Check out this dyno graph. I was talking to LV Vette, and in conversation, he asked if I had any crazy dips on my dyno curve at high RPM. When I described what I have, he said that it is probably valve float, and I should go ahead and change my springs. Here is my dyno graph:



After doing some reading, I have to agree with him. I'm guessing I'm do for a spring change.

 

Thats funny it looks jus like my dyno graph Bob @ EPP told me he thinks it valve float... He said new springs and get some new pushrods and that should take care of it ... So i got some 916 springs , havent got the pushrods yet . He said i could have bent one and that could mess with it too..... jay

 

 

The more I talk to people about it, the more I hear it is springs. However, I never thought of changing the push rods. I definitely need to change my springs out.

BTW, how tough of a job am I looking at. I have the manual, but I'm wondering if anyone has done just this. I'm guessing it's just a matter of pulling the intake and valve covers. From there, it should be pretty close. I know that's oversimplifying, but I'm guessing it can't be more than a couple of hours. I'm also guessing I'll change the retainers while I'm in there. I guess I need to figure out a laundry list of things I need to do while I'm in there.

 

No need to pull the intake...take off the coil brackets, valve covers and sparkplugs...there is a special too for an air compressor that you put in place of the sparkplugs that fills the chambers up with air so the valves don't drop in the cylinder...they sell many spring compressor tools out there the choice is yours and thats it. good luck
-John

 

Sounds pretty easy. I need to also look at my GM manuals to see what it says. I'm sure it shows some lengthy process, and there's probably an easier way. I need to check LS1howto to see if they have a write-up on it.

 

It's not too noticeable - but I broke a couple of springs with the ole stocker shortly after this, and it had some quivers in the graph near redline

 

I'm still looking into whether or not it is valve float. I'm hearing that valve float will not recover after the dip, like mine did. I'm sure there is something going on with the springs, but do you think it really is valve float? I'm hearing that once valve float starts, it doesn't recover like that.

Edit: Damn, it's more common that I thought.
http://www.hptuners.com/forum/showthread.php?t=11169

 

It's most likely a spring resonance. Happens when rpm matches the resonance frequency on single springs, that's why it occurs in a "window" instead of getting worse as rpms increase. Not exactly like valve float, but messes up the valve action in a similar fashion. Fairly common on our cars.

 

So, it sounds like changing the springs should fix it. A single spring with a different natural frequency or a double spring should do it, if that is the case. I think I may sit tight until I change the cam as well.

Thanks

 

Could be springs but it doesn't look like it to me.Looks like a timing dip.Was the dyno pull logged?

 

I agree with Slowhawk looks more like KR to me I would log it to be sure before throwing valve springs @ it.At that power level you can definitely run into spring issues. We use a tool from crane cams to swap out springs on the car It is LSx specific and saves alot of time over some of the crobar types.

Brent

 

I really am not sure if it was logged. I will try to find out, but either way, wouldn't the A/F ratio show if the timing dipped? Also, what could cause the timing to dip at that point?

 

When you change valve springs, the stock LS1 pushrod becomes a weak point. Might as well change the pushrods when you have the covers off.

 

Does your boost fall off at the dip ?...I had similar issue with dyno graph, and it was belt slip. Turned my 6 rib into a 3 rib

oops, did not see boost reference below dyno graph, guess it's time to log off...LOL

 

i've had those dips in some of my runs too. i already have prc dual springs so i didn't think mine was valve float. the dyno operator also told me once you float the valve you usually don't recover. afr stayed dead on trough the dips too. still not sure what the dips are. we figured it was some sort of miss between the software and the rpm pickup. not sure what else to look for.

 

Actually, that wasn't boost. It was just RPM vs. RPM (kinda stupid). It was just me playing with the display winpep, or whatever the dynojet software is. I actually meant to put A/F ratio.

However, I don't know what the boost was doing at that time. They didn't log it for me.

 

That's kinda what my tuner said. They said they have seen it a bunch before, but don't know what it is.

 

If you have HP Tuners log your runs. Dr. Phil had me log my runs and we discovered KR. Dr. Phil tuned the car on Sunoco 94. The gas here seems to be watered down 93 octane. It is probably more like 91 octane. I have also learned that I have to push the test button on my meth each and everytime and if too much time goes by b4 I hit full boost test it just b4. I had a similar dip. My timing did not change. The logs showed I was losing 5 degree's of KR. Dr. Phil never got a chance to finalize my tune because of time constraints on both of us. I was told to change the valvesprings to CC921's and have them shimmed. I did that last November. Dr. Phil said once you change the springs there is a chance the car might be a little leaner so watch the WB. Well last November I was so busy I only got a chance to run the car hard once and discovered I still felt the car go a little flat. I then decided I would troubleshoot the next time I came home. I got home and started troubleshooting. Dr. Phil asked me to log my WOT runs. I did and I sent Dr. Phil the logs. IMO I think I had valve float the first time in Michigan and then when I got to Florida with our watered down fuel I ended up with KR. To make a long story short.. Log the data.

 

I always log FI cars on the dyno for problems like that.I'd say it's belt slip or false/real kr.