Mid 70's 350's

[thebikedoctor33]

What did chevy change from the late 60's into the 70's that killed the power that their 350's made? I know its all emissions and all that crap but what exactly did they do?

[jveik]

they used really wimpy cams with less than .300 inch lifts,

really crappy exhaust systems especially catalytic converters,

really bad intake manifolds for horsepower at least, although carbs were not the worst in the world,

REALLY CRAPPY heads,

very low compression ratios, i think they were less than 8:1 for some?

all these emissions-compliant parts added up to 350's making only 160 horsepower and the worthless 115 horsepower 305... it was a very dark time, contrasted to the pre-emissions 350's that were offered at up to 370 horsepower. wikipedia claims that a certain type of big block 427 (67-68 L88) from pre-emissions times made 560 horsepower.

before emissions, many small blocks made or exceeded one horsepower per cubic inch, with the legendary 302 that is said to have at least 320 horsepower. lol emissions really sucks dont it?

[Paul_Jones]

it was all for emissions control!!!!! its terrible that they took away all that raw power!!!
Paul

[jveik]

yeah pretty much... many of todays high performance aftermarket parts are really pretty close to stock small blocks from the sixties... imagine having a stock 370hp 4 bolt 350!!! they actually lasted a decent amount of time too, unlike many of todays equivalent modded small-blocks lol where rednecks pump a completely cast parts shortblock with over 400 horses of top end parts and it lasts maybe 50,000 miles at best lol...

[AlmostStock]

While it's true that actual HP dropped during this period that's not the whole reason for the drastic difference in posted HP ratings. In 71 - 72 the manufactures switched the ratings from "gross" HP to "net" HP. This alone accounted for a big difference. I have a 71 Nova brochure that lists both ratings, and for that year it was approximately 190 net / 250 gross, or there abouts, for the same 350. (I don't have any listings in front of me right now.) So the mighty "one HP per cubic inch" motors of the sixties were probably around %25 lower if rated with the newer "net" scale.

[jveik]

manufacturers should start rating engines on a particular vehicular basis(for rear-wheel and front-wheel drive cars), as in, they should strap the actual vehicle up to a dyno and use actual power at the wheels, which would be more accurate in that different vehicles loose different amounts of power from the drivetrain and transmission and thereabouts. the only problem would be that some companies would use like a 6:1 rearend just in the vehicle in the test lol, they would have to standardize stuff or say the parts must be included on all production vehicles lol

[abaird]

Originally Posted by thebikedoctor33

What did chevy change from the late 60's into the 70's that killed the power that their 350's made? I know its all emissions and all that crap but what exactly did they do?

Switching from leaded gasoline to unleaded. Lower octane means you need lower compression. Engines with high compression will always have more power than the same engine with a lower ratio. Thats why we see all the original musclecars with 12:1 and new vehicles with 8 or 9:1

[jveik]

yeah lol i saw some leaded gas era specs for the big block 427 that said it had 13 to 1 compression lol. i guess with over 100 octane gas back in the day that was probably not out of the question, maybe thats why it was claimed to make over 500 horsepower lol