has anyone looked into how much boost you can run before the valve starts to open with the piper uprated valve spring in place?
im getting some springs made up with less coils, so you can get more valve lift than 10.8mm and have told them to use the piper spring as a guide.
maybe piper might know.you colud give them ring and ask
Mark, do you mean to say it's possible for boost pressure in the inlet manifold/head to open valves not being actuated by a cam lobe if it's more than the spring rating?Originally Posted by Sparkie
maybe piper might know.you colud give them ring and ask
i did yesterday. they buy their springs in.... i did send an email to their technical section, but didnt get a rely. I'd imagine they dont know.
trev- thats exactly what im saying. you need to work out the area on the back of the valve and see what psi is exerted on it.
Well I never. Has anyone had issues with this to your knowledge then, or is it a suspicion based on some forethought concerning what you're planning to do with the springs to get the extra lift?
am i correct in saying that no matter what valve springs you use
an what set up you have,the springs are never supposed to be
coil bound?,or is that not entirely true?
trev - yes, a guy who drag races at work mentioned it.... i can see that in theory it is possible...
J$£5GTT - the springs should not even come near getting coil bound...ever.
Let us know what you discover.
I wonder if 'valve creep' (for want of a better word) unbeknowingly affects members on here who run high boost levels with standard springs.
That is the idea, however if the cam is high lift, then it can cause a coil bound situation on standard valves. on my recent flow bench tests, the standard valves were going coil bound at 8.4mm(i believe)
the standard valves can cope with the lift the piper cam(lifts to 10.8mm?? sorry theyre all off the top of my head lol)
you would want to use the lightest springs possible to cut down on power loss through friction.
i think what you really need to look at is how much boost and what cam....
im gonna go for the suck it and see approach
you say lightest springs,titanium?That is the idea, however if the cam is high lift, then it can cause a coil bound situation on standard valves. on my recent flow bench tests, the standard valves were going coil bound at 8.4mm(i believe)
the standard valves can cope with the lift the piper cam(lifts to 10.8mm?? sorry theyre all off the top of my head lol)
you would want to use the lightest springs possible to cut down on power loss through friction.
i think what you really need to look at is how much boost and what cam....
people do rave about the piper an you can get cams made to your
own profile i think,saying that i am also under impression that the
standard one is still up to the job?
he means the lightest pressure springs. not the lightest material.you say lightest springs,titanium?
people do rave about the piper an you can get cams made to your
own profile i think,saying that i am also under impression that the
standard one is still up to the job?
however i did read a site that suggested that as the springs are not all under full strength compression all the time then the stronger pressure springs dont create huge frictional losses on the engine.
Infact the site suggested that you need a high spring pressure to stop the cam follower jumping off the cam once it goes over the top of the lobe and come crashing down on the other side - which as we all know wears the piper cams out nice and quick - maybe the piper springs arent strong enough!
piper will match the profile you come up with out of one of the ones for other cars they have on the shelf. - it will be close, not necessarily exact.
the standard springs will not take much of a high lift cam before it gets coil bound - or did you mean the standard cam is ok?- ok for for what? - the shopping run?
i suppose it depends how picky you want to be and how much money you have
what your saying does make sense, but when the cam is trying to open the valve, it is only overcoming the spring force that the valve spring is exherting. so the easier that process is the more 'free power' there will be.
the vtec racing boys do try and lighten they're valve train as much as possible using titanium valves and valve springs, however haveing the valve caps slamming into the cam isn't an ideal to say the least lol
i'd push the boat out and say i don't know of a single Piper Cam that hasnt suffered pitting on the lobe somewhere....
I think the problem is the stupidly narrow lobes the cam has, it's just all getting a bit marginal, in terms of loads, on lairy profiles. The Ford x-fow (basically same pushrod set-up) has got lobes probably twice the width.
This issue of inlet valves being blown open, could someone explain to me exactly why this is such a problem? There was a time when engines didn't have cams for the inlet and the engine just sucked the valve open against a light spring (called automatic valves). The whole point of tuning is to get as much air through an engine as possible, if a condition exists where the cylinder is at such a low pressure relative to the charge air that the valve is blown open then all the good, you've almost got something for nothing! The valve springs need to be of a certain minimum strength to avoid valve float and bounce. As long as they're strong enough to avoid these, then the "blowing open" just won't be an issue.
