marshall13
Senior Member
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the first step is to admit your ignorance
Posts: 301
Fort Lauderdale FL
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remember, this engine is 1/8 of a 320 cubic inch v-8, so examine the headers designed for say a mopar 318, or 340, or a chevy 327.... smaller primary pipe diameter(headpipe on the bike) gives better scavenging at lower revs, larger better at higher(the higher velocity through the headpipe gives the exhaust gas a higher dynamic inertia, thus increasing the venturi effect on both the intake valve, and the tail end of the exhaust stream).... so what rev ranges do you run at mostly? with the stock iggy box set to retard your spark at 6000 rpm or so, we can assume our powerband will be between say 1500 and 6500 rpm max.... what size primary pipe do the race boys run on smallblock v-8s in that rev range? 1 1/2 inch.... 1 1/4 for say a mopar 270..... if you're a redline maniac, and run high revs most of the time, then a larger primary will be a better compromise (1 3/4 inch).....but, the bottom end of your curve will lose torque, because of the 16% greater cross section of the pipe(lower velocity stream)..... clear as mud now, huh?...lol
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