Is it better to bore my stock 350 which still has (70k miles on it) or a new 383. And which would be the best 383?

 

About the same, assuming your existing block is good.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Depends on what you plan on using for a crank. If you're buying an aftermarket crank then either ideas will do. If you plan on using a 400 crank to build a 383 then just build a 400 instead. No sense waisting a good 400 block (providing you can still find one)

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley