Effect of displacement on Camshaft selection

[hotrodfeguy]

Looking good Dave, I would set the chain/cam advance 4* also if you can yet. But man that looks really nice now that its all painted. I think for a "TOW" truck that thing is going to rip off some time slips, and you could run some grudge/cash races  With all that detuned Iron look you will have going on. Would make most Bow tie boys go to sleep when looking in the engine bay.

[jayb]

Boy that's a lot of seat pressure!   What's your open pressure?  Didn't know they make hydraulic roller lifters that can handle that much.

I think Jon may be talking about the open pressure, not seat pressure.  Maybe he can confirm...

[lovehamr]

7k rpm with a hydro roller?  That's a lot of mass flying around.  I know mine won't do it without floating.

[jayb]

There are folks who run hydraulic roller setups that high, but the valves are floating and they are kind of playing with fire after 6000 RPM.  I did a lot of work on making a hydraulic roller cam work at higher engine speeds back in 2005 and 2006, and the most I ever got out of one before valve float set in was 6300 RPM.  What I found was you needed a lot of seat pressure, like over 200 pounds, but open pressure had to be limited to around 425 or so.  The interesting thing was that the engine still sounded good for a few hundred RPM over the point where valve float occurred, but you could tell by the horsepower curve from the dyno data that the valves were floating; the curve got very choppy and power started dropping off.

[fe66comet]

No that was seat I am not sure of open @ 590 lift? The Beehive spring came either 330 close ( too light ) or 350, kinda heavy but all comp cams makes. Spec on the spring was 340 open but at my installed height it worked out to 349 or something like that. Barry said with that setup and the light weight race lifters I have it will start to float around
6800 on the dyno. I gotta say all that was not your usual 2000 dollar kit, more like 4500 bucks in can and valve train without rockers.

[jayb]

Are you sure about that?  I've never seen a beehive spring with that much seat pressure.  I assume this is a Comp cams spring?  What part number?

[fe66comet]

Therese are it
http://m.summitracing.com/parts/cca-26981-16

[JamesonRacing]

Check out where you can buy those springs:

http://www.sears.com/comp-cams-competition-cams-26981-16-beehivevalve-spring/p-SPM7503546011?prdNo=14

[fe66comet]

Here they are installed

[fe66comet]

Ha Ha buy em at Sears in the tire department.

[fe66comet]

Now that I look at it again I went with those.because they are strait rater with no compressed rate.progression, 347 all the way through the stroke.

[mmason]

Here are the specs
http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=26981-16&Category_Code=

[afret]

You might hit coil bind with those springs.  At an installed height of 1.7", you could probably safely run about .535" or so lift since coil bind is supposed to be at 1.115".  I would measure actual coil bind to be safe.  Your seat pressure is pretty low too for such a radical hydraulic roller. 

Is that rust on your springs?  I would check them closely to make sure there's no pitting.  If you break a spring, it might be pretty serious since beehives are single springs.

[fe66comet]

No that is condensation I believe I mentioned it is terrible here in another post. I sprayed then down and brought them inside after that pic was taken they are always stored in a plastic tub with silicate beads , as soon as you remove them on a cool rainy day that is what you get. The spring specs are what comp cams said to use, 347 and they gave me the part numbers of what was recommended so I went to the higher rate spring in that range. Barry did all the setup on the head design with that camshaft already shelved for me so I would trust he checked that. We built the heads with 600 lift in mind. I just basically told him what I wanted and Survival did the make happen magic.

[jayb]

Those springs are a 347 pound per inch spring rate, not 347 pounds on the seat.  The Comp catalog says they are 110 pounds on the seat with an installed height of 1.700", and 292 pounds open at a spring height of 1.175".  I think you will need a lot more spring with that cam if you want to run past 5000 RPM, and I too would be concerned about hitting coil bind, unless you increase the installed height.