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6 years is a good run. My 327 had made it over 50 years. I blame the lack of Zinc in the oil. Has noting to do with racing wide open trottle with trick DZ heads. I hope my 467 makes it at least half the 50 years.
LOL, for once, I wasn’t actually beating the tar out of the car. I was cruising sanely on the highway when it happened. Just merged on and got up to the speed of traffic, shifted into fifth gear, cruising along at 70 and boom, game over. No warning.
 
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67 Camaro L78 M20 Convertible
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LOL, for once, I wasn’t actually beating the tar out of the car. I was cruising sanely on the highway when it happened. Just merged on and got up to the speed of traffic, shifted into fifth gear, cruising along at 70 and boom, game over. No warning.
What exactly happened? No oil pressure? valve drop?
 

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BBC engines are hard on valve springs. They work harden and break over time. The higher you twist the engine and the more lift you have the the sooner they will break.

I run solid rollers with lots of lift so I check my springs for pressure (on the heads in the car) every time I change the motor oil. They (valve springs) are a consumable part, so I have a box of springs ready to install if any come up weak. I have lost 23 BBC engines to dropped valves over the decades of racing. Since I started checking my spring pressure I haven't lost another.

Big Dave
 

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Dave, the crazy thing is that the valve broke where the stem meets the actual valve itself. The springs and remainder of the valve were still intact. The head broke off of the valve and dropped into the cylinder which destroyed the piston, connecting rod, and the cylinder block. Anyone ever have a valve do that before? No warning at all. Cruising at 70 MPH in fifth gear turning 2300 RPM.
 

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Dave, the crazy thing is that the valve broke where the stem meets the actual valve itself. The springs and remainder of the valve were still intact. The head broke off of the valve and dropped into the cylinder which destroyed the piston, connecting rod, and the cylinder block. Anyone ever have a valve do that before? No warning at all. Cruising at 70 MPH in fifth gear turning 2300 RPM.
haha, i dropped the exhaust in cylinder 4.. my condolences.

How come the intake drops? Normally they wear not nearly as fast as exhaust valve stems and their guides. They are not exposed to super hot exhaust gases..

In my case all 8 exhaust valves had lik 2-3 mm (!) play stem-to-guide! All 8 intake valves were superbly tight...

I didnt check the stem-to-guide-play, only did a valve head to seat ring check by measring compression while turning. That was super good. But of course gives no info about the stem-guide-play..

well i payed the price. On my 9.7:1 compression 396 with 38cc dome piston engine i increasing timing from 37 to 40 degress (stock L78 in 1970 was 40°) - using 95 premium fuel.
After the fifth acceleration the valve let go exactly at the friction point were the stem meets the guide in the intake runner..

Then i checked the heads: Different exhaust valves from different manufacturers.. cheap ones like 80 cent per valve.. some original guides, some replaced.. what a chaos low quality head job this was.

Then i wasnt surprised anymore. The quality just has to be low enough, then even the best engineered design fails in no time..
 

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haha, i dropped the exhaust in cylinder 4.. my condolences.

How come the intake drops? Normally they wear not nearly as fast as exhaust valve stems and their guides. They are not exposed to super hot exhaust gases..

In my case all 8 exhaust valves had lik 2-3 mm (!) play stem-to-guide! All 8 intake valves were superbly tight...

I didnt check the stem-to-guide-play, only did a valve head to seat ring check by measring compression while turning. That was super good. But of course gives no info about the stem-guide-play..

well i payed the price. On my 9.7:1 compression 396 with 38cc dome piston engine i increasing timing from 37 to 40 degress (stock L78 in 1970 was 40°) - using 95 premium fuel.
After the fifth acceleration the valve let go exactly at the friction point were the stem meets the guide in the intake runner..

Then i checked the heads: Different exhaust valves from different manufacturers.. cheap ones like 80 cent per valve.. some original guides, some replaced.. what a chaos low quality head job this was.

Then i wasnt surprised anymore. The quality just has to be low enough, then even the best engineered design fails in no time..
My heads were Brodix RaceRite oval port cylinder heads bought fully assembled Brand new from Brodix with their valves installed. Everything on the heads was good quality. I was not expecting those heads to be the point of failure. Live and learn.
 

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Intake valves are heavier than exhaust 9same spring for both.) As valve springs get weak the valve to piston distance decreases as the springs allow more travel, and they can not resist harmonics as easily. A broken valve head is usually caused by the valve hitting the piston, Which snaps off the stem where it was friction welded to the valve head (sounds scary, but it how poppet valves are made; unless you want to go billet.)

I am convinced that the big block has two fatal flaws: the valves are too small for the potential displacement, and the valve springs wear out too fast. It would be nice if it had a hemi head, but then it wouldn't be a BBC anymore (despite what Sonny Leonard claims about his 1000.5 ci big block that has a Hemi head.

Big Dave
 

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I am convinced that the big block has two fatal flaws: the valves are too small for the potential displacement, and the valve springs wear out too fast.
The small block's fatal flaw is it's a small block. hehe
 
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L88 427 vs, LS5,LS6 or LS7 454 Mark IV 2piece Main Seal
Other than the clear cubic inch difference is there an advantage of shorter stroke to wind up faster? Remember all the mouse talk about 327's and 350's in corvettes. Sure If you ask whether you want a cast crank or a forged crank, forged wins. Big Block debate........Which do you choose? Thank you
You have a good question. Lots to think about. I like a 427. Being internally balanced and I like a quick winding engine. The gear you have plays a role in the engine as well. Most camaros require less torque to get the job done with lower gears and overdrive transmissions. Then there is the saying No replacement for displacement. If putting a crank in a 454 why not go 496? Unless this is a track car I'm thinking the 427 would be fun. Personally for my first gen I just don't want to thrash on it too much because it is just to hard to find a good one.
 
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