302/347 vs. 351w/408w

[smoktf250]

10~10.5:1 compression would be a good starting point. That should run good at altitude.
Heads could be argued forever. I would recommend a 2.02/1.60 head. Those huge valves probably have flow issues when run on a standard 4” bore engine. Now if you were running an aftermarket block with 4.125” bore then they wouldn’t shroud the valves so much.

500 HP is your only goal? Do you want any low end power, street driving, economy? An engine that makes 500 HP is fairly easy with a nice big cam and carb. The ability to enjoy it anyplace other then high RPM on the dragstrip is another issue.

well yes I do want a decent all around powerband...with good top end...what shoudl i expect fuel economy wise with a 408?

 

[Broncobowsher]

500 HP on paper is easy to come up with. Big heads, big cam, big everything and you are ready to go.

Drivable big engine, big heads are fine, largish intake is good (remember a large intake for a 351 is only a good sized one for a 408). No stock parts for the breathing duties.
Keep the cam fairly mild. 408 is a long stroke engine, High RPM isn't really a great idea. That will also keep the drivability and reasonable gas mileage.

as for economy, if you build a torquey engine (which will be fun), stay off the pedal that much it shouldn't be that bad. Low teens? With some fun with the skinny pedal high teens should be seen from time to time.

Little thought. The local drag strip wouldn't let me run one night a few years back. Centerline of the crankshaft was more then 24" off the ground. They were enforcing that rule because some nut was racing a lifted toyota pickup with a bottle fed small block. He wasn't the safest person to be around so they pulled that rule out of the rulebook and started enforcing it. Slower trucks got overlooked, but the faster ones got that rule thrown at them to keep them off the track.

 

[HoosierDaddy]

well yes I do want a decent all around powerband...with good top end...what shoudl i expect fuel economy wise with a 408?

Judging by that last comment , I'll second the "build for torque" comment. That's what is gonna plaster you to the seat when you jump on it from a stop , and with a healthy 408 , it will keep you plastered there for a bit.

You're getting some great advice from Broncobowsher and the rest of the group, so I'll bud out now.

 

[Broncobowsher]

Was throwing out magazine I collected at SEMA. The December 2007 Popular Hot Rodding magazine has a build of a 500+HP 408 Windsor. There build came in at $8000 or so. Nothing extra, money spent where needed and not on extra stuff. There dyno pulls start at 3,000 RPM and it peaks the HP at 5,900. Compression is 10.9:1 which is the upper limit on premium pump gas.

Between HP ant torque, torque is a lot more fun to drive. Torque throws you back in the seat and kicks you across the intersection. HP is something that takes a moment to get into. It also gets you into trouble. Torque is the scoot, HP is the speed.