631 WHP/ 554 ft/ib WTQ, GT35R stroker!
Originally Posted by scorke
....The time that it takes for the valve to go back to the seated position is determined by the lift of the cam, the ramp rate of the cam and the pressure/force exerted by the spring
Scorke
Scorke
valve float is when the cam is moving so fast, that it (and or the follower) will seperate from the valve retainer because the valve spring cannot move fast enough to follow the down ramp of the cam profile. it is called floating because essentially the valve is opened all the way due to the cam physically pushing it open all the way, but when closing the cam moves faster then the valve spring, so the valve doesn't have time to close before the open slope of the cam hits it again. ireally wish i could have a cool little flash diagram but alas i have no programming or drawing skills 
Everyone is speaking the truth on what is valve float but the issue at hand is what the OP is suggesting. He is suggesting that he is experiencing valve float at idle (after a drag run and after a high RPM session)
This to me doesn't make sense and without actually being able to hear the car or see the situation I certainly couldn't diagnose it over the intArweb.
This to me doesn't make sense and without actually being able to hear the car or see the situation I certainly couldn't diagnose it over the intArweb.
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Originally Posted by KevinD
it has everything to do with time. if you use a soft valve spring, it is weak, doesn't make enough force to counter the inertia of the valve and will take considerable longer to return the valve to its seat. if you revv the engine slowly, it will be able to return it. as you revv the engine faster, that valve spring doesn't have the force ( f = m*a where the m is the valve mass, and the f is the spring force)to achieve the high accelerations to return the spring in a reduced cycle time due to the higher revvs.
if you use a stiff spring, it will have the force to change the direction of the valve much quicker, thus returning it to the seat in considerably less time.
if you use a stiff spring, it will have the force to change the direction of the valve much quicker, thus returning it to the seat in considerably less time.
ON this particular engine, the same thing happens with the HKS springs but it only happens on boost above 32 psi and nothing below that. DYno runs over and over have confirmed that. Misfires and power drops off. I can post a graph of that particular run when it happens. Definitely not from improper installation as both cars have shown the same problem.
What could it be?
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Originally Posted by Ted B
The chart looks a bit strange because due to the difference between the hp and torque scaling, the two curves cross just past 6000rpm as opposed to 5252.
The drop in the torque curve represents the limits of mechanical efficiency at that point, and there are several ways to address this if so desired. If big midrange torque is desired (and this motor definitely has it), it appears to be largely a non-issue.
The drop in the torque curve represents the limits of mechanical efficiency at that point, and there are several ways to address this if so desired. If big midrange torque is desired (and this motor definitely has it), it appears to be largely a non-issue.
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I believed so and still do that valve float usually occurs at extremely high rpm and the drag Evo 3 we have explains so happening at 9000 rpm but symptoms are similar and seems to be boost related. You just don't get it at lower boost levels but replacing valve springs does help. With the HKS its impossible to even run at 35 psi. With these Supertechs, everything seems ok and as I mentioned before, it happened just that once on the dyn earlier. Will post the graph up as soon as possible.
what ecu are you running? and what ignition system are you running? although i have never personally experienced it (partly because i'm only mildly modded) many people running high boost blow out the spark thus no ignition. high powered ignition systems always seem to cure the problem from what i have read over and over.
do you have any means of logging the knock? basically if you can give a run down of the electronics you are using we can at least narrow the problem down be it electronics or not.
MAF, or MAP for your fuel tables? if MAP, what sensor?
do you have any means of logging the knock? basically if you can give a run down of the electronics you are using we can at least narrow the problem down be it electronics or not.
MAF, or MAP for your fuel tables? if MAP, what sensor?
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We're running an Autronic Pnp ecu with a Map sensor at the throttle body. THe problem is definitely not spark cause its not like a miss and you go on when you nail it. The car idles irractically after that for a little while. Ignition system is currently limited to Nology wire conversion kit still utilizing the standard coils with plugs gapped down to 24 thou.
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Latest update guys, we retuned the car using VP Import and also played around more with the cam timing and were able to run more ignition timing but at a lower boost levels. Car belted out 670 WHP but a lower 545 ft/ib of torque!! Amazing.
Have even managed to take out that dip at the 6500 rpm point. The car is a blast to drive now and am gonna take it down to the tracks tonight at a sanctaioned drag event. Looking to run a low 10 sec pass in it!!
Ang Weng Yan will help me post this new graph up today and by Monday results from the track!!
Have even managed to take out that dip at the 6500 rpm point. The car is a blast to drive now and am gonna take it down to the tracks tonight at a sanctaioned drag event. Looking to run a low 10 sec pass in it!!
Ang Weng Yan will help me post this new graph up today and by Monday results from the track!!
^Is anyone else sportin a chubby from that graph???????? If only tq and hp crossed at 5252 and the tq was where it should be it would probably be less impressive, but man, a car whose tq is above 400 ft lbs from 4k to 8k mmmmmmmmmmm.
Scorke
Scorke
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Sorry guys, there must be something that went wrong with the conversion from sae to std, will re post it in sae format again later... rather impossible to make 780 ft/ib of torque!!
Originally Posted by GTREVO
Sorry guys, there must be something that went wrong with the conversion from sae to std, will re post it in sae format again later... rather impossible to make 780 ft/ib of torque!!
Very nice numbers man, keep working at it!
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Thats right, I failed to pick that up... so the torque is right after all. Anybody here knows whether I can just run a shorter belt if I decided to take out the ac compressor from the block? Am gonna drop the ac system and whatever I can for the next race...
