Please help me with spring choice for GM845 cam!
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Joined: Oct 1998
Posts: 3,144
From: Jackstandican
Re: Please help me with spring choice for GM845 cam!
Originally Posted by stereomandan
The cam I’m looking at is the GM845, 214/224 @ 0.050”, 0.521”/0.543” lift with 1.6 RR’s.
O.k., I’ve narrowed it down to three choices:
CM 612’s
CC 918’s
CC 915’s
I’m installing this cam on stock unported heads and valves. I plan to keep the rev’s to 6000 rpm, MAYBE 6200 rpm, but most likely 6k. Currently, my redline is set to 6k. I have 1.6 NSA Pro-mags, on 7/16” studs with GM guideplates already on the car.
I’d like to go with as little spring pressure as possible, but still control the valve, for longevity purposes, as well as taking it easy on the lifters. I’m not familiar with choosing correct springs, so please school me on the calculations for choosing a spring.
Which would you choose? These are all single springs, and the CM 612’s are a heck of a lot cheaper if they will work well, that would be great.
O.k., I’ve narrowed it down to three choices:
CM 612’s
CC 918’s
CC 915’s
I’m installing this cam on stock unported heads and valves. I plan to keep the rev’s to 6000 rpm, MAYBE 6200 rpm, but most likely 6k. Currently, my redline is set to 6k. I have 1.6 NSA Pro-mags, on 7/16” studs with GM guideplates already on the car.
I’d like to go with as little spring pressure as possible, but still control the valve, for longevity purposes, as well as taking it easy on the lifters. I’m not familiar with choosing correct springs, so please school me on the calculations for choosing a spring.
Which would you choose? These are all single springs, and the CM 612’s are a heck of a lot cheaper if they will work well, that would be great.
Thread Starter
Registered User
Joined: Jun 2003
Posts: 3,620
From: Saginaw, Michigan
Re: Please help me with spring choice for GM845 cam!
Originally Posted by SS RRR
What does the manufactuer recommend?
The cam card says to use
Closed seat 125 lbs @ 1.8" installed height
Open 334 lbs @ 1.34" open height
They claim valve float of 7100 rpm with this combo.
Going with the Isky-235-D springs, the closed pressure is 123 lbs @ 1.77" and open pressure is 313 lbs @ 1.23" by my calculations. Is 313 lbs enough?
The Isky springs look like a good option. $99 for the springs from summit. I can reuse my LT4 retainers and locks, and the L98 seats would cost me about $50. $150 looks better than the $276 for beehive springs, seats, retainers and locks. I'm only revving to 6k rpm, maybe 6200 rpm at the most so the isky's look pretty good, as long as 313 lbs is enough open pressure.Dan
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