Valve Spring Pressure

[6SENSE]

What is too much?
Ive heard different #s mentioned as good, usually between 90-110 lbs. What is stock?
I just finished doing a bunch of porting work on my heads and then dropped them off to a machinist who I used to work under and have great respect for. I asked him to take care of them and do whatever he felt they needed. He gave them a performance valve job (3 angle valve job), got rid of the guide sleeves (I think they were copper) and put in screw-in type. These sleeves by the way were part of the problem that had me taking the engine apart in the first place. One had an exhaust valve stuck open. He also put in all new exhaust valves (as mine were pretty well worn), rusurfaced the heads (.010 came off), and new seals of course to fit the new type of guides.
Okay, back to the question. He set the spring pressure to 130, and felt that this would be good. I expect it would be good for topend, which is fine by me, only worry I would have is that it would be rough on the cam. He told me that some engines have the spring pressure at 500!
What do you guys think? I really respect his views as he has been doing this for 40-50 years, but would like some more input.

 

[TRENT THOMPSON]

the common consencous would be that is too much spring pressure for the hydraulic flat tappet camshaft. Your first guess at 90-100# seems too be right. I would think at 130# you could run into difficulties.

 

[Russ Merritt]

If it were a roller cam, 130 would work. Not for a flat tappet though. Your right on! 90-105ish not much more than that.

 

[6SENSE]

I just spoke to the machinist. He said that he used .015 shims to bring the pressure up to 130. He said that if we took the shims out that the pressure would probably be right around 100.

 

[ronbuick]

I would run 80-90lbs seat pressure, no more that that, just my 2 cents, and definately not that 130lb that you had when it was shimmed, for a stock motor that will see stock or a little above
in rpm's.
Ron

 

[NoNos38]

I like 100.. But everyone is differant. I have heard of people running 130 (Precision turbo) sells springs right around there, but IMO, that is ... 80 is to soft...

Matt

 

[6SENSE]

Originally posted by ronbuick
I would run 80-90lbs seat pressure, no more that that, just my 2 cents, and definately not that 130lb that you had when it was shimmed, for a stock motor that will see stock or a little above
in rpm's.

motor is basically stock bottom end with .030 forged pistons. Heads are ported and polished (+ 3-angle valve job), LT1 valve springs, Intake is completely ported out, cam is 204/214, and turbo is a TA33 which is basically a 49 in a hotair casing (supposed to be able to flow 700 cfm). In the future I may be modifying it to a 60. Stall convertor is 2800. Not sure what max rpms would be, but guessing in the upper 5000s. Is this still qualified as stock motor?

I was thinking that 130lbs sounded a little high from what Ive learned in the TR community. I was surprised when the machinist told me, because I know he knows his stuff. I didnt know what to think. He was talking about a benefit with the valves opeining/closing. Im guessing this has something to do with stopping valve float? Does his logic not apply to our cars? Im sure it does. I know our cams arent made out of different/weaker material than other engines, right?
I just want to be able to get the most I can out of my combo, but I dont want to wipe the cam in the process (I want mph!).

 

[NoNos38]

Originally posted by 6SENSE


(I want mph!).

Buy a Lockup Converter.... That will bring on the MPH..

Matt

 

[6SENSE]

Originally posted by NoNos38
Buy a Lockup Converter.... That will bring on the MPH..

Yep, its a lockup.

As far as stress to the cam, isnt that regulated with lifter preload? I may be getting different than stock pushrods anyway after I check my preload. If this is the case, isnt there benefit to having more spring pressure? Or does this through the valvetrain geometry too much out of whack? Maybe this is how Precision uses the 130 springs?

 

[87LtdT]

Just curious...but how many .015" shims does your machinist say will need to be removed to drop the spring force from 130 to 100 lbs. While you are asking him, ask what spring rate the LT-1's have.

If the springs are LT-1's which have a spring rate of about 325 lb/in the answer should be six .015" shims. In other words, he has added .090" worth of shims to raise the spring force from 100 to 130 lbs.

And I too think 130 is way too high for our slow revving engines...I just don't see the need for high spring force to slam the valve closed quickly...

Nte: there seems to be a lot of confusion on LT-1 springs...I bought a set from Jack Cotton long ago, took them to work and measured their force on calibrated spring tester...their calculated spring rate was 325 lb/in...

Bob

 

[ChrisCairns]

I got curious after reading this thread so I went out to the shop and took some brand new "stock replacement" springs that I'd bought some years back then put them on my spring tester.

It showed exactly 80 psi at a 1.71 height.....and then I measured at 15 thou less (duplicating your shim) and it came out right on 120 psi.

