Cam lift is .571 intake, .556 exhaust.

I'm running a dual valve spring with the following specs:
1.290 O.D., 0.674 I.D.
140#@1.800; 385#@1.15; 650 Max lift; 1.100 Coil Bind
377# inch rate intended use for LT1

Pushrods are standard 7.200".

I'm running the stiff spring becaues this is intended for a 15-18 psi boost application.

My main problem is I forgot to order locators to fit these springs.

Does anyone know which locators will fit these specs on STOCK head castings?

I've looked at summit and found the CC 4771 locators but unless I am misinterpretting the specs, a "0.690 inlet diameter" is not going to work on a spring with a "0.674 I.D." Do I even NEED locators, or can I just use regular shims? I am very unfamiliar on this topic and I hope some of the experienced people will step in so I can learn something worthwhile.

BTW, my measured install height WITHOUT the shims or locators is about 1.830". I will have to double check but I think my locks are just standard (not +.050").

 

The 15 psi acting on a 2" valve will have a force of 47 lb. I think a stiffer spring is needed here.

 

You can use a CC 4695-16 if you cut your guide OD down to .500.

 

Ok what's the PN spring you are trying to run here?

YOU NEED LOCATORS!!!1

 

Well, that was easy enough...I just called the company who made the valve spring and they have a locator with these specs:
1.300 OD
.570 ID
.675 inlet
Looks like a perfect match!

However, to address sssalah's concerns, I ran the numbers for seat pressures. They will be high while not under boost, but he is right, they appear to be low while running high boost

...so the question is, just how low is TOO low with stainless valves?

It seems that the primary functions of seat pressure (shouldn't it be seat "force?") are to seal and to allow the head to conduct heat out of the valve. I suppose the precision of the valve job would actually be a large factor in each of these functions since it dictates how well the valve surface meshes with the guide surface.

Assuming a 1.760 install height, at 18psi I should have a seat force of approximately 97#. At 15 psi and the same install height, I should have a seat force of approximately 107# and it seems that my open force is 370#.

Are these seat forces too low?

It seems that on a NA engine you shoot anywhere between 115#-140#.

Thanks for your help!

 

SStrokerAce,
thanks for making it clear that I need locators! Just for your reference, I'm running PBM Star Series Dual Springs, PN 4125.
http://www.pbmperformance.com/downlo...g2005_1_33.pdf
Scroll down to page 32 to see a brief description of the springs themselves, but the actualy 4125 part number is not currently listed.

Can you explain to me WHY locators are needed on our heads rather than only shims? I understand they help locate the spring, but are there heads which only run shims? If so, what makes them different?

 

I don't mean to keep talking to myself with 3 posts in a row but here is an informational post!
I just got off the phone with Manley Performance Products tech support and he said running the RPM's I am (around 6000rpm) that these forces on the seat will be fine. He recommended Manley Valve springs PN 221-426 or PN 221-436 which are VERY similar in spec to my PBM valve springs...so I guess I should be alright then. It will be interesting to see how long these PBM springs last since most people run Comp Cams, Manley, Kmotion, and other better known companies. We have a few dirt tracks around here and alot of guys run PBM products with success.

 

You need to control the bottom of the spring from moving around, especially when there is aluminum under it because the spring will turn into a aluminum file and cause all sorts of carnage!

Bret

 

But if you have a flat shim in place wouldn't that protect the aluminum? Obviously it would not control the spring, but it would keep the aluminum from being filed away. Apparently valve springs have a tendency to move around more than what I believed if control is that big of a problem! Thanks, Bret for the explanation. At what spring rates would one need to upgrade from say a Comp Cams OE style lifter to the Morels or something heavy duty?

 

No because most shims are not hard enough so it would eat them away. Videos of springs on a spintron tell you a lot about what is going on, the springs dance around something crazy in there.

You would need to look at the open pressure and the rocker arm ratio to determine the peak pressures the lifter is seeing, plus too much side loading from high lobe accelerations cause most issues in a hyd roller lifter.

Bret

 

Here is the slow motion video of the beehive spring in action, it still floors me every time I see this:
http://www.racingsprings.com/movies/PRI%20Web%204.wmv

 

That was pretty neat!

 

You must remember that the entire valve surface is not exposed to the intake side pressure due to the valve seats and valve stem taking up some surface area. In my GN the springs are 85# closed seat pressure and running 27-29# of boost is the norm without any issues, some even do it with stock worn springs which may have only 65-68# of seat pressures.
If the valve is open, then the pressure difference on each side should be dramatically decreased so the boost would not work to open the valve. If the valve is closed, the cylinder pressures are going to be much greater than 15psi except maybe at the end of the exhaust stroke.
The seat pressures need to be higher for the higher lift cam and the agressive closing ramps on the lobes to close the valve without it floating...so when the intake is closing, the cylinder pressure should already be equal to the boost pressure.

I'm no expert here, just thinking out loud because I've never really given any thought to spring pressures on boosted engines..just seeing the post got me thinking about how the GN operates with such low spring pressures...its also a flat tappet cam/lifter with no where near the lift of the LT1 cams.