It could be something silly and simple like it happened to me who knows I'm going say something that was a personal experience, my car was never dynoed but I had similar problem, The car ran perfectly fine up too about 5500rpm after that it would fall flat on its face, what ended up being is I was using wrong mark on the timing pointer.... I found out by putting on #1tdc and realized that I was timing off the wrong pointer... just something to check. After timing with correct mark my car pulls up to 7k rpm any day.
Yup I know the cam is the brains of the engine. The cam guy had all info about engine, tranny, rearend, and weight of car. He even asked what RPM car was goin to be shifted at and what the expected RPM was at the 1/4 mile mark. Told him gear ratio in rearend, tire size and dia.too.If yoy pm me your phone number, I will call you. Thks again Ron
a cam(especially a solid roller) the size mentioned earlier(249/254@50,593lift,108CL) should easily pull past 5700 for peak horsepower. and while I do agree that the 10.5CR is definately a bit low for that funnel webs large runners.. they are a peaky manifold to begin with even on larger motors... and should still pull past 5700 with ease..even wth small'ish cams. I've also seen plenty of cars and dyno results that show greater potential even on smaller motors than your 347. I also see an issue with that tighter lobe seperation. Good for a torquer cam with narrower band.. but not so much for peak horsepower up top. 110-112 may suit that manifold better.. but I would swap to a airgap since it will have better average power without losing 40 horses on top.
it sounds like a restriction to me. all your parts should not be restrictive but it sounds like the motor can not flow any more air in or exhaust out at 5700rpm. my first thought was the heads may be restrictive but then i kept reading your post and see that there are no major components that would be restrictive. so my next thought is that a carb gasket, intake gasket or header gasket is too small and restricting the flow through the motor. more i think about this the less likely any of these could be the problem. i really dont know but cant wait for you to find out a post the solution. i dont really care about horse power on chassie dynos, just constancy to measure tuning changes. different chassie dynos can have over 100 hp differences.
Bryant has point here...............have you checked to see if you are getting both throttle plates fully opened @ WOT? Not sure if you have vacuum secondaries of mechanical...........and if you have vacuum...does it work???? If the secondaries weren't opening you might experience a flat HP/TQ curve, but I would think the motor would start to lean out considerably and you wouldn't get the 12/13 AF readings you got. On my Maverick when I started tearing it down I found the secondaries were not fully opening because the throttle cable was hanging up on the throttle stop............even though I backed it off all the way................but I never checked to see if the primary and secondary throttles were opening all the way @ WOT.....................makes me wonder if I could have done better than 9.801 on the last pass before tearing the motor down..................guess I'll see soon enough.
Well we checked for WOT and yes we are gettin WOT.Dis covered near the start that the cable was hanging up. fixed that real fast. We also matched the intake gaskets( felpro) to the heads so there would be no restrictions. The carb is 750 HP ,so no choke or horns on the top. Mech secondarys also.
I have a friend calling me in the morning i sent him the link to this site so he knows whats going on.He works at Engine Research and Development http://www.erdengines.com/ and builds 2500hp engines daily.If anyone can figure this out its him.
So..................who's heads do you have, I know you mentioned 210 runners and big valves with springs that should a healthy lift. What happened when you advanced or retarded the timing during the dyno session. Did you go over 36 degrees and as low as ????? I've already made one bad suggestion on here today without doing my homework, but my gut tells me it's the cam.................just wish you were closer.
Just one more thought before I call it a night. When you set up the geometry on the valve train, what length push rod did you come up with....................I am assuming you used an adjustable one to determine lenght............right? You also mentioned valve spring pressure of 200 closed and 600 open, these pressures aren't that far from mine, and my cam is .704 lift with only 660 open and 200 closed. Just wondered if you have them verified or just took the word of the head manufacturer..................no offense meant, just wonder if they were verified.
Well you are right. Push rods were custom, I think 7in. These were figured out with a adjustable P R. This kept valve geometry correct. Well the heads are pro comp castings but have been built with manley valves, comp springs, 10degree keepers,and springs installed at 1.850 height.Has 7/16 screw in studs too. Coil bind is 1.17.Wanted the stiffer springs to avoid valve float. Played with timing from 31---38 degrees. On the dyno the engine made most HP and TQ at 33*.Well you are not the first person to think it might be the cam.Even though hit 7000 a few times, have not valve floated the engine.
Hey Derek. Waiting to see what he comes up with at ERD. Some have said it looks like its acting like a Marine engine cam. Low rpm and holds onto power levels
