Given this is not going to be a race car I'll be the only one in this thread to throw up a caution about doing anything bigger than it needs to be. Bigger blowers CAN make more power but they definitely suck more power, take up more real estate and are less responsive in the lower RPMs (don't build boost as quickly at lower RPMs). Not always a happy combination on a non-race car.
To put things in perspective, please consider the difference in displacement between a 6-71 and an 8-71. The ancient but venerated numbering scheme might lead the uninitiated to think that the 8-71 has 33% more displacement per revolution. 8 is 33% more than 6, right?
Unfortunately, that's not the case. A 6-71 displaces a theoretical volume of 411 cubic inches of air per revolution. An 8-71 displaces 436 ci per revolution. That's a difference of ONLY 6%. (It's a positive displacement pump, please remember, not a compressor, so this is a very relevant number- no compressor maps or any of that crazyness to worry about.) How important is that 6% to you given that a pulley change can easily make up most of that difference and also give you a little better low RPM responsiveness?
Not going to suggest one over the other becuase the difference is so slight there isn't much to argue about either way. I'm just saying that you are not going to be putting yourself at any significant power disadvantage by going with the smaller unit, especially something that isn't going to be purpose-built for racing. You won't run a 6-71 out of lungs on that combo and you won't get a huge power increase by going with the bigger 8-71, either. Your call.
To put things in perspective, please consider the difference in displacement between a 6-71 and an 8-71. The ancient but venerated numbering scheme might lead the uninitiated to think that the 8-71 has 33% more displacement per revolution. 8 is 33% more than 6, right?
Unfortunately, that's not the case. A 6-71 displaces a theoretical volume of 411 cubic inches of air per revolution. An 8-71 displaces 436 ci per revolution. That's a difference of ONLY 6%. (It's a positive displacement pump, please remember, not a compressor, so this is a very relevant number- no compressor maps or any of that crazyness to worry about.) How important is that 6% to you given that a pulley change can easily make up most of that difference and also give you a little better low RPM responsiveness?
Not going to suggest one over the other becuase the difference is so slight there isn't much to argue about either way. I'm just saying that you are not going to be putting yourself at any significant power disadvantage by going with the smaller unit, especially something that isn't going to be purpose-built for racing. You won't run a 6-71 out of lungs on that combo and you won't get a huge power increase by going with the bigger 8-71, either. Your call.
