Thread: 460 push rod length with roller cam and rockers

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should intake and exhaust be the same,

Yes, I don't know why they'd be different

Alot of new cams are split duration ,with higher lift and duration on the exaust,which leads to a different spring than the intake or shimming it for more pressure.
Ideally they should be the same and on a mild 100,000 mile engine they are ......but in a performance engine ,you should never take the lbs rating to heart.Usually each individual spring gets set with a shim for installed pressure and over the nose pressure ,resulting in each spring being a different installed height.The engine does not care ,as long as you have the proper lift clearance on the springs to prevent coil bind ,the rest gets made up setting the valves and push rod length.
On a real race motor ,probably every single spring is a few thousandths different than the others to get the proper seat pressure with in a few lbs along with the over the nose pressure,alot of the time its a compromise on the seat and the over the nose to get a good installed height ,without stepping up to a taller spring or a increased rate per inch,but thats probably out of the scope of this build ,I thought I would just throw that out there for infos sake.

Originally Posted by shawnlee28

Alot of new cams are split duration ,with higher lift and duration on the exaust,which leads to a different spring than the intake or shimming it for more pressure.

Whether a 429/460 camshaft needs to be split-profile or not, and whether the exhaust needs to have more lift or not, is dependent on the overall engine package. Most split profile shelf grinds favor the exhaust due the the nature of the factory cylinder head design. Different springs may be necessary under extreme circumstances but this is very rarely the case as most spring packages fit cam lobes that, between intake and exhaust lobes, are within a few thousanths difference anyway.

Originally Posted by shawnlee28

Ideally they should be the same and on a mild 100,000 mile engine they are ......but in a performance engine ,you should never take the lbs rating to heart.Usually each individual spring gets set with a shim for installed pressure and over the nose pressure, resulting in each spring being a different installed height.The engine does not care ,as long as you have the proper lift clearance on the springs to prevent coil bind ,the rest gets made up setting the valves and push rod length.

What should be the same? The pushrod length or the spring pressure? And why does this apply to 100,000 mile engines? I would think that both are less likely with such a high mileage engine. Try to use as few shims as possible. I view them as a crutch, so to speak...but indeed sometimes they are a necessary evil.

Originally Posted by shawnlee28

On a real race motor ,probably every single spring is a few thousandths different than the others to get the proper seat pressure with in a few lbs along with the over the nose pressure,alot of the time its a compromise on the seat and the over the nose to get a good installed height ,without stepping up to a taller spring or a increased rate per inch,but thats probably out of the scope of this build ,I thought I would just throw that out there for infos sake.

On a "real race motor," there are no compromises; instead, the proper spring package is utilized that satisifes the needs of the build.

Paul

Originally Posted by dilling

should intake and exhaust be the same,

If we are talking about conventional 429/460 cylinder heads/valve train layout and you just executed valve train geometry correctly in a performance engine, then you will very likely find that the pushrods for the exahust valves need to be longer than the intake valve's pusrhods.

The production 429/460 has equal length pushrods from the factory to facilitate production.

Paul