Freshening up my Ramjet 502

[chevynut]

Regarding valve springs, my springs have 140 pounds load at installed height. At .600" lift they should have 361 pounds of load. How much do you need to control a 2.25" valve at 6000 RPM?

[chevynut]

I found this chart that I thought was interesting. It doesn't really have all the info I need, but you can infer some things from it...

http://www.hotrod.com/how-to/engine/...-valvesprings/



Looks like a BBC with a hydraulic flat tappet cam with 220/226 duration and 525/.530" lift running at 6000 RPM needs around 130 pounds on the seat, and around 320 pounds open. They don't say what the valve size is.

A BBC with a hydraulic flat tappet cam with 230/236 duration and .533/.556" lift running at 6500 RPM needs around 140 pounds on the seat, and around 345 pounds open.

A BBC with a hydraulic roller with 230/236 duration and .612/.607" lift running at 6500 RPM needs around 170 pounds on the seat, and 415 pounds open.

None of these say what the valve size is, or other specifics. I assume duration matters because it affects ramp speed. Why does a roller cam need more spring, is it because of the lifter weight or are the profiles more aggressive? I read an article that said you can get the same valve lift profile with a flat tappet cam as a roller.


So I wonder how much of a cam I can run with my stock springs using a 2.25" intake valve at 6000 RPM....or conversely, what spring pressures would be needed to run around 230 duration and .600 lift with a 2.25" intake valve. I assume you only need to be concerned about the intake side since the exhaust valve is smaller and lighter so I don't understand why the chart shows both intake and exhaust specs.

[markm]

I am starting to understand why your car is not done you over analyze every detail.

[chevynut]

Some more stuff...

"Hydraulic Roller Cams Hydraulic roller (HR) cams require higher pressures to control the inertia of the heavier roller lifters and the faster acceleration of valve train components allowed by the use of the roller follower. Pure street small blocks should have 260-300lbs open pressure. For performance use, aim for 300-350lbs open. Racing small blocks that regularly see 6,000+rpm need over 400lbs open pressure. At these pressures, premium valve train components including a “billet” type cam are required. Even with these components, there will be reduced service life and the consequent need for more frequent parts inspection and replacement. Big blocks need closer to 300lbs open pressure for street driving and 350-375lbs is preferred for performance use. A racing big block needs 450lbs. As with small blocks, premium components including lifters are needed at higher pressures and rpm. As with solid lifter cams, seat pressures should be in the range of 105-125lbs for small blocks and 115-130lbs for big blocks for performance street cars. Blower cars and race cars will need higher seat pressures."


I can't find any good guidance on this subject anywhere. Everything I read says use the "recommended" spring loads. Who recommends them?

Seems like someone should be able to come up with a chart or software where you enter the wight of your components and cam specs and get a reasonable answer.

[chevynut]

I am starting to understand why your car is not done you over analyze every detail.

It's better than following your advice and sticking in a cam that doesn't work. LOL! You said you need more duration to change anything...all it does is shift the torque curve higher, and that's not what I want to do. Trial and error isn't the way I typically do things. I want the parts to work together the way they're supposed to to make a reliable setup. If you don't have any useful input on the subject, or any other subject, then STFU.

[55 Rescue Dog]

It's better than following your advice and sticking in a cam that doesn't work. LOL! You said you need more duration to change anything...all it does is shift the torque curve higher, and that's not what I want to do. Trial and error isn't the way I typically do things. I want the parts to work together the way they're supposed to to make a reliable setup. If you don't have any useful input on the subject, or any other subject, then STFU.

You probably already have the perfect cam, but you will never know, after you have blown a bunch of "extra money" on a different cam you don't even need.

[Rick_L]

Your post #60 says it all. You make a convincing argument NOT to change the cam. Read it back to yourself.

As you say, a roller lifter is heavier than a flat lifter, especially the hydraulic ones. This requires a bit more spring force, all else equal. The other thing is that a roller cam DOES allow quicker valve action, contrary to your statement. With a roller cam, you can grind it with a local concave profile, and the roller will follow it. This potentially can be used for very quick valve opening. A flat lifter requires a cam profile that is convex so the there is only 1 line of contact. Also with a flat tappet you can't have the cam contact the edge of the lifter. We used to use a lobe like this on race engine, called it the "peanut lobe" because that was its shape. Now, a street engine won't use something that radical, but you can definitely get away with more action when you use a roller, and the cam companies do take advantage of that.

[markm]

Actually I find cam choice has too many personal preferences and variables associated with it and its about like trying to advise someone what to look for in a wife.

[55 Rescue Dog]

If you really want to make bragging rite power, even at high altitude, why not just blow it?

[chevynut]

Your post #60 says it all. You make a convincing argument NOT to change the cam. Read it back to yourself.

I did? I'm looking for 50 or so "easy" HP and more torque in the 2500-4000 range and it looks to me like at least a couple cams fit that goal. All I want to do is move the torque curve upward like the dyno graph I posted. I don't want to shift the torque curve higher.

I'd spend another $200-400 or so on an upgrade if it made a noticeable difference and didn't destroy streetability.

I think I'll give Lunati a call and tell them what I'm looking for, and have them tell me if it's reasonable.