six pack engine build

[magnumdart]

O. K. Let me say this as simply as possible. I have a 440 that I want to build that would closely resemble an original six pack engine. I am looking to modify it to the tune of maybe 450 horsepower. Without the bottle. Porting and polishing the heads, boring, hotter cam, and other mods are all possible, but I have not decided exactly. Any suggestions here would certainly be welcome, however that being said, my real and most important question is, how much power can I make using the original exhaust manifolds? This engine is for a '68 b-bod. When it is done I will start on a 340 for my Dart, also to be based on a six pack engine with mild modification and stock manifolds. Thanks

 

[demon seed]

Now that's a good one, I'd be guessing but say that 475HP with the old cast manifolds and 3" exhaust is possible but why would you consider it. That engine, 68, probably has the good 906 heads on it and with a good cam(.509-.525 hydraulic), headers and a 6 pack would easily go 500 HP with a little head porting and 10 to 1 compression.

Terry

 

[moper]

There are two schools of thought IMO.
1> Keep it a 440, simple performance rebuild. Good solid parts, a good 5 angle valve job and gasket match/bowl blend. Dont port. You dont need to, and it could hurt low end an responce with stock manifolding. I'd add a cam that is designed with manifolds in mind to it, and poof..you're at 450hp.

2> Build it bigger, with the expectation of losing some power thru pumping losses of ramming air thru factory manifolds. A 496 with factory cleaned up iron heads and a decent cam would eclipse the 450hp mark with ease, and make way more torque at a lower rpm than the 446 would. Stroking will cost about $1000 more when you're all said and done. Mostly for crank, rods, and port work that the new engine requires. You'll be buying all the other parts anyway. So it's not too bad a deal.

I have seen FAST type cars make mad power thru big inches pushing air thru tiny ports, and I have built a bunch of 440s in the 480hp range with hydraulic cams and pump gas that look less stock but perform as good. Manifolds will limimt power in the end, but you can build around the idea of runnign them and you will not lose as much. So set a budget, then decide the course.