[GTOGEORGE]

What valve spring pressure are racers using for their BOOSTED roller cams?


GTO George

[JSPONT]

There is a formula depending on how much boost and how big the valve is. I run low boost 10 psi, added 40 lbs to the seat pressure over the recommeded amount. I had called crower cams (I have one in the car) they told me what I should run.

[mgarblik]

2.250 intake valve, 1.750 exhaust valve, 400-420 lbs. closed, 1120-1160 lbs. open, 35 lbs. boost.

[JSPONT]

wow! I am 235 closed I forgot the open, only 10 psi, 2.11 1.77

[johnta1]

Here is my calculator for it:

Boosted Spring Calculator

2.250 intake valve, 1.750 exhaust valve, 400-420 lbs. closed, 1120-1160 lbs. open, 35 lbs. boost.

Did you use any calculations for that or just what was recommended?

[twooldgoats]

2.300 intake, 1.750 exhaust, 375# closed, 950# open, 12# boost (so far)

Jim

[mgarblik]

Our pressures are based on a few factors, but recommendations are probably the best way to summarize our choice. We started out with less pressure and saw evidence of loss of valvetrain control at high RPM's. We were initially around 335-350 PSI closed on a stock size cam core and we shattered several lifter wheels. Also the harmonics were bad enough that the valves were hitting each other at high RPM's from the resonant frequency's being generated by the valvetrain and the extreme heat of the exhaust valve. In a Nitro engine the exhaust valve is heated to the plastic state during the run. At the end of the run, the valve would be bent. The higher spring pressure and the change to a 55mm core has more or less eliminated these problems. I have worked on some Brad Anderson and Alan Johnson nitro heads and they seem to use spring pressures in this same general range. We have also talked to Tim Wilkerson, Bill Miller and some others for their recommendations. I will check out the calculator also. Always want to learn as much as I can. We are getting a season out of a set of springs. Pretty happy with that. They are a triple, 1.677" OD. Our valvetrain is better in some ways than a hemi as far as angles. Our valves are very long, 6.7 ", and have long guides for decent support. I just plugged our numbers into the Wallace Calculator. Interesting, it said 486 PSI intake closed, 1086 open, 431 closed exhaust and 1031 open. So we are in the general ballpark with the calculator. I really enjoy the Wallace site and all the cool calculators. Use them all the time with my students.

[Elarson]

Additionally, some of the other nostalgia nitro folks told us that dipping below 400 lbs seat is a pretty sure way to make the motor mad and blow parts off the top of the engine.

Eric

[GTOGEORGE]

I checked mine and came up with about 270 at 2".


GTO George

[mike leech]

Originally Posted by GTOGEORGE

I checked mine and came up with about 270 at 2".


GTO George

If that is your installed height you don't have enough for a low RPM naturally aspirated engine.

[GTOGEORGE]

Originally Posted by mike leech

If that is your installed height you don't have enough for a low RPM naturally aspirated engine.

That's why I couldn't throw no boost in it.


GTO George

[dci]

George like I told you last year, you needed springs with more seat pressure especially after you told me that you couldn't build more boost. Unless your rings are toast or you have a gaping intake leak that's the only place the boost can go. Does your blower have teflon strips and if so have you changed them lately? Put some 400 psi on the seat springs in that thing and crank it up. I guarantee you will go 7's, but be ready to find the next weak link LOL. Right now with the spring your running you have a built in rev limiter LOL.

[carl455]

OK what I'm I doing wrong can't seemed to get calculated to work.
2.11 intake
1.77 valve
Dia 11/32
165 seat na
365 open na
15#
What do I need to add

[johnta1]

Use decimal equivalent of the 11/32"? (.34375)

Here is the result:
Closed Intake Spring Pressure Under Boost - 216 PSI
Open Intake Spring Pressure Under Boost - 416 PSI

Closed Exhaust Spring Pressure Under Boost - 201 PSI
Open Exhaust Spring Pressure Under Boost - 401 PSI

[GTOGEORGE]

Originally Posted by dci

George like I told you last year, you needed springs with more seat pressure especially after you told me that you couldn't build more boost. Unless your rings are toast or you have a gaping intake leak that's the only place the boost can go. Does your blower have teflon strips and if so have you changed them lately? Put some 400 psi on the seat springs in that thing and crank it up. I guarantee you will go 7's, but be ready to find the next weak link LOL. Right now with the spring your running you have a built in rev limiter LOL.

Don (Buddy, Pal),
I got Teflon strips in my blower, I've had the blower checked its fine. Working on valve springs. No weak link in my car/engine.........maybe the gears on my Dana. My smallish 8-71 will only give me around 18-19 lbs of boost........it is what it is!


GTO George

[carl455]

Originally Posted by johnta1

Use decimal equivalent of the 11/32"? (.34375)

Here is the result:
Closed Intake Spring Pressure Under Boost - 216 PSI
Open Intake Spring Pressure Under Boost - 416 PSI

Closed Exhaust Spring Pressure Under Boost - 201 PSI
Open Exhaust Spring Pressure Under Boost - 401 PSI

thanks should have known to use Dec.
Will that much open pressure wipe out a solid (non roller cam)

[dci]

George is your blower a high helix with the newer retro case?

[GTOGEORGE]

Originally Posted by dci

George is your blower a high helix with the newer retro case?

I wish............its a GOOD old fashion nostolgia (piece of junk) Roots Blower.


GTO George

[mike leech]

Originally Posted by GTOGEORGE

Don (Buddy, Pal),
No weak link in my car/engine........


GTO George

No offense but that is a foolish thing to say. There is a weak link and if you make more power you will find it. Trust me. Right nowI would be concerned about your lifters. And how many passes on those rods?

I hope your engine is as bulletproof as you think it is. But I will not act like a hole that you did when other people break when you find out something isn't up to snuff

[GTOGEORGE]

Mike,
No engine is bullet proof.........SH_T can always happen BUT I do try to buy the best parts (over kill) for my car. Yes you are correct lifters and rockets arms that's a possibility I forgot about them.......not because they aren't great parts BUT it's time they get replaced. I just replaced my rods.........besides they are over kill for my engine (pro mod rods) 800 CI.....5 stages of nitrous rods. It's s drag race engine.........like I said, nothing is BULLET PROOF. I still like my ODDS!


GTO George