Do stock unported 1968-71 340 heads flow about the same as the Big block 906 Heads?
Thank you.
Through the stock mani, they flow very similar which is why the 68-70 340 has almost the same NHRA HP factor as the 68-69 383.
Isnt the factory weight of the car the motor comes in a consideration as well when factoring?
Factory weight and HP rating are used to find the car's natural class, NHRA may change that factor higher or lower depending on how well the average car of that combo runs, that's the very simplified explanation. As an example the 68 Barracuda with a 340 was factored to 299 from 275, with the 383 it went down to 295 from 300. so the 68 Barracuda with a 340 would have to weigh 42 lbs more in F/SA @ 10.5lbs per HP which is where they frequently run. Also note that the same cars in Super Stock would have the 383 @ 19 HP more than the 340 where the stock mani is no longer the equalizer.
