Who knows what valve float looks like on a dyno? Please explain what the graph would look like.

 

Relatively smooth until the top of the graph where it starts to get a bit wavy. That's what everyone I've seen looks like.

 

If you want take of the valve cover then the rockers and look at the tip of the valve if you see a star patteren on the tip the valves have float.That is just one spot to look at and the easyest.

 

Maybe my graphs will help. The first one I have the smoothing at 1. On the second one the smoothing is at 5.

 

bump to the top

 

I've seen several mustangs dyno with old valve springs and when they floated the readings dropped like a rock. It would fall short of where it should still be gaining power.

 

I would say that simply looked like MINOR ignition breakup or the effect of minor fluctuations in timing. It is progressive due the increasing rate of accelleration increased load and change in power level.

Valve float usually shows as a prominant drop depending on the severity. Your curve still had a very normal progression to it .. no radical drops. I have many curves like yours. I would not be worried.

 

I'm glad someone started this thread because I believe I'm experiencing valvefloat myself....I'm switching my springs out in about 2 weeks to see if that solves the issue.

My 408 gets to about 4700-4900 RPMS and starts to "sputter" or "break-up". It does it very consistently. On the dyno the the power fell off big time at that point on 9 pulls. Boost should climb to 13+ PSI and only gets to about 8-9PSI. We never tried to pull past it because I was afraid we would hurt something on the new motor.

Here's what I have ruled out so far..

plugs-good "newer"
wires-good "new"
coils-appear to be good (got ahold of a new coil and moved it around on Bank #1 (1,3,5,7) and it still breaks up before 5K no matter what cylinder position it's in)

I have HP Tuners now and also have logged with EFI Live and there are no reported misfires to speak of. The only noticeable change during "break-up" is Bank #1 OEM O2 Sensor goes lean (hence moving a new coil around on Bank #1 as I stated above)

I beginning to believe it's valvefloat since I'm on the edge with Comp 918's (581/592 lift on my current cam) with "Boost" and they have 6500 miles on them. 918's are only good up to .600 and that's based on NA.

The more I think about it, my stock bottom motor which made 587 rwhp on 12 PSI only had a 563/563 lift cam. The one difference between motors....the camshaft! I switched the camshaft figuring the bigger lift cam would support the 408 better. Since the 918's are rated for .600 lift I figured I'm okay.....but I have heard that with FI those numbers do not always hold up. Which makes sense with additional pressure of "boost" on the top of the intake valve the spring has to overcome the cam lift and the addition of the boost pressure.

Given the Bank #1 O2 data, I'm just wondering if the the lean condition indicates an intake valve or valves are "hanging" open or "floating" allowing more air in. Maybe I'm such on the edge it's only a couple springs that can't handled the load.

Any more input would be appreciated!

 

Ill be changing my springs in the next couple of weeks. I will probably go with patriot duals, since they seem to be the best all around spring. I will have the 918's checked out to see how they have held up. Ill post back my results.