9550

i installed a new cop cam.
previously had a ford f-303.
the f-303 went in with the gt40 heads and the springs were allegedly matched with the cam.

now, with the new comp cam, what do i need to consider to determine if i can keep the same springs or not? is it just comparing the lift of the two cams? the comp page doesnt give any info on what parameters to use in the springs.

also, i want to replace the valve stem seals while i have the heads off and the valves out. problem is, i have no idea what size they are or does size even matter. do i just get a caliper and measure the stem width? however, if i dont replace them at all, they are either going to be sealed fine (best case) and allow the proper lubrication, or, they are worn and will allow too much lubrication (worst case). so if its worst case, i burn oil but theres no performance lost? or worst case i burn some oil and other bad things happen?

thanks in advance


heres the two cams in case it matters
new -http://www.summitracing.com/parts/cca-35-351-8/overview/make/ford
old (f303) - http://www.fordracingparts.com/parts...tKeyField=2029

dawson1112

They both have a .512 lift. Im not sure you would have to worry about new springs if the old ones were bought for the f cam. Should be able to get away with the same springs and rods.

You will have to check piston to valve clearance as a precaution though. And its a good idea to change valve stem seals just because the heads are off. Worse case if you don't change them they leak and you burn oil, foul out plugs gunk up cyliners .
You should be able to order seals for the gt40 heads and go with those. summit carries them.

barnett468

i would not guess at the springs. you need to measure the trapped length then have a machine shop test them to determine what rate they are and set them up to the cam mfgs recommended spec. for a roller cam that size they should be around 125 closed and 330 open.

9550

thanks
i had looked up the seals in summit, but i got stuck when they specify stem diameter, which i dont know. i even looked up what i believe to be my valves, and there is no info on stem width, only stem length.
this is as far as i can get:
http://www.summitracing.com/search/p...rder=Ascending

am i on the right track? i dont see anything that says its good for gt40, but some do say good for cobra, so im guessing thats what i need. in the link above, the first one says its good for gt and gts and valve stem 0.344. the middle one says good for V6,gt, gts, cobra, cobra R, but valve stem is 0.342. wtf. how can the 0.342 and 0.344 both be good for gt? does that .002 not make a difference?

also, i have two different color seals on my heads. orange on the exhaust valves, and black on the intake valves. any reason for this that you know of?

lastly, my valve seals have these metal clips or rings or something around them. i need to get those off the old ones and put them on the new ones? doesnt appear the new ones come with the clips

thanks again

barnett468

you do not need to remove the clips they come on the seals. but there are different types of seals. the orange seals might be high temp for the ex.

9550

so i checked the cam card that came with cam. it just says to use comp springs part number 986-16
http://www.summitracing.com/parts/cca-986-16
the info just says the spring rate is 322lb/in. i assume thats the open rate. how do i figure out the close rating?
from some minor research, it appears these are the springs i have now:
http://www.fordracingparts.com/parts...artKeyField=44
the M-6513-A50. they say the minimum loads for new springs is closed 123lb, open 303lb.
the current springs do have a thin shim. i dont know what the shim affects. i assume it affects the open rate?
are the 986-16 and what i have now way different than each other?

another question: how much of this getting the exact spring rates process is just fine tuning and how much is absolutely necessary? like, is 322 vs 303 a difference that will make the engine blow up, or is it just like a matter of somehow boosting efficiency by a few percentage points? (those examples may not make sense, but i think you guys get what im saying)

thanks again

9550

thanks. summit didnt indicate the clips come with the seals, so i had no idea.

barnett468

hi;


the shim affects closed and open rate.


you need

the trapped distance of the spring as i already mentioned

spring rate which you have.

spring length from the mfg's site.

valve lift

a calculator


example:

a 322 lb spring that is 1" long

your trapped length might be .700"

32.2 lb per .1000" so 3 x 32.2 = 96.6 lb closed, this is too low.

valve lift of .500, so 5x 32.2 = 161.0

add 161.0 and 96.6 to get 257.6 open.

this open pressure would be too low for that cam.

you need to do your own trapped spring measuring, we can calculate the rest for you if you want.

9550

thanks.
how do i measure the 'trapped length'?
is trapped length the length of the spring when it is in place but not compressed (other than the amount it is compressed to be held in place by the retaining clip thing)?

9550

ok so, trying to work through the numbers using my old springs. from what i can tell:
springs are about 2.08" based on my measurement in my garage
trapped length is 1.8" (i got this from http://www.fordracingparts.com/parts...artKeyField=44. the min loads closed 123 @ 1.8, so the installed length is 1.8", yes?)
lets say the lift is .512
now what? the numbers dont make sense.
i dont get it
i dont think i have a known spring rate, so by calculating it using the method you described (and the spring info from below):
303-123= 180
180/(1.8-1.25)= 327.2 per inch, so 32.72 per 0.1"
spring is 2.08" so 2.08-1.8= .28"
2.8x32.72= 91.6
so 91.6 should be the closed pressure, but below it says seat load is 123? im very confused


heres some info on the springs i have in case it helps:
Seat Load: 123 lbs @ 1.800"
Open Load: 303 lbs @ 1.250"



also, you said in your example, 96.6lb would be too low for my new cam. how did you determine this? is there someplace that says the minimum pressure should be xxx? or are you basing that on th comp cam people saying to use certain springs which have a closed pressure of 132lb?


i want to smash my computer into little pieces right now


one more question:
why does any of this matter? like, why does the cam care how strong the springs are? i think i get that if the spring had no resistance, the valves would fly open and maybe jam up or something, and maybe would close too slowly?
and if the springs are too strong, the cam wouldnt be able to open them. fine
but if we are the ballpark, does 5, 10, or even 20 lbs matter? im just trying to understand.
if comp cam springs are
Installed Height (in):1.750 in.
Seat Pressure at Installed Height (lbs):132 lbs.
Open Height (in):1.250 in.
Open Pressure (lbs):293 lbs.

and the ford springs i have are
Seat Load: 123 lbs @ 1.800"
Open Load: 303 lbs @ 1.250"

i mean, this isnt close enough or am i missing something important?

thanks again

btw, how does the rocker ratio affect any of this, if at all?