best way to get more out of a 1974 400???

[Paul-ish]

Hi there all!! This is my first post. I have a friend with a 74 charger with a 400 in it and it needs a rebuild
I have no experiance with mopar performance but i do with chevy stuff so that should help.
I'm looking to get some more hp out of this motor...a lot more.
Factory rating was around 220hp? I think 400 would make that car a lot more fun to drive.
So i'll start at the bottom...
Factory block/crank/connecting rods...all reusable?  pistons will be new .030...best piston choice? Maybe bump up the compression a bit?
Heads...what can i do with them? Porting...bigger valves? I know from gm stuff this is the best place to get power. would like to use the factory heads.
Intake?? Carb?? reuse stock stuff or go bigger better? edelbrock intake?
It will get headers and 2 1/2 inch exaust
anything else to look at?
I'll pick the cam last...

Thanks Paul

[greenpigs]

Take a look in the proven combo section first. I don't think there are any 400 builds but I know there are 452 builds. A stroked 400 and your best bet more so if he wants to keep the stock block.

[Mike DC]

  
It's not a bad motor to build up despite its classic rep for being a dog.  

The heads & short block of the 400 was basically very similar to the 383 & 440 magnums.  The 400 motor just has such a bad rep because in the 70s the factory was giving it weak-ass low compression pistons, 2-barrel carbs, the rear axles in those cars were often 2.94 and 2.71, etc.  But once you've fixed those obvious things, the 400 fits right in with the other hi-po big blocks.  
 
 
The 451 talk comes from the stroker possibilities.  All the big block wedges are good stroker candidates, but the 400 became a particularly common candidate due to the fact that the 383/400 B-blocks used slighly smaller main journals on the crank than the 440s.  (Maybe just so nobody would accidentally mix up the cranks at the factory & dealerships!)  So if you get a 440 steel crank with a spun main journal (usually viewed as worthless) + a 400 block (veary cheap too) the crank can be machined down to 383/400 size and used in the 400 block.  The end resulting motors were commonly ending up about 451" when the smoke cleared.  

[Paul-ish]

Thanks for the imput so far...
I'll keep the stroker idea in mind but I would like to keep this as low buck as possible.
I always thought 1hp per c.i. should be  easy to achive.
Right now the motor is running(badly, he thinks it has a stuck valve) but only has 60k miles on it. It has been sitting for 15 years.
I havent heard it yet but will this weekend. I figure ill put some good gas with seafoam additive to help clean it up in there.
Then pull the valve covers and find which valve is the problem. Hopefully i can get it unstuck and running better or i'll have to pull the head.
If the bottomend doesnt need to be pulled apart i probably wont do it
For now a good carb/intake/headers and exaust with the right cam (hydro roller?) should at least get this thing in the mid 300's for hp
If the heads or block are damaged the itll be another story

thanks Paul      ANY MORE INPUT WOULD HELP ALOT!!!!!!!!

[greenpigs]

A roller cam and hardware is expensive for a Mopar. Many run Eldelbrock performer RPM intakes and stay away from edelbrock carbs. I run headman hedders and they fit well. I'll let others chime in on a cam. I dont think you can reach 400hp with the stock pistons.

[firefighter3931]

As mentioned above, the big problem with those 400's is the low static compression and the big open chamber heads. Usual compression is in the 7.5-8:1 range so a piston swap is the easiest way to make more power. 

If you're going to leave the shortblock intact the best couse of action would be a set of closed chamber heads (516/915 castings) to improve the static compression. A cam designed to trap some air in the cylinders and improve torque will be the right choice to wake up the off idle throttle response. Good stall and rear end gearing are crucial as well...these are heavy cars and need some torque multiplication to get moving. 



Ron

[71383bee]

I agree 100%.

The best way to gain easy compression is a swap to closed chamber heads (516 or 915) and use newer pistons. 

My 383 had built 906 heads and kb162 pistons and was a PITA to hold a tune and keep running.  Now it's been redone with a built set of 516 heads.  With the same bottom it runs real well.  It dyno'd at 400/430 with a fairly small cam (.474 lift, 233/240 @ 0.050").

Stroking is always a great option, but 400hp out of a 400 is not hard at all to do. 

[Cooter]

I would like to keep this as low buck as possible.
I always thought 1hp per c.i. should be  easy to achive.
ANY MORE INPUT WOULD HELP ALOT!!!!!!!!

Low buck and 1 HP per cubic inch don't even belong in the same sentence when dealing with a turd 400 from the mid 70's....Even a set of RUNNABLE "516", 0r "915" Closed chamber heads are only worth about .5 point of compression...Ok, your up to 8.6:1, and you've spent at least $500.00 on these heads..

It's gonna take you at least $2500 for a basic low comp, BS rebuild with minimal machine work....The cheapest bang for YOUR buck, would be to buy an early 440 and forget about that old stuck up 400....MY  

[greenpigs]

So tell us how you realy feel Cooter.

[Paul-ish]

I should also add I work for a dodge collision center and can get mopar parts at cost plus %10
I have a friend who runs a machine shop and gives me great prices and I buy a lot of performance parts and get a wholesale discount at my local speed shop.
This motor will never see the track and wont be raced. Just for the size of the car It needs a few more ponys to make it fun to drive.
Dosent need to be 400 hp but even 350 would be a big improvement.
Where are the casting numbers on mopar heads? I will look around and see if i can pick up a cheap pair of those heads.
Also I didnt realize this motor was that low of compression. If i do put pistons in it ill get some hypers and shoot for 9.5 to1 to keep it on pump gas.
I'll probably change the rear end gears to around 3.55 and not sure on the converter yet.
I know hydrow roller cam set's are expencive but this guy isnt going to want to change valve lash


Thanks for all your imput   Paul

[Paul-ish]

Hmmm...this is gettng harder then expected. I 'm having a hard time finding pistons for this thing.

