In reading my chiltons manual, i have discovered that in 1971 the hp was 210 @ 4600 rpm and in 1974 it shows 140 @ 3800 rpm. whats up with that? this is in reference to a 302 V8 w/out electronic ign.
Around 72-73 they changed the way they rated HP. Another factor, making engine cleaner with less emissions,,, or so they say,,,
If you notice in your Chilton manual, in the engine specs, the engine also dropped from 9.5to1 to 8.5to1 compression ratio. On an old school engine like that, it is enough for a huge hit in the hp and torque. Also, that was the start of the emissions/smog era.
"Gross" vs. "Net" horsepower. They used to dyno the engines with no accessories attached. No water pump pulley, alternator, etc. The Man decided around that time that it was unrealistic, so they made manufacturers switch to a "net" horsepower rating by putting standard accessories on the engine when they ran it on the dyno. This exaggerated the amount of power that actually was lost by the compression drop and other emissions modifications they had to do. The actual difference isn't quite that much.
If you can find the engine specifications to compare you'll notice that the engines are the same but, as Drew stated above, the manufacturers had to dyno the engines differently. Bruce
They were ? Compression ratio took a 1.5 point hit from 71 to 72, then as rthomas just pointed out, the valve timing was retarded by 4*. And all this was compounded by the switch in measuring HP
I noticed the pistons were different (cant say im 100% sure due to it was a 70 motor i tore down) early 70s had a early 90s design with the dish and valve reliefs mid and late 70s had the flat top design with valve reliefs
I think you got it a little confused. The 68-71 pistons had a slight dish with 4 reliefs. The 72-76's had a huge deep dish (about .250" deep) then Ford went back to the earlier piston design for (slight dish)77-85, then resumed this again for 87-95.
So when did the flat tops come in? Ive had both a 77 and an 80 that i know for a fact 100% were flat tops. And every big bumper 302 maverick i have torn down had flat tops? Not that im trying to piss you off... i'm just curious.
So... with all that i have read in this thread, im gathering that the 74 motor has just about the same hp as the 71. fair statement?
No..see post #8. Lower compression and retarded valve timing took some of the HP out of the '74. Bump the compression back and change the timing gear set and it will be very close. I think the cam grind should be different too but I have no numbers for proof.
You could call the 77=up pistons flat tops, as the dish in the center is only a few thousandths deep. Comp ratio was 9.5 to 1 from 68 to 71 with a 58-60 cc head, then down to 8 to 1 with the deep dish added, then back up to the 8 to 9 range in 77 by going back to flat tops and those huge 70 cc chambered heads til 84. There's probably minor differences in piston tops between the 68-71's and the 77-85 pistons they're not identical, but close.