 

[6SENSE]

I see only one shim used for each spring.

Let me make sure we are on the same plane here. I told him that factory height was 1.727 and that some go with 1.750. This is the height at which the pressure #s we are talking about reference to, right?
As far as the LT1 springs. Maybe they are not 325 lb/in? (Maybe they arent really LT1s). Dont know how much it mattered but They have about 14,000 miles on them.

Forgive me, Im still learnin'

 

[6SENSE]

Hey Chris. That sounds close to my situation. I cant even picture six .015" shims installed under a valve spring

 

[Lee Thompson]

spring pressure

90 PSI MAX. DO NOT use 130 open spring pressure on a flat tappet cam. 1.700 -- 1.750 installed height will work fine just make sure you have enough distance between the bottom of the retainer and the top of the valve guide. I recently help a friend tear his eng. down. He had a cam with .450 lift and only .420 distance between guide and retainer----wiped cam lobes in short time.
I will check today, but I don/t think .015 shim will raise the pressure that much.
I have a steel billet roller and only use 130 open pressure--good for 6000 rpm.
It your eng. and you can do whatever you like but I can assure you you will have it apart again in the near future with too much spring pressure.

 

[blackbuick87]

Dont forget LT1 and LT-1 valve springs are totally different, the one we use is the LT-1 springs from the early 70's Vette. The LT1's are from late model Camaro's and are much stiffer.

130# seat pressures are for SBC's running 6500rpm, not our diesel engines

 

[87LtdT]

Well I was tryin to be helpful and have confused things...story of my professional life!! Assuming Chris's eyes and spring tester are correct... where is my math wrong??


"Approx 325 lb/in spring rate times how much in shim height = 30 lbs difference in spring force?" is the question. The answer to the above is .092"...ie six .015" shims.

Chris...to get a 40 lb spring force difference between 1.71" and 1.695" (.015") the spring rate would be 2667 lb/in!!?? Chris, did you mistype or does your spring tester give you psi...or pounds force? I think pounds is the result...like a weight scale only the weight (force) is applied by smashing the spring.

Not trying to insult anyone...but to calibrate us. 15 thousandths[/U (.015") is about the same as the thickness of 4 or 5 sheets of paper. Chris....if you compressed your spring an additional 15 hundredths (.15") then the spring rate would be 267 lb/in which is almost exactly what is expected for stock replacement springs??? In fact, CC980's are advertised at 307 lb/in, but mine calculated to 269. (CC979's adv at 267, calculated at 239)

My whole original point was to be sure the machinist didn't put in too many shims, and was figuring on about the right spring rate...

Is there something wrong with my math, me personally, or ??

One other thing...a lot of guys use the original spring cups with their new springs...the cups are .035" +/- thick and act as a shim..

Bob

 

[87LtdT]

Well ****...wanted to underline thousandths and hundredths above...but ended up underlining the whole thing that now sort of reads as an in your face insult...not intended.

6Sense...I'd be glad to send you the spring measurements and resulting calculations I took a couple years ago as I searched for a replacement spring for me....tested CC979, CC980, LT-1, and my 34k miles originals after removal.

Bob

 

[6SENSE]

Thanks Bob, that would be great.
Again, there is only one shim used per spring. I was told they were .015" and that the springs were @ 130lbs, so maybe its the spring cups? That would be .050" (.015+.035). From the info you supplied, that would still be .040" or .042" off, to get the pressure to 130lbs (from the info you supplied). Unless the equipment at the machine shop is off, these springs have got to be stronger than 325lbs/in. Only thing I can think of doing before my head starts hurting anymore , is to go by the machine shop and test one of the springs to see it for myself. What would the 325lbs/in LT-1s rate at with just one .015" shim like Ive got (+ the stock cup)?

I sure wish I had my own spring tester right about now. Put that on the list, hmm...where to got one?

 

[JDEstill]

Bob - I think the problem with your math is that springs aren't linear. There's some equation that describes them, something like 1/2*k*x^2, where k is the spring rate and x is the length. That's probably not the right equation, it's been too long, but I'm sure someone here knows what it is. Anyway, working with the correct equation will show that 0.015" will make a bigger difference in pressure that what you might initially think from the 325 lb/in spring rate.

John

 

[ChrisCairns]

Bob....yep that's what I did. 15 hundreds. From 1.71 down to 1.56.

As penance I'll get my wife to slap me around a bit although I admit I'm starting to enjoy it too much.

6sense....you can buy a simple spring tester from Summit...it's around 75 bucks if I remember correctly. And I do have a photographic memory....the problem is that it's out of film so the price may not be correct.