Valve float on a datalog

[Mike Taylor 3601]

I'm no expert on boosted stuff,or anything else as far as that goes,but in your description you said 5800 was like hitting a wall, I would check springs first. n/a engines will act like that if intake valves are leaking,blows compression back up runner,basically blows fuel back up runner,messes up carb signal,etc
usaully they will get a certain rpm and act like has a governor,had one once on dyno would get to 6500 and shut off like you killed ign.
If you are blowing valves open could act the same as leaking valves.
I'm gonna say that if valves are blowing open you could add fuel and A/F ratio would probaly not change like it should,it probaly would'nt richen as much as it should.
Mike Taylor 3601

[buzzinhalfdozen]

Ok, 20 degrees of timing with 12 PSI of boost? Again I'm certainly no expert on boosted engines but seems high to me, certainly at 12.5 AFR, have you ever looked at the plugs on this thing? While I'm all in on the weak valve spring theory, maybe as Adger had eluded to you have a few issues instead on merely one. BTW is this a new engine, I mean fresh engine and have you spoken to the engine builder? Who engine controller are you using? Joe

[dart440]

The plugs look good. The engine builder.....that would be me! Yes its a fresh build

[buzzinhalfdozen]

Ok, then can we assume you assembled the heads and if so what did you use for springs, XXX's lbs. @ XXX installed height. This alone should indicate whether you have enough spring on it thus solving 1 mystery.Has this engine been tuned on either an engine or chassis dyno or did you start with a base map? Joe

[ss3011]

Which brand is your ECM ? What rpm limits are in the calibration ? Silly me, but I ran my engine on the dyno with a low rpm chip in the MSD, took a few pulls to figure that out. Opps !

[dart440]

I'm using a MS3x for ecm. The rev limiter is set for 7000 rpm. No dyno time (yet)
The valve springs are stock 100lbs@ 1.7" and 325lbs @ 1.5"
Valve lift is .550"

[Dirk Olson]

I am not expert but I guessing a 100pds on the seat is way too light. Not knowing alot about your setup you need to spend some money on valve train parts. Is this a street strip combo?

[Kevin Panzino]

100 lbs on the seat is not even remotely enough!!!!!!!
And your 12.5 lbs of boost is taking off 39 lbs, so you are left with 61 lbs of seat pressure only!!! Float city!!!!!!!

[Mike Taylor 3601]

We typically run 140 seat 400/425 open on street N/A hyd roller and you need to raise that,coming up with spring probably won't be big deal,the problem is when you start going over that whether the lifters will handle it. When start going over 140/400-425 a lot of lifters will start compressing,there are lifters that will take more pressure,but don't think stock ones will take it.

You'll probably need 180 ish seat 450-475 open.
Don't know all info that need to know,these are just ballpark recommendations

Mike Taylor 3601

[Adger Smith]

With a low lift like you have and the low spring installed ht. you need a spring that has a lot more seat, like 200+ and a rate that is very tough ending up with at least 550 to 600 open. That may be hard to find. Then when you get enough spring you need a real stiff pushrod. Those engines have a nice short pushrod with good angles. I would use at least a .125 wall and if it will fit a 3/8 to 1/2 double taper .150 wall pushrod. You need to remember that a boosted engine has trouble opening the valves. The pushrods in an A/fuel engine that I've helped with look like drillpipe.
BTW those are just a good starting point for spring pressure. You could need more because of cam profile and valve/valve gear weight.