I posted this here because I would like a higher understanding so I can purchase the right vavle train components THIS time If its not advanced to you guys please move!

I hear alot about "binding" and "seat pressures", "valve float" and while I can fathom idea's on the subject I don't really understand.

From a personal standpoint I have a hot cam kit that in the higher r's just ain't doing it, especially in third I was reading in hot rodding that that could be an issue with "valve float" In third it feels like the brakes getting applied at around 4500K. I am adding a 100 shot right now and afraid this will applify the problem! My times are the same when I shift at 5700 and 6300??

So I just want some understanding before I spend 300 on spring another 200 on vavles and 250 on a rev kit

Thanks a bunch just trying to get the most out of my motor

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93 Purple grey TA, WS6 chrome rims, Firehawk hood, hypercoil spring, kyb AGX's. Hotcam fully ported heads, mac headers etc..., 3200 viglante, rebuilt tranny all the good stuff! 12.69 @105.88, 1.74 60ft with Nitto's

 

Hey Bobby!

Well, I'll give it whirl since nobody else will.

Coil bind: Usually occurs when the lift of the cam/rocker ratio exceeds the amount of lift that the springs can handle. It can also occur from valve float (see below). Evidence can be seen by inspecting the springs and usually is indicated by a wear pattern on the spring coils where the contact occurs.

Seat pressure: This is the amount of pressure the spring places on the seat of the valve at installed height. Usually a seat pressure of 110-130 is good for a hotcam. The higher of these seat pressures will also keep the valve from bouncing on the seat with the upper rpms.

Valve float: This is where the springs can no longer controll the valve action, and the weight of the valvetrain combined with high rpms, makes the lifter lose contact with the lobe of the cam. When the lifter reaches the top part of the ramp, it wants to continue upwards like a jump, and then slams down after the peak of the lobe. Depending how bad it is, valve float can occur at fairly low rpms (like 4000 or less).

Anyone else care to elaborate on these?

Also, since you have the original hotcam springs that came with the kit, I seriously doubt this is your problem. I would wait and see what the tranny does after the rebuild because IMHO, I would tend to think that may have been the problem all along. When a tranny burns up in 4000mi., it probably wasn't locking up or getting full line pressure. This would cause slipping etc. which would feel very strangley (like what you described). I would get a full detail of what they find after the shop tears into that tranny. My guess is they find the 2nd and 3rd gear clutch pack to be burned.

But, that's just my .02 worth.

You looking at some LT4 heads now?

Mike



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97 Z28 Black 6sp
N/A w/stock short block 12.39@114mph
In The Works:
Stroker w/ S-trim & Aftercooler
Parts Accumulated:
Oliver Billet Rods, Wiseco -20cc Pistons, (I need a forged crank)

 

The guy never got back to me, but if I get them they are going strait to your house

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93 Purple grey TA, WS6 chrome rims, Firehawk hood, hypercoil spring, kyb AGX's. Hotcam fully ported heads, mac headers etc..., 3200 viglante, rebuilt tranny all the good stuff! 12.69 @105.88, 1.74 60ft with Nitto's

 

Out of all the valvetrain problems people have probably the most common problem is weak springs. Since your springs are new we can rule out that problem but even springs 1 year old can be worn out if on a true race cam which you don't have.

The next common problem is coil bind. As stated above, it's when the cam lift combined with the rocker ratio exceeds the maximum compression of the spring.

Each valve spring has a specific spring rate and seat pressure at installed height. You can't just swap a set of factory springs with an aftermarket set without knowing the installed height. Most SBC springs are installed at 1.700". Factory spring seat pressure is around 80# at the installed height. Installing an aftermarket spring advertised as 120# at 1.800" will have 2 affects. First it will have more seat pressure than 120# since the installed height will be 1.700 if the spring seats haven't been cut down. Two, the spring will have coil bind since they're being installed .100" less than the recommended height. The amount of lift that a spring can handle is calculated by taking the installed height minus the coil bind height (given by spring manufacturer) minus .050 for clearance between the springs.

Stock SBC replacement spring. 80#@1.700. Coil bind is 1.150". This means a factory spring can only handle .500" lift. Add to that, people using 1.6 rockers to get more lift without changing springs and it's possible to get coil bind even quicker.

The valve spring is always trying to close the valve. When the coil reaches bind the valve can't open without being forced which can distort or break the spring.

Valve float isn't at the peak of the cam lift but at the end of the duration. Since the spring is constantly trying to keep the valve closed a weak spring won't do it. When the valve comes down off the ramp near the bottom is when the spring pressure is at it's weakest. This is where the valve will bounce. This bouncing allows cylinder pressures to escape and will reduce power built by the engine. It's most noticable at high rpm and will feel like the engine has hit a wall and refuse to rev any higher.

Before you buy any parts, consult with a machine shop to have the heads properly setup. Getting better springs usually means having to get the spring pockets enlarged. Swapping parts in your own garage is only good if the parts you are swapping are the same as the ones you're taking off.

I'm getting head work done right now. I bought a set of assembled Merlin heads for my BBC last fall. The salesman said they will have no problems with the cam I'm using but I got a spec sheet after dropping 2 valves this weekend. Maximum lift for the springs was .570" and my cam has .593". The heads are now being redone with proper springs and are being modified so a cam with .637" lift can be installed at a later date. I was feeling valve float at 6800 rpm.

I dropped my valves at the bracket finals in Yakima last weekend. Dropped one on Saturday afternoon and got it fixed by the evening. Sunday morning I dropped another one. The engine still ran and I was able to stage for 2 more rounds. The first round I won against a red light and I didn't even have to go down the track. . The last round my opponent didn't red light or break out while I sat on the starting line.

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Stephen's racing page
or check out the race car

87 IROC SuperPro race car
461 big block
Best ET on a time slip: 11.099
Best MPH on a time slip: 119.7
Best corrected ET: 10.983

Altitude corrected rear wheel HP: 480
Best 60 foot: 1.546
Member of the Calgary Drag Racing Association

[This message has been edited by Stephen 87 IROC (edited September 11, 2002).]

 

Thanks for the help both of you I think my think head is starting to get it Bolt ons were so much easier

Stephen that car is a Monster I love it sometime I wish I would have kept the 84 Z I had a while back it would be something now

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93 Purple grey TA, WS6 chrome rims, Firehawk hood, hypercoil spring, kyb AGX's. Hotcam fully ported heads, mac headers etc..., 3200 viglante, rebuilt tranny all the good stuff! 12.69 @105.88, 1.74 60ft with Nitto's

 

Cautionary tale: always check for coil bind when installing new valvetrain parts. Don't rely on specs or on someone's assurances!

Rich Krause

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'95 Z-28 383: Vortech, nitrous, etc.
AIM: rstevenkrause