Stock 340 springs vs comp 901-16

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Ok so did some measuring. Got comb chambers all cc'd and I had tried to measure the install height on the factory springs. A pain in some springs to get micrometer down to the seat. As it turns out springs have been shimmed. So all that measuring was for squat.
Free height on springs for #4 Intake 1.9340"
#4 EXHAUST 1.9300".
Spec in fsm is 1.94". I would assume good? The reason in my mind for the shims Is as mentioned before ....to compensate for loss of material in valve job?
Shims were .0535" and .0580"
Looks like new guides, also new exhaust valves?? #9183 on the stem?? A quick Google search brought up squat.
Also I wonder why the umbrella valve seals on exhaust valves? Vitons on intake.
Once cuda is outta hibernation I can measure the 901's

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Posted this info in my "build thread".....it appears we have been running 747-16 Double spring retainers with 901-16 single springs?? Since 2012?? Heres a pic I took in 2012 when Badsport shipped us the goodies.
Advice?
Thanks!

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Called Comp Cams tech. and they said that I could run the 901 springs with the 747 retainers(I have for 6 almost 6 years).The difference between the 740 and 747 retainers is the diameter difference of diameter #2. 740 is 1.060" 747 is 1.050" I mentioned to him the setup(270 S cam n lifters etc) and he said there will be no issues.
Now if we could get a mild spell this week. Going from 7* yesterday to -24* tomorrow morning lol
 
I blame Putin for all the cold air LOL

Your free length is a modest indicator of springs not having settled. Not a guarantee but at least a decent indication. If the springs had really weakened, the free length would drop a lot more.

There is no consistent suction (vacuum) on the exhaust ports so those guides don't need as good a seal. Some engine have used just an o-ring riding the valve shaft as an exhaust seal.
 
The predictable thing about Mother Nature is she gets more unpredictable Putin deserves -60 lol
I remember seeing umbrellas on a 383 i redid years ago. Makes sense on the exhaust side.
Yeah 340 springs were close to stock specs. Good to know on on significant change in free length.
I have to wait till cuda comes home to see if I'll need the shims that are on xheads now with the 901 springs.
Thanks again!
nm9stheham said:
I blame Putin for all the cold air LOL

Your free length is a modest indicator of springs not having settled. Not a guarantee but at least a decent indication. If the springs had really weakened, the free length would drop a lot more.

There is no consistent suction (vacuum) on the exhaust ports so those guides don't need as good a seal. Some engine have used just an o-ring riding the valve shaft as an exhaust seal.
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No, the only thing that matters is the closed load at your measured height, the load at the measured closed height minus (the lift of your cam times the rocker arm ratio), and the cam manufacturers specs.
 
I understand the load with valve closed at installed height. (Basically right height and spring psi)?
But can you explain rocker arm ratio vs lobe lift? 273 adjustable rockers will be used 1.5 ratio
Thanks!
66fs said:
No, the only thing that matters is the closed load at your measured height, the load at the measured closed height minus (the lift of your cam times the rocker arm ratio), and the cam manufacturers specs.
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Thanks Mike, so let's plug in my numbers.
Cam 270 S lobe lift is same for both int and ex. 0.313" X 1.5 rocker ratio = 0.4695" which is valve lift. How do we apply/verify this number against the spring specs?
I printed off 2 different tech sheets from comp on the 901's. Slightly differing specs....go figure lol(see pic).
So the valve lift of 0.4695, which number does this get "verified" with?
Thanks guys!

toolmanmike said:
Lobe lift multiplied by rocker ratio = valve lift.
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We're getting ready to check installed height/shim our 901 valve springs.

If I may ask, what is the inside diameter of your shims?

I'm assuming the outside diameter is 1.50?

Thanks. Eric
 
The first thing is what height are you going to set them up closed? Then what loads does the cam manufacturer want? Since your rate is 330 lb/in, .47 in x 330 lb/in = 155 lb will be added to your closed load.

If running 340 springs .47 x 386 lb/in = 181 lb added to your closed load.
 
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Hi Eric, these shims were installed with factory 340 springs. I haven't used them with 901's.
Thickness is 0.0585" OD is 1.4980" and ID is 1.0295"
Has "103" stamped on it and "this side up"
prorac1 said:
We're getting ready to check installed height/shim our 901 valve springs.

If I may ask, what is the inside diameter of your shims?

I'm assuming the outside diameter is 1.50?

Thanks. Eric
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Thanks FS. Here is a pic of cam sheet. I see no recommended spring rate/load? Or am I missing something? Also cam spec sheet lists the 901's as recommended.
I'm not sure what closed height on 901's would be once installed on x heads? Spec sheets state 101-104(psi) at 1.650"
Thanks for the help.
**Also where did you get 0.47" from in the formula?**
Thanks!
66fs said:
The first thing is what height are you going to set them up closed? Then what loads does the cam manufacturer want? Since your rate is 330 lb/in, .47 in x 330 lb/in = 155 lb will be added to your closed load.

If running 340 springs .47 x 386 lb/in = 181 lb added to your closed load.
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Typically then most flat tappet cams want about 100 Pounds closed so you should shim the 901-16 springs to 1.65 or something close. Then you will have 255 open which should be fine.
 
Ok so valve lift(0.468) multiplied by spring rate(353lb/in)= 165 lbs. Then add seat load of 101 lbs to 165 gives us max spring of 266lbs. Correct?
You asked about cam mfg recommended load. I don't see it on spec sheet. Ideally they should be an "x amount" of percentage above calculated max spring load??
Thanks again!
66fs said:
Typically then most flat tappet cams want about 100 Pounds closed so you should shim the 901-16 springs to 1.65 or something close. Then you will have 255 open which should be fine.
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I would not be surprised to see you end up at .430 actual lift or less.

Lash, crappy lifter angle and rockers that are rarely if ever a true 1.5 ratio contribute to actual lift losses.
 
crackedback said:
I would not be surprised to see you end up at .430 actual lift or less.

Lash, crappy lifter angle and rockers that are rarely if ever a true 1.5 ratio contribute to actual lift losses.
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MmmmHmmmm, see post#33..............
 
4spdragtop said:
Ok so valve lift(0.468) multiplied by spring rate(353lb/in)= 165 lbs. Then add seat load of 101 lbs to 165 gives us max spring of 266lbs. Correct?
You asked about cam mfg recommended load. I don't see it on spec sheet. Ideally they should be an "x amount" of percentage above calculated max spring load??
Thanks again!
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I've never seen a recommended spring load on a cam spec sheet so no surprise that it is not there. There is a lot more to actual load on the cam than just the spring load times the rocker ratio.... that is just the static load part. The dynamic load part comes when the valvetrain is being accelerated into motion from closed to open in each cycle; that adds another force that is highly dependent on parts' speed (RPM). Plus the spring loads are also dependent on what the valvetrain needs to not 'float' all the way up to the intended max RPM's ... i.e., all the parts stay in contact and in motion together. So the cam mfr's just give you a recommended spring to do the job, and if you keep close to those spring rates and closed valve loads, you should be OK.

Your math is right BTW, minus any changes due to valve lash.
 
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