Please Double Check My Installed Height Math

[b.guggenmos]

I have read several threads on the proper installed height for valve springs. The newest ones all seem to be for beehive springs which are a bit different. This is a standard solid roller cam setup for drag only. Springs are PAC 1225. Stated coil bind is 1.150. Cam is .692 lift on both. Valve lash on card is listed at .030 which seems a bit loose to me?
1.150 Coil Bind
.692 Cam Lift
.050 Popular Number to add to coil bind
- .030 lash
___________
1.862 installed height

Thanks, Brian

[JoePorting]

I'd set the minimum install height at 1.9". But I think the bigger question is what is the seat pressure at 1.9"? Hopefully it's around 250 pounds.

The pac site says those springs are supposed to be 250 @ 2". If the cam requires 250 on the seat, then I'd set them up at 2".

[blykins]

Well, the thing is, you really don't know where the spring binds up until you check it. I think the spring manufacturer's coil bind numbers have a safety factor built into them.

A .050" coil bind clearance is probably a smooch tighter than what I would go unless you're absolutely went through all the install height measurements for each valve and have set up your valve train geometry and measured actual lift at the retainer.

You may also want to go a little backwards and figure out which spring pressures that you actually need for your particular combination and then go from there.

[user-612937456]

You also have to consider are your rockers and push rods precise? For example if you are using 1.6 rockers is every one of them precisely 1.6 or are they all over the place from 1.57 to 1.64? I would set your installed height at 250 psi and make sure toy have a safety margin of more than .100 beyond coil bind.

[wyrmrider]

don't run any more spring that you have to
spring takes HP

[cnsperf]

I didn't think that valve lash was normally included in this calculation. I would figure it like this:

1.150 coil bind (need to measure and verify)
0.100 coil bind safety factor
0.692 valve lift (also needs to be measured and verified)

1.942 installed height (or 1.992 if you use 0.050 coil bind safety factor) - pretty close to the recommended 2.000 from PAC


Also need to check retainer to guide clearance and retainer to seal clearance


On really wild solid roller stuff I set the springs up at the open height (xxx lbs. pressure @ max lift) and just let the seat pressure fall where it falls.
Most cam grinders will provide a max lift spring pressure recommendation.


Hope that doesn't muddy things up too much for you.

Chris

[b.guggenmos]

Thanks everyone. Just trying to get it right. Sometimes the more I read the more confused a person can get! I did not measure the actual coil but I will to see whether or not PAC's 1.15 is truly coil bind? I am using Manley stainless valves which the 2.19 intake are pretty heavy 139 grams. Comp actually has a spring listed for this cam that shows 353 lbs. at 1.9" and 800 lbs. at 1.25 with a coil bind of 1.130. Big Joe and a few others felt that was way to much spring. The PAC 1225 should fit the bill if I can get the installed height I need?

Most of the posts I have read seem to stress the theory of nearly coil bind plus .050 or .060 is in stability of the spring and spring life. I am not a rookie but it has been awhile since the last engine build. Last time I used the springs that came with the cam and just checked coil bind with a feeler gauge between the coils.

Thanks again for the help. Lots of good information on this forum.

Brian

[blykins]

Bind them up in a spring pressure tester or in a vise. I usually bind each separate piece (outer, inner, damper, etc.) just to "map out" where each piece binds up.

The amount of spring pressure will depend on the cam lobe, weight of parts, and how many rpms you're turning.

[DaveMcLain]

I have read several threads on the proper installed height for valve springs. The newest ones all seem to be for beehive springs which are a bit different. This is a standard solid roller cam setup for drag only. Springs are PAC 1225. Stated coil bind is 1.150. Cam is .692 lift on both. Valve lash on card is listed at .030 which seems a bit loose to me?
1.150 Coil Bind
.692 Cam Lift
.050 Popular Number to add to coil bind
- .030 lash
___________
1.862 installed height

Thanks, Brian

Figuring out what the loads that the spring will produce at different heights is very easy if you know the spring's rate per inch. On the PAC 1225 that rate is 644lbs/inch. The way you do it is like this. If that spring is rated to install at 2 inches giving a seat load of 250lbs and you're going to put it at 1.862(a difference of .138) take the rate of 644 times .138 (89lbs) and add that to the seat load of 250(339lbs). To figure your new open load take your .692 times the spring rate of 644(445lbs) and then add that to your new seat load of 339 to get the open load of (784lbs).

Now of course this method depends on the accuracy of the data but otherwise it is accurate. Many engine builders don't know what the actual open loads are in their builds even though it is easy to figure if you know the lift at he valve, seat load and the rate of the spring being used.

[cnsperf]

I didn't think that valve lash was normally included in this calculation. I would figure it like this:

1.150 coil bind (need to measure and verify)
0.100 coil bind safety factor
0.692 valve lift (also needs to be measured and verified)

1.942 installed height (or 1.992 if you use 0.050 coil bind safety factor) - pretty close to the recommended 2.000 from PAC


Also need to check retainer to guide clearance and retainer to seal clearance


On really wild solid roller stuff I set the springs up at the open height (xxx lbs. pressure @ max lift) and just let the seat pressure fall where it falls.
Most cam grinders will provide a max lift spring pressure recommendation.


Hope that doesn't muddy things up too much for you.

Chris

I made a math error in this. The 0.050 coil bind safety factor figure should have been 1.892 and not 1.992 - Sorry!

[b.guggenmos]

I completely compressed a spring and got 1.13 which very close to PAC's spec of 1.15 for coil bind. That would leave me to believe that PAC does not give any safety margin from the 1.15 spec. I will go off of this number and move forward. Off to the machine shop tomorrow. Thank You. Brian

[Adger Smith]

Don't forget about the effect of the retainer steps on springs. Both for coil bind and pressure.