so if you were to put a 408 together with about 9.5:1 to 10:1 compresion some nice heads and a small blower cam and top it with a radix it should make a bunch of torque downlow. but how would it do if you went up to say 6000 to 6500 rpms?

 

Well, with a 2.8 pulley, you'd be spinning it up around......?

Come on you guys with the formulas and calculators!

Once you start getting up to 17,000-18,000 RPM's with a Radix, your getting very inefficient.

 

the idea would be to keep it below 6000rpm. basicly you'd be taking advantage of the cubes and long stroke alone. trying to get a boosted 408 that will spin 6500rpm past the emissions boys in cali anyway is just looking for problems. for an everyday driver that would get some respectable fuel milage and pass emissions without much trouble i don't see where you could go wrong with a mild 408 and a radix. i keep seeing the comment come up of big power. in the case of the person asking the question he's running a 5.3 with a mild cam. why would you want to go through the trouble to build a 6.7L and turn it higher. if real big power were the goal a 408 that could turn 6700 or so and run 18psi would be a blast. somehow i don't see that as a happy daily driver idling in traffic in 100+ degree weather with the air on for up to an hour or so at a time. there was a time when somethig like this was built just for the cubes. now i don't get it. someone will go from a 5.3 with 8psi or so and their next goal is a 6.7L that runs 20psi and rev's to some 7k or so. i think running the same powerband that a stock 5.3L runs with a 408 would make the killer daily driver that has power all over the rpm range and can idle in traffic without acting like it's race day.

 

You nailed it zipman, that's the crux of the matter. I like my power curve just the way it is right now....max torque at about 1200 RPM's and rock-solid steady up until 6000....I just want it 150 RWHP higher so I can roast them at will. Too bad I'm not closer to TN, I'd love to see and experience what mr. whitt has assembled for himself. Sounds pretty sweet.

 

My Radix 402 makes peak power at 5900rpm but it does'nt fall off until above 6800rpm so I shift at 6800rpm,which puts me right back at peak torque 4000rpm in the next gear.I have plenty of torque at 1500rpm but it's not nearly at it's peak.