68-71 Factory HipO 340 Horspower Rating..who has the real answers?

[kawahonda]

I know someone that thinks 275HP is MAX that 68-71 340s ever made.

I'm curious based on experience of people that have lived during this time.

What did a factory 68-71 HiPO make at the flywheel? Distributor re-curving/advancing is fair game. Flipping the air cleaner lid/different element is fair game. Re-jetting is fair game. Things that normal people do is fair game.

Anything else isn't fair game (headers, intake, etc). Sticking on a 440 AVS carb isn't fair game, although I read that 340s seem to love that.

Curious to hear real world, factual experiences.

From all the information I can soak in, it appears that a well tuned "fair game" 340 from this time period is a 300 horsepower engine. I've read 315 from allpar.com when the engine is set in a perfect environment. I've read 281 HP from hotrod.com with out any distributor tuning or AVS tuning. It makes me think 300 is a very real-world number without the bullshit. Is this correct?

[Chryco Psycho]

Real world the 340 was way under rated , 310 is a good estimate , I have never seen a 383 outrun a 340 without major mods to the 383 , Keep in mind the 383 is also about 100 lbs heavier .
I ran a GTO 69 , Ram air 3 , 4 speed with my 340 s Cuda & embaressed him not by a car length or 2 but a train length to 60 mph

[RUNCHARGER]

I agree 310HP is pretty accurate. I think NHRA factored the 4 bbl to 315 and the Six Pack to 325, something like that anyway.

[mccannix]

I agree and it was too bad about the HP factoring for the 340-6, since in my time and area, factory 340-4V cars most always had a hand up on the factory 340-6 car

[RUNCHARGER]

Okay: I had to look it up;
1970 340 NHRA factor 300HP
1971 340 NHRA factor 325HP
1970 340+6 NHRA factor 330HP
Surprisingly
1972-1973 340 NHRA factor 280HP
1974 360HP NHRA factor 290HP
I seen a few good running 1974 360's back in the day.
The 1971 340's ran good if the carb was in good shape, not sure if they were 25HP stronger than an AVS though.

These are from a 1980s DC Chassis manual.

[mccannix]

Sheldon, good info...does it show 68-69 figures.
68-9 Darts with 340 always hauled good, seemed to have the right weight transfer.
68 Dart 340 4 speed had the hottest factory cam, just wondered if it was the same as the 1970 figure....or higher ?

[RUNCHARGER]

They rated the 68-70 all the same. I agree I'll take a 68, 4 speed A-body as the fastest 340 with their special camshaft.

[jimynick]

I had a late '67 340 out of a smashed GTS in front of a 4 speed and 3:91SG in a '67 2dr post Valiant and the only thing that ever beat it was a '67 Fairlane 427 2-4's 4speed and that was only by a fender. The Fairlane was rated at 425hp. It seems to me that somewhere, not long ago, somebody did a pretty much factory re-build of a 340 and it was pretty close to 350hp; around 340 which would be a horse per cube. Pretty good stuff from the factory! I've still got the block. LOL

[kawahonda]

So the HiPo 340 put out about the same power as a 383, if not a little more?

[Chryco Psycho]

And it weighed less

[kawahonda]

LOTS of good information on the 340 here:

https://www.swinger340specials.ca/340-review

[Todd489]

Okay this is my experience with 340s and 383s, over the years I've had owned 3340s and one 346 pack for my TA Challenger, on my first cuda convertible, I had 340 rebuilt the factory specs! Every motor I have done I have dyno tested, it dynoed at 286 hp.  My other 340 for my 69 cuda, again factory rebuilt, exactly 279 hp, and my 340 6 pack, again factory rebuilt, but this time it was headers,  323 hp!  Imo they were not underrated! Dynoes do not lie.

[Chryco Psycho]

Which dyno tho , Mustang dynos always read lower than the rest

[Todd489]

It wasn't a mustang Dyno! I thought mustang dynoes were only for chassis , I will have to find out.

[Chryco Psycho]

I have only seen Mustang Chassis dynos , but dynos do read differently , for example a Dyno Jet water dyno typically reads about 15% higher than the same car on a Mustang dyno
They are a great tool & if you always use the same dyno you can see where you are gaining or losing but comparing #s from different dynos can be misleading