I'm using a Comp 292H hydraulic flat tappet cam, with Scorpion Racing 1.6 ratio rockers. I plan to shift around 6100 RPM (5800 RPM peak HP).

Am I asking for any trouble with the 972-16 spring? Some say I'm good.
Some say I'm going to float the valve.

The 972 has about 10# more pressure across the board compared to the
recommended 986 spring. I figured the 972 would account for the 1.6 rocker.

Seat pressure is 125 lbs @ 1.8"
Open pressure is about 280 lbs @ 1.266"

Coil Bind is 1.195"
Spring Rate is 328 lbs./in.

World Products Sportsman II heads with their valves (not sure of valve weight).

Aside from that, when does valve float become a problem? When the valve
comes crashing down on the seat and bounces?

If the valve came down in a controlled manner, would it not HELP to float
the valve (increase effective duration)?

Is there any danger of piston to valve contact in a float situation,
or will this happen during the overlap period if the bounces?

If yes, then seat pressure would be more important than open pressure?

 

Yeap what you are asking about is lofting the valve... Comp has some cams that are called the Launcher Series... Problem with them is that they are very hard on parts. Every part in the system is important as well, the pushrods act like a pole vaulters pole to help the lifter loft over the nose, team that with the right spring and cam and the thing goes for a wild ride.

I'm not a huge fan of this in anything that has to live for a long time.

For spring recomendations... I would look at a 26915 for a flat tappet setup. You can drop the seated pressure even more and over the nose pressure, loose some deflection in the system and control the valve better.

Float becomes a problem when the valve bounces off the seat and allows the lifter to pump up and the DCR to lower... basically nothing good comes from excess valve bounce.

Bret

 

Sounds like ya are light on the springs. shoot for about 140-150 seat and 300-325 nose before break in.(they will loose about 20/25lbs after a few heat cycles) If ya can't find any in your installed height consider .050 up retainers or keepers or both.You must have gone up already at 1.800 and ya might have to go higher and with a double spring(good for safety)Don't be affraid to put enough spring pressure to control the valve,ya give up more HP with weak springs than ya ever will with stiff ones(within reason of course)

 

Valve float won't be a problem with round lobes. 150# on the seat on a street cam?

A good set of flat tappet springs won't lose 15% of their load after being run. The key to long spring life is to let them warm up before revving the hell out of it. Second guessing the cam makers reccomendation doesn't always work out the way you would expect. Comp will whisper to you that they already over spring their cams. The 986-16 is a dual spring and presumably is engineered for better high rpm/harmonic control. Besides your flat tappet will have a warranty with the reccommended spring.

Over the nose pressure, or more importantly closing valve control is the important part. If you control the closing motion of the valve and it follows the cam motion the the valve won't bounce on the close, at least in theory. Comp is one of the pioneers of spintron use and they have some neat videos of valve motion during operation. Scary stuff, like locks and retainers just hanging in space....not touching each other!

 

That's not what I wanted to read, but I was slightly afraid of this.

My last setup used a 1.5 ratio rocker with 0.501" lift. The spring was a Speed
Pro Single coil. The dyno graph looked amazing up top.

Previous spring spec:

O.D. 1.264
Closed Pressure (Lbs.) 110 at 1.700"
Open Pressure (Lbs.) 294 at 1.21"
Rate: 353 lbs./in.

I figured with the extra pressure on seat and nose, I`d be fine. Now the locker
room talk has me worried...hence my post. Just wanted to get some real
world answers from people like yourselves.

I`m thinking I`ll just slide some shims under the spring to get more pressure
on the 972-16 (already installed).

Video and audio of idle:
http://gmthunder.com/tino/killeralive.mpg

(Don`t mind the greased up old pants )

My biggest concern is piston to valve contact and valve bounce. I`m hoping
this wont be an issue with the modest camshaft.

 

The 972-16 coil binds at 1.195. Your installed height is probably in that 1.800 range. This doesn't leave much room for shimmimg. 986-16 coil binds at 1.150. The 292H is .501 w/1.5 rockers .534 w/1.6.

 

150-15=135 and they will loose 20-25 lbs if they aren't a set of $500.00 springs or beehive.Haven't seen a set yet that I have installed that didn't.
Seat bounce is what most people are considering
valve float and it ain't the same thing.

If you tear up a cam the will most likely say it was installed wrong or broke in wrong.

 

Yes, I'm sitting at 1.800" install height +/- a few thou (across the train).

1.8 - 0.534" = 1.266"

1.266 - 1.195 bind = 0.071"

0.050" - 0.060" clearance...leaves about 10-15 thou shim.

That would get me about 6 lbs!

OK, plan B...

 

Seat bounce comes from loss of valve control. There are specially designed closing ramps on the cam to control the motion and eliminate/minimize bounce. If the valve follows the closing ramp there isn't a problem and the seats look good at teardown. I have never had the seat pressure loss you mention on flat tappets and make it a habit to check. The only springs that I have used that had a problem were pacaloys, and I abused them routinely with stainless valves and 8800 rpm. But it was a budget 1/8 mile heads up combo.

And by the way, Comp is about the most lenient company with their warranty.

 

You are already in the 95th percentile because you're actually thinking about it. You would not believe the amount of people who install that cam with stock, or Z springs. Its been that way for years. If you install the recommended spring you will be happy with the results.

 

Is it me or are we all talking about a HYD FLAT TAPPET CAM?

Seriously the 26915 beehive is perfect for what you are doing here. Not too much spring pressure for break in and you don't have to reshim or change the locks.

Bret

 

Initially, I was going to install the 986-16. I bought them, but the inner diameter
of the inside spring didn`t clear the valve boss on my head.

(a little mix up with the distributor)

My options were to pull the head and machine the boss down, or fit another
spring.

The 972-16 was the best I could find to fit the boss and spring pockets of
the head.

Now I sit here analyzing the cross reference chart and all of your recommendations.

We`re talking about 8 lbs. differential at each lift point between the springs.

Decisions...decisions...

EDIT - Yes Bret, it`s a flat tapp hyd.

Here`s the cam card:

Chevy 262-400 Drag Race 292H-10 Cam
http://www.compcams.com/Technical/Se...umber=12-213-3

 

How will he locate the beehives?

Maybe a shimmed 982-KIT is in your future. (conical) They will fit the inner 1.25" step of those heads. Not the best solution maybe, but practical.

 

You have run more of the behive's than anybody I know,so ya know what works.

IMO doesn't make any dif what cam is under the spring as long as the spring has enough poundage to control the valve at a given RPM and ramp rate both opening and closing. I have seen those soft closing ramps on a SPECIAL grind but haven't seen any on an off the shelf cam.

 

The closing ramp in on all cams, even stock ones.