what did chevrolet do to engines in the 70's
to make them so bad? i have 75 camaro rated at 145 hp with a 2 barrel. it has 8.5 to 1 compression. do they have really bad camshafts,heads or intakes(the 4 barrel version in 75 has 155hp).

<font face="Arial,Verdana" size="2">do they have really bad camshafts,heads or intakes</font>
Yes, Yes & Yes is the answer.

Also the compression was lower, exhaust more restrictive & early emission control devices started to be used.

Mileage & emissions were the main goal then, not HP.

Most of them were just de-tuned by lowering the CR about 2 numbers!!

The cams and everything else stayed mostly the same.. Until they started the EGR thing for NOx control reasons..

Then they went into the crapper fast!

And remember that around this time they went from gross dyno hp numbers to net which made the engine changeover to smog/emissions controled look a lot worse then it actually was back then..

pdq67

Also, in the 60's they exaggerated the hp numbers, then when insurance companies started to raise rates based on HP automakers lowered them.

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<font face="Arial,Verdana" size="2">Originally posted by pdq67:
Most of them were just de-tuned by lowering the CR about 2 numbers!!

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And that is a BIG difference.

<font face="Arial,Verdana" size="2">Originally posted by Daniel:
Also, in the 60's they exaggerated the hp numbers, then when insurance companies started to raise rates based on HP automakers lowered them.

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They weren't so much exaggerated, as they were measured differently. They measured the HP in the 60's with no exhaust or accessories. Hence the term Gross HP. They started measuring it differently in 1973 (or thereabouts). In 1973 (or thereabouts) they started measuring HP in NET numbers with all the accessories and exhaust installed in an "as installed" configuration. Basically you had to subtract the accessory drag, and exhaust losses to get the "net" figure for the 60's and very early 70's engines.

Not just chevrolet...

remember the oil crisis, emissions regulations, etc..

the GOOD thing is that just changing a couple things, you can turn your boring 145hp 1975 350 into a 300 or more HP fun to drive 350.

new set of decent pistons, some work on the heads, or new ones, a nice camshaft and of you go.

moving from 8.5 to 1 compression to 9.5 to 1 .. is a BIG change.

Smog engines, de tuned for lower emissoons.

Very slow mech. advance curve, total timing set retarded more, low compression, big chamber heads.

'75 would be in the middle of the emission BS so old lead pellet filled cat. converter, crimped small exhaust, EGR set up, etc.

All the emission year cams was pretty tame too. Very low lift and duration, wide LSA's