[10secbird]

I am experiencing a complete fall off of power at 5000 rpm. It is most obvious in 1st gear as I attempt to rev to 6000 shift point. It does not misfire it is just flat as hell at 5000 rpm like it hits a brick wall.

I always assumed if valve springs were weak enough to affect engine performance that the result would be misfire/valve float....ie some kind of misfire. But it just falls absolutely flat at 5000 rpm

I would like to hear your experiences with weak valve springs and how it affects engine perf ....

thanks

[firechickenman]

I have never experienced valve float, but my car will sometimes do exactly what you're describing and only in low gear. My A/F ratio meter shows it's very rich when it happens. Usually happens only when the ambient and engine temps are up. I never have figured it out but I've got a new hood and air cleaner set-up and am hoping that helps.

[694.1]

Sounds EXACTLY like an Olds 455 in a friend's 442.
Just as you were ready to pull back on the shifter, Blaaa. Nothing, but she would start to sputter again if you keep your foot in it for a sec or two as the revs fell.
New valve springs & she was a terror

[TCSGTO]

I had a 5.0 Mustang and a 68 AMX that would just rev very slowly once they got close to 5000 rpm. No missing just lazy. Springs were shot. New springs made both engines rev much quicker and higher.

[jimmy daniel]

Fuel delivery?!

[Steve C.]

On the Speed Talk forum a statement was made by a gentlemen with experiance and a lot of authority in the area of valvetrain stability. In part, he mentioned that often the term 'valve float' could be mis leading and went on to address the issues of a valve bouncing off the seat as it closes, in part due to inadequate spring pressure to control the situation. My point here is not as much about the engine losing power and nosing over at rpm due to this situation, but he mentions that if the situation continues the valve springs will further degenerate. If so now distruction starts !


.

[10secbird]

Thank you for your replies people ...
I just pulled the engine to address a tore up flexplate ring gear. I'll be testing valvespring seat and open pressures too.

[74Grandville]

not really a race engine, but i put an 066 cam in an old 301 once. it would hit a wall at 4,000 rpm. to this day I believe it was valve float due to the springs, but i guess it could have also been the wacky intake ports. the 301 had little tiny single springs compared to the normal stock double springs found on other pontiacs.

[54nomore]

Originally Posted by 74Grandville

not really a race engine, but i put an 066 cam in an old 301 once. it would hit a wall at 4,000 rpm. to this day I believe it was valve float due to the springs, but i guess it could have also been the wacky intake ports. the 301 had little tiny single springs compared to the normal stock double springs found on other pontiacs.

I wish I hadn't seen this post. I just built a 301 with the 066 cam for my Astre clone. I really hope I don't experience the same thing, but at least I am using better than stock replacement springs.
That'll teach me for straying beyond the street section. LOL. Wish me luck.

[74Grandville]

Originally Posted by 54nomore

I wish I hadn't seen this post. I just built a 301 with the 066 cam for my Astre clone. I really hope I don't experience the same thing, but at least I am using better than stock replacement springs.
That'll teach me for straying beyond the street section. LOL. Wish me luck.

ha! you'll prove my point if you are able to rev past 4,000 rpm. =)