What is this sound ?
At the top of the rev range, just on gearchange I am hearing this noise.
I have just put in a new tune, with a shift in change points and rev limiter.
i thought at first that it might be touching the rev limiter, but I have become suspicious that what I am hearing is valve bounce...
I would like peoples opinions.....
Cheers...
http://users.tpg.com.au/ashnak68/memo.m4a
Dosent play.. i think im missing codec for it can you maybe put it up as .wav or .mp3?
Can't - it's proprietary quicktime from my iphone.Originally Posted by cds
bump - Will play on any quicktime player
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Yeah, that doesn't sound like hitting rev limiter.
I'd say value float... new springs should cure it....
If it is valve bounce.... Ive changed valve springs with the heads off, can it be done without much risk with the heads on ?
COncerned about droppoing a valve into a pot of course.
Exhaust Guru
It can be done. There are a couple of ways to do it. One is to get an attachment that screws into the spark plug hole with an air valve on it. You pump compressed air into the cylinder to hold the valves closed. Another way is to feed a piece of rope in through the spark plug hole and this will hold the valve up.
See how you go with the other tune, the shifts are a little lower then you will know if it's the limiter or not. I can't get the file so I dunno. But I wouldn't be at all suprised since you have those big ratio rockers. I've allways thought they had no chance of hanging on at any kind of decent rpm on the standard springs. I used rope fed into the bore to change mine, takes a while but works well
Edit: Heard a VT on the limiter on youtube, it's not that even thos the limiter will be faster, I don't think THAT fast. Sure doesn't sound like pinging either so it's got me beat, doesn't leave many options
Last edited by greenfoam; 28-11-2009 at 07:57 PM.
dah dut dut da dah
to change valve spring/collet place cylinder at top dead centre.
remove sparkplug and compresse with air and change collet/spring.
the compressed air will hold the valve up quiet easly while you do the work.
Research has shown that men usually sleep on the right side of the bed.
Even in our sleep we happen to be right.
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I was half asleep half awake before on the sofa, then I fell asleep but importantly. Before I fell asleep I had a moment of clear thinking.
I decided this is a big sound and that it might be the lifters leaving the cam and then landing again, then I thought why would they do this....... But thinking about it. These rockers have the pushrod hole moved toward the centre, this must reduce the spring pressure on the back side of the cam lobe as the valves are closing by whatever amount the ratio has changed so you could/will end up with 20% less pressure holding the lifters onto the cam so you are going to need 20% more pressure and by then you will probably have used up the extra kw from the high ratio resulting in a zero gain. I figure it must be slightly unstable at least 500 revs before you hear this so it it's probably costing power before they loose the plot even if you can't hear it.
Anyway that's all I noted during my half sleep :0, Rich's car is shifting at right near 6000 also but with the stock rockers and has no issue. I could almost convince myself this is the reason so many high powered ecotecs break lifters
Hey Foamy.
You could be right, i am not convinced though. At rest, where the spring pressure is least, the difference in pivot point travel will tiny. The pushrod is the same length as factory, the pushrod angle is slightly greater, but seat pressures should be similair.
It certainly wouldn't have any effect when the valve is open.
Either way, I don't see any value in really revving it that hard, unless theres head work to back it up so a reduced rev limit is the way to go.
I remember my old boss has a Cobra that he races with a mild cam and high ratio rockers, that thing had sooooooo many problems with valve bounce over 5000 rpm that in the end he just ended up not reving it over 5000. Once taking it just to a mild 5500 rpm it actually cliped 3 valves onto the pistons bending the valve heads and the pushrods. Which I thought was a bit rubbish when it should have been still singing fine at well over 6000. Back then we never could realise why the springs wouldn't be stable, we even tried a much stronger spring but that did pretty much nothing (only added a couple hundred rpm). The rockers were allways the suspect but we never did try stockers (should have).
But anyway, you tell me where the shifts want to go and that's where they will be on anyones car with rockers just to be sure
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