Difference between 71 and 72 455 engines

[Austrian455]

Hey,

maybe I should be ashame to ask this question, but what are the differences between the 71 and 72 455?
71 rating: 315 hp
72 rating: 250 hp

both had 8.5:1 CR

As far as I know they had the same combustion chamber cc´s, same size intake and exhaust valves, 800 CFM Q-Jet, ??
OK, the 72 has this SMOG-crap. Was there a difference at the camshafts?
I don´t think that only the SMOG passages in the heads make the difference.
Because that would mean that my 455 should have 315 hp with the performer intake installed. :confused4:

[Jimsss]

The biggest difference is the rating, 71 is SAE/Gross HP and 72 is Sae/Net HP
72 Also have a smog pump, I'm not sure that the 71 has one.
I think a 71 and a 72 have about the same power.
The smog pump takes tops 10 hp away if any...
250 sae/net hp equals about 315 sae/gross hp
/Jim

[Austrian455]

OK, so if I understand that correct: 71 rating was 315 hp on the crank without waterpump, alternator, fan, PS pump....
72 rating was also at the crank but with all the stuff running.

Correct ?

[Jimsss]

Yes, correct


The 1972 rating is closer to the truth on what power you're getting.
And it's more like an estimate than actual truth, they didnt do any
measurments back then. My 1972 feels just as strong as my older cars felt.
If I step on it from a standstill it will smoke the tire(s) from here to Chicago.
These engines produce massive tourqe right from idle but not much hp over 4500rpm.
I think a well-tuned 1972 can be more powerful and responsive than a slighly out of tune 1970...

[The German]

Perhaps this is interesting for you :

http://neptune.spacebears.com/opine/horsepwr.html

[Austrian455]

Thanks Rolf,

Good post, that answers all questions.
That would mean that my Centurion should have 250 hp at the flexplate.
=> should make about 200 hp at the rear.
Ohh man, I have to save some money.
When I look at the shape of that Coupe it wasn´t built for 200hp.
Looks more than a "400 hp at the rear" car