I've got a 4:1 header on my PV's engine. If it isn't an IPD style one then it looks just like one. I got it used because it came off a PV, and IPD specifically states in their catalog that theirs is 'not intended' for 544 or 240 cars, so I worried about the fit and knew that this one would at least fit. I got a big performance boost when I put it on, *BUT* that was because I also replaced a single downpipe old style cast manifold and replaced the 1 1/4 inch inside diameter system (seriously - and the pipe was about as thick as water pipe too!) with 2 1/4 inch pipe. Dramatically improved the power above 4000 rpm, but I would imagine that if I were to bolt on a double downpipe manifold and hook it to the same system I wouldn't notice any difference.

I'll probably get a 4:2:1 header at some point. I don't know how long this one will last because I've already had to MIG up a couple of small stress cracks on it. But until I need to replace it I'm loath to spend several hundred for a nearly subliminal increase in power.
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I'm JohnMc, and I approved this message.