Barry, I assume you are going to be carb'd on this....I would highly suggest you send your carb to Dean Nickerson to modify. He will fully flow the carb, square it up, fix the air bleeds, etc. He did mine on a full roller454 and all I had to do then was adjust the idle speed 100 rpm when reinstalled. No over-rich condition, black transom or fouled plugs....EVER. It started like it was injected...instantly. No one does it better!! Glad you are going the P'charger route as your outdrives will last a lot longer!

at this time i am considering going with a arizona speed fuel injection to overcome some of the posssible problems of a carb.

Barry.... I caution you about EFI.....
it happened this summer...meltdown an engine due to an injector stoppingup/leaning out, and not at high rpm either, just 3000 rpm..... It won't ever happen that way carb'd. fuel pressure regulation is also easier on a carb version...7-8# versus #37-45#. A sudden lose of a few # of pressure is serious business with EFI, not so bad with a low pressure system. Heck, just a 2# drop in pressure can stop an EFI cold, it won't even idle. I would go with the carb starting from scratch, no ECM remapping to worry about either! Way too expensive a conversion. I am on #2&3 P'C's now with EFI and wish they were carb'd!
My 02.

I have had 50% luck with the nickerson's. The carbs run awesome when they are brand new, you can't beat them. But he does so much work with the mixture circuits try adjusting the mixture. You will never get it the same again, unless you have a flow bench. I had 3 nickersons I rebuilt once, and had to send all three back to him to get the idle mixtures correct. He told me that they would be very hard to adjust, and he was right.

Not to say he doesn't do bad work, but have fun rebuilding one.

Mr. Gadgets, see Powerboat magazine issue August 2001. Cobra has a small explanation on some of the problems they had when they used Big Chiefs. At around 40 HRS the roller rockers would loose their needle bearings and would destroy the motor. They have since changed to standard BBC heads and the problem went away. The Big Chiefs have some wierd valve angles which make them very powerful, but harder on parts than standard heads. Also Big Chiefs work best with huge lift that can only be produced by a solid roller or perhaps a Schubeck 1" radius lifter. Huge lift and pleasure boat shouldn't be used in the same sentance. Dart or Brodix make conventional heads that will support the wildest pleasure boat engine without the added valvetrain problem potential. Just my opinion.

.... I have found it!!!!!!
the answer is: blown 632

Sorry but I guess I have to defend the Big Chiefs. First I am on my third season with them on some 507 cu in motors which made 750 at 6700. With a hyd roller made 650 at 5500. Proper initial setup is critical, as with any package. Then you need to maintain properly. Initially I had to much spring pressure, no additional oiling and life was around 25-30 hours. KE then set up. Titanium on intake, a Ferra Comp+ on exh. Solid roller. Here's the deal. I am running over 100 hours each season, this year at 120. My spring pressure is at 210 at seat. Isky tool room steel springs. Cam is .678/.651 and .399/.383 at .050. Lifters are Crower severe duty with the extra oiling mod. Here is a major difference, I have valve spring spray bars and KE installed a spray bar in the intake valley to keep lifters cool at lower rpm operation. Max rpm I run would be around 6100. I normally cruise at 2800-3500. Although we did run up to 6700 on dyno.

In winter, the heads come off. Jessel goes over the rockers. We check out springs and touch up valves/seats. Motors currently have Kinsler inj and are very fuel efficient, even with dominator. I average 26 gallons per hour total usuage (for both motors) with about 10 % idle time and running rpms at 2800-3500. At 6000 it is like any 700 hp motor.

For what ever it is worth, I think Big Chiefs are a very efficient cyl head and can provide good service life if given half a chance. Granted, a pair of 10-71's on top would also be nice!

asked him what route would he go. He said in about a 1/2 second. Blower
I asked why and he said you have to turn a N/A so much rpm to get the hp out of them. He said he liked Vortex if he didn't want to go thru the deck.

I have 632 cu in 850 hp and have not had any problems
they will last forever at 5000 rpm which is where i run them
tyson 417-437-0665

[QUOTE]Originally posted by jdnca1
[B]I currently have a Merlin 632 10.5:1 that makes 850 hp @6000 rpm and 820#TQ @ 5000 on pump gas. Here's the combo; Dart 360 fully ported and polished heads (flow mid 420's)

jdnca 1

What intake volume did you end up with after porting? Those are some impressive numbers for a 360 cc head. At what lift do they flow mid 420's? curious