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.

 

There have been a few issues with the 612's
the 918 beehives will work, but are for more agressive cams


Try Cranes 10308-1 kit

 

Thanks, but those look to have even more seat pressure and open pressure than the 26918's! Aren't they even more aggressive than the 918? Maybe I'm missing something?

Thanks for the reply.

Dan

 

http://store.summitracing.com/partde...5&autoview=sku

Well these particular springs are more or less for milder cams. 918's are for bigger cams.

 

Dan,

I can't remember if I sold my 26915s or not. I'll have to check the garage.
But I would recommend them. It's what I would be using now if not for the
wild goose chase I had a while back. I'm sure you will like the 845.

 

O.k., thanks Mike. I know you looked into this a while back when making spring choices. Do you know If I'll have to shim the 26915's for my application? Were you targeting a specific closed and open spring pressure?

I'm also wondering if I need to use the beehive locators as well, or are the stock ones o.k.? I've read that the beehives don't sit perfectly on the stock locators.

Dan

 

So does anyone know if the Beehive 26915's will work for the GM 845 cam? 214/224, 0.521”/0.543” lift. I don't want to step up the the stiffer 26918's if I don't have to, especially since I'm using the stock lifters.

Is shimming required? Any help would be appreciated.

Thanks,
Dan

 

Sorry for the delay Dan. It's been a couple of busy days at work. This is just
my opinion on the beehives based on my personal observations. Definately
use the locator designed for the spring (Comp 4705), which is thicker than
the stock locator. I compressed both the 26915s and 26918s on my arbor
press with the stock locator and the spring base would not sit flush with the
locator. Why would you want to start out with a situation like this where the
inside of the bottom coil is rubbing on the locator and not sitting flush?

Here is my pic:Beehive and LT4 spring seat You can see the spring is not even touching the locator.

I was not targeting a specific pressure because the springs are designed for
an installed height of 1.80" and without longer valves there is no way to
achieve this. I went for the most installed height I could get off the shelf
which is to use the 10* hardware with the +.050" locks. This puts you in the
1.75" range. If you use the 7* hardware (+.050" locks are not available) the
installed height is about 1.73". I went with the 10* to get the most installed
height.

It's too bad that a .045" locator is not made for this setup. Maybe some
machining on an LT4 locator would be the compromise. I did not try it since
these parts are usually hardened and removal of the surface material would
compromise that.

 

I believe that the 26915s would have worked fine with the Crane 104227.
Because I had the OBDII problem that was initially thought to be valve float
I swapped to the 26918s before going OBDI. Especially installed at 1.75".
If the lobes on the 845 and 104227 are close in design the 26915s should
work fine. My OBDII problem is shown in this dyno graph:

OBDI and OBDII Comparison

You can see that after 5500 rpm the curve is fine. If there was a problem with
the springs it would show in this part of the curve.

 

Thanks for the info. I just wish the beehives weren't so much $$$.

The lift on the 845 is 0.010" less on the exhaust side than the 227 you have. It's 0.543" with 1.6 RR's. I'm hoping that gives me a little extra room to play before any binding.

So the 4705 locators, even though they are 0.060" thick, are o.k. for installed height with the 10* retainers and locks? I'm not sure of the calculations to figure this out, as I've never looked into it. I thought you used a machined Manley locator or something because it is thinner to get you more installed height.

Dan

 

The 918's are great because they don't over stress the stock lifters so don't worry about that. Run those because you can change cams later on if you feel like you need to and not have to change springs.

Bret

 

I belive the 4705 locators are .062" (not that it matter that much). The
reason I went with machined Manleys is because the 4705s were not
available at the time. You will be fine with the 4705s as long as you
go with the 10* hardware and +.050" locks.

Edited to add that the Manley locators are the same thickness as the 4705s.
I wish someone made a .045" thick locator for the beehives on an LT1 head.
The 7* steel hardware is quite a bit lighter than the 10* steel hardware. I
weighed everything but don't have the info with me. I went with the Ti
retainers to try and get the weight down on the 10* setup. You are right
in that going with beehives is a very expensive option when you consider all
the parts necessary.

If you want to keep the cost down you may want to consider the Isky 235-D
springs. They are good to .550" and use stock parts except for locators in
which you use the L98 locators (about $1.50 each). If you do end up considering
this I have a set of Ti retainers (I believe Comp 728s), but the LT4 pieces will
be just fine.

 

O.k., I see that the L98 locators are 0.050" thick. I'm using LT4 retainers and locks. (which I think are the same thickness as stock correct?)

If I go with the Isky 235-D springs, will I need shims to get the correct installed height? It looks like they want 1.75" for closed pressure of 130 lbs. Can I get that with the L98 locators and LT4 retainers? How close will I be to coil bind with the exhaust lift of 0.543"? Looks like I'll be 0.057" from coil bind right?

Thanks a bunch.

Isky 235-D
Recommended Camshaft Style Roller hydraulic
Installed Height (in) 1.750 in.
Seat Pressure at Installed Height (lbs) 130 lbs.
Open Height (in) 1.200 in.
Open Pressure (lbs) 320 lbs.
Outside Diameter of Outer Spring (in): 1.260 in.
Coil Bind Height (in): 1.150 in.
Damper Spring Included: Yes
Spring Rate (lbs/in): 350 lbs./in.
Inside Diameter of Outer Spring (in): 0.886 in.
Inside Diameter of Inner Spring (in): 0.886 in.

Dan

 

The stock installed height is 1.78" with a locator that is about .035" thick.
This will be the same with the LT4 retainers because they are the same basic
dimension as the stock retainers. If you use the L98 locator, which is about
.048" thick, you will have an installed height of 1.767". In my checks with the
235-Ds I think the installed height was actually 1.77". I called Isky to see if
installing the spring at 1.77 was OK and they said no problem.

To answer your main question, shims are not necessary because you don't
really need the 130 pound closed pressure. The extra thickness of the L98
locator is helping you out and by installing the spring at more than the 1.75"
recommended height you gain more margin to coil bind. At 1.77" you will have
a margin of .077". If you shimmed to achieve 1.75" your margin will drop to
.057". I like the sound of the .077" better, and your closed pressure will still
be 120.

If anything, your shimming will be to achieve a standard height across the board
if possible. I found that my stock heads were so close that shimming did not
help me out because of the very small variations in installed height. I think I
have a Comp shim set that was never used (more parts from my goose chase).

Maybe Bret or another spring pressure expert can chime in regarding a 120
versus a 130 closed pressure for the GM 845. You can easily shim to get
the 1.75" installed height if thats the best choice. You will definately need
a spring height micrometer. I'll loan you mine if you want. One thing with
the micrometer is that it does not work with the beehive retainers. I should
say it works but not as designed. The smaller beehive retainer ends up on
the first shoulder of the mic so you have to factor this into the reading. I
added that just in case you borrow it and end up going the beehive route.

 

Thanks a lot for the info. EXACTLY what I was looking for. And thank you for the offer on the spring mic. You've been a great help. I'll be in touch.

Dan