434 SB Valve Train Questions

KJL

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Hello-
I am a new member of this forum looking for some advice regarding my build. My original intent was to build a naturally aspirated engine for my 72 vette and use for the occasional weekend "race what ya brung events". The build specs are shown below. Ultimately the car has not yet made to the strip but has seen dyno time and is mostly a street driven car. The engine has about 1700 miles on it and can sit for a month or 2 without being driven. My best dyno was 573 Hp at 6350 rpm and 514 ftl-bs at 4820 rpm.

Last week I was changing my oil and thought I would pull the valve covers just to do a general inspection and spot valve lash check. What I found was a broken spring on the #6 cylinder intake. I am an active member on the Corvette Forum and some folks there seem to think I have WAY too much lift which is causing and going to problems and others think the lift is fine and probably just a bad spring and other say 1700 miles is a lot of miles for a racing spring and they should be changed anyway. I am currently using the PAC 1225 springs and per their recommendation swapping to their 1300 series spring which is supposed to be more durable. That said, before I drop 500+ for all new springs, I was thinking about dropping to 1.6 or 1.5 ratio rocker to reduce stress on valve train. This will cost a lot more $$ but may prolong bigger problems down the road. I will lose some top end power but may gain some lower end torque. There are so many opinions regarding this topic.

1972 w/ 434 Dart Sportsman Small block, Forged 4340 crank, Oliver Billet Rods, JE pistons, Holley 950 cfm, AFR 245cc Tony Mamo Ported Heads, AFR Titan Intake, 11.0 CR, Solid Roller Cam, 257/263 @ .05, Lift .731/.736, T&D 1.7 Shaft Rockers, Isky EZ Roll Lifters, 3/8 Trend push rods, TKO 600, Rebuilt Diff w/ HD Bearing Caps & Bolts, Tuned and Polished Eaton Posi, Carbon Fiber Clutches & 3.73 gear, Spicer U-Joints, Kooks 1-7/8 Headers Thru 3" pipes & Super 40's.

Thanks for the help!
 

007dragracer2.0

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Might not be the lift as it's more likely an aggressive lobe profile that's may be causing the problem.
 

KJL

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If you're not coil binding, it's probably harmonics. What clearance do you have that max lift?

Or it could be nothing. Sometimes things just break.
Installed height is 2" and actual measured lift with springs installed and lash adjusted is:
INT: 0.711"
EX: 0.719"
 
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