Max valve lift engine rules

[d4490]

I am looking at building a SCCA American Sedan Mustang and the full race specification engine is limited to Edelbrock 602479 spec heads with no porting and limited machining in the seat area, Edelbrock Performer RPM 7121 intake and Holley 4776 carb.. The camshaft is limited to a maximum lift of .500" measured at the valve will zero lash. I see plenty of .500" lift cams in catalogs, but these are based on stock ratio rocker arms. Would there be benefit to get a custom cam designed for a different rocker ratio? Cam must be solid flat tappet, rocker arms are open to stud or shaft mounted and no specification on rocker ratio.

[BlitzA64]

Yep, need to get them open quick and dwell at max lift long as possible. Within valvetrain limits of course. Light valves, retainers, locks, small diameter springs are you friend if allowed

[nhrastocker]

Go with a custom camshaft from this site Moderator, CamKing who has lots of experience in road racing.
I would also recommend Precision Products Performance or Trend DLC coated tool steel solid lifters and steel shaft mounted rocker arms from Crower, Jesel or TD.

[Stan Weiss]

Do the rules say anything about lifter diameter?

Stan

[gmrocket]

To get all the lift you can.

Go with a tight lash design lobe.

Pick your rockers first and mock them up with approximate running pound spring to check the actual ratio. This will tell you the ratio with deflection loss(or gain sometimes)over the nose at the retainer...

Then order your lobe to get you close to .500” at the valve as possible.

[d4490]

Max lifter diameter is .875" Stan.

[Walter R. Malik]

I am looking at building a SCCA American Sedan Mustang and the full race specification engine is limited to Edelbrock 602479 spec heads with no porting and limited machining in the seat area, Edelbrock Performer RPM 7121 intake and Holley 4776 carb.. The camshaft is limited to a maximum lift of .500" measured at the valve will zero lash. I see plenty of .500" lift cams in catalogs, but these are based on stock ratio rocker arms. Would there be benefit to get a custom cam designed for a different rocker ratio? Cam must be solid flat tappet, rocker arms are open to stud or shaft mounted and no specification on rocker ratio.

In that class use something around 240 to 248 at .050" and as much maximum lift dwell as the RPM will allow.

[CamKing]

Do they limit the valve spring ?
Is there an RPM limit ?

Since you are limited to a .875" flat tappet lifter, you are limited to the maximum velocity you can lift that lifter, without over-riding the face of the lifter.
By going to a higher rocker ratio, you can increase the velocity of the valve, while keeping the velocity of the lifter the same.
When you increase the velocity and acceleration of the valve, you will need more spring pressure to control the valve. If you're spring limited, you may be better off, not increasing the rocker ratio.

[JBM770]

I see plenty of .500" lift cams in catalogs,

If you have a 0.5" valve lift limit you cant run a 0.5" lift cam because the rocker ratio will lift the valve too much.

Just my 2c.

[d4490]

JBM770, these cam's I am referring to are .500" at the valve not at the lifter. These are designed to use the stock rocker ration for that engine, so 1.6 for a Ford or 1.5 for a Chevy. Sorry if I confused everyone.

[Walter R. Malik]

JBM770, these cam's I am referring to are .500" at the valve not at the lifter. These are designed to use the stock rocker ration for that engine, so 1.6 for a Ford or 1.5 for a Chevy. Sorry if I confused everyone.

I have a customer who surprisingly, simply uses a 289 Ford "Lemans" cam with a 1.5/1 ratio rocker arm and he runs up front all the time and wins his share of the local races.
... work on the car; it's not a drag racer.

[Krooser]

Do they actually inspect the engines? Asking for a friend

[Walter R. Malik]

Do they actually inspect the engines? Asking for a friend

Only for National S.C.C.A. events ... and then they choose only a few specific rules to check on the top finishers.
Maximum valve lift is easy to check and is usually one of them.

Nobody really cares if the 8th place finisher is illegal.