Did the 340 really make 275hp?
340 wasnt the only engine underrated. I mean cmon,ya really think the 426 hemi made only 425 h.p? Chrysler was bad for underrating motors,just like the other's. Sure it makes that much h.p,but at 4000 rpm's,lol. Nevermind the fact you can wind em up to 5500 rpm,lol..
Detroit horsepower ratings were changed for the 1972 model year from gross rating numbers to net ratings.
Net ratings were supposed to be more realistic real-world numbers, because the new testing methods utilized different methodology more in keeping with "as installed" conditions (accessory drives hooked up and operating, and exhaust running through a stock exhaust system, including mufflers.)
But, along with this new rating system (about 30-percent lower numbers, usually,) the 340 went through a "de-tuning" that year that included smaller intake valves, and lower campression. So, an "apples-to-apples" comparison with the '71 engine wasn't possible.
My 318 2bbl 1972 L-A engine went from 230 HP down to 150 HP with no mechanical changes from '71 (gross) to 1972 (net) rating.
Tht is a change of 35 percent! (.35 X 230 = 85.)
They were wildly inconsistent with this; if they had used that figure (35-percent) on the 275 HP 340, even with NO changes, it would have resulted in a drop of 96 HP, down to a net rating of 179 (ridiculous!) instead of the 240 they claimed.
I remember the '72 motors as exhibiting noticably less "grunt" on the drag strip (about half a second) but the NHRA experience has shown these 1972 motors to be only VERY SLIGHTLY less powerful than the 10.3 compression '71 340s. Racers somehow, have found a way around at least some of the power-robbing changes the factory introduced in '72. The NHRA HP factor for the '71 340 is 314 HP. the '72, 298... 16 HP for the lower compression and smaller intake valves... not much of a change (on the order of 5-percent.)
The exhaust manifolding (particularly, on the drivers' side) was just awful on these 340 cars; a decent set of headers made a huge improvement, and of course, they were jetted really lean from the factory, so a set of headers and some richer jets would really wake this engine up!
It's too bad that Ma Mopar didn't see to it that a set of W-2 heads were on every 340 that left the factory; Brand X would not have stood a chance! :cheers: