I'm wondering how much power I could make with a 4-71 on a Ford 24 stud flat head V8? Navarro heads, Isky 3/4 race cam, machine work etc. What compression ratio is safe? And what could I do for the bottom end? Like to get a better set of main caps. Along with forged rods and caps. Will a stock cast crank do? I've thought about a stroker kit.
Anywhere between 50 and 500 hp. You are randomly firing questions out there with out expressing much strategic planning. Start with answering what you want the motor to do, and then pick a power target to accomplish that goal. Next pick the right combination of parts to get to that goal. Start with Joe Abbin's "How to build a Flathead" Book. This book covers 3 builds, the 3rd is a blown motor. ScOT blower, but the engine details will help you out. Some general rules of thumb to help you make choices. - Forced Induction flathead engines respond well at lower compression ratios. Unshrouding the valves and getting good exhaust flow becomes paramount because it is easy to get air into the cylinder with the blower. Typically the increased air flow more than makes up for any loss of compression. - Blower motors require strong bottom ends for longevity. Cut down another money tree for the rotating assembly. Billet Caps, Crank girdles, forged bits, etc are all good choices, but will depend on engine use and power level. - An Isky 3/4 Race cam designed for a naturally aspirated motor may not be the best choice for a blower motor. Forced induction responds well to proper cam selection, again prioritizing exhaust flow.
Since I have built {and continue to build} a lot of 471 blown flatheads for the street I can answer your questions based off of my experience.. The horsepower on a typical build with a 3-5/16 bore forged pistons and 4 inch stroke Mercury crankshaft is easily 300 at the crank. Compression ratio should be no more than 7.4 to 1. The bottom end will handle the horsepower easily including the Ford 8BA connecting rods if they are shot peened and the assembly is balanced correctly. The additional support needed on the bottom end is a 1/2 inch thick steel strap across the center main bearing cap. If you need what I feel is the best intake to use for the 471 let me know I always have a few in stock I also have the steel main bearing straps as well. Ronnieroadster
How much with the Ardun heads? I have always admired your car, and more so since I have seen it in person.
I agree with the guidance in purchasing Joe Abbins books. Walked in Joes office one night, he was setting at his computer laughing (he does that a lot) He was working on a computer program to model flathead V-8 builds to project the horsepower based on all the variables, the stock engine as a baseline. He found humor in that his model showed that a stock motor lost 'half its power to internal losses'
Oh boy add Ardun heads and the power increases easily another 150. But the cost adding the overhead valves is usually the limiting factor!
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