406 will not pull past 4800RPM

[Walline]

I have a 406 chevy that started laying down about 5000RPM. It started doing it after 3 passes at the track. If you try to press it on it will starting poping and banging. I first thought it was ignition, because the tach would go erratic, but after swapping out ignition parts it still does it. I now think it does it worse when the engine is hot. In the stall it will rev 6500rpm, but put a load on it and it just gets lazy. I have seen springs act like this before, and that is what I expect. It is a .675 lift roller, with chet herbert springs. I drive this car on the street, so I drove it until engine was around 180F water temp, and pulled the valve cover off, to try to check spring seat pressure. I temp gunned the rocker arms and they where 200-230F. Seems hot to me. I run 5w30 oil, and I was wondering if that is not enough for street duty. I think it may of whacked the springs(heat)! Any thoughts would be great. The engine has about 6-10 passes and 30-50 miles on the street.Chris

[Robert Kane]

When you say the tach is erratic, is it jumping around, or just following the sputtering rpm's? If its bounces up and down it sounds like ignition/electrical. Do a complete voltage drop of the ignition primary circuts, from B+ to the coil. You don't want more than .5V drop. If possible check it when it is hot and the symptom is there. Also if you can check coil output (KV) and see if it is up to specs. I have seen coils test good though and when they reach upper rpm's they cant saturate and build secondary voltage quick enough to fire the plugs under load. Also check for tiny cracks in the magnetic poles that could be opening up when they get some temp in them.
Is the fuel pressure ok?
Hope any of this helps.
Robert

[hbps1978]

Just wondering if you are way to lean with your fuel system and carburetor jetting? If you very very lean your engine will not rev and will pop, miss etc. Check your fuel flow from your fuel pump. What size jets are you running in your carburetor? Hope this may help.

[k-star]

Bad spark plug????

Keith

[Walline]

I do not beleive it is ignition, because I have swaped it all out. Except the crane HI6 box. I first thought it was ignition, because the tach looked to go very erratic, but after further testing, I think it is just the RPM. What is strange about the whole thing is, say I get on it and it feels normal, then about 3500 I can tell it is reving slow, until about 4800. No popping and banging just lazy. Then if I try to push it past that it goes to popping. Very strange.

[John Wallace]

Valve springs shot?

[Nwguy]

Sometimes the cam gets installed too deep in the block, and lobes will hit the wrong lifter. Everything seems fine till higher rpm.

Had it happen to me with a flat tappet. Just a thought

[Walline]

I am sure it is springs. I had the same problem a few years ago with chet herbert springs, on a customers flat tappit SBC. I was just wondering why? Junk springs, or to much heat? just interested in spring cooling with light weight oils?

[hitchcock]

Check and see if you need a different heat range spark plug. Sounds very similar to a friend of mines problem, he changed carbs, ignition and it turned out to be too cold of a plug.

[ClassKing]

No one mentioned the battery. Under load.

[joe]

I'd say a combination of factors all related too the springs themselves , I doubt oil weight has anything to do with it .
Obtaining and maintaining the absolute purity of the spring wire after 1st ensuring that it is held too VERY tight chemical tolerances all but require that only the most stringent suppliers of spring wire will get the job done ,with modern intense cams.
PSI gets their spring wire from kobelco which is a highly regarded japanese firm that forbes considers a "model" on many levels.
Making springwire is just about the toughest job in hot rodding ,ALL KINDS of sundry steels have been tried down thru the years and still springs lag behind cam/valvetrain potential generally .
vascomax c350 is a steel somewhat like 4340 which is being used for some spring wires ,someplace . This metal is capable of supplying over 350,000 psi tensile strength ! But that don't qualify it as a spring wire .. nevertheless it is being tried and may prove very useful .

[SWB]

What kind of fuel pump are you using? Somtimes a mechanical pump will cause problems, also check that any regulators or filters flow up to par. I did a head for a pinto circle track car and the guy would go like a bat out or hell untill he drained the fuel bowl and the mixture started going lean. He ended up junking the el-cheapo pressure regulator he had and after that he was able to actually finish his heat races, say nothing of the main.

Just another idea for ya...

SWB