Originally Posted by Aubrey N Bruneau
Gee, Alan, I have 230 / 470 on the intake. It's seems good to about 7000. Trouble is, the engine is spinning 7200 through the traps now. I have about .065" piston to valve, and I've never seen evidence of the intake valve ever getting close. The exhaust however, at .035" piston to valve, leaves quite a "map" !... though no actual contact.
Where the valve float tell-tale sign is.... is the valve locks. The exhaust are all nice, clean, and black, like they just came out of the package. The intake are ALL scuffed up, hammering the lip off, and "peeling" the groove in the valve a bit.
I respect your guidance completely, Alan... however, this is my third time around in the valve train, crushing the most spring pressure that can be fit in there... and it just CONSISTENTLY goes out of control. I'm convinced that it's simply an inappropriate lobe for the application.
Greg, that is the mis-conception ! ! ! !
A large port 409 is really NOT a big torquer ! The 63-65 340 horse small-port car engine, and the truck engines, have fueled that "big torque" belief... but like an L78 compared to a 366 school bus engine.... it's a VERY different animal.
Oh, my valves are 141 and 124 grams.
I got off lucky this time, as far as damage goes. It DID put a light crack in the num 4 cylinder, which was sleeved from the last time this happened. But it doesn't seem to leak coolant there. The head of the valve broke off, and got tossed through the intake, into num 1 intake runner. No problem there. The stem got bent and knocked up away from the piston. Engine still ran, and I actually limped it at 40 MPH to the finish line.
The valve seat area is a bit of a mess, and that's where the coolant leaked. Not catastrophic though.
As far as RPM.... a 63 425 horse 409 ( I'm allowed that cam ), from the factory, routinely gets shifted at 6200-6300 RPM. The late 64 425 HP engine, which used the Z11 cam, would do 6500.
The cam I'm looking at, stretches my advertised duration on the intake, from the current 290, to 299 ( my stipulation to Comp, was that I wanted to maintain my current duration @ .200" ). My concern is that this will really bleed off cylinder pressure below 5000 RPM.
Am I right to be concerned ?
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