Looking for some guidance from some of the more knowledgable members with the required experience.

Long story short, I had an issue with the Del West Ti exhaust valves in my current 243's. Rather than repair my 243's, I decided to purchase a new set of heads and reduce down time.

In anticipation of doing a stroker motor ranging in the 383 - 40X C.I range, I purchased a beautiful set of MAST Black Lable 225cc small bore heads.

I am in the process of setting my valve springs which are PAC RPM series 1207X. My smallest measured installed height is 1.775" and my largest is 1.780". My current locators are .060" and I can get .045" lacators to fit my bronze guides. How **** should I get about the 1.800" recommended install height? I am only .020" off now and the thinner .045" locators get me .015" closer. I would mostly be about .005" - .010" off with them. I do understand that the smallest readily available shims are .015" so shimming will mostly not be an option with the .045" locators but, are they a better option? Should I let my OCD go, rock what I have and call it a day?

Remaining setup I am using is LS3 Scorpion 1.7 rollers so I should not have to be overly concerned with the open pressures. The cam has a gross lift of .57X intake and .57X exhaust. I also have a Novi 1500 on the car which is why I chose the 1207X spring as recommeneded. Also, I have Johnson 2116LSR lifters should that matter. Bottom end is bone stock with the exception of the chain and oil pump.

My rough calculations (correct me if I'm wrong please) with the smallest installed height on the intake has me at around .143 away from coil bind using a .060 safety margin. Coil bind is at 1.000" on the 1207X spring.

1.775" - .57X" gross lift - 1.000 coil bind -.060" safety net = .143" to spare.

Sorry for the long winded explination of my question. Just want get get it right.

-James

 

I have never seen an LS head that sets up at 1.800". The 1.800" value provided by the spring manufacturer is not a setup height, rather a height from which to determine stiffness,etc.

I would be more concerned with the spring seat value (closed force). I would shoot on paper for 140 lbs on the seat and see what installed height is required to achieve that value. From there you can figure out your open value and confirm the forces are high enough to control the valve train. It appears you have plenty of spring height to play with to tighten them up with more shims and a higher seat force.

Just ensure that any spring forces won't exceed the Scorpion rocker capacity. I am not too familiar with their capabilities.

 

Understood. I thought I saw somewhere that the factory GM spec was 1.800" that is why I had that value in my head. I believe I should have more seat pressure than the 140# now. Spring specs are 155 lbs @ 1.800, 436 lbs @ 1.150, Coil Bind 1.000", Max lift .700". Scorpion says in the documentation that their race series lifters can handle 950# max open pressure and .950" max lift, so should not be a problem.

Now I need to figure out the formula to caculate the spring pressures at my current height.

-James

 

my question is, are your valve seats machined so differently that your installed heights is off by that much? would that affect your geometry? im not sure.

 

and theres a tool to measure spring pressure. i would trust that more than some formula.

 

The only variables would be the seats and the spring pockets. I used the same valves (brand new stainless and inconel), retainer, locks and locator to measure the height. Most are within .002" of one another, the max variance being .005". Things can be machined etc. to bring them to wherever I want but, I doubt 2 - 5 thousandths of an inch matter much in this case. My primary thing was wanting to get as close to 1.800" installed height I thought was GM's recommended height.

As far as math. Unless it is done wrong it doesn't lie. As much as I would like to add another expensive tool to my kit I would have to go to the machine shop and have the springs tested. For me, PAC's reputation makes the rough math good in my books.

-James

 

To figure out the spring force at the seat and the open (note it is a force and not a pressure) you need the spring force at two positions. From your post above:

Stiffness = (436-155)/(1.800-1.150) = 432.3 lb/in

The seat value based on 1.775 is: 155 + [(1.8-1.775) X 432.3] = 165.8 lb

The open value based on your seat and 0.575" lift (you didn't provide the actual lift in your first post): 165.8 + (432.3 X 0.575) = 414.4 lb

 

Thanks my friend. I appreciate your help.

All things being said, I gather I should just put them together, have fun and stop worrying.

-James

 

What do the valves weigh in at? Have you talked to the spring manufacturer as to what they want to see as far as height and distance from coil bind. Might be a good idea to ask Pac and see

 

You might want to discuss with the spring vendor first. Some springs maintain better control when run closer to coil bind than you plan. I would see if they have tech support and tell them your setup to ensure they are OK with your numbers.

 

I will try to contact PAC and see what they have to say. I asked BTR what they thought and they seemed to be fine with the numbers at my lift.

I will have to weigh the valves and see what they come in at. I am unsure of the manufacturer as they came in single unmarked bags with the heads. The only thing on the bag is made in Argentina. I will check with MAST on that one.

Thanks again for the input.

-James