Cutout/exhaust dump size?

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Shadowfirexz

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Wondering if anyone can tell me the best route here. I have a 1970 340 4speed duster. I have hooker long tubes on it and am running 2.5 inch exhaust. So I’m looking at putting some manual cutouts/exhaust dumps on it. Now the headers have a 3inch collector so would I want to put a 3 inch cutout on it? Obviously the 3inch cutout would play the same part as the 3 inch collector on the header ya? Anyone know what I’m saying and can give some input. 3inch or 2.5 cutout?
Sorry if this is posted in wrong area, new to this site
 
I run cheap a$$ Summit headers with the 2.5 exhaust kit, 2.5 manual cutouts aft of the trans cross member. Tough to get a cutout before the cross member. Car runs .1 quicker in the 1/4 with open cutouts. Mufflers are quiet (what I want) and choke the motor a little on the street.

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Ya I know there’s not a lot of room between header collector and the crossmemeber but I’m just wonder cause when you in cork your headers it’s exhaust escaping that 3inch diameter collector giving the gains. So I’m guessing if I used a 3 inch cutout so the exhaust had that same 3inch hole to escape It would be best vs using a 2.5 cutout. As in the 2.5 won’t be as good as the 3inch .. follow me?
 
I ran 3” straight back from the headers and welded and fitted the 2 1/2” into the sides on my old set up. Andrew

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I did the same thing with my new system, but ran 3” into a 3” Xpype and stepped down to 2 1/2” before the rear kick due to clearance issues. PG classics or BE&A sell the different size factory style tips as well. Glad it helped. Andrew
 
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