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Old 12-14-2006, 06:14 AM   #21
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Synlube I think had an article on cam load and the effects of better lubrication on the cam with their lubricants - they got into power needed to open valves etc. and load on the timing chain/belt and the effects of wear reduction. Also the rate of cam lift on the closing side determines the spring rate as well as the valve train mass needed to be moved by the spring. If you lighten the valves and springs and retainers you can use a lighter spring without any problems and I am sure there is plenty of margin in the spring pressure for less than peak rpm operation. Isn't red line the max continuous operating speed??
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Old 12-14-2006, 06:19 AM   #22
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Originally Posted by JanGeo
Isn't red line the max continuous operating speed??
The red line is the maximum recommended operating speed.
The continious operating speed (under full load) is considerably less.
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Old 12-14-2006, 09:47 AM   #23
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Ok, here is my perspective on using weaker valve spring's to try to improve gas mileage. I wouldn't do it.

The problem's I have with using weaker valve spring's is that the spring's primary job is to close the valve's, quickly and firmly. In closing quickly and firmly, it allows the valve to sit against the seat more solidly. The amount of time the valve is closed and how solidly it is seated is a factor in how much time and how well the valve is able to be cooled by the valve seat, in the head of the engine. If the valve is unable to be kept cool, by the valve seat, the head, the cooling system and the valve spring pressure, then the valve will develop hot spots, warp, burn, split and all sort's of nasty thing's.

I can disassemble and rebuild the head on car's. However, I don't like doing it and IMO putting weaker valve spring's on a car is just inviting a significant overhaul problem for a unmeasurably small amount of possible fuel saving's.

The risk just isn't worth the reward, for me.
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Old 12-14-2006, 10:26 AM   #24
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One of my initial assumptions is that the valve springs are over-engineered, so there must be some margin for reducing their strength before you compromise durability or performance of the valvetrain.

Also, I was only considering this on a car that rarely (if ever) sees 50% of its maximum RPM.

But I don't pretend to know what that margin is.

And I also agree the savings would likely be small, but that's OK.

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Old 12-14-2006, 11:48 AM   #25
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Quote:
Originally Posted by Gary Palmer
The problem's I have with using weaker valve spring's is that the spring's primary job is to close the valve's, quickly and firmly. In closing quickly and firmly, it allows the valve to sit against the seat more solidly. The amount of time the valve is closed and how solidly it is seated is a factor in how much time and how well the valve is able to be cooled by the valve seat, in the head of the engine. If the valve is unable to be kept cool, by the valve seat, the head, the cooling system and the valve spring pressure, then the valve will develop hot spots, warp, burn, split and all sort's of nasty thing's.
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Hi GP

?In closing quickly and firmly, it allows the valve to sit against the seat more solidly?
The speed that the valve returns is controlled by the profile of the cam lobe and not the springs pressure.

?The amount of time the valve is closed and how solidly it is seated is a factor in how much time and how well the valve is able to be cooled by the valve seat, in the head of the engine. ?
This again is controlled by the duration of the cam , and note that in milder tuned engines the valve is seated for a longer time than in high performance engines.
This is purely cam geometry.

?If the valve is unable to be kept cool, by the valve seat, the head, the cooling system and the valve spring pressure, then the valve will develop hot spots, warp, burn, split and all sort's of nasty thing's.?
Split head or burnt valves are caused by excessively lean conditions and rarely from a lack of spring pressure.

Intake valves are cooled by the incoming charge ,so they rarely burn.
Exhaust valves dont get much cooling during overlap so they rely on transmitting the heat to the valve seat (75%) and to the valve guide (25%) for cooling.

Exhaust valves (or just the valve head) are made from tougher alloys to handle the extreme heats.

The reduction of spring pressure that is being talked about isn't a reduction to almost nothing.
A seat pressure of 40 pounds would still work very well in a low RPM engine application.

gregW:-)


PS.. ford 351W V8 engines had a spring presure of 60 - 65 pounds.
A high performance cam for the same engine would have 120 pounds.
This almost double the pressure is required for the extra 1 or 2 thousand rpm redline.
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Old 12-14-2006, 03:50 PM   #26
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Quote:
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Got any favorite brand(s) of epoxy?
ive read that jb weld works just fine in the intake ports.
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Old 12-14-2006, 07:18 PM   #27
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When I and my Taurus I looked into valve float because it was an interference engine. And found out that valve float occurred at 6600rpm sending multiples of valves into the cylinder as the piston is coming up to meet them. If i remember correctly(didn't read any of the links ill do that tommorrow) having softer springs on your valves would be bad. Because from what I understand if your reach the max rpm or get close to it your going to reach a point where both valves are open at the same time causing a decrease in mpg. What would happen in a non-interference engine when you reach valve float. Would the valve shoot upward instead of into the cylinder or would the spring collapse and seal closed that inlet/outlet valve?
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Old 12-14-2006, 10:07 PM   #28
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Quote:
Originally Posted by MetroMPG
One of my initial assumptions is that the valve springs are over-engineered, so there must be some margin for reducing their strength before you compromise durability or performance of the valvetrain.
I think you're onto something, although every car is different. I'm not sure how you'd test the safety margin on your motor.

I had the chance to test the safety margin built into my motor a couple of times. I did it by accidentally mis shifting. I was racing at the track and hit my shift point of 6800rpm in 3rd gear, then quickly shifted to 4th. At least I thought it was 4th, somehow I got 2nd gear instead! Ouch! My tach showed a peak of around 9300 rpm! :O And redline is 7000rpm. There was no catastrophic failure. I'm still driving it today. I don't recomend testing your motor this way. HTH!
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Old 12-14-2006, 10:45 PM   #29
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Quote:
Originally Posted by Rstb88
And found out that valve float occurred at 6600rpm sending multiples of valves into the cylinder as the piston is coming up to meet them.
SNIP
Because from what I understand if your reach the max rpm or get close to it your going to reach a point where both valves are open at the same time causing a decrease in mpg. What would happen in a non-interference engine when you reach valve float. Would the valve shoot upward instead of into the cylinder or would the spring collapse and seal closed that inlet/outlet valve?
Hi Rstb88

In a conventional sprung poppet valve system there will always be at some high REV a point reached where the valve will not follow the cam lobes profile and the valve will float.
Manufacturers will choose a spring stiffness which they think will return the valve correctly up to the maximum expected RPM of the engine.
Excessively low spring rates will limit high rpm use and on the other hand an excessively high spring rate will reduce power and cause valve and valve train failures and excessive wear.
So they guess a happy medium.

Normally valve float will be noticed by a marked drop in power ,,,or a wall like RPM barrier limiting higher RPM's.

Only in very extreme over revving cases would the valve head be still low enough to get slapped silly by the upcoming piston.(a dropped valve)

Softer valve springs would only be recomended with a cam profile that did not encourage higher RPM's
A cam choice with maximum power at around 4,000 , and maximum torque at 2,000 would probably work well for FE.

This would put the point of valve float above the usable RPM range so it is of no concern.

gregW:-)

PS.. especially on 6's and 8's valve train losses are not as bad as expected because as one valve is opening another one is shutting.
The compressed energy in 1 spring is being released helping another one to open.
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Old 12-15-2006, 06:18 AM   #30
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Quote:
Originally Posted by onegammyleg
PS.. especially on 6's and 8's valve train losses are not as bad as expected because as one valve is opening another one is shutting.
The compressed energy in 1 spring is being released helping another one to open.
Which suggests my antiquated 3-cyl 6-valve Metro motor might benefit the most (relative to engines with more cylinders) from matching valve spring strength to low RPM engine use.
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