Valve Springs w/ Colt Cams C.542.s

[theczechone]

I am in process of rebuilding and upgrading a N42 head and I'd like to incorporate a cam I acquired with a car I bought a while ago. The cam is brand new and I have it which is 98% of the reason why I'd like to run it. 

 

Here is link to colt cams website: http://www.coltcams.com/html/camshaft/index.cfm

 

They list 0.510" valve lift which is misleading, I have contacted them and they send me a sheet stating that they assume a 1.5/1 rocker ratio, and I believe that the L28 uses a 1.429/1, right? This would mean the valve lift is only 0.485" right?

 

Now the problem becomes that the factory springs bind at 0.460" valve lift or higher, so I know I need new springs but I don't know which would be best. I spoke to a friend who has experience in design and development of valvetrains in race cars. He suggests that I need to get a springs that will bind at ~0.050" below my valve lift, springs that bind deeper than that can produce resonance in the valve train. Therefore my bind height of the spring should be: installed height - (0.485+0.05).

 

I have looked at schneider and isky springs and both of those seem to bind much lower than that, so I wanted to get advice on if anyone has experienced unwanted resonance in their valvetrain when running these springs. 

 

Thanks for reading. 

[Xnke]

1.48:1, approximately, and it varies throughout the rotation of the cam. 1.48 is the "average" I belive.

 

Call Isky; he's got springs in stock that will fit up to a 0.610" lift cam; Schneider also has a spring set for the L28. Rebello has some spring sets as well, but he also supplies Isky springs for some cams.

 

Consider also your valve lash and that you want NO LESS than 0.050" of room before coil bind, as you will have some valve lofting at some RPM. Consider also that your resonance will likely be at high RPM and it's considered very difficult to coax valvetrain instabilities into the L-series valvetrain.

[TimZ]

I'm using the Isky springs and .536 lift -  no issues here.  If you want to be closer to the bind height with your cam, you could always shim the springs.

[theczechone]

I looked at isky's catalog and contacted them in regards to the springs. I wouldn't think to consider the valve lash in the calculation as I thought with thermal expansion  the lash would be taken up.

I have heard of shimming the springs and that makes sense. I guess I'll wait to hear back from isky and then probably purchase the springs from them.

I've also aksed them to explain getting new retainers. Most people mention getting new retainers for the springs and I am just wondering why is that necessary?

And finally how do I size my lash pads? I know there is a thread talking about it but I haven't found it yet. If someone could post the link I'd be grateful.

Thanks, also good to see someone that's local, Tim!

[Xnke]

You will definitely need retainers to fit that cam...it's not really the springs that make the difference, it's the lash pad thickness. Lash pads thicker than about 0.170" will need taller retainers. Others will say they got away with the stock retainers, but the taller retainers are made for a reason. Real easy to chuck a lash pad and a rocker arm; possibly unseating a valve lock...could be a real train wreck. I was unseating lash pads with 0.185" inch pads in stock retainers consistantly at 6300RPM. Your milage may vary.

 

The base circle diameter is and the valve stem height are what determine your lash pad thickness, for the most part. If you have set the valvetrain up with a cam of known base circle, the the SAME head with the SAME valves can have the lash pad thickness roughly calculated (you can get within 20 thou) by taking the starting lash pad thickness + 1/2 (basecirclenewcam - basecircleoldcam) = new lash pad thickness.

 

If you install other valves, have a valve job done, or machine the top surface of the head, or any combonation of the three together or individually then your lash pad thickness will likely change.

 

If this is a new head or you have had machine work done to it then you can figure the lash pad thickness by using any flat-bottom pad (any non-factory fitted pad) plus some shims cut from feeler gauges or shim stock to fit the lash pattern up. Then, add the thickness of the pad to the shims you used and call Nissan Motorsport so they can tell you they don't have that size...order something close but bigger and get a machine shop to grind them down to the size you need.

[theczechone]

This weekend i spend some time with my engine builder friend and we went through the valve train. We started off with centering the wipe pattern on the follower. We used thin feeler gauges to measure the added thickness to the lash and we would be happy with about 0.138" lash cap. Since that is not available i will go with 0.140". I'll have to recheck anyway as I just sent my followers to Delta Cam for regrind. 

 

As far as the springs we measured the bind height of inner and outer as well as forces at installed height and max lift. It seems that the outer spring could handle my lift just fine but the inner would have just 0.005" of clearance to bind during max lift. My friend has a nice machine shop so he suggested that we just machine down the inner spring seat to give ourselves more clearance. 

 

Then we calculated the inertia force of the valvetrain by weighing all the components and setting my max RPM. It seems that stock springs are good up to about 7250 RPM.

 

Since my cam is suppose to top out around 6500rpm, I am just going to reuse my stock springs. and from the sound of it i might even be able to reuse my retainers with the larger lash cap.

 

I have spreadsheets showing all the measurements and calcs if anyone is interested. 

[roger280zx]

Yes stock springs are good for 7250 rpm, and they are also only good for about .460 lift in most cam applications.  Rpm is not the only way to float valves.