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Is there much of a power difference using 1 7/8 headers over 1 3/4 headers? With and without a big cam? I seen somewhere that 1 7/8 picked up 5-6 hp over the 1 3/4 at higher rpms and low rpms but the 1 3/4 made slightly more hp or tq in the midrange maybe 3k-4400rpm?
IMO you might see some higher HP numbers on the chassis dyno but on the street no.
Locally there is a guy that builds headers for the circle track boys. When I built the headers for my 67 Nova 427 LS swap he was kind enough to give me some great advice on header design.
He would say one of the key things for a really great flowing header is keeping the primary? tube coming out of the header flange as straight as possible until curving it down towards the collector.
Pic of the header in the mock up stage.
1 7/8 vs 1 3/4 was worth about 10hp peak on my 402. However the dyno sheet shows the real story. Much better curve with the 1 7/8 and the engine didn't want to rev with the 1 3/4. Also, if you notice more HP and TQ everywhere.
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1 3/4 vs 1 7/8 headers dyno or power difference? 