[Cooter]

Well then, that changes everything....I'd go with a typical .030 overbore if it will clean up at that, order up a set of Forged pistons (Not that hypereutectic crap, that has to have specific ring gaps or you'll leave the tops of the pistons in the bores), Add a good set of Closed chamber heads (Casting numbers are the last three numbers and are found under the valve cover on the intake runner next to the valve springs), with a full port job and larger valves(2.14/1.81), Zero deck the block, Nice set of H-Beam rods, with a STEEL crank out of a 383 so it will be internal balanced and you can run either a 4-speed OR an automatic (The stock crank in that 400 should be cast/external balance and cannot run a 4-speed very easily), Performer RPM intake with around a 750 Eddy, or Holley Double pumper, Cam Should try and stay around .550 lift and under with around no more than 238 @ .050 Duration and you should have nice, fat 400 with around 425 HP....

[Paul-ish]

That sounds alot more like what I was thinking...
Maybe a little further than he'll want to take it but at least now i can look up parts and come up with some options...
The cast crank and connecting rods wont hold up to 400 hp ?
I can find 318/383/440 pistons but that's about it..any recomondations?
This car is an automatic and will stay that way forever...he's not that ambitious.
Thanks again...Paul

[greenpigs]

Not many build a 400 and keep the stock stroke. I would look at stroker kits at muscle motors, Indy etc.

[firefighter3931]

If this is going to be a low budget deal then the first thing to do is get it running and take a compression test. Look for uniformity between all the cylinders....10 psi variation is acceptable. Run both wet & dry tests if you find one weal cylinder to isolate the problem (pressure increases with squirt of oil means the ring seal is shot)

Assuming the shortblock is fine and it passes the comp test then you have a few options. If it were mine i'd pull the heads and have them freshened up with a valvejob and new seals with the appropriate valvesprings for the cam i'm gonna recommend below. The PN for those springs is Comp Cams #911

Next it's camshaft time. The Comp xe 256 extreme energy grind is what i would use. It will help bigtime by closing the intake valve early and trapping some air in the cylinder. This will increase torque and make the engine snappy off idle.

A double roller timing chain is cheap and should be installed when the cam is swapped out. I would install that cam on a 106* intake centerline...it should be degree'd in.

Intake manifold is easy ; a stock 383 4bbl manifold will work fine with a 650 cfm vacuum secondary holley/proform carb on top.


Ron

[71383bee]

That sounds alot more like what I was thinking...
Maybe a little further than he'll want to take it but at least now i can look up parts and come up with some options...
The cast crank and connecting rods wont hold up to 400 hp ?
I can find 318/383/440 pistons but that's about it..any recomondations?
This car is an automatic and will stay that way forever...he's not that ambitious.
Thanks again...Paul

The cast crank is fine for 400 hp.  If your really worried about it go find a 383 crank.  Most of those are forged and they are the same stroke.  I do agree that the cost to build the motor is practically the same wether or not you stroke so it is just the cost of the stroker kit that is an add on.  But I am pretty sure that a piston change, some decking and maybe different heads and a cam are really all you need to get 350ish hp.  Closed chamber heads are not that hard to get ahold of and you don't need anything fancy. 

[Paul-ish]

What cars/trucks were the 516/915 heads used on? I will check out the local bone yards for some.
I will look at a stroker kit and also going to look at some aluminum heads( if the old dodge ones are $500 plus porting/machining/bigger valves might add up to just as much as a new set)
Before the week end ill come up with at least 3 possible combo's for his motor.
I'm not sure how far he will want to go but it's nice to have options.

Thanks for all your input guy's

Paul

[Paul-ish]

Also did these motors come with hydrolic roller cams from factory???

[alcusswhen]

40 off the heads with steel shim head gaskets gives you 9:5 to 1 CR with your 452 heads. A 440 six pac cam, headers, Edlebrock intake and 750 Holly carb will put you right 370 horse.

[Cooter]

Also did these motors come with hydrolic roller cams from factory???

NOPE..NO Big Block Chrysler came with a roller ...

[71383bee]

Don't quote me on the dates, but i am pretty sure that most closed chamber BB heads were pre 69.  My 516's were 67 and came with the motor with a spare set of 906's.  

[firefighter3931]

Here's a set of 516's for sale on e-bay  

http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=260490892036&ssPageName=STRK:MEWAX:IT

Another option ; fully machined with fresh valves, springs, retainers, seals for $599. They also have a hardened exhaust seat option ($80) which is highly recommended for unleaded fuel. That's about as cheap you'll pay for a set of (fresh) rebuilt closed chamber heads. 

http://www.aeroheadracing.com/id6.html


Ron

[Cooter]

Don't quote me on the dates, but i am pretty sure that most closed chamber BB heads were pre 69.  My 516's were 67 and came with the motor with a spare set of 906's.  

Just FYI here..
From the very first 350 Cu. In. Big Block Mopar in 1958, Closed chamber heads were on every one of 'em until 1968 when the EPA got involved...Up until around 1964 I believe, the heads had what I like to call "Rocker stands" that unbolted from a machined flat area, instead of the more common cast rocker stands. Also, some of the early heads were 4 FOUR bolt valve cover instead of 6 bolt....Chrysler changed to 6 bolt around '63 or '64 because of leaks...

[greenpigs]

Areohead offers close chamber heads also...

[71383bee]

Really?  I thought they always had opens...i'll go check.

Yep...$599/pair.  Not a bad deal really.  I would request 915's if they offer it. 

http://www.aeroheadracing.com/id6.html