I've been running a crane 227 cam with comp 918 springs and from day one the valves have floated above 6000 rpm. I've done enough research/had enough people look at it to believe it is either 1. Inadequate seat pressure or 2. Lifter pump up (i was running 3/8 turn after 0 -lash)

Details on the setup:
cam: 210/224, .511/.553 (with 1.6s) 112 lsa.
Lifters: Comp OE replacements

From what i understand increasing my spring pressures could potentially resolve either issue, so this is the route i'm going. I pulled off the comp springs (~40,000 miles on them) and using a spring pressure tester found that i was only getting anywhere from 95-110 lbs of seat pressure at my installed height (~1.78, varied slightly across valves). Crane recommends 130 lbs for this cam.

Since the springs are in obviously bad shape (almost 20% off from the spec-ed pressures for 918s - maybe this was the problem from the beginning, or maybe i accidentally got 915 springs), i got a new set of the PAC 1518 springs. My intent with these new springs is to run a more seat pressure by shimming to get a ~1.72 installed height. This will still allow plenty of clearance before coil bind (I actually could run up to .570 lift safely) and would bring the seat pressure to around 150. Open pressure will be 330 lbs.

Is this going to be too much pressure? The crane cams tech guy I talked to seemed to think that as much as 165 lbs @ set was totally fine. He also made some comments about how the spring rate was going to be a factor at higher rpms, but wasn’t able to explain it very well. The crane recommended spring has a rate of 391 lbs/in vs the 1518s which have 313 lb/in. The tech guy said this will cause my springs to have trouble at high rpms. I don’t understand how the rate matters, since my seat and open pressures will better than their spec anyways.

If anyone sees anything obviously wrong with what I’m doing, please let me know.

 

The 227 is a 6000 RPM cam and will float above 6500 RPM. If your springs have insufficient pressues this will also cause float---I do believe that my stock springs caused float at higher rpms and therefore lost power on top.

Crane recommends using the dual spring 99893. The 227 exhaust lift with 1.6 is 552. The lift with this spring is well into the safe zone.

I use the 99893s with my 227 and feel very confident in their ability to control the valve train especially since I am running SA RRs. JMHO

 

I can't say if those pressures are correct for the cam as I am not familiar with the cam. But they are not too high. Crane should be able to tell you what seat pressure and spring rate to use and an approximate rpm max before valve float.

Rich

 

120 lbs closed @1.875 or 17/8
312 lbs open @ 1.375
Min. RPM 2000
Max.RPM 6000
Float: 6500 RPM

Spring 99893
Closed: 130 @ 1.875
Open: 402 lbs @ 1.150
Max net lift w/.060" clearance 0.710
Average Spring Rate: 391 lbs/in

 

I really dont believe that cam is made to rev that high.It doesnt have enough duration.That is probably what you think is valve float.It isnt breathing enough above 6K.Its meant for low end.

 

Yeah, its definately a low-mid range cam, but check out the graph (link below- dyno was run up to 6300). The power shouldn't just nose-dive like it does. I'm not expecting it to peak any higher with the new springs, just that i'll be able to rev a little higher to hit the optimum shift point (which given where the peak is, i think should be around 6200 or 6300)

http://www.putfile.com/pic.php?img=7443199

 

Agreed -- with the right spring setup i should be able to run as high as 6500 without float. Not that this is the ideal shift point, but the power should gradually drop off and not nose-dive. How high were you shifting the 227?

 

thanks, i was a little worried since i don't know even ball park figure for what is too much. On that note, what would be an "excessive" seat/open pressure that would cause problems? It's limited by the lifter right?

Also, can you explain how the rate makes a difference if you seat/open pressures are within spec? What would go wrong if the rate was lower than required?

 

I was running the same cam and springs.

I ran 918s installed at about 1.74 to 1.75 which puts them in the 130 range
closed and have had no problems. You can see my mods list for all the info
regarding my current setup. I'm going with Crane 96872 springs with my Ai
185cc CNC heads so the 918s are off now. I don't think you will have any
float issues with new 918s installed at 1.75". There is no point to install them
any lower.

I had a strange problem that I thought was valve float that turned out to
be an OBDII problem. Problem solved with OBDI.

 

Update on the results of my spring swap. I went from worn out Comp 918 springs setup at 1.780" (+/- .010 across springs) to new PAC 1518 setup at 1.720" (+/- .005). This is with LE2 heads and a crane 227 cam.


I think you have to click on the picture then pick fullscreen to see it well. Blue is the new graph green is the old graph:



There's a pretty clear increase in area under the curve above 6000 rpm, as much as +22 rwhp at 6200. I'm a little confused why the old graph has that "bubble" of +7 hp right between 5600 and 6000, which i lost in the new run. The AFR is slightly leaner on the old run which is maybe contributing, and also the timing has been changed a little in that range, maybe i added too much.

 

Here is my experience with the Comp Cams 26918 beehive springs. This is an older set probably when they first switched away from PAC. I was experiencing what some called valve float above 5000rpm with my XFI268 cam. It looked like reversion as my KPA was bouncing around to much. It would go into real valve float around 6200rpm.

When I first got the springs we checked them and they were around 115# at the 1.800" dimension. When they were installed the seat dimension was 1.750". I figured without checking the springs that would be good to go.

With the possible valve float problem we decided to go with the Manley beehive spring with 150# at the 1.800" dimension. Yesterday after we removed the 918 springs and checked them they were down to between 95# and 100# at the 1.800" dimension. We checked them at the installed 1.750" dimension and the needle on the gage hardly moved at all.

I also decided to go with a custom cam and more duration. IMHO 95 to a 100 pounds of seat pressure is way to low for an agressive cam such as the XFI series. Comp rates the 918 spring at 130# on the seat.

By the way the Manley beehive valve springs were right on the money. One more thing those springs had less than 3000 miles on them.