Actual output of the '72 340 engines..Just to add my input if I may, from what I do know and of my experiences with my '72 Duster 340. I will use the '71 340 as a comparison because it was set up more like the '72 than any of the early 340's, using the same carb and intake manifold. The only changes to the '72 340 over the '71 was in the pistons and the intake valves. Whether you have a cast or steel crank really has no effect on output so I won't include that in the comparo here. The '71 was factory rated @ 275..LOL we all know that was a JOKE to gain an edge at the drag strip. Ever witness a run between a chevy 327 rated @275 and a duster/ dart 340 also rated @ 275 then and you will know what I mean,..half track comes to mind. LOL. NHRA IMMEDIATELY refactored the '71 340 to 330 horsepower, which I believe is accurate. They refactored the '68-'70 to 310 horsepower . I have seen MANY dyno pulls over the years on stock and stock rebuilds (stock heads ,stock compression, factory camshaft ect. )of the earlier AFB equiped 340's they ALL pulled in the 310-315 range. So with what we know..how much is the 2.020 valve worth being that the heads are identicle other than the intrake valve. On my flow bench the 2.020 valve is worth 10 cfm @ 28" over the 1.880 valve as cast all else being equal with NO mods whatsoever. Using the superflow formula 1 CFM is equal to 2.06 horsepower. That would be just about 20 horsepower..as close as we can get. So with this we have 310 horse for our '72 340 engine. Now the compression and how this changes things. We also know that for every point in compression it is equal to 4 % , once again..as close as we can get. so 4 % of 310 is just about 12.4 horsepower , but as has been stated the actual CR was really lower than the stated 10.5 CR for the '71 340, More like in the 10.0 - 10.2 range. so we will use 11 - 12 horsepower for our comparison. That will give output for the '72 340 engine right at the upper 290 range , 295 would be more than fair which is as I believe to be accurate..close enough . My '72 Duster 340 ran before my rebuild with stock heads , with Offy port O sonic intake using the TQ with adapter and An Alliance .480 hyd. cam , 1 5/8 heddman headers with 3.91 gears on stock tires 98,000 on complete drivetrain with Auto went 13.50's @ 103-104 regularly , best being 13.53 and would go 13.60 on any night shows that the '72 340's were some great performers. 103-104 mph in a Duster/Dart would take just about in the 340 horsepower range . The intake, camshaft and headers would be in the 50 plus range so that would also support the 295 range as stock output for the '72 340 engines. The factory rated the '72 @ 35 less than the '71 is mighty close. Mopar rated the '71 @ 275 , this had to have been the SAE rating even though that wasn't officially used until 1972. JMHO.
Terry
