Why would low lift head flow hurt power?
You’re kidding right? So every OEM almost EVER got it wrong? With .450 lift they damned well should have had 30 degree seats.
And you’re thinking that 30 degree seats don’t seal or won’t live is DEAD wrong. Millions of pontiacs had 30 degree seats and went hundreds of millions miles with them and they sealed.
Diesels use a 37.5 seat and how many miles do they go?
I’ll say it again. Curtain area is over played. If it was THAT CRITICAL every lift rule engine EVER would have 30 degree seats and no one I know does that.
Yes Pontiac did use 30° seats to good effect. What I said was a 30° seat tends to sealing issues, not that they do not seal. This is more prevalent with faster ramp rates causing bounce. Those old engines had lower lift than is common now, many rarely exceeding 0.400" lift and fairly gentle ramp rates.
Yes some diesels use 30° or close to that and go hundreds of thousands of miles. Done many Cat and GM/Detroit Diesel heads in my time.
Regarding curtain area, this depends on your max valve lift. You need to have a discussion with DV on this topic
So is using a smaller primary throttle bore and venturii size a reasonable compromise to make to overcome a lack of vacuum generation due to a the aforementioned issues?
Seems I read years ago that the General on designing the Rochester spread bore carbs were looking for good fuel atomization on the primary throttle bores were most driving occurs. Thus the very small primary throttle bores and venturi diameters. They also incorporated a dual booster for high signal and air velocity which in the third venturi creates shattering of the fuel droplets to much smaller size. More surface area exposed to the air aids vaporization. This enabled a 750CFM carb to be used on the limp wrist 305 engines with smooth throttle response.
Where the Chev 305 suffered, other than the high performance Camaro engine, was the camshaft and intake valve diameter. I had a 1982 Blazer with the 305 lopo engine. About 12MPG, low power and shift cycled with the 700 R4 transmission on the hiway. That got me researching camshafts, and I found out the intake was missing about 0.050" lift. This inhibits airflow past the small intake valves, so measured vacuum at the carb was low. This created the poor power.
In the TRW catalogue, when they still had catalogues on the parts counters, was the std 305 cam, another cam and then the 350 cam. There was another cam and another step up was the commonly refered to RV cam. If I remember correctly this had 204°/214° @ 0.050" lift and 0.425" valve lift. After installing this cam I got better vacuum, fuel economy (3.5MPG better) and driveability. Shift cycling was vastly reduced.
For the Hipo 305 Chev installed bigger intake valves in heads with smaller combustion chambers, as well as the 350 cam.
Ford did the same for their 302 engine in most autos and trucks. When they brought out the HO Mustang, the engine got the 351 cam with about 0.050 more intake lift.
Ma Mopar did the same on their emissions 318, lost 0.050" intake lift. I do not recall Chrysler with a hi output 318 sporting the 360 cam. About this time the K car was introduced and Chrysler went all in on FWD.
So in all this, valve curtain area and seat profile is extremely important for the average street engine utilizing fairly low lift.
Regarding the Engine Masters builds, this is a venue for builders to show off their skills. Many of these are not exactly long term street engines. Rockers with 2.0:1 ratio and valve lifts approaching 1.00" were seen. These engines would be very costly and involved much dyno time to get that years entry dialed in as best as possible within the rules.