School me on spring pressures and rates....

4

496 BB

New member
Can someone school me on what spring pressures do and how they are important and also same with the rates? Like why you have to shim springs and such. I know obviously why you cut the pockets for coil bind but I know nothing else about this. Trying to learn this.
 
As a rough rule of thumb, the more a spring is compressed, the more force it takes to compress it. In other words, the "rate" increases. It might take 20lbs to compress one 1/8 inch and 40lbs to compress it 1/4 inch. Next, it is generally assumed, the higher the spring rate(stiffer) the more rpms can be turned before valve float. So its generally considered a little more spring pressure is a good thing. The reason to use valve spring shims is to "compress" the spring a little (thickness of the shim) so that the spring rate (stiffness) is a little higher so you can turn a few more rpms. Keep in mind this a a very gross generalization and a broad and rough explanation. Hope this helps.
 
Im feeling that. That makes sense. So generally speaking on a short short bull ring track this may not even come into play if Im not turning very high rpm with say whatever springs are needed for a 308 cam. Thinking a may only hit 7800 rpm and thats even a stretch.
 
You only require enough spring to seal the valve and allow the valve to follow the profile of the camshaft without floating, or bouncing off the seat. Excessive pressure is hard on valve train parts , valve face and seat.
 
Kart43 said:
You only require enough spring to seal the valve and allow the valve to follow the profile of the camshaft without floating, or bouncing off the seat. Excessive pressure is hard on valve train parts , valve face and seat.
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This is what alot of people dont understand, and wonder why parts wear out quicker or break when they're using 26lb springs in a build that would work better with 10.8 or 18lb springs
 
the lighter the spring you can go with in these small motors will also let the motor be more free so I will turn rpm faster
 
I agree, more pressure than what needed is wasting energy. I put a set of 18lb Honda springs on a AKRA legal engine (just to test), and it lost power..put the right springs back on and it was back where it was.
 
There is a strange belief among some, they think that the engine hits 6600 and they want more RPM all they need is stronger springs. I do always get a kick out of the first posting for every problem is get new springs.
 
Yea I understand all that. Was just trying to get a feel for what the technical side of things were. Whats a common spring for a 308 cam and under 8000rpm? 32lbs be ok?
 
32 would be to much for a 308 most run the 26 and its just fine.
you can do a self test.take a spring and push down on it on a scale
until it coil binds.we did a few 26 and it took 16lb of pressure to coil it.
not the best way to test but gives you a idea.
 
The spring I use in most of my builds are 22.8 lbs@.850 vs most 26 lb. advertised. springs which average about 25.8 lbs@.850 However my springs have a much better spring rate and will not coil bind until .455 whereas the 26 pounders. bind at .400;Also I use them with my Hi-Ring locks which increases "nose pressure",Gives you more valve thru retainer height,so you can use lash caps (rotators) and, also not have to grind rockers on Hemis for rocker to retainer clearance.I have complete sets w/retainers,locks and springs. pm me w/ any questions....Dave
 
modifiedman said:
32 would be to much for a 308 most run the 26 and its just fine.
you can do a self test.take a spring and push down on it on a scale
until it coil binds.we did a few 26 and it took 16lb of pressure to coil it.
not the best way to test but gives you a idea.
Click to expand...
Ha! I got 26lbs on my BP2 now. Of course this was told to me by someone before I did my research and learning.
 
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