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can valve springs alone = 15HP gain ???

  
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can valve springs alone = 15HP gain ???

 
buzzinhalfdoz buzzinhalfdoz
User | Posts: 234 | Joined: 07/12
Posted: 05/19/13
07:32 AM

the 1973 455 is all stock except for 702 lunati cam and lifters ,comp roller tip rockers,and heads cut .040.(yes i reused my 40+ year old valve springs, they were good to break in the new cam.)
i have a friend who before health issues was a circle track car mechanic for about 20 years.
he says that by changing my wore out springs to what lunati called for (120lb springs), that i could get 15-20 hp. he swears he has seen it on the dyno.
i have been wreching on v-8s for over 35 years, i graduated NADC in nashville in 1981, i thought i understood engine operation, but i dont understand this.
if the old springs are closeing the valve why would stronger springs add any power???
any thoughts???
ps- max redline 5000rpm.  

70bird 70bird
Guru | Posts: 1064 | Joined: 02/13
Posted: 05/19/13
09:03 AM

Hello


All i can think of off hand is that a weak spring is more prone to allowing valve "bounce".  

buzzinhalfdoz buzzinhalfdoz
User | Posts: 234 | Joined: 07/12
Posted: 05/19/13
04:56 PM

thanks i know i should have changed the springs with the rebuild but was trying to save money.  when i can afford it i will replace them and c.  

barneyformula barneyformula
Addict | Posts: 3306 | Joined: 01/07
Posted: 05/20/13
06:13 AM

The only way a stiffer spring is going to make more HP is if the springs already in use are inadequate to keep the valvetrain following the cam lobe profile. I've heard this statement from "experts" saying that you could gain power in a stock 305 by putting better valvesprings on it. Suuuurrre! And jacking up the rearend makes the car think it's rolling downhill too!
Always use the springs recommended for the cam unless you are running a really mild cam and the stock springs are adequate.
Steve  
A little help... 'cause we don't all have to learn the hard way!

70bird 70bird
Guru | Posts: 1064 | Joined: 02/13
Posted: 05/20/13
07:54 AM

Hello


"The only way a stiffer spring is going to make more HP is if the springs already in use are inadequate to keep the valvetrain following the cam lobe profile."

I thought about that also but then figured if the lifter was not "following" the cam lobe the only other thing it could do would be to make it seem like it had a "bigger" cam ie more duration, more lift, as the lifter flew off the back side of the cam lobe thereby actually adding hp, lol.


"And jacking up the rearend makes the car think it's rolling downhill too!"

You mean it doesn't, lol. You're breakin my heart Barneyformula.  

idrivejunk idrivejunk
Addict | Posts: 5168 | Joined: 12/09
Posted: 05/20/13
10:38 AM

If a stiffer (or shimmed) valve spring can allow a few hundred added RPMs before float and the power was increasing at the old redline, more power might be had by allowing the higher revs. But then stiffer springs are harder to open, too. Taller ride height at rear could help aero by sending the wind over the smooth side of the car. But yeah we're splitting hairs at this point. Hard to believe theres much gain to be had by swapping valvesprings that work.  
idrivejunk

buzzinhalfdoz buzzinhalfdoz
User | Posts: 234 | Joined: 07/12
Posted: 05/22/13
05:31 AM

my engine only spins to 5000rpm in first and only 4800rpm in second. it is still pulling hard when it shifts out of first at 5000 rpm ,i really believe that the stock springs are doing fine at this low rpm.
should i change or leave alone???  

barneyformula barneyformula
Addict | Posts: 3306 | Joined: 01/07
Posted: 05/22/13
09:09 AM

If you aren't getting any valve float at the rpm you are turning and there was no coil bind when you assembled it, I'd leave well enough alone for now.
Steve  
A little help... 'cause we don't all have to learn the hard way!

buzzinhalfdoz buzzinhalfdoz
User | Posts: 234 | Joined: 07/12
Posted: 05/22/13
01:29 PM

amen, leave well enough alone-if it ant broke, dont fix it...
ps- the 40 year old springs might be making more hp low and mid, than new ones...