Most Flat Tappet Spring Pressure You've Gotten Away With(Mechanical)

How much pressure and how long did it live? What type of motorsport and how aggressive the cam? I've been reading a lot of other people's opinions on the world wide interweb, but would appreciate stories from you fellows. I know that many here have been there and done that, so to speak.

No specific combo. I was doing some bench racing last night and figured you gentlemen might have some thoughts on the matter.

I had 300 on the seat and 800 open on a set of DOVE's, and the new one is right at 1000 open. Both mechanical rollers.

"Stocker" B.B Chevy L-88 stuff with a flat tappet will run 210# seat pressure and 550# open with only .540" valve lift and stock 1.7/1 stamped steel rockers.
NASCAR "cup" stuff is higher spring pressures than that.

320 lb.seat pressure on an 8620 billet bull nose flat tappet with carbon faced tappets.

Just a question if I may? Also please keep in mind, my inquiry is of engines that must operate with a flat tappet design camshaft. NASCAR applications not acceptable.

Is there a sincere need for valve spring pressure to exceed 150 PSI on the seat and 400 PSI @ maximum lift with a mechanical flat tappet type camshaft, excluding NASCAR applications? I would think a NHRA Stocker would be a candidate of the more efficient valve train and I feel sure the engines that will operate at high engine speeds have the lighter valve train and not require such extreme valve spring pressures. With the enormous amount of light weight valve train parts and special designed valve springs, the extreme valve spring pressures mentioned surprise me!

Just more uneducated mumbling,
Dave.

LivermoreDave wrote:Just a question if I may? Also please keep in mind, my inquiry is of engines that must operate with a flat tappet design camshaft. NASCAR applications not acceptable.

Is there a sincere need for valve spring pressure to exceed 150 PSI on the seat and 400 PSI @ maximum lift with a mechanical flat tappet type camshaft, excluding NASCAR applications? I would think a NHRA Stocker would be a candidate of the more efficient valve train and I feel sure the engines that will operate at high engine speeds have the lighter valve train and not require such extreme valve spring pressures. With the enormous amount of light weight valve train parts and special designed valve springs, the extreme valve spring pressures mentioned surprise me!

Just more uneducated mumbling,


Dave.

The application on the one I did was in an 8.3 Cummings diesel converted to alky with staged twin turbos on it. Two things pushed me towards the flat tappet deal, one was the major problem involving being able to put a roller set up in the block (cam on one side of the block just above the cam no room for tie bars and no way to machine a key way for keyed lifters.

Also this engine was running 90 lb of boost, and we had problems with the boost making the valve bounce off the seat. This cam had lobes that you couldn't tell by looking that they weren't roller profiles. The tappets were nail heads with a .625 body and 1.200 face. The actual valve movement and acceleration was faster than a comparable roller . RPM was below 6000, it made unbelievable power.

Dave,

You mentioned NHRA Stockers and Super Stockers as having lightwieght valve train parts. They don't because they can't by the rules. Titanium valves are not legal in either.

In Stock Eliminator, they are limited to factory rocker arms and stainless steel valves of stock dimensions (-.015" to +.005" on head diameter), and furthermore they are limited to stock "lift" camshafts. 40 years ago the duration had to check also, but they did away with that part of the rule, because it wa so hard to tech and verify. So nowadays you have a solid or hydraulic camshaft with say .490" lift being the limiting factor. Therefore a true "Stocker" camshaft from Lunati or whomever has almost rectangular lobes with piss-poor harmonics, but the point being to get the valve open to .490" as quick as possible and hold it there for as long as possible. Because the acceleration and jerk are horrendous with this cams, they have to run a ton of spring pressure in order to try to control the valve, because there ain't no such thing as setting the valve down gently in order to control bounce. The lifters used for this application have exotic coatings to say the least.

In Super Stock Eliminator, you can run a BIG roller camshaft with unlimited lift and duration, aftermarket rocker arms (such as Colin's shaft mounted Jesel's), but you still have to run stainless steel valves. The engines can rev higher, but again you run killer spring pressure just to control the relatively heavy valves at high rpm. The S/S guys pay close attention to their stainless steel valve weight and I have seen as much as a 12 gram difference between identical dimension big intake valves, but from different manufacturers. That's very important to the S/S guys.

Charlie Evans

As Charlie said, the instant open / instant close, "squarish" cam lobes run in NHRA STOCK require that much spring pressure simply to control the "stock valve train parts" at the RPM they need to run to be competitive.
Plasma Nitrided camshafts and Casidium coated lifters are the norm.

c.evans wrote:Dave,

You mentioned NHRA Stockers and Super Stockers as having lightwieght valve train parts. They don't because they can't by the rules. Titanium valves are not legal in either.

In Stock Eliminator, they are limited to factory rocker arms and stainless steel valves of stock dimensions (-.015" to +.005" on head diameter), and furthermore they are limited to stock "lift" camshafts. 40 years ago the duration had to check also, but they did away with that part of the rule, because it wa so hard to tech and verify. So nowadays you have a solid or hydraulic camshaft with say .490" lift being the limiting factor. Therefore a true "Stocker" camshaft from Lunati or whomever has almost rectangular lobes with piss-poor harmonics, but the point being to get the valve open to .490" as quick as possible and hold it there for as long as possible. Because the acceleration and jerk are horrendous with this cams, they have to run a ton of spring pressure in order to try to control the valve, because there ain't no such thing as setting the valve down gently in order to control bounce. The lifters used for this application have exotic coatings to say the least.

In Super Stock Eliminator, you can run a BIG roller camshaft with unlimited lift and duration, aftermarket rocker arms (such as Colin's shaft mounted Jesel's), but you still have to run stainless steel valves. The engines can rev higher, but again you run killer spring pressure just to control the relatively heavy valves at high rpm. The S/S guys pay close attention to their stainless steel valve weight and I have seen as much as a 12 gram difference between identical dimension big intake valves, but from different manufacturers. That's very important to the S/S guys.

Charlie Evans

Man I should have known that you would chime in and it's obvious you didn't absorb my post!
I didn't mention NHRA S/S, TI, nor NHRA rules! Let me explain "Hillbilly", about those light weight parts I mention! Most NHRA Stockers don't have the big valve train weight simply by the application, relative to the big power builds presented on our beloved 429-460 website. Schubert, Trend and others offer cam followers to not only allow a weight advantage as well, designed to accommodate the aggressive lobes you mention. Pushrods, well that's another story. If an application offers a light and heavy pushrod, I've seen both preferences used, at each competitors discretion. Too, I thought I read where the cam manufactures ground the cam's closing ramp to somewhat "cushion" the valve's approach to the valve seat.

Now back to my post of the "most everyday" application of the solid flat tappet, I don't see the need to exercise the high spring pressures with everyday flat tappet applications!

Lem always told me you were too quick to jump to conclusions, and I believe he's right!

Now, you have even more of my uneducated mumbling!
Dave.

Dave,
Just last summer I dyno'ed a pretty normal Edelbrock headed B.B. Chrysler with a normal aggressive flat tappet camshaft with .700" valve lift and 276*/284* duration. I originally set the valve spring pressure at 155 pounds on the seat ... it floated the valves at 6,100 RPM while the horsepower was still rising rapidly.
To make a long story short, after bumping the seat pressure 3 times to end up at 190 pounds on the seat, the engine finally went past peak power at 7.200 RPM without floating valves.
That engine was a pretty a normal drag race engine with Titanium retainers, 1.7/1 aluminum roller rocker arms with, of course, the production MOPAR style shaft rocker system.

Thanks Randy, good information. It simply hasn't applied itself to my junk ... yet!

Dave.