From a guy who grenade many many engines over the years racing, my main concern is heat and flex poor design where form does not follow function. More on this later.
Specially here, heat means excess heat, flex means dynamic flex ( non-controller harmonics).
Heat robs motor oil of lubrication properties over time. Heat destroys the valve spring life span. Then you have valve float then the piston smacks the valve, may break it off and engine eats it. Bam.
Heat can cook the motor oil and may even set it on fire. Heat can cause cracks I the block and cylinder head. Heat can warp cylinder heads and cause blown head gaskets. Heat can cause loss of coolant by changing liquid to steam and booom
Flex is where the load is more the original design limits. Flex of the crank shaft means poor lubrication, scored bearings eventual failure. Flex can mean crankshafts crack then break. Flex in valve train components mean erratic valve timing possible valve float, possible timing chain breakage. Flex here may be due to weak skinny push rods, weak timing chain /belts, accessories driven off cam timing irregularities ( distributor flex). Flex of cylinders in the engine case (block ) is horsepower robbing and long term liability.
This is one area severely overlooked when designing race engines.poor design where form does not follow function – Number one consideration is the oil system. Stock oil systems are great for grocery getters but terrible to race. Oil does two things, lubricate and cool. Too much oil pressure can be as bad as too little. Oil must be controlled at all levels of performance. Oil under pressure shoot up to the bottom of the piston and cools it. Too much and the piston rings are overcome and can not control it. We have smoke, fouled spark plugs and a mess. Not so obvious is the danger of too high oil pressure in the upper oil galleries. Typically the oil is meant to flow up top then make many right angle turns to various other engine components. When the speed gets too great, the oil ha a difficult time making the 90 degree turn, hence, poor oiling. One more danger is oil aeration. Passing many moving parts creates potential for introducing air bubbles into the oil and air don’t lube too good! In the old days valve lifters were in the oil gallery and after the oil passed all the way past 3 lifters the oil capability of number 4 was dramatically reduced. We found that we could supply oil into the oil galleries from both ends of the block and the oil would meet in the middle and then back fill all the 90 degree turns a lot more effectively. Proper oiling means controlling the oil to the valve train to keep the valve springs cool but not to over pump oil top side and overcome the valve seals. Oil should return the ethe oil pan as soon as possible. You don’t want a bunch of oil slinging around inside engine block as it robs power and goes where it should not. Oil sling can cause parasitic drag.
Flex – One of the most impressive engine blocks I ever saw was the 292 CID straight six truck block Ford made. It has 7 main bearing caps. I never heard of a crankshaft busting all the time this engine was raced. If you look at the small block Chevy V8 block the main bearing caps are bolter to the flat block surface. No lateral support against flex. This is one reason the y had to go to 4 bolt mains. The old Mopar (Chrysler) B block had enormous lateral support. Monster Hemi’s had the same deal and added a main cap bolt 90 degrees to the crank thru the engine block.
Mopar small blocks were famous for blown head gaskets. The cylinder head design was for 4 head bolts on each cylinder. The small block chevy had 5. One other flaw was the deck thickness the small block Mopar. This was the design engineers light weight thin wall casting block concept. They wanted a light weight V8 for the compact cars in the early 1960’s. But thin wall design meant ----- FLEX. We had to pour a concrete metallic mixture into the engine block at the water coolant passages until it was about an inch thick, This stiffened cylinders and tied them into each other to prevent flex. It still did not help the thin deck (thickness of iron material flat surface the cylinder head bolts to) but it helped longevity. Did not impact cooling either.
Any way that’s my take on things to consider.
ere's what a crankshaft looks like under stress (deformations are emphasized to better see them):