SlwSVT

Hello all,

Just got my recently built 404LS2 on the dyno for some tuning. It is a Livernois 404 with 243 heads (330cfm, 240cfm), Pat G spec cam 239/247 .623 114+2 on LSL lobes, ported FAST and supporting mods. She pulls nice and steady and is making 498rpm right about 6200 while still climbing then all of a sudden it hits a wall and nose dives. From 498rwhp at 6200 to about 400rwhp at 6800. Tuner thinks it is valve float. I have Patriot springs in there. With the cam sheet it called for a 7.40 in push rod, but with a 7.35 the geometry was right on. Do you all think it is the valve float due to weak springs?

Thanks

Chuck CoW

Hey Pal.... Thank god I'm not alone! I just built a max effort LS2 in an 05 (E40) Vette....and I think I've got the same problem...

Call me so we can talk!
914-332-0049
Chuck CoW

1.8t

Can you post up the dyno graph?

narcszm

...it could also be the tune. Maybe someone forgot to keep going in the spark table.

99blancoSS

iTrader: (115)

post graphs

Robin L

First a cam card cannot tell you what length your pushrd should be. It can tell you how much smaller the base circle is and how much needs to added to make up the diff. But the machine work on the heads and block will change everything so don't depend on the cam card.

Also some of the less expensive springs loose their pressure very quickly.

With Valve Springs you cannot skimp on the cheap or favorite of the internet.

I use the Lunati/Pac springs on my dyno mules.

Really there are a ton of reasons that you can hit a wall on the dyno.

Springs, cam design, tuning, fuel system are all good places to start.

We have stock cammed GMPP Crate engines that will pull to 7000 RPM with the yellow LS2/LS6/LS3 springs. A radical ramp on the cam profile can cause a lot of problems also. More pressure could help there.

Lets see some logs of the tuning software.

Also let us know if the first pull is going higher than the following pulls.

Good luck!

Robin

racer7088

Valve float depends like Robin said on the Lobes and the springs and how they are setup and on how heavy the valves etc are. It's a system and only the place that set that deal up knows what is going on and not anyone on the internet. FWIW we have Patriot Xtreme deals that spin 7000 easy with no issues and seem to last forever.

SlwSVT

Here is a graph.

Thanks

SlwSVT

I should of been more specific when I said cam card. The cam was spec'ed out by Patrick G and his sheet recommeded the push rod length based off of what pistons, milling of the heads, thickness of head gaskets and so forth. It called for a 7.40 inch length, but the 7.35 geometry was spot on. Thanks for the help!

narcszm

It is not fair to say it's still climbing at 6200 RPM. Your torque is falling off pretty dramatically and it's normal that the HP will plateau around there.

The HP falloff from 6200 to 6700 is not too concerning, except for the little dip at 6360 which appears to foreshadow what happens at 6700. It definitely looks like valve float, or lifters compressing / collapsing.

This is just a guess, but you may not have enough pre-load into those lifters with a 7.350" pushrod. Otherwise, your valve mass is overcoming your valve springs at 6700 and they're floating like ice cream in root beer.

SlwSVT

The cam spec'd with the flow on the heads we were expecting it to keep pulling all the way to 7k. Projeceted shift point was 6800rpm. So I was hoping it would peak at about 6500rpm. I am ordering the Patirot dual gold springs and hope that will take care of it.

narcszm

You may consider this kit also.