Spring locator for PAC-1218X spring

[travis]

I’m trying to find the correct locator for a PAC-1218X spring. Spring dimensions are 1.290” base OD, .885” base ID.

Relevant head dimensions are 1.540” spring pocket, .560” guide OD.

The supplied springs that came with these heads are dual springs with 145 pounds on the seat, 325 open at .600” which is lighter open pressure than what my cam calls for by about 25 pounds, but the seat pressure is ok.

[GARY C]

I’m trying to find the correct locator for a PAC-1218X spring. Spring dimensions are 1.290” base OD, .885” base ID.

Relevant head dimensions are 1.540” spring pocket, .560” guide OD.

The supplied springs that came with these heads are dual springs with 145 pounds on the seat, 325 open at .600” which is lighter open pressure than what my cam calls for by about 25 pounds, but the seat pressure is ok.

I wonder how much the open is rpm dependent? I have never checked open pressure on a spring in all my years...

[steve cowan]

I would be looking at spring rate for application
Open load - seat load
Divided by net lift at valve
Equals spring rate
Eg- 325-145 = 180/0.600"
300 psi/ rate
I run 380-400 on my cast core comp cams oval track cams to 6800 rpm
No valve float or cam wear after 12 months on street and track

[travis]

Per Mike Jones, “For spring pressure, I recommend 130/320lbs for a beehive spring, or 140/350lbs for a double spring. I ran the PAC 1218X.”

Maybe what I’ve got is close enough?

[steve cowan]

My flat tappet stuff is dual spring
145-345
0.500-0.520"lift
What net lift are you using??

[Geoff2]

Correct locator is CompCams #4705.

[travis]

My flat tappet stuff is dual spring
145-345
0.500-0.520"lift
What net lift are you using??

This is a hydraulic roller...264/268@.006, 218/222@.050, .544/.544 lift

[travis]

Correct locator is CompCams #4705.

Thanks!

[travis]

I’m trying to find the correct locator for a PAC-1218X spring. Spring dimensions are 1.290” base OD, .885” base ID.

Relevant head dimensions are 1.540” spring pocket, .560” guide OD.

The supplied springs that came with these heads are dual springs with 145 pounds on the seat, 325 open at .600” which is lighter open pressure than what my cam calls for by about 25 pounds, but the seat pressure is ok.

I wonder how much the open is rpm dependent? I have never checked open pressure on a spring in all my years...

If this was a less aggressive cam like a FMS E or X cam, I would run it as is. These are advertised as hydraulic roller springs

[steve cowan]

Travis,
I still believe you need to check open load at the lift you are intending to use.
The 1218x spring has a rate of 313lbs/in
This is fine for mild hydraulic roller but the rate is calculated for 328lbs at 0.600"
You won't have 328lbs at 0.544"
Your spring rate will be under 300lbs/in
More like 270-280 lbs/in
If someone can confirm that is ok for the cam you are using then all good but I don't know.
Just trying to help, I have beat up plenty of valve tips with wrong springs over the years.

[travis]

With 140 pounds on the seat, I calculated 310 open at .544” lift with fresh springs. That does seem a little light. Hopefully Camking will chime in here.

Granted, I’m looking at 6000-6200 max rpm, so maybe that was a consideration when he recommended those springs?

[Turbobuick6]

The 1218X sets up at 140 @ 1.800. With 0.544 lift your open height will be 1.256" and will net roughly 309 lbs. Spring is fine for what your doing.

Seat P/N is PAC-S111

[steve cowan]

Turbo
Thanks for confirmation

[GARY C]

I’m trying to find the correct locator for a PAC-1218X spring. Spring dimensions are 1.290” base OD, .885” base ID.

Relevant head dimensions are 1.540” spring pocket, .560” guide OD.

The supplied springs that came with these heads are dual springs with 145 pounds on the seat, 325 open at .600” which is lighter open pressure than what my cam calls for by about 25 pounds, but the seat pressure is ok.

I wonder how much the open is rpm dependent? I have never checked open pressure on a spring in all my years...

If this was a less aggressive cam like a FMS E or X cam, I would run it as is. These are advertised as hydraulic roller springs

Yes with the more aggressive lobes and the weight of a hyd roller it would probably be more critical.