Valve Spring Diff. - Single vs Double

[241Libby]

I am about to order Edelbrock Performer RPM heads for my 460 marine and the Comp Cam XM270H gives .556 valve lift and calls for 924 springs (doubles) and the heads come with single springs. The seat and open pressure on the single springs incl. w/ RPM heads are very close to Comp's specs. Whats the diff. between single and double springs?
Thanks, Rick

[cstraub]

A single spring can have as much spring rate as a dual spring. The single will be larger diameter wire and usually a larger OD to increase the spring rate. The dual spring is an assembly of 2 springs together (inner and outer) to come up with a combined spring rate.
Now marine engines see more sustained running rpm then an automobile engine. Not many of us running our cars for 10 minutes at 5000 rpm but put us in a boat and we will do it all day. I would highly recommend when you get the heads to take them to a machine shop for a good valve job, have them check the guide clearance, and upgrade to a good double spring. This would be just good cheap insurance.

[Jetaholic]

I am about to order Edelbrock Performer RPM heads for my 460 marine and the Comp Cam XM270H gives .556 valve lift and calls for 924 springs (doubles) and the heads come with single springs. The seat and open pressure on the single springs incl. w/ RPM heads are very close to Comp's specs. Whats the diff. between single and double springs?
Thanks, Rick
At the high RPMs that a marine motor sees, they are more susceptible to "valve float". This means that the stock spring pressure is not enough to close the valve as quick as the cam wants it to. If it doesn't close fast enough, the piston will come up and close it for you, which is definitely not a good thing.
Typically a cam with a high ramp rate will require a stiffer spring to close the valve quickly so that you eliminate valve float.

[Unchained]

I have had multiple problems through the years with the flat damper springs that they put with the big single springs. I've had several break and have even found pieces of them in the oil pan.
Go with the double springs.

[241Libby]

thanks guys. My luck, the single springs being larger dia., will also conflict with the roller rockers I am considering. I will go with the Comp Cam recommended springs (doubles) and hold my breath. I am debating the roller rockers by Trick Flow TFS-53400621 or Harland Sharps CSP-S4005, both from Summit Racing.

[Ryan00TJ]

Duals for sure. My Father used to have a Biesemeyer with a warmed over 454BBC and broke a spring on a spring test run. Luckily the outer cracked and the inner kept it together until he was able to get it back on the trailer.

[lucky]

another benifit to double/ triple springs if you break a coil your valve will not drop into you Piston and destroy eveything around it :)-- Ohh assemble your heads , check pushrod legnth and also buy a good set of retainers -what Valves are you Running - Make sure you have a nice set of Stainless steel valves - What rpm are you planing on running in your motor ? don't foget to degree your Cam , makes a difference

[241Libby]

Thanks lucky. Will do. The cam is 4* advanced with 226/236 duration at .05 and has been in the engine since last spring. (complete rebuild with exception of heads and exhaust - ran out of cash and yes, I had some issues above 4000 rpm with stock heads and springs-some backfiring and a little bit of reversion at idle with stock OMC manifolds and thru hull exhaust but I made it thru the season with no damage to the core engine). I also replaced the OMC cobra drive (clutch dog/ignit. interrupt crap) with a new Volvo SX drive last year. What a positive move that was. The heads, rockers and Lightening headers go on this spring and that should do it, or at least it better! Should be at 450hp +