1/4".
barb fittings and right angle fittings are very restrictive. Every barb fitting/hose joint is additive in its restriction to the total system flow.

Your fuel system has an overall effective inside diameter of 1/4", not 3/8". So you have a 1/4" fuel system feeding a 400+hp BBC. It's going to run out of gas in the top end. faster than you think. You should be using 1/2" or twin 3/8" fuel line from the tank to the carb. Avoid right angle fittings and barb fittings.
Avoid lengths of rubber fuel line on the feed side of a fuel pump. A very short piece that joins two pipes together is fine. If you need a right angle get a curved fitting. You're probabily giving up 100RWHP with that fuel system as it is.
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