Paul, Thanks for the questions. I have great friends, but when I show them something interesting about the engine or race car, they look at it and then they say, "hey you have a new calendar on the wall"!!! It's nice to chat with someone who is truly interested.
Your questions about the heads, compression loss and cam lift are valid. The heads are 471 castings and are a common replacement for "F" code engines. They have lower compression than the "G" heads but that is necessary to let the engine live a little longer with reduced detonation and Tim McMaster thinks they may flow every bit as good. Tim did a great job on these heads. I have been running them for about 5 years now and they are an integral part of making these Y Blocks fly. The relieving does contribute to making the compression even lower, however it is necessary for the valves to clear the cylinder walls. During a chassis dydo session for rear wheel horsepower and considering a 17% parasitic loss from all the drive train components, the little 258 cu in Y Block made 454 flywheel hp with these heads. All this on 5 lbs of turbo boost makes me a believer in Tim's work.
Another mention was of the extra lift in the cam and whether the extra lift was necessary (requiring deeper cylinder wall relieving). The personality of these turbo cams are quite different than normally aspirated engine cams. First of all most of the duration overlap is eliminated. The lobe separation is 114 and the center lines are 110 on the intake and 118 on the exhaust. When the exhaust opens too early, the boosted charge escapes to some degree into the exhaust headers. What the turbo setup does like is higher lift. I have put as much lift into the valve train as I can afford.
These engine specs and choices of parts are not optimum. Aluminum heads etc. would be nice, but I'm happy with what Tim has help me build so far. The little 258 cu in Y ("E" motor) went 161 mph (on a 158 record) at Bonneville last September and I couldn't be more pleased . This new build (actually, the new short block was created over 4 yrs ago) will jump two classes to "C" and the record there is 192 mph. Will this new Y Block measure up to those aftermarket scrubs? It did in "E", but 192 is a tall order. I calculate it will take 650 hp to make that happen and the new short block (albeit more cubic inches at 338) won't get me there alone. I have some changes on the top end that hopefully will push me closer to the 200 mph goal.
Charlie Burns Laton, Ca (South of Fresno)
BurnsRacing981@gmail.com