# TECH: OBDII Valve Springs. Installed height vs lift.



## tdogg74 (Mar 1, 2002)

Wanted to put this to bed, once and for all......
Purpose: To illustrate the lift differences to the OBDII single valve spring. The fabled lift max for these is .432". One publication states the "ragged edge" is between .425"-.429". It's often asked whether a dual spring upgrade is necessary. I'm hoping the pics below shed some light on how very dumb it is to run high lift cams (over .432") on the stock springs.
I measured out the installed height of the single valve spring off an OBDII head. The installed height, from the spring seat to the top of the retainer = 1.400". I put a retainer/spring in my vice and cranked it up to 1.400". It looks like this:








Then I fully compressed the spring. The height of the compressed spring was .945" which gives us .455" of distance from the installed height to the compressed height to utilize for valve lift.
The lift of the stock OBDII cam is .417". Deducting the .417" lift to the installed spring height looks like this:








As you can see, the lift of the stock cam brings the spring to the edge of lift distance that's left. The coils on both the bottom and top are binding. Due to the nature of the coils, one side is more compressed than the other. One side of the spring is fulled binding, while the other side has some space left to compress. As you go with higher and higher lift, that space decreases rather quickly. For a cam with a .432" lift (260*, 268/260*, ect) the space between the middle coils is about .017". For those lazy ones that run an Autotech 270 (.449" lift), the space left between the middle coils is about .008". Add to that the higher rpms run with these larger cams and you got a recipe for disaster. Once the spring fully binds, you put excessive wear on the nose of the cam lobe which increases wear and eventual failure. 
Like mentioned above, even the stock cam puts these springs to the edge of usefulness. Swap to dual springs....the distance between the coils is more over the sockers, which is what allows for the increased lift capacity.
Also, this is the distance in lift between the stock cam and an Autotech 270* (.449") or a Techtonics 276* (.450*) cam:








Doesnt look like much, but to a spring almost compressed, it really is a lot. 
Hope this helps. Don't be a fool....do it right the first time. http://****************.com/smile/emthup.gif


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## tdogg74 (Mar 1, 2002)

*FV-QR*

Another thing to keep in mind if you are one of the few that said "**** it" and didnt upgrade.....
Although I took great care in taking as accurate of measurements as I could, it's still not 100% accurate. Due to the nature of the machining processes and differences in each particular head, I would honestly factor in a good +/- .005" wiggle room in my measurements. This means that there might be more compression space on some springs, and _less_ in others. Like I had mentioned before, when you run these springs to the max, you then run into issues where the nose of the lobe has problems passing over the lifter face. And what _could_ happen is that the spring fully compresses and the extra compression needed is taken up by the lifter. So not only are you compromising the spring, you are compromising the lifter as well. And I think it goes without say what happens when you rev these springs high. 
Is an extra $120 not worth it for a safer running engine?


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## El Cletus (Apr 18, 2002)

*Re: FV-QR (tdogg74)*

I love the info you have here, very very spot on! But I ask this only to foster some discussion... I have built race motors designed to float valves and coil bind, our cams were cut with fast ramps to float the valves, but stay within legal specs. The chances I think of floating a valve with the mild Autotech 270 are minimal for the "normal" driver... and floating one won't hurt the cam, floating will hurt the lifter and valve spring over time. So, if the cam won't coil bind I say run it because after all, less spring resistance is more power for the motor, and .005 sounds like a perfect safety margin to me.


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## tdogg74 (Mar 1, 2002)

*FV-QR*

If these springs were even remotely performance oriented, I would tend to agree. But they're not. Stock, these motors run out of steam by 4500rpms, by 5500, you are just wasting gas trying to turn the motor that high. Which is probably why they switch to a single spring set-up, along with the reduced energy required to compress a single spring over the dual springs.
Putting in a 268* (.440" lift) or a 270* (.449" lift) increases your rpm ceiling to about 6500...which is too much for these. (my opinion, of course)


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## El Cletus (Apr 18, 2002)

