What a great time to be alive when all these top engine guys like Bryce just tell us like it is! I came here after listening to Darin Morgan's new youtube channel. And David Vizard is doing the same... These guys are some of the nations TOP guys for making HP, and they're sharing this stuff for free! Now if only I wasn't too old and poor to still be into the racing scene myself. Honestly though, I get as much enjoyment listening these guys share their decades of R&D derived experience as I would sweating in a shop building stuff. I never realized the dimensions inside a prostock Harley engine. Truly amazing, a 2.75 intake valve opening 1.200 inches, opening and closing 60 times per second @ 10,000 RPM if I remember my math correctly! These bike engine internals dwarf an 500CI NHRA prostock. 5.140 bore and 700 CFM intake in these bike engines, holy shit! I'm curious how the newer Mil 8, ported 4 valve head compares to a decent street 2 valve head intake flow numbers? And yea, I tend to go with the all intake flow focused efforts. Seems like the pressure and velocity of the exhaust in a running engine would be so far removed from a flow bench numbers from exhaust testing that they'd be nearly useless. Only option left in your bike engine would be open the exhaust earlier (add duration) unless total redesign heads, moving valve centerlines etc... But I'm sure you been down the more ex duration road... as you said. Very interesting your observations with increasing exhaust area picking up HP though... Be cool to see followup on this. With the bikes being single cyl air cooled heads, would seem easy enough to CNC some experimental dyno run-able stuff? Seems good Ex port "shape" and cross section would be more related to reality of running dynamics than flowing air at 28 inches. Hell I'm kinda surprised "steady state" intake flow bench numbers (compared to all the dynamic chaos of running) have become so accurately able to predict HP. I recall reading years ago in a forum, you pointing out the importance of what I interpreted as a larger valve "bowl volume" for increased HP. I always thought this may show little to nothing on a bench, but makes perfect sense when combined with dynamics during running.... Why has no one set up (think spintron) a complete test engine, spin it over @ race RPM, have to figure out how to get the air out of the cyl's without real exhaust pressure/velocity (suction scavenge pump?), to test overall intake flow volume with valves open closing, pistons pulling in charge, etc? Thanks for sharing Bryce, you sound like a really cool, humble guy. Someone I'd enjoy drinking a beer with while we shared race engine talk.
Bryce, good job. It take the community to develop new and better. When were not afraid to speak it only benefits the entire community. Myself I've been afraid to do what you're doing because people are so quick to try and shoot others down and argue. Maybe in a group I'll get to the point that I can open up more and we have honest conversations where everyone is a contributor to the thought.
Great food for thought. I wasn't thinking about the larger surface area acting against opening the exhaust valve. I have stayed using smaller valves to avoid cracking between the seats. On upcoming builds, I have been entertaining the idea of using larger exhaust valves on the turbocharged engine. I will be giving it extra thought now as to the potential tradeoffs.
George, have you ever had a conversation about exhaust flow out the valve and port with Larry Widmer? He was an aeronautical engineer that applied his knowledge to hot rods and developed the Boss 429 heads for Ford SVO that Bob Glidden used to win NHRA World Championships when they bumped up to 500” in 1982. Larry had his own company in Ft Worth, Tx called Endyn. Larry knows the exact valve size/port cross section to get the proper exhaust velocity to get a cylinder bled down! He currently has a C2 Corvette with an LS engine, street driven that will annihilate most things on the street. If you don’t know him, he would have been someone to know in your racing days, he’s an airflow genius. He was going to merge his business with some company in your neck of the woods before covid, but don’t know if it went through.....
@17:00 Therefore I flow at 70" tp. Both intake and exhaust. maybe 70" is overkill at higher valve lifts ...but it sure is too low for exhaustport... @18:00 That answer I got 20 years ago from Ferrea why they didnt make bigger exhaust valves in 3/8" : Anything bigger they would like to use but nothing is up to the forces of residual pressure in the cylinder : not the stem , rockerarm , rockershaft , pushrods and lifters . Anything bigger than 2.1" .....its impossible so why make a exhaust blank which is say 2.3" and is almost ALWAYS turned down to 2.0 to 1.9" ??? great video . Greetings from the Netherlands!!!
Just done check of inline 6 ford 4 litre has exhaust to intake percentage of 87.23.has 3.63 inch bore 41mm exhaust 47 mm intake.got enough room to put a 2 inch valve seat but throw a 2.02 inch valve on that seat.before I forget I live in Australia.peace
