Originally Posted by Harris Roc Malouda
What is a "two four with vertex mag" ?
And what exactly do you mean by "ate a lot of valve"?
I am impressed by that numbers.. what lifters, rockers, springs, Speck you have?
Btw Chris told me that his rockers are up Tasks in sky high 8500rpm. And the limits travel morel lifters up to even more.. so basically the valve weight + spring Combination determines the max... and in my case - stock valves - that 7400 seem to be a limit...
"two four with vertex mag" I raced back in the good old days. I had a 1968 Camaro RS/SS clone of Grumpy Jenkin's Pro Stock from 1970 (Grumpy's Toy IV). It was powered by an over the counter 427 L88 with an Edelbrock tunnel ram and two 660 cfm Holley carbs. Because point bounce and voltage was an issue with points style distributors I ran a Vertex Magneto that had strong springs on the points (that burnt up quickly) and out put ever increasing voltage to the plugs the faster I spun up the engine.
The BBC Chevy engine was designed to be a race engine. But to pay for the tooling it was produced mostly as a truck engine. This means the bottom end was designed to run 300,000 miles at wide open throttle. The bottom end was bullet proof. However because of the canted valves there were strong harmonics that developed in the springs (valves were tilted on two different axis). If you didn't run a damper on a dual spring the spring would break from metal fatigue as the engine reved. You also had to run over 450 pounds of open pressure on the springs to control the valves at high RPM. Because of this you were required to run a solid ROLLER lifter (the spring pressure would wipe the lobe off of a flat tappet cam). This didn't prevent spring failure (were the valve dropped down into a running engine destroying the piston, head and valve by the engine "eating" the valve), it just prolonged the interval between failures.
If you checked the spring pressure on the heads with this tool:
You could find a weak spring about to break before it created carnage. I also ran triple wound springs instead of double wound springs to get one more spring to keep the valve from falling into the engine. Parts are cheap compared to the price of a complete engine being destroyed.
If you are going to wind a BBC up (Pro Stocks are now limited to only 10,500 RPM on shifts instead of winding them even higher) then you have to consider valve springs to be a consumable and replace them regularly.
Back in the early seventies I couldn't afford Titanium valves so I was limited to only 10.13 time slips while "da Grump" was capable of turning in 9.70 ETs.
Stock valves are made of a 5100 steel alloy that is friction welded (valve head to valve stem welded by heat of friction). I prefer tuliped stainless steel swirl polished valves that offer more flow at low valve lifts and are lighter than the stock steel valve. Titanium valves and retainers are a race only part due to the titanium metal quickly metal fatiguing and breaking apart. You also have to run lash caps with a titanium valves to keep the ends from mushrooming under the beating of a solid cam and 400 plus pounds of spring pressure.
One other thing is at high RPM the the actual rocker arm studs flex under the pressure so you have to run a stud girdle (in addition to ARP studs) or roller rockers on a pedestal (Jessel or T&D) which drives up the price. Since I keep my big blocks at a more reasonable 7,800 RPM instead of over 10 grand I can get by with a rev kit under the head and a stud girdle (old school). I run an HEI style distributor triggering a seven series ignition box now instead of a Mag, which has no points to bounce at high RPM.