At what seat pressure are break-in springs required?

[PackardV8]

Talking semi-streetable cams here, not full-race. Most old-school OEM OHV8 springs seem to be between 70-95# seat. Most performance springs start between 90-120# The more serious performance springs go 120-150# and race is up to unbelievable.

Yes, I know lifter quality varies, cam finish varies, and these days, cam intensity is getting crazy, but give me your thoughts. At what seat pressure would you say a lighter or outer-only break in spring would be required?

Is it a generally accepted statement that the old-school slow-ramp-low-lift performance cams (think 30-30 Duntov) cams don't eat their lobes at the same spring pressures as latest-greatest CompCamsXtremeInfinityIntensity grinds?

[CamKing]

It's not the seat pressure, it's the open pressure you have to worry about.
I wouldn't break-in any flat tappet cam with more then 310lbs of open pressure.

[PackardV8]

Thanks, Mike. Very few of my obsolete cams go over 300# at the nose. It's just the change in oil formulation and EOS formulation, plus the xtreme intensity, has everyone worried.

The old cams also don't have much lobe lift. That's also why the more recent cam designs eat lobes. Yes, it's intensity, but mainly more intensity longer to lift higher. Today's cams have much greater lobe lift than the old school cams. Then, put them on 1.6, 1.65 or 1.7 rockers and heavy lifting is being done.

[DaveMcLain]

Thanks, Mike. Very few of my obsolete cams go over 300# at the nose. It's just the change in oil formulation and EOS formulation, plus the xtreme intensity, has everyone worried.

The old cams also don't have much lobe lift. That's also why the more recent cam designs eat lobes. Yes, it's intensity, but mainly more intensity longer to lift higher. Today's cams have much greater lobe lift than the old school cams. Then, put them on 1.6, 1.65 or 1.7 rockers and heavy lifting is being done.

This is also why in some cases a lobe that's less intense, less X-Treme and less aggressive can have some advantages in certain applications such as endurance, marine and real world street use where they cost little to nothing in torque or horsepower.

[Dbore]

Can 1.3 rockers do the job for a sbc hyd (Jones) circle track The lift is .429 with 1.5. The springs are JRC15 Could have asked per phone call but figured I’d ask here since I was lurking about the site.

Adam

[mag2555]

I would think you also need to factor in if your braking in Mopar .904" lifters or GM .

[novadude]

It's not the seat pressure, it's the open pressure you have to worry about.
I wouldn't break-in any flat tappet cam with more then 310lbs of open pressure.

Doesn't rocker ratio play into this? 1.7 is gonna load the cam lobe / lifter interface more than 1.5, no?

Maybe I am over thinking, but it seems like 310lb open load on a BBC will result in different forces at the cam than a SBC with 1.5 rockers.

Also... personal curiosity question for an upcoming project: What about a FT cam that has run for 10k miles? If you swap heads, do you need to worry much about using new springs with higher open and seat loads (as long as not excessive)?

[CamKing]

It's not the seat pressure, it's the open pressure you have to worry about.
I wouldn't break-in any flat tappet cam with more then 310lbs of open pressure.

Doesn't rocker ratio play into this? 1.7 is gonna load the cam lobe / lifter interface more than 1.5, no?
Maybe I am over thinking, but it seems like 310lb open load on a BBC will result in different forces at the cam than a SBC with 1.5 rockers.

Yes, you are correct. Rocker ratio plays a roll. Base circle also plays a roll( the larger the base circle, the wider the nose radius, for a given lift curve). Acceleration rate also plays a roll.
My rule of thumb is to keep pressure under 300# for break-in. Of course, some applications can get away with more pressure, but why risk it?

Also... personal curiosity question for an upcoming project: What about a FT cam that has run for 10k miles? If you swap heads, do you need to worry much about using new springs with higher open and seat loads (as long as not excessive)?

If you are just switching heads, there's no issues, as long as the spring pressure isn't too high for the valvetrain.

[dannobee]

If you can borrow a set of break-in 1.2 ratio rockers, that would help a lot.

When we were forced to run flat tappet cams by rule in nascar, we'd break in with the little rockers and just pray. But our cams were a bit more aggressive than street cams. Then again, working at GM dealerships, I replaced a LOT of flat cams in the 80's. A LOT. And none were high lift by any stretch of the imagination.

From one of my earlier posts after someone else experienced a flat cam during break-in.

<<When you first lit off the engine, was EVERYTHING set and ready to go? Was the engine cranked over excessively, perhaps to time the distributor? Was the engine allowed to idle at any point in time for the first 15 minutes? Was the engine stopped, for any reason, in the first 15 minutes?

EVERYTHING needs to be ready before you light it off for the first time. Distributor in correctly, timing close to base setting. Coolant/water needs to be full. Carb needs fuel in the bowls and in sufficient supply to support running for half an hour. Idle screw on carb turned in a few turns so that engine can't idle below 2K RPM. Sufficient oil and any oil lines double and triple checked. Only then can you light it off. If you screw up any of these things, or shut it off for any reason, you'll probably lose a lobe on a race cam. Even excessive cranking to fill up the carb bowls or timing the distributor can cause a cam to go flat. It's THAT critical.>>

[Walter R. Malik]

I would think you also need to factor in if your braking in Mopar .904" lifters or GM .

Not really, if the cam lobe profile is designed to that size lifter diameter ... the rocker arm ratio needs to be considered though
I would say that for break-in, about 450 pounds force at the lifter/camshaft point is about as high as you'd want the open pressure across the nose.

[Walter R. Malik]

If you can borrow a set of break-in 1.2 ratio rockers, that would help a lot.

When we were forced to run flat tappet cams by rule in nascar, we'd break in with the little rockers and just pray. But our cams were a bit more aggressive than street cams. Then again, working at GM dealerships, I replaced a LOT of flat cams in the 80's. A LOT. And none were high lift by any stretch of the imagination.

From one of my earlier posts after someone else experienced a flat cam during break-in.

<<When you first lit off the engine, was EVERYTHING set and ready to go? Was the engine cranked over excessively, perhaps to time the distributor? Was the engine allowed to idle at any point in time for the first 15 minutes? Was the engine stopped, for any reason, in the first 15 minutes?

EVERYTHING needs to be ready before you light it off for the first time. Distributor in correctly, timing close to base setting. Coolant/water needs to be full. Carb needs fuel in the bowls and in sufficient supply to support running for half an hour. Idle screw on carb turned in a few turns so that engine can't idle below 2K RPM. Sufficient oil and any oil lines double and triple checked. Only then can you light it off. If you screw up any of these things, or shut it off for any reason, you'll probably lose a lobe on a race cam. Even excessive cranking to fill up the carb bowls or timing the distributor can cause a cam to go flat. It's THAT critical.>>

We used to have an inter-house contest of how fast the engine would light-up.
Over that 16 years, the least was only 160 degrees of crank rotation and the engine was running.

[Bob Hollinshead]

Someone said recently that the 20 minute break-in rule went out the window. Oil needs to be warm but better to do many short runs to keep the heat down on the cam and lifters.

[rebelrouser]

It's not the seat pressure, it's the open pressure you have to worry about.
I wouldn't break-in any flat tappet cam with more then 310lbs of open pressure.

I have always been under the impression that seat pressure did matter, because as the cam begins to open the lifter starts to spin and if the seat pressure is too great it inhibits the spinning of the lifter. No spin of the lifter no proper break-in. I would like this post to start a discussion of how and why the lifter needs to spin to properly break-in and operate over a long time.