I'm sure someone can come up with a dramatic example of this not being the case, but for what we're talking about here, you'll almost certainly find, it is.
As we know, Piper push the ramps to the limit for the small diameter followers in the Cleon engine. You can see that when you look at the wear pattern on an old lobe (it necks down on the flanks). That said, it's generally the peak that wears, and maybe the original 285 lobe with less lift was kinder? I'm not sure that the C1J gains anything for that extra on top, maybe it's more of a marketing tool?.
https://www.rtoc.org/files/Technical%...85%20chart.pdf
partly that, and partly the small diameter followers.
If I started my engine again I'd be looking at machining the block to take followers off something like a chevy, maybe even rollers, and use a catalogue profile from one of the big US cam grinders - they know a bit about pushrod engines...
btw, the lobes on the Gordini cam are wider than the GTT ones.
I think that would be a good idea. Some of those big block profiles....
thats interesting,so whats the difference/dimension of a chevy follower
compared to the c1j ?
Considering that we're referring to valves not being actuated by a cam lobe, i.e. valves that are opening a small amount during periods of the combustion cycle in which they are intended to be shut; I'd say the resultant problems are self-explanatory!
my old setup suffered badly from valve bounce , and in the end i recon was the cause of the eventual destruction of that engine , to my knowledge it was running a piper 275 and standard springs , but after i sent the cam to andy cooke it turned out to be a 285which was running with standard springs .
the new setup is a bit trick with the dbl valve springs ,i dont know much on the technical side of the springs used , surprised not to see others trying this route although i cant see there really being a problem if using the 285 with the uprated springs ?
are they piper springs? - cos the cat cams ones i have have less coils in them i'm sure....
i was running double springs...but i wore the top of one of the lobes clean off the cam.
I think it's only possible on the induction stroke, hence "something for nothing".
My latest 5GTT head, done a couple or three years ago now under Big Jims supervision, has longer somewhat firmer springs in lowered seats. The standard and new springs weights and length at appropriate compression were first measured on their machine.
Specifically done for the 10.8mm cam.
So no coil binding. Lightish springs. Should stop and float or bounce.
I really don't know why everyone else is not having the same.
Hi Ian.
That's not what Sparkie seems to be saying though and if it were only possible on the induction stroke, I can't see there being a problem. That valve is being hit by a cam lobe anyway. Plus, all the air in the m/fold is destined for that cylinder, so neither do I see any advantage. Or are you saying that the valve is opening via air pressure a fraction before the cam lobe hits thus effectively increasing (cam) duration? I'm not sure that's possible either however as that cylinder will be finishing it's exhaust stroke and pusing the inlet valve shut through pressure...
What I'm more inclined to think is that the inlet valve on the cylinder that's on its combustion stroke could be being pushed open and that wont provide any benefit that I can think of, in fact it will rob some of the charge from the cylinder that's supposed to recieve it. Hence this thread... ??
does anyone know what the cylinder pressures are at all parts of the combustion cycle? - at any point when the inlet valve is shut is it less than the pressure pushing on the inlet side of the inlet valve?
Erm, combustion stroke? Think about the way an engine works. The pressure to drive the piston down ALL comes from the combustion stroke, At no point will the pressure on this part of the cycle be lower than than charge pressure. The only points were the valve may be blown open will be at the closing and opening points of the inlet valve, and this is were you can envisage some possible advantage. BUT, I'll say again, if your valve springs are light enough for this to be happening to any noticeable extent you will be getting horrible valve bounce elsewhere.
Double valve springs by themselves shouldn't be wearing out cams, unless they had been installed at the wrong fitted length or were just too high a rate, their real benefit here would be dealing with valve train harmonics.
You've misunderstood my intention. I agree entirely with what you're saying above. What I'm trying to work out is where the problem resides that Mark (or Mark's contact more pertinently), believes exists. The rest of us are pretty much all saying that we can't see how this can cause a problem and I was merely searching the waste grounds of illogic to make sure.
I'm still of the opinion that any advantage to be gained is microscopic but I'm happy to be shown otherwise.
its my contact, who used to drag race a 2.8 waterboxer VW engined Rail Car.
he is prone to exaggeration, forgetfulness and slight bending of truth.
Now you tell us
Lol. And we're
well, when he told me, i nodded and said yes, and i could partially work out in my tired brain see what he was trying to say.... however - after further thought and this thread it seems to make less sense.
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