Exhaust Diameter
 

I currently have stainless marine manifolds with short risers for corsa cutouts.I am going to ditch the corsas and extend the inner tube to the transom to lessen reversion.The outlet on the risers is 3''.Is this big enough to suport a 502 cid that will produce around 500hp.It is real easy to extend the risers and easly reversible if I stick to 3''.I could go 3.5'' but it would involve cutting the riser apart.To add the 3'' piece I made a mandrel to strech 3''stainles and it slips over the outlet pipe on the riser and can be tig welded up once positioned correctly.by doing this I'm getting the riser about 10'' longer.Will this help with reversion avoidance.

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Yes it will help. A very good idea.