For those unfamiliar with the Volvo B20 series engines, some clarification: it so happens that when Volvo went to SAE net numbers in 1972, coincidentally the B20E ("the" ITB engine) disappeared at the same time in the US market. It was replaced by the B20F, which had a different head casting and was 8.7 to 1 cr vs 10.5 to 1 for the "E". Bottom line... there are no SAE net hp numbers directly available for the engine used as the ITB bogey.
So if we accept the premise Josh outlined above, we have introduced an error of a little over 6%. The factory advertised number used for the '71 Volvo 142E (the only year the B20E engine was available in the US spec 142) would have been 130 hp, and it was indeed a "gross" SAE figure. I've put that adjective in quotes though, because although 130 was certainly not SAE net, it was more conservative than most SAE gross hp claims of the day. If you look at other Volvo B20 series engines that were produced with
no mechanical changes whatsoever spanning both ratings periods (up to 1971 vs 1972 and later) and use those comparisons to extrapolate the 1971 B20E SAE net hp number, you come up with something between 121 and 122 hp.
Furthermore, the B20E's were also being produced for the european market (but identical to our target ITB engine), so they were also rated per DIN standards - at 124 hp. As has been discussed on these pages before, DIN can be converted to SAE net; divide 124 by 1.014 and we come up with just about 122 hp... again.
However comma
:
If we do the IT math - 122 hp * 1.25 * 17.0 = 2592 lbs. (FWIW, I personally think the 1.25 number is pretty close for this engine.) To continue, if we add 50 pounds for double a-arm front suspension, we end up at 2642. The car is currently classified at 2640, or about as close as you can get.
What did I miss? Maybe take the 50 pounds back, due to the truck axle at the rear? You're still only 50 pounds from target - a long ways from 6%.
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