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Thread: Disabling VVL at rev limit?

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Posts: 11-18 of 18
2009-07-25 17:24:23
#11
I know a few of the guys in P.R have been doing this for a few years now. I've never heard anything bad happen from this, maybe Payu can chime in.
2009-07-25 17:34:25
#12
Originally Posted by Jrios
I know a few of the guys in P.R have been doing this for a few years now. I've never heard anything bad happen from this, maybe Payu can chime in.


If you have over revved on the high cam then why would you want to go to a smaller lobe which to cause even more over rev issues. All I see is complete annihilation of your valvetrain/pistons.
2009-07-25 23:36:34
#13
Originally Posted by SE-L
Do we know this for sure as in someone has done this?
Yes yes.......... I completely agree ..... PSSSSST ....Last edited- post number 7 guys!!!!!!!
2009-07-27 02:18:30
#14
Originally Posted by totaled200ser
The best thing to do is become better at shifting.


Well duh there's always the possibility of human error, and if this could be a way to reduce the likelihood of a piston-valve bust-up then why not?

Originally Posted by se-riousclassic
If you have over revved on the high cam then why would you want to go to a smaller lobe which to cause even more over rev issues. All I see is complete annihilation of your valvetrain/pistons.


I'm not following your logic here - so lower lift & duration = more valve travel? care to elaborate?
2009-07-27 05:16:03
#15
Honestly since your doing this as a fail safe I do not see a problem with it. I do hope if you do miss a shift, that you decide to just dump the run instead of adding continuous throttle. The way you make this sound is as if you mis shifts on a regular basis(which I don't know why we are not driving hondas). I mean this process is the equivilent of taking a spring and droping it from a certain height. There is always recoil once it hits the floor. This recoil might just make one of the valve shims fly out and cause serious damage.
2009-07-27 05:20:54
#16
No, it's not a common thing... I did it once and it made me think about the consequences. If it'd been a DET I'd have probably thrown a rocker. Nor did (or would) I keep my foot up it...
2009-07-27 16:43:38
#17
Valve float is all about the harmonics created by the cam lobe as it rotates at x rpm and accels from x rpm to x rpm. the cam lobes create a lot of different harmonics and resonance while it is rotating and opening and closing the valves. There is a lot that goes into designing a cam profile and valve springs. I actually just did a header/ exhaust install on satarday for a customer and he went to the dyno right after and blew his motor. he had some aftermarket cams, valves, springs, everything rated at 10,500rpms... he was only reving to 8600-8800rpms. on the last run he thought he heard some detonation so he clutched in at about 7000rpms and the motor rev'd very fast ( still under load because he depressed the clutch right before letting off the throttle) datalogging only recorded 9100rpms and he bent all the valves in his motor and broke the valve heads off and destroyed the entire bottom end as well.. classic example of honda guys being cheap and running a large mix of parts and having no idea what is compatible.

A lot of valve spring resonance and surge has to do with the valve opening and closing rate. also known as valve velocity. Take for example N1 cams. nissan rates these at 288* 12.0mm lift and the std sr20ve cams 264* 10.7mm lift. this is nissans rated numbers at .016" lift. If you degree these cams in or run them in a cam doctor you will see that the N1's do have more lift but the valve opens much slower than the 20ve cams. these cams create different harmonics and because of this N1 cams are safe on stock valve springs to well over 8000rpm and sr20ve cams will usually bend valves and or start to float by 8000rpms.

the same thing goes for the small lobes. Generally most manufacturers of VVL cams will use a shorter duration and more lift profile to open and close the valve faster at lower RPMs to achieve a higher cylinder fill. Open the intake valve right around the end of the exhaust valve closing for low overlap, pop that valve open fast and close it fast right after TDC so you do not get any fresh air/fuel charge reversion back up the intake port.
These cam profiles are taken into account when the valve springs are designed but they are not planning on the small lobes being active with the motor @ redline.

When you rev your motor to 8000rpm on the large lobes and let off the throttle, the large lobes are still active. Even honda keeps the large lobes active at all throttle and MAP positions above X RPMs because of several reasons including valvetrain harmonics on the small vs big lobes.
2009-07-28 10:37:21
#18
Thanks for your input Charles. So for anyone with a VE, make sure your VVL switch wiring doesn't crap out otherwise things could get expensive...
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