I'm wondering what the parasitic loss is through the valve springs. Our NHRA stocker was running a very "square" lobed cam, requiring about 200lbs of seat pressure. We have since switched to a less square more normal camshaft that doesn't require as much pressure. I haven't changed the springs yet. Wondering how much horsepower i am loosing vs a set of 140 lb springs. any input?????

 

Reseach shows very little is lost. While the camshaft is straining to open one valve, a similar spring is assisting camshaft rotation by allowing another to close.

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thats kinda my thought, but my dad disagrees with me

 

That doesn't mean that springs that are stronger than necessary don't put an undue load on other parts, needlessly, but as for parasitic losses, they are slight. It's been tested. Remind your dad, that what goes up, must come down.

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i think he is just judging off the fact the motor is harder to turn over on the stand. Oh well i already have the springs, and Stock is a game of hundredth so i have a feeling i will be changing them.

 

if you find a difference post what you find out

 

I was thinking of your stock class comment, overnight. And I agree that stock IS a matter of just hundredths. For that reason, and to ease the strain on other parts, I think a change is in order.

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Friction = force or pressure x the coefficient of friction x the area (or something close to that). The coef of friction of the lifter sliding accross the lobe of the cam doesn't change and the area of lifter contact doesn't change so increasing spring pressure will increase rotational friction by definition. I think the real question is does it make any effective difference, or is it too small to measure. What if out of a couple boxes of lifters you ran only the ones with the most crown? That would reduce contact area. Just my thoughts on the subject.

 

I have always increased seat pressure until no HP gain is found on the dyno. The square lobe hyds. and solids I've used ,usually end up at around 140 -150 lbs. I'm surprised you are using 200 lbs. ; normally the lobes will fail pretty quick at that pressure.

 

we are running schubeck lifters so cam wear is a non issue. I think we are going to swap the springs between Gainesville and Montgomery.

Also to whoever suggested going through and picking lifters with teh most crown, the schubecks are supposed to be dead flat. And at damn near $800 a set i'm not gonna test teh theory

 

That's stock class racing!!!

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Yea that and 200# seat pressure gotta be stock somewhere though

I get a kick outa the guys pullin the front wheels 2 feet in the aiir and carrying them for 1/8 mile down the track in "Hot Street" class, gotta be alot of those cars on the street somewhere too

Serously though I would run the manufacturers suggested spring pressure for that rocker ratio and cam

 

Although a lot of NHRA stockers pull some great wheelies, the difference between "Hot Street" and NHRA "Stock" class racing is night and day. NHRA "Stock" racing separates the men from the boys. I feel like a snot nosed, 17 year old, wannabe, next to the MEN of NHRA class racing, in spite of my bracket racing Wallys.

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I recently learned allot about springs in my research into what I needed for my solid roller project. I learned to not judge a spring by it's seat pressure. Also required spring pressure is a function of valve train parts weight VS rpm.

The Comp Cams sight has some interesting articles. I was looking at the possibility of using the Behive springs. Then I found an article on Nextel Cup restrictor plate motors. In the last five years the engine departments have only really found new power in friction losses. That's why i run 5W-30 motor oil and with tight bearing clearances can still have 80 psi of oil pressure at anything over 5000 rpm hot

One of the friction reductions being valve springs. They have been running behive "Nextel-Cup" springs with 140 lbs seat pressure. Everything is the lightest possible in the valve train. But do to the restrictor plate, the engine max rpm is limited to @7000. They run these motors on the edge of valve float and they do fail from time to time.

Well upon digging further and looking at realisticly priced springs in the sub $400 catagory. When your looking at springs rated in the .700 or greater lift range the price just jumps over the lessor lift @1.550 inch diameter springs.

I've known for years about .050 offset retainer locks and shimming for larger than listed spring installed heights. an example off the comp Cam web site is: Go to this page after determining what weight of spring to use. The inch pound rating is more important than seat rating. I could have a 200 # seat and a spring rate of 366# and have only 320# open at .600 lift. That's a very wimpy low rpm spring. Where as spring #2 with 160# on the seat and a spring rate of 560 # has 450# of open pressure @.600 lift.

So don't get hung up thinking about seat pressure - Spring rate is the key

So anyway this is the only documentation that lists taking a spring installed height and changing the installed height to taylor your springs. Look down the below chart till you find the spring part number 999 installed height 1.900 inches and .700 max lift. then go down and you will see that when installed at 1.900 it's 196 # on the seat. But what I did was installed it at 1.950 and it's only 165# Then if you lift that spring .600 and look at the chart of #'s at 1.350 its would have an open pressure of 544# Now that's a killer 8000 rpm spring because of the high "Spring Rate"

Then look at part number 9290 and it's 140# on the seat and @.600 lift it's only 380# open. Very low friction to turn the motor over because of the lower 437# spring rate.


http://www.compcams.com/Technical/cu...ml/340-349.asp



http://www.compcams.com/catalog/302.html

 

Thanks Gkull!

 

I don't recall saying anything about the two classes being the same, similar or anything in between, just having a little fun with the names of the classes and how far from a stock car NHRA "Stock" class is and how far from anything on the street the cars in "Hot Street" are, nothing to take seriously here.

 

you'd surprised at how "stock" some stuff in stock really is, especially in the lower classes and the EFI cars

 

I didn't say that you did say there was any similarity. But since you didn't mention the afore discussed "stock" classes, it wasn't easy to tell if you knew the difference between them, or not. As it is, it appears you merely changed the subject with no warning or introduction.

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