26918 Valve Springs Question

[OUR87GN]

Here’s the deal. I am building a new engine for my 87 GN and I’m using cast iron ported heads with a roller cam that has a lift of .507 (at the valve), hydraulic roller lifters and roller rockers. I decided to use comp cams beehive springs part number 26918. The spec sheet calls for an installed spring height of 1.800 which would yield a seat pressure of 130 lbs, or an installed height of 1.750 yielding a seat pressure of 146 lbs. The LC3 engines have an installed spring height of 1.727 (mine varied from 1.630 to 1.672) So if I go with the 1.750 height, this means that I need to cut the valve spring seats a maximum of .120 (1.750 minus 1.630).
I had an old scrap head laying around so I decided to drill the valve spring seat area and see how much material there was in this area. I found out that there was only about .210 of material until I ran into the water jacket, keeping this in mind if I had the spring seats milled down .120 this would leave me only about .090 of material!!! Way to thin for this much spring pressure. So my question is this. What do the guys do who run these springs? Or possibly I made a mistake in choosing these springs – these are the ones Comp Cam suggested. Any words of wisdom for me?
Mark

 

[87GN_70GS]

Can you get longer valves or a retainer that allows additional installed heigth?

 

[OUR87GN]

Can you get longer valves

I don't know of anyone who makes longer valve stems, but that is an option.
thanks

 

[JeffG]

I think you should be able to get retainers to afford you a bit more height too.

 

[Russ Merritt]

Don't mill the spring seats! Comp has a part # 795 that is a 10 degree, steel retainer that will give you more installed height. We have been talkin to Comp tryin to figure this out as well. My iron heads are not assembled yet but that is what we are tryin now. Last week we had cut down a stock retainer to fit in the spring. It looked great but on further inspection the groove the factory milled into the top of the retainer made it too thin (.030) and would break. I'll keep you posted on progress...........

 

[OUR87GN]

Jeff and Russ thanks for your input both very good points.
Here's what I found out today. I placed a call to Comp Cams and spoke with Matt and I believe we discovered where the problem is. I had purchased spring retainers part number 774 which he said will put the retainer lower on the valve. What I need are the part number 787 retainers. I ordered them today and we'll see if they do the trick.
Another interesting thing I found out today is that diferent valve keepers will affect the retainer height. I have some aftermarket ones and they put the spring retainer .032 lower than the stock ones. Something to keep in mind if you are looking for exact spring height.

 

[Russ Merritt]

You gotta use the +50 locks.............