[prostreet64]

I am in the process of installing new valve springs on the 403 in my Trans Am. These springs are being setup at 1.805 closed and with .500 lift that translates to 1.305 open. The pressures measure at 140-145 closed and 315-320 open. My concern is whether or not the # for closed is too much for the hyd flat tappet cam that I am running. It is an UD that has been in the engine since 2007 and has performed very well. Specs are 226/233 at .050 and I only spin this motor up to 5500. I could set the installed height at 1.850 which would bring the closed # down to 125, but then the open # drops to 295-300 range which I think might be marginal.

[PAUL K]

For a HFT I'd go with the 1.850 IH

[Steve C.]

curious, how far you would be from coil bind at net valve lift if the change was made.


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[steve25]

Since you Cam and lifters are broken in already you will be fine as after 1 to 3 blast up to 5500 the springs will have dropped off 10 psi already!

For added safety just add a bottle of Lucus breakin additive .

[prostreet64]

Steve C., coil bind is at 1.110 so the Lunati spec sheet shows a setup of 1.85 for .600 lift to leave .140 before coil bind. I only have .500 lift so there is a lot of room before coil bind.

[Steve C.]

Not here to suggest you have or will have a issue with your specific combination and use involved. Just a fwiw, and tid bit, some suggest anything more than 0.150 inch may cause spring surge, which can greatly reduce the available spring load needed to close the valve.


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[steve25]

Are these a duel spring set up your running?

[Steve C.]

If it is the Lunati 73100 dual w/damper rated 125 at 1.850 (1.110 coil bind) with 0.500" net valve lift it would be about 0.240" away from coil bind.

According to Comp Cams about 0.060 inch used to be, or still is, the textbook safety margin, with more OK and even desirable. That's still an acceptable standard for everyday performance use. However depending on the intended use and the spring and cam-lobe design, coil-bind safety margins can now vary from 0.015 to 0.120 inch, with tighter numbers predominating on very stiff valvetrains. That said, note the cam lobe in use and he only spins this motor up to 5500.

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[Steve C.]

Presented for for interest only and entertainment value.....

Video: The Death of a Valve Spring. From the beginning, we find the spring suffering severe surge and undamped oscillation.

https://www.macsmotorcitygarage.com/...-valve-spring/


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[prostreet64]

Yes, the springs in question are the Lunati 73100 and you touched on my other concern which was that with only .500 lift I might have too much clearance before coil bind. All of the other engines that I have assembled I have set up the springs with coil bind in the .060 to .100 range.

[Steve C.]

Related, I'm in the middle of changing cams and valvesprings and was trying to use a spring where I didn't have to use and purchase different titanium retainers. Two were a drop in with the same diameter and a pressure that's workable but one had a coil bind dimension that placed the distance further away.

You also need to verify what you read in catalogs. Two good examples, PAC lists their 1243 spring with 1.100" coil bind, but their tech dept says its actually 1.070". The Pac 1227 is listed with 1.130", it is actually 1.110".
PAC generally recommends setting up for coil bind at .060-0.100
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[prostreet64]

Good point about verifying what the catalog gives for specs. I have found deviations before when doing my own measuring. Back to the issue of coil bind I must admit to lying in post #10, not intentional, but caused by lack of memory. The original springs that I used with this UD cam were the Lunati 73949 and I set them up at 1.66 closed, which yielded 1.160 open. With a coil bind of .950 that gave me a clearance of .210 before coil bind. I ran them this way for 6 years until 2013 when I had the heads off and checked all the springs. I found some had dropped off to 104 closed and 280 open. I shimmed them back into spec and continued on for 6 more years until I had a head gasket issue in July. While I had the heads off I checked the springs yet again and had to shim them even more to get back into spec. All seemed okay until the last test n tune in November. I usually go through the traps at 5700 but the engine was flat-lining at 5300-5400 rpm in 3rd gear somewhere around 1200' out. Checked all the possible culprits and found nothing amiss so decided that 13 year old springs were probably the problem. So here I am with the Lunati 73100s. Probably should just go back to the 73949s but undecided.

[Steve C.]

As you have found out over time your spring constant declined and it had effects on the performance. It is suggested a valve spring is a fatigue failure waiting to happen.
On your next set of springs consider the benefits of Cryogenic technology, typically valve springs exhibit a longer life after processing.

Call Paul Carter who posts here on PY:
http://www.cartercryo.com/index.html

I've had him treat my springs and we monitor them regularly with a on the head spring tester. They have gone many years without a loss of pressure.


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[prostreet64]

Steve C. thanks for the tip; definitely something to consider.