Here's some of the issues involved:
To make generous power with a standard displacement iron head Clevo is easy & possible, but 500 bhp (flywheel) at 6000 rpm may be asking too much. I've seen good engine builders achieve 500 bhp at 6500 rpm, and 500 bhp at 7000 rpm is easy! Horsepower is (torque x rpm)/5252. Therefore to achieve 500 bhp (flywheel) requires the following torque at peak bhp rpm:
500 @ 6000 rpm = 438 ft/lbs
500 @ 6500 rpm = 404 ft/lbs
500 @ 7000 rpm = 375 ft/lbs
A standard displacement Clevo will produce about 440 ft/lbs torque at peak, with cams in the 0.600" lift range. This requires either a flat tappet solid lifter cam, or a roller cam (hydraulic lifter or solid lifter). The Clevo's combination of valve spring, rocker arm ratio and camshaft base circle size can open the valves in that range while maintaining reliability.
To make peak torque of 440 ft/lbs at 4000 to 4500 rpm and still have enough torque (438 ft/lbs) to make 500 bhp at 6000 rpm looks impossible to me.
To make as much power as possible in the 2000 rpm to 6000 rpm range (or any range for that matter) requires the following preparation:
>Good flowing intake system
>Good flowing exhaust system
>Well prepared 4V heads
>Camshaft ground to work best with the flow characteristics of the heads
>The best obtainable piston ring sealing
>Dyno tuned carburetor and ignition
Keep in mind that a peak bhp number is just a number, what is really important here, to provide a motor that has a good kick on the street, is crisp carburetion and a wide flat torque curve that is as strong as possible at low rpm and pulls hard to 6000 rpm. The further we design a motor to pull in the upper rpm range, the harder it is to maintain a hard pull at low rpm and the harder it is to maintain a decent idle and good drivability characteristics.
As far as intake manifolds go, I say use what you got. To make a broad spectrum generalization, out of the box, unmodified, any of the two plane intakes (Ford, Edelbrock or Blue Thunder) will work about the same below 5000 rpm, which is where the majority of your powerband is. The Blue Thunder will make a bit more above 5000 rpm than the others and is a good compromise intake providing two plane power below 5000 rpm and a good pull above 5000 rpm. The single plane intakes (Holley Strip Dominator, Parker Funnel Web or Edelbrock Torker) will make better power above 5000 rpm at the sacrifice of power below 5000 rpm. The Holley Strip Dominator is a long time favorite of Cleveland engine builders, and the Funnel Web is a good design that came on the scene more recently. The Strip Dominator or Funnel Web with a "designer" Holley in the 750 cfm range, would be a good combo for making the most torque over the widest streetable rpm range (idle to 7000 rpm). However with our more modest powerband goals of 2000 to 6000 rpm, the two plane intakes are only giving up power in the last 1000 rpm. So my advice would be to start with what you got, and spend the money elsewhere for now, you can always bolt on an intake later and compare it to what you were running before. I would rather see you spend the budget elsewhere.
You mentioned that your carburetor is running "fat" (rich). Getting the carburetor jetted properly would find a lot of horsepower and would make throttle response more crisp and seamless. This is a must do. You also mentioned your carburetor is a 700 cfm model, in my experience that is a bit small, 750 cfm would be more ideal. So with more power and crisper throttle response as a goal, it may be time to consider a new 750 cfm "designer" carb. Holley makes their own line of designer carbs, the "HP" carbs, I've read generally good feedback about the out of the box jetting of those carbs.
I don't have a clear idea of what your exhaust system is composed of, but if the tubing between header and muffler is only 2" OD, its too small. I consider the GTS exhaust system as a standard by which to judge other exhaust systems, the tubing of the GTS exhasust is 2 3/8" OD. I would advise you to upgrade the tubing on your exhaust system to 2 3/8" OD or 2 1/2" OD tubing. Free flowing mufflers are also needed, some are louder than others, some fit the Pantera better than others, they all have a different look, but that is an area you need to investigate. Dan's advice about installation of an O2 sensor bung is very good. It may come in handy down the road to help with tuning problems, or to upgrade to fuel injection.
As far as camshafts go, a custom ground cam is preferred over an off-the-shelf cam. MME is your source for a knowlegable Cleveland engine builder who can spec a good cam for your motor and your power goals. I recommend a roller cam for the reasons mentoned by Dan (lack of zddp in motor oil, cam lobe & lifter failure issues) so if there's room in the budget, that's the way to go. Off the shelf roller cams that fit your goals are the Crane #529551 hydraulic roller or the Crower #15480 solid roller. If a roller cam isn't in the budget, then my fall back off-the-shelf flat tappet hydraulic cam is the Comp Cams XE274. One last time, I want to emphasize, a custom spec'd cam will work better than these off the shelf cams.
This last recommendation is going further than you intended to go, but I bring it up just to give you something to think about. Cylinder head port work by an engine builder who understands using the 4V Cleveland heads on the street would be necessary when seeking max power. Low lift flow is weak with the 4V head. The head grinders will perform some port & bowl clean up, extra work on the exhaust port roof and the exhaust port short turn radius, and finally multi-angle valve seat work. However, before spending money on 4V head port work, its time to sit down and consider if an investment in other heads would have a better pay-off. Considering we're working with a standard displacement motor, our power band goals are 2000 to 6000 rpm, drivability and crisp throttle response are a big factor in being happy with the motor, camshaft lifts in the 0.570 to 0.610 range will be utilized, the power goals are 500 bhp or less, a set of small port heads would actually provide superior results. Food for your thoughts.
What ever you do, have fun with it!
cowboy from hell
