How to make a '71 H.P. Engine

[gary]

Hello All, Which parts are needed to Build a stock HP 440 that would be found in a '71 GTX, W/O six-pack.
I want to replace a mid '70's truck/motorhome engine .I have a pair of correct heads (346) being checked out at the machine shop as we speak. I have a rebuildable 440 from a '68 300 (non HP).I know the cam is different for a HP engine but, what else? I will be going to a forged crank from a cast one (new torque conv.needed)
No racing in the future ,just want engine to be as close to stock 440 HP as possible .Thanks in advance

[71bird]

I thought the correct heads were 906's?

[Eric]

I believe the 346s were introduced for the 71 model year and would be correct on a GTX/440.

[road chicken]

The crank should be fine. From what hear the cast units are good to 500 HP.
I think the only difference from 70- 71 would be the 346 heads and the pistons are 9.5:1. Everything else should be the same as 70. I don't know if the original cam is still available, but the 4286677 ( 455/272/112 cl/48 overlap), should be the closest replacement. If not , especially with a 440, the 474/280 cam would work as well with a little more thump. The 4286677 cam is a great street cam and about all the intake/stock heads/and exhaust will handle.... especially with a stock 11" converter and 3.23/3.55 gears.

I just pulled mine to upgrade to the 484- 284-108 with a lot of mods ( RPM intake, heads, ported exhaust manifolds/ 4.10:1), but I have a friend with a 72 440 ( 8.5:1 compression/ 12 in converter/ 3.23 gears Stock manifolds) that made the 484 mistake, ( a yugo could kick his ass to 30 mph), so this cam will remedy that for him.

[71_bronze_gtx]

Aside from the cam and heads, I believe the differences between HP and non-HP are numerous - the engine taken as a whole including intake, ignition, and exhaust.

The service manual shows different part numbers for distributors, fuel pumps, and carburetors.

I believe the pistons are the same and the bump in compression from 9.0 to 9.7 comes from a reduction in the combustion chamber volume in the HP heads. The new heads for 1971 were intended to help reduce emissions and increase fuel economy by providing more complete combustion. I think that all they really did was change the valve angles. The 906 head seems to be the desirable one for perfomance. Maybe they flow better. You would think more complete combustion might mean more power, but not necessarily.

Possibly the intake and exhaust manifolds would be different. I can't find any info on these in my quick research.

[moparite]

The 906 head seems to be the desirable one for perfomance. Maybe they flow better.

The 906's flow the best out of all the stock heads(with no mods). The down side is they dont have hardened valve seats. Check out the link below, It has a lot of useful info on casting #'s
http://www.mymopar.com/index.php?pid=20

[71_bronze_gtx]

The latest Hot Rod mag has an article about the 440 six-pack. It says that the way Mopar went about dropping compression was to have the top of the piston farther down in the bore, which seems to mean different pistons (but could mean shorter connecting rods instead).

[71440 gtx]

71440 4bbl hp

has 346 heads 9.7 pistons six pack rods - crank .vibration damper hemi oil pan
and they are external balance

71 440 4bbl np

are internal balance