*Re: FV-QR (tdogg74)*

This post rocks, very informative, and I cannot disagree with the just wasting fuel. 
My thoughts here are playing part devil's advocate, part experience (I've run the 270 in my car for years after confirming it wouldn't coil bind, and then sold my dual valve springs) and part just seeking knowledge and opinions (I've always thought about just taking an afternoon and upgrading it)...
So, the way I think about it is with a hydraulic lifter there has to be a certain amount of preload, and although the cam lists .XXX for the lift, the lifter will probably adsorb .00X of it, adding a little more safety to the equation... and if I remember my top end correctly, you can't really over-preload these like a push rod V8, but as the lifter wears more and more, preload would start to diminish, and safety margin would increase... 
Bottom line still is correct - $120 is cheap insurance *for those that beat on their toys*


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## tdogg74 (Mar 1, 2002)

*FV-QR*


_Quote, originally posted by *El Cletus* »_
So, the way I think about it is with a hydraulic lifter there has to be a certain amount of preload, and although the cam lists .XXX for the lift, the lifter will probably adsorb .00X of it, adding a little more safety to the equation... 



If your preload is enabling the nose of the lobe to turn over the lifter face, two very bad things are happening:
- You are at full coil bind
- You arent getting the full lift of the cam lobe


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## Minor_Threat (May 12, 2009)

*Re: FV-QR (tdogg74)*

lower seats must be machined for dual springs correct?


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## tdogg74 (Mar 1, 2002)

*FV-QR*

No, not for Mexican OBDII heads. _Only on German OBDII heads._


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## envy. (Jul 27, 2009)

excellent write-up tdogg.
this is DIY/FAQ material. a lot of new kids need to see this.


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## Minor_Threat (May 12, 2009)

*Re: FV-QR (tdogg74)*

well I have an obdII german head, well its at the machine shop now, I'm sure they'll figure it out. I'll post back later this week when the bigger valves are installed.


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## tdogg74 (Mar 1, 2002)

*FV-QR*

Please dont hijack this thread. You already have a half dozen build threads on your motor already.


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## El Cletus (Apr 18, 2002)

*Re: FV-QR (tdogg74)*


_Quote, originally posted by *tdogg74* »_
If your preload is enabling the nose of the lobe to turn over the lifter face, two very bad things are happening:
- You are at full coil bind
- You arent getting the full lift of the cam lobe 


I guess I'm just thinking out loud now, but let me try to phrase what I wash thinking in my head... with a solid lifter you are going to have a certain amount of valve lash and over time it will increase due to wear. This is why on the old motors you'd have mr mechanic listening to and adjusting the valves, or using the appropriate feeler gauge. With a hydraulic lifter the same concept applies except now they are more or less self adjusting, except as the face wears with the CAM and so does the cam, effective lift is decreased by thousandths... thus brand new cam, brand new lifters, and old valve springs is the combo that is the riskiest... however I believe that, right or wrong, putting in the new cam with the old lifters, and old valve springs would be safe... but... once again $120 is cheap insurance.


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## veedubbermike (Jun 10, 2012)

*whip it!*



El Cletus said:


> This post rocks, very informative, and I cannot disagree with the just wasting fuel.
> My thoughts here are playing part devil's advocate, part experience (I've run the 270 in my car for years after confirming it wouldn't coil bind, and then sold my dual valve springs) and part just seeking knowledge and opinions (I've always thought about just taking an afternoon and upgrading it)...
> So, the way I think about it is with a hydraulic lifter there has to be a certain amount of preload, and although the cam lists .XXX for the lift, the lifter will probably adsorb .00X of it, adding a little more safety to the equation... and if I remember my top end correctly, you can't really over-preload these like a push rod V8, but as the lifter wears more and more, preload would start to diminish, and safety margin would increase...
> Bottom line still is correct - $120 is cheap insurance *for those that beat on their toys*


All good Vdubs need to take a beating... if you don't beat it someone else will. :facepalm:opcorn:


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## vacuumnoise (Jun 1, 2009)

I'd lilke for their to be a thread for those who have ran any cam bigger than the 268/260 cam on stock single springs and had cam failure...

Not as an insult to this excellent thread, but more just to see _how many_ people have had cam/lifter failure on the stock springs...


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