Found this article from Hot Rod on line. It's from 2017, so sorry if I missed it and someone has posted about it before. But I thought it was a great read about the 340.
I had a 340 in my 73 Road Runner that I built to earlier specs. It ran awesome!
https://www.hotrod.com/articles/bad-mopars-340-beat-ford-chevy-shocking-new-data/
"Everyone knows Mopar factory horsepower ratings in the muscle car era were the most honest of them all; if the 440 Magnum was advertised with 375 horsepower, that's what it made. And let's not forget how the 426 Street Hemi was cleverly under-rated by the ad guys. Rather than tout its nearly 500 horsepower at 6,000 rpm (and give the safety watchdogs even more to chew on), Chrysler intentionally stopped counting at 5,000 rpm, where 425 horsepower was legitimately on tap.
But what about the 340, launched in 1968 specifically for lightweight A-Body installations, then spread throughout the B- and E-Body performance models in 1970-'73? Did it really make "only" 275 horsepower in pre-'72 mode with 10.5:1 compression and 2.02-inch intake valves? And what about the 1970 SCCA-inspired 340 Six Pack installed in those special Challenger T/A (2,399 built) and AAR 'Cuda (2,724 built) E-Bodies? Was the claim of its 290 horsepower (5,000 rpm) and 345-lb-ft (3,200 rpm) realistic?
We've always wanted to know, and tagged along with Donnie Wood and Steve Chmura of R.A.D. Auto Machine to watch the assembly of a nearly stock-specification 340, and the subsequent dyno test comparison with factory 4-BBL and 6-BBL induction setups. The results was surprising and not surprising at the same time.
On factory claims of 275 horsepower at 5,500 rpm and 340 lb-ft (3,200 rpm), we got 320 horsepower at 5,500 rpm and 368 lb-ft at 3,500 rpm. So it's clear Mopar understated the facts by 45 horsepower and 28 lb-ft. Then we replaced the manifolds with a set of headers and got 352.1 horsepower and 395.9 lb-ft (at 3,200 rpm)—77.1 horsepower and 55.9 lb-ft higher than published peak claims."
<More text on-line - follow link>
I had a 340 in my 73 Road Runner that I built to earlier specs. It ran awesome!
https://www.hotrod.com/articles/bad-mopars-340-beat-ford-chevy-shocking-new-data/
"Everyone knows Mopar factory horsepower ratings in the muscle car era were the most honest of them all; if the 440 Magnum was advertised with 375 horsepower, that's what it made. And let's not forget how the 426 Street Hemi was cleverly under-rated by the ad guys. Rather than tout its nearly 500 horsepower at 6,000 rpm (and give the safety watchdogs even more to chew on), Chrysler intentionally stopped counting at 5,000 rpm, where 425 horsepower was legitimately on tap.
But what about the 340, launched in 1968 specifically for lightweight A-Body installations, then spread throughout the B- and E-Body performance models in 1970-'73? Did it really make "only" 275 horsepower in pre-'72 mode with 10.5:1 compression and 2.02-inch intake valves? And what about the 1970 SCCA-inspired 340 Six Pack installed in those special Challenger T/A (2,399 built) and AAR 'Cuda (2,724 built) E-Bodies? Was the claim of its 290 horsepower (5,000 rpm) and 345-lb-ft (3,200 rpm) realistic?
We've always wanted to know, and tagged along with Donnie Wood and Steve Chmura of R.A.D. Auto Machine to watch the assembly of a nearly stock-specification 340, and the subsequent dyno test comparison with factory 4-BBL and 6-BBL induction setups. The results was surprising and not surprising at the same time.
On factory claims of 275 horsepower at 5,500 rpm and 340 lb-ft (3,200 rpm), we got 320 horsepower at 5,500 rpm and 368 lb-ft at 3,500 rpm. So it's clear Mopar understated the facts by 45 horsepower and 28 lb-ft. Then we replaced the manifolds with a set of headers and got 352.1 horsepower and 395.9 lb-ft (at 3,200 rpm)—77.1 horsepower and 55.9 lb-ft higher than published peak claims."
<More text on-line - follow link>
