HD Valve springs V stock + shim

[Mark McClure]

What is the difference between a stock valve spring with a shim.....good for 8,000 rpm vs a heavy duty spring. The cost of the stock is a lot less that the standard. Pelican only sells the shim and states that it is good for quite high revs.

If you use a high profile cam would the shimed spring bind? where as the HD would not?

Cheers

Mark.......

[911pcars]

You can shim, but you also have to be aware of coil stack. That is, make sure there is adequate clearance between the coils at full lift. Otherwise, things will break (not good).

Sherwood

[snowman]

Shims are for setting installed height, not spring tension. A couple of lbs one way or the other can be had this way, but the basic spring rate should be the same. Differen't cams require differen't spring rates, eg 300 lbs at 0.5 inch lift vs say 250 lbs. Shims may adjust a 295 lb spring to 300 but won't go from 250 to 300 lb. THe basic spring rates are determined by the cam grinder. Does this help?

[911pcars]

Jack,
That's true for constant rate springs, but the spring rate changes if the spring contains variable pitch coils, or variable size coils or the wire thickness is variable, (all of which may not apply to a Porsche valve spring, btw). Since max engine revs depends highly on the onset of valve float, attention should be paid toward lightening the load so the rev limit can be extended without fear of valves kissing pistons. Using lighter retainers, springs and/or valves reduces the need to use heavy (or as much) spring tension to keep the parts together at high rpm. Does PAG have any tricks here?

Here's a domestic V-8 using aftermarket conical springs (big block Chevy I think). Notice the smaller (and thus lighter) valve retainer used as a result. The spring is also lighter due to the reduced OD of the coils near the retainer end. The roller tip is also a nice feature to reduce friction.



Sherwood

[snowman]

I don't think Porsche uses anything like a variable spring rate in their valve springs nor do any aftermarket ones I am familiar with. On the other hand I do not have a broad range of valve spring experience.

Porsches do not need extreemly high lifts, ie 0.45 to 0.50 is usually as high as needed. The main reason is that the heads breath very very well at very low lift. One consequence is that they are less prone to valve float to begin with. WIth Titanium retainers, and for the hotter setups titanium valves, the springs stay quite reasonable. Porsches also use valve followers rather than lifters, another weight savings. In other words valves kissing pistons is not a Porsche weak spot. One thing that is, is the max bearing and or piston velocitys. They tend to be the more limiting factor. At least thats been my experience.

[911pcars]

From my seat-of-the-pants opinion-meter from previous threads, it seems mis-shifts in the region of 8500 rpm (911 engines) seem to introduce valve-to-piston contact. So anything that can lighten the valve train load in lieu of heavier valve springs, the larger the cushion for those unexpected or anticipated revs in the 8,000 rpm region (notwithstanding the robustness of the bottom end) and less wear and friction loss in the valve train.

These conical springs look promising, but it's difficult to control harmonics as it's near impossible to fit a mating damper spring inside; maybe multiple conical springs or something would work.

Sherwood

[Mark McClure]

The planning that I am going to for this engine is HUGE! Every time I go to put an order in there is something else to consider.

Does anyone know or know where to get the information from for a GE60 cam. If the engine is limited to 6,800 is the standard spring ok....from the previous posts it appears that the rating would be wrong. What HD spring should be mated to a GE60 cam?

[cstreit]

Mark,

What motor?

I know plenty of race motors with stock springs running 6800RPM. YMMV but this has been my experience. I ask what motor because some of the later (3.0L+) have some pretty big (heavy) valves and are more suceptible to float at higher RPM's...

[snowman]

The best source if the maker or regrinder of the cam.

[Mark McClure]

Cstreit it is a 79 SC 3.0.

Snowman.......There is no mention of springs on any of the web sites. Because the prices are so high in Oz I am ordering from the US. I will have to work out the time differences and give them a call.

Thanks

Mark......

[camgrinder]

Mark, The GE-60 cam is similar to the Elgin 306/288 grind. It requires more spring pressure than a stock spring can provide.
We offer a set that drops in place of the stock spring and is fine up to 7000 rpms with steel valves. Less than half the cost of our racing springs too.

[Mark McClure]

John,

Can you either reply or PM me with a price for your 306/288, including specs and your spring prices....... ( 3.0 SC 79 )

Cheers

Mark........

[Bill Verburg]

Sherwood, thats interesting the only use of the conical springs that I had seen before was on the 996 engines.

[TimT]

Wasnt there a guy trying to develop roller rockers for 911 engines? I believe he posted here sometime last year?

[camgrinder]

Iskenderian was selling conical wound springs for 350 Chevys in the 1970's

I have seen a few attempts at roller cam 911's. So far none have proven to beat the factory style rocker arm. The problem is reducing the radius the cam lobe contacts on the rocker arm slows the cam action down.
What is needed is a factory style rocker arm with a longer pad. With a longer pad we can increase both lift and duration.