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 johny rotten
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| posted on May 19th, 2004 at 10:34 PM |
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seat pressure
whats the norm with valve spring pressures on a bug engine with wild cam / webers etc ??
is 50kg seat pressure a reasonable figure ?
rev range o- 7000rpm
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Cam
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| posted on May 19th, 2004 at 10:55 PM |
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Damn dude, thats a good question 
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AdrianH
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| posted on May 22nd, 2004 at 10:39 AM |
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Running dual bugpack 4046 springs I set the springs up at 1.56" installed height, the seat pressure was 195lbs, at full opening (.555" lift) I got
320 over the nose. I could have shimmed them up a bit tighter, but that is working fine, no problems with valve float (7000 rpm, 86B cam, 1.45:1 ratio
rockers).
If you use a really severe cam, changing valve springs becomes regular maintenance !!!
You need to look at the pressure over the range of the spring movement, different cam profiles will require more or less pressure to keep the follower
on the cam !!!
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tassupervee
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| posted on May 24th, 2004 at 10:57 PM |
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Fug me 195 seat pressure!!!!!
I set the seat pressure on the F-Vee to 65 Lb LOL
Good for about 6400rpm with stock springs!!
L8tr
E
[Edited on 24/5/04 by tassupervee]
Im not a complete idiot, quite a few parts are missing....
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AdrianH
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| posted on May 25th, 2004 at 06:10 PM |
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I have heard some single spring stories !!!
Out of interest, what sort of numbers are you running lift, duration wise ?? What sort of pressure do you get at full lift ?, and last but not least
what sort of life do you get out of them ??
The springs I am running are fairly standard for a set of duals, the bugpacks use a slightly smaller gauge wire to allow a bit more lift, I could go
to .600" lift without bind problems... Fairly normal setup for a 42mm valve with 8mm stem in my experience.
Your results may vary...
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johny rotten
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| posted on May 25th, 2004 at 06:54 PM |
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thanks looks like i might need different springs.
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tassupervee
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| posted on May 25th, 2004 at 08:27 PM |
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Heheheh
The cam is a bog stock 1200 40HP item which is a pretty soft item which allows us to get away with using stock springs and light seat pressures.
The issue against using higher seat pressure springs is more to do with power loss than controlling bounce.
The springs I am using in my old vee motor had been installed in that motor since at leas 1983!
The car was parked at the seasons end 1986 and the car did not turn a wheel untill 2002. We ran that engine happily to 5200 untouched. I ended up
freshening those heads and reused those springs with a bit of shimming at about 68 Lb and that engine is still running happily above 6000 rpm!
We dont make a habit of revving them a lot over 5500 rpm as the heads are pretty restrictive up there bit they still happily rev up there with no ill
effects.
I cant tell you the full lift pressure as I to be honest I have never bothered to check it.....
L8tr M8
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Im not a complete idiot, quite a few parts are missing....
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AdrianH
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| posted on May 26th, 2004 at 08:48 AM |
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Heres some more valve train info... from a guy in the US who builds prostock engines --- I guess he knows what he is talking about.
Another excuse I've heard for not using stiff valve springs is that they take more horsepower to compress. My reply is that each spring stores
energy, and for every valve that is opening another one is closing. Anyone who has been whacked by a torque wrench while turning a crankshaft can
testify that the valve springs exert considerable force on the closing ramps!
I have never installed stiffer valve springs on an engine and lost power; the improvement in valvetrain dynamics more than offsets whatever
additional power is required to overcome the springs' resistance.
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tassupervee
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| posted on May 26th, 2004 at 06:19 PM |
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That may well be the case dude but, there are a legion of F-Vee engine builders right round the world, some of whom do know and some that may not
know, but who will all disagree with you and this other prostock guy.
Given that the heavy spring pressure required to keep valve operation under control is largely overided by the inertia of the valve itself and valve
float is never very far away so the theory begins to fill with holes when at high rpm there is very little spring pressure actually being exerted on
the lifter/cam face on the closing ramp of the cam.
At low revs, or not running at all, both of which are largely irrelevent in a competition engine, the heavy springs shoving down on the cam may be
so.
F-Vee engines are not rocket science like really hi-po, hi-rev engines the likes of a pro-stocker and another factor that needs to be looked at is the
added friction that heavy springs encourage from a plain lifter face working on a plain cam face.
May not be much of a drama with a million rpm pro-stock engine more than likely using roller rockers but it must be an issue, and a relevant one, if
every F-Vee engine tuner round the world specifies much the same seat pressure and all state much the same reasons.
There you go. Worth pondering.
L8tr
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Im not a complete idiot, quite a few parts are missing....
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AdrianH
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| posted on May 27th, 2004 at 07:11 AM |
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http://www.rehermorrison.com/techTalk/03.htm
Lifting .900" may have something to do with it !!! Definitely drag race driven, Ive never had anything to do with roundy roundy cars, its all been
straight line based.
I guess theres more than one way to skin a cat :-) Horses for courses, and other sayings !!
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tassupervee
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| posted on May 27th, 2004 at 04:53 PM |
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Beejeezuss thats a shitload of lift!
Rocker geometry must be rather interesting.
L8tr dude
E
Im not a complete idiot, quite a few parts are missing....
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