Im pulling my hair out trying to figure out theoretical spring pressures...



TSP .660 dual Spring specs:

1.81 instal heights

415lbs at .660

160lbs closed

1.015 coil bind



I can calculate the spring stiffness as 320.75 with confidence, but next I get a bit lost in internet BS.



What is the formula to determine new open and closed pressure based on the installed height of my springs?



Ive gone round and round forums and youtube. I will spare you me trying to explain my formula but

my calculation for the above spring is as follows:



@1.8 install height

163.86 closed

403 open

.155" to coil bind





at 1.785 Install height

169 closed

428 open

.140" inches to coil bind



1.77 installed height

175 closed

442 closed

.125" to coil bind



I find none of this is optimal for me.

My lifters wouldl ike to see no more than 400, maybe 420 lbs, they are gatermen.

I would like to see no more than .100" from coil bind.



These are texas speed springs and they have told me I will be fine at 1.81 install height. In fact Derek told me on the phone yesterday to get it as close to 1.81 as I can. I got very specific and asked about valve control at 7000RPM and he said not to worry about it. But every hot rod magizine, web page and youtube says otherwise. IM watching weingartner, powell cams and othres who konw their ****. Im sure TSP knows what they are talking about too..

 

In your first set of numbers you say 1.015” at coil bind … I think you mean 1.150”

What is the lift of your cam?

 

the cam is a ss3 the loft is .350 my rockers are 1.8 so the total lift is .630. If it were factory rockers it would be .595

 

If the spring is 160# at 1.81" installed height, and 415 lbs at .660" from there, the rate is ((415-160)/.660) ==> 386.35 lbs/in.

Formula for pressure at height X ==> 160 + ((1.81-X)*386.35)

Pressure at 1.115" (.100" from coil bind) is 160 + ((1.81 - 1.115)*385.35) ==> 428.5#

If your cam has .630" lift, and you want to run the springs at .100" from coil bind, your installed height is 1.115" + .630" ==> 1.745"

Pressure at 1.745" is 160 + ((1.81 - 1.745)*386.35) ==> 185.1#

If TSP is happy with the springs at an installed height of 1.81", I'd probably run them there. If you want to be a little closer to coil bind, maybe run them at 1.78", because that would put the open height at the same distance from coil bind as a .660" lift cam installed at 1.81". If you start futzing around with other heights, you're probably overthinking it. We don't have as much information as TSP regarding the capabilities of this spring (we didn't design them), so I'd be a little hesitant to go very far outside of their recommendations.

 

If you run them at an installed height of 1.8” as recommended by TSP, your open pressure will be 403.4#, which will make your lifters happy.

 

heres what I came up with. Let's try this again. Heads are off getting milled. I hope this helps someone in the future...



I have measured an install height of 1.7838.

Thanks to Topfun who helped me realize a mistake in my math. Use the manufacturer's lift spec, not the actual lift, unless otherwise noted Okay, on to the math



To find the spring rate, you look at the manufacturer's spec and perform the following calculation:

(open pressure-closed pressure) / lift=spring rate

(415-16)/.660 = 386 lbs per inch



To calculate the new seat pressure, the formula is :

closed pressure + [(old install height - new install height) + the spring rate]=seat pressure for new install height



160+ [(1.81-1.7838)*386]=170.1132 which will round down to 170lbs on the seat





Now, to calculate the new open pressure, perform the following calculation:

(ACTUAL lift * spring rate) + new seat pressure=new open pressure



(.630*386)+170.1132=413.2932lbs over the nose





I spoke to the lifter manufacturer on the phone (gatermen) and they said my lifters are rated to 450, but many people push them well beyond that at 8K and have no problems.



Furthermore, the cam is a billit elgin cam. I emailed them a while ago asking about 380lbs and was told the pressures are a bit high but should be ok on the billet core.



Finally, the distance to coil bind

install height - actual lift- spring coil bind height = distance from coil bind

1.7838-.630-1.015=.1388" from coil bind





Lastly, I am positive I have the right calculation based on an email from PSI to check my work. I used the above formula(s) with the data from the PSI ls1516 spring. Next, I compared my computations to the data that PSI gave me for a different install height. That screenshot is below.



Stated differently, use the formulas above on the spring specs below to check you are using the formulas right. They are simple, but it took me a littl while to find it all and figure it all out.