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Have a set of exhaust cutouts and want to know for performance purpose how far do they need to be from collector for max performance?
383 strocker
440 hp
480 to
Quadrajet
77 c3
Also not an expert but, I put mine just after the trans cross member basically dumping out right in front of the rear tires. As for horse power gained? Not really sure, but the top end charge feels a bit faster. Or maybe I just think it’s faster because everything is so much louder!
Also be weary of ground clearance! I welded up my own two bolt flanges (vs typical 3 bolt) for increased clearance and they are still the lowest part of the car.
The idea of dumps or cut-outs is to have the ability to run open headers by simply and rapidly removing six nuts. To obtain the maximum H.P. you want the cut-out as close to the header as possible. Some cut-outs have the 3" collector & 3 bolt pattern to mate up with the header flange. Check out my profile photo first album, last picture.
Additional horse? Easily 20-25 with open headers, no restrictions.
Rarely are the header flanges located at the optimum length for power. Back in the old days, we would bolt a 2’ length of 3” collector onto the header flange. Put a stripe of white paint along the collector and run a couple of trips down the strip. Look for the spot where the white paint was burned and cut the collector at that point. Nobody back then had a chassis dyno. The car always made more power with some length of 3” pipe bolted to the header.
HeadsU.P. are your dumps running parallel to the ground or are they slightly angled down? Hard to tell from the pic. I plan on running the same setup you have except with hooker headers and am curious.
HeadsU.P. are your dumps running parallel to the ground or are they slightly angled down? Hard to tell from the pic. I plan on running the same setup you have except with hooker headers and am curious.
They are angled down. I don't really have any choice because the bolt holes will determine the outcome. In other words you would have to rotate the unit one third for the next bolt hole to line up. Not an option. I really like them though. I have all six bolts tack welded on the flange so as not to spin when I remove the nuts (only need one wrench that way). They are loud, but I like the downward turn away from the flooring. I use a good quality gasket to seal the end cap.
The ultimate would be electric remote-controled cut-outs. But they're pricey.
I've got the fish mouth cuts finished and the dumps welded to header extensions but don't have the 3 bolts header flanges welded on yet (waiting to get headers installed) So I will set the rotation as best I can before then. Planned on tacking the bolts just like you did and using wing nut for the plates I made. Electrics would be nice and I have a standard 2.5" 3 bolt welded on the dump just in case I go there in the future.
Keep in mind to keep that "open exhaustheat" away from the floor area. And some C3s have fiberglass floors. Anyway, the bad side of my setup is the dumps flange is the lowest point of the car and first place to drag / scrape on speed bumps, dead squirrels, dead cats, etc.
Basically my system is 2½" straight pipes that I can add a muffler to quiet them down-
I'm using a w/ a toggle of a switch- well actually a sunroof switch that resembles opening and closing!!!
I have a SS 304 straight pipe 2½" inside a 4½" SS outer pipe. The straight pipe will be opened/closed by a QTP electric cutout motor.
For the motor- I used some bronze valve guides-cut down and stepped to hold the stainless steel butterfly in place. Just need to make some standoffs to mount the motor.
QTP motors-
Design-
Close the straights- and I'll have a 2ft glasspack muffler
Glass pac- perfed SS and a couple SS insinkerator garbage disposal flanges for spacers...
Exhaust cutout location
