Valve Spring Questions
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 1,234
Likes: 5
From: Herriman UT
Valve Spring Questions
A few valve spring questions:
1. I'm currently running the Comp 26918 springs with a .581/.581 lift cam. How many miles (not racing) can I put on these springs before thinking about replacement?
2. Comparing the Comp 918's to the PAC 1518's, I notice the the seat loads are identical but the 918 Open Load is 367 @ 1.150 and Rate is 372 where the 1518 Open Load is 337 @ 1.150 and Rate is 313. I'm sure both springs are fine for my set-up but I'm just wondering about the differences in the specs. Anyone care to explain?
3. Which Valve spring compressor is better, the Crane or the Comp?
Thanks
1. I'm currently running the Comp 26918 springs with a .581/.581 lift cam. How many miles (not racing) can I put on these springs before thinking about replacement?
2. Comparing the Comp 918's to the PAC 1518's, I notice the the seat loads are identical but the 918 Open Load is 367 @ 1.150 and Rate is 372 where the 1518 Open Load is 337 @ 1.150 and Rate is 313. I'm sure both springs are fine for my set-up but I'm just wondering about the differences in the specs. Anyone care to explain?
3. Which Valve spring compressor is better, the Crane or the Comp?
Thanks
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
See below. 
A few valve spring questions:
1. I'm currently running the Comp 26918 springs with a .581/.581 lift cam. How many miles (not racing) can I put on these springs before thinking about replacement?
Some of this will also depend on the cam design/ramp rate. Mileage is a tough thing to determine without removal and testing of the springs.
2. Comparing the Comp 918's to the PAC 1518's, I notice the the seat loads are identical but the 918 Open Load is 367 @ 1.150 and Rate is 372 where the 1518 Open Load is 337 @ 1.150 and Rate is 313. I'm sure both springs are fine for my set-up but I'm just wondering about the differences in the specs. Anyone care to explain?
The PAC 1218's are the same as the older version of the Comp 918 as they were made by PAC. Comp has a new vendor and may be using different steel size, etc. in the manufacturing of the springs. Without the other data it is hard to detail the why for difference. Free height, number of turns, spring thickness, residual stress, etc. all play a role.
Valve springs are usually sold with an installed height value (and this is somewhat arbitrary) with a corresponding seat force value and then an open force value. The seat value at a height is established through the spring stiffness and free height. So if the two spring have identical forces at 1.800" and one is stiffer, its free height is also likely shorter since it requires less deflection to establish the same force.
3. Which Valve spring compressor is better, the Crane or the Comp?
I have the Crane and like if very much. I have modified it to fit my latest AFR heads as well.
Thanks
1. I'm currently running the Comp 26918 springs with a .581/.581 lift cam. How many miles (not racing) can I put on these springs before thinking about replacement?
Some of this will also depend on the cam design/ramp rate. Mileage is a tough thing to determine without removal and testing of the springs.
2. Comparing the Comp 918's to the PAC 1518's, I notice the the seat loads are identical but the 918 Open Load is 367 @ 1.150 and Rate is 372 where the 1518 Open Load is 337 @ 1.150 and Rate is 313. I'm sure both springs are fine for my set-up but I'm just wondering about the differences in the specs. Anyone care to explain?
The PAC 1218's are the same as the older version of the Comp 918 as they were made by PAC. Comp has a new vendor and may be using different steel size, etc. in the manufacturing of the springs. Without the other data it is hard to detail the why for difference. Free height, number of turns, spring thickness, residual stress, etc. all play a role.
Valve springs are usually sold with an installed height value (and this is somewhat arbitrary) with a corresponding seat force value and then an open force value. The seat value at a height is established through the spring stiffness and free height. So if the two spring have identical forces at 1.800" and one is stiffer, its free height is also likely shorter since it requires less deflection to establish the same force.
3. Which Valve spring compressor is better, the Crane or the Comp?
I have the Crane and like if very much. I have modified it to fit my latest AFR heads as well.
Thanks
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
My understanding is the 1518's have additional surface treatments that will extend the life of the valve spring over the comparible 1218. Make sure that you use a valve spring compressor that presses on the retainer and not the claw type that grabs the spring itself. The surface treatments that extend the life of the spring do not penetrate deep and scratches imparted by the wrong tool can shorten spring life.
