Just curious to see if any of you guys ever ran into valve float that was associated with running high boost pressures. I was thinking about it one day. I mean, it is really a possibility seeing as how the extra pressure in the intake charge could actually try to keep the intake valve open. If this were to happen, then piston to valve contact would almost be guaranteed. Would simply running valve springs with a higer seat pressure be more benefical at this point especially as a safety measure? Just looking to see what you guys think about it...



Trying to become the most modded out N/A 2nd gen sunbird 4 cylinder on the org with a..... screw that, I'm going turbo!!!

2.Slow OHC I4
Ported cylinder head, intake and exhaust
Relocated IAT with a custom WAI with a 6x9 K&N conical filter
All this, and I still can't go fast.............yet!!

it take alot of force to open a valve spring, it is possible but very unlikely that intake pressures are gonna hold your valves open on a regular boosted engine, maybe when your getitng into extreme perofrmance but thing about it, there is very small amount of time that the theres no intake valves opens (if at all) so your intake pressures have an escape almost all the time, and top of that there are 6 other intake valves that are closed, the chance of overcoming the spring rates on 6 valves while almost always being vented into a cylinder is not likely thats its somethign your gonna have issues with, especially to the point of valve to piston contact

I don't know much about the spring rates on your motor, but my Eco (L61) is right now at 335/358 whp and no sign of positive pressure valve float.
Spring rates for Ecotec motors are 50lbs closed valve and 140lbs at dead top of cam lobe.
Given that the springs fatigue over time 10-15 lbs, that gets down to sometimes low as 35-125, on older engines, so for older engine it would be a smart move to do somthing like that.

One thing that will give you HP loss is valve bounce.
Since you have 20 psi in the combusition chamber from your Turbo or whatever there is just that much pushing your valves closed after the completion of exhaust or intake cycle so that pressure makes the valves smack the seat and they should automaticlly close so the other ones can do the job, they accutally bounce off the seat a couple of a few times before they close making you lose HP. Makes sense?? I think it is pretty easy to understand.

Getting stiffer valve springs not so much at the open part but when the valve is closing will shut the valve quicker and will not let it bounce.
Imagine dropping a rubber ball from a few feet up in the air it bounces a few times before it comes to a stop due to gravity pull, in engine case it is the boost pressure pushing on the bottom of the valve that is acting as gravity.

Hope that helps,



Best time:"""11.946""" @ 114.73 mph @17psi 1.83--60"
11 second daily driver!!!!
Race Related 727-561-9440
Shop of choice for your 11 second J body!

Also, built bottom end and or top end LSJ and L61's available.
13's ----12's ----11's ----10's

at the same time though you can't just go out and get the stifffest springs you can find, stiffer springs rob HP as well, if it take X amount of force to open the valve with sock springs and you go with springs twice as stiff the engine uses up twice as much enegery to open that valve.... think of it liek how the super charger robs power by having to make it spin, same concept you go higher it takes more power just to run. The hard part is finding the nice median

Well of course. lol



Best time:"""11.946""" @ 114.73 mph @17psi 1.83--60"
11 second daily driver!!!!
Race Related 727-561-9440
Shop of choice for your 11 second J body!

Also, built bottom end and or top end LSJ and L61's available.
13's ----12's ----11's ----10's

i know you know that, others might not

SunCavi_L61T3/T04E wrote:Getting stiffer valve springs not so much at the open part but when the valve is closing will shut the valve quicker and will not let it bounce.

ding.

Darkstars wrote:at the same time though you can't just go out and get the stifffest springs you can find, stiffer springs rob HP as well, if it take X amount of force to open the valve with sock springs and you go with springs twice as stiff the engine uses up twice as much enegery to open that valve.... think of it liek how the super charger robs power by having to make it spin, same concept you go higher it takes more power just to run. The hard part is finding the nice median

True, but more power will be lost through valve float than through increased spring pressures (assuming they're reasonable of course). You DOHC guys don't have to worry about this problem much because you don't have as much post-cam inertia as the OHVs (most being due to pushrod flex).



fortune cookie say:
better a delay than a disaster.