Suggestions for engine build plan

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RogerRamRod

RogerRamRod

The Older I Get, The Faster I Was
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I'm sorry for the Wall-O-Text. I want to start putting together a plan for the motor for my 68 Dart project. I currently have a 340/833 that I ran on the street from 88 to about 2001. It ran strong, but I have no idea of its history or specs. Then it was parked. I occasionally shot WD-40 in the cylinders and turned it over. Fast forward to 2016, It has not been run, but I have spun the oil pump and turned it over by hand. My intent is occasional track days, both Drag & Autocross, no single purpose, but an all around FUN car. My rebuild plan is: Machine work, a forged stroker kit, heads from somebody like IMM, Air Gap & FiTech EFI or similar & TTI Headers. I have a few questions- knowing that the 340 was the better factory piece, but today there are options.

1. I figure a roller cam is going to help a stroker be able to breathe better, by having more duration, yes/no?

2. Since I have the 340, & with the availability of roller cam kits for the 340, and that I plan on a crank & head change anyway-Should I build that or will I be ahead by finding a Magnum 5.9 to build?

3. There is someone near me with a 5.9 for sale with a spun bearing. Not worried about the bearing, but, would that be a sign of neglect that would say the motor might have other problems. Should I find something else, or should that not be much of a concern?

4. I like my 273 Shaft Mount Rockers. Am I correct that there is no way to use Indy LAX heads on a Magnum block (Magnum ports & chambers-but with LA valvetrain) because of oiling-no reasonable mods, correct? Is this not a concern because the Magnum rocker system is fine? -OR-
5. Do I need to figure on MAX heads & upgrade the valve train? At that point have I reached the balance point of having gone the roller cam in the LA 340 route instead?

I am not worried about originality, but I want a somewhat period correct look, so if I go Magnum, I will be using LA pulleys, valve covers, etc. Already have the headers though, so no hunting the elusive manifolds. I also know this hinges on whether the 340 cylinders can/need to be bored etc.

Any suggestions or insights are highly welcome. Thanks FABO for the previous help during the sheetmetal phase.
 
If you want to go stroker, I'd leave the 340 alone. Get a magnum 5.9 and some EQ heads. You have to tear down an engine to see if it is any good. OEM magnum heads are prone to cracking, so magneflux them before you put any money into them. If the mains are spun it usually is not worth the fix. You should also be able to find a standard bore block and just hone it with honing plates. Just use the Magnum valve train, you will already have a roller cam.
 
Semi disagree because your stroking the engine (correct?) and that would require (if your wise) a line home and the possible overbore to the block. Since the block is this far down, it will come completely apart. Oil galley plugs removed for cleaning, block deburring, squaring up the block, torque plate bore and home if need be and I bet it will if it needs to be bored or not, it's the smartest way to go.

The 360/Magnum engine has a minor bennifit to it over the 340 & that being it is all ready set up for a Hyd. roller cam.

IMO, there is nothing wrong with the 340 block for use with this endevor.

I'm not so sure about the EQ heads, but, they can flow a decent amount of air when ported.

I'd also step up and away from the OE rockers.
 
if the 340 has the 1968-71.5 steel crank, why not use it? how quick do you want to go in the 1/4 mile? use the LAX heads and the 273 adjustable rockers. roller lifters are cool, just check the 340 block for large chamfering at the top of lifter bores.
 
For
My intent is occasional track days, both Drag & Autocross, no single purpose, but an all around FUN car.
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It's hard to beat cubes and small to moderate cam.
-A 5.9 with 3.55s and good flowing heads and a 230* cam,would be a ton-O-fun
-But a stroker would be yet more fun.With a small street-friendly roller,you might get into too-much compression issues,though.The stroker allows a little more flexibility in gearing,too.
 
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If you were willing to go away from period correct look, there are a lot of good gen 3 hemis out there.

I realize this is zero help, but it's always a fun alternative
 
Got with a 5.9 magnum for your project. If you are building a stroker you are already replacing the crank rods and pistons. No need to worry about past history other than main bearing bores and cylinder bores.

Magnums can be easily modified to use oil ports. Any competent machine shop can drill the oil passages. The bosses where they pass through the block are there. They just aren't machined.
 
RogerRamRod said:
1. I figure a roller cam is going to help a stroker be able to breathe better, by having more duration, yes/no?
Yes - but any cam with more lift and duration will get more power. IMO, a roller will make you not worry about the break in period. But it is not "needed" for your application. A solid flat tappet will suffice. If you do go with the roller block, a mild street roller will work well even with factory Magnum lifters.

2. Since I have the 340, & with the availability of roller cam kits for the 340, and that I plan on a crank & head change anyway-Should I build that or will I be ahead by finding a Magnum 5.9 to build?
A 340 block will work but need more cash for a roller setup. Lots more IMO, although some do less and call it good. The Magnum blocks are really quite good - but any block should be sonic tested to make sure it's good enough for the levels you want to make, and will need full, complete machining. Not just the basic cleanup rebuild stuff.

3. There is someone near me with a 5.9 for sale with a spun bearing. Not worried about the bearing, but, would that be a sign of neglect that would say the motor might have other problems. Should I find something else, or should that not be much of a concern?
Could be neglect. Could be running issues, could be part wear. Doesn't matter because you're making everything better than new.

4. I like my 273 Shaft Mount Rockers. Am I correct that there is no way to use Indy LAX heads on a Magnum block (Magnum ports & chambers-but with LA valvetrain) because of oiling-no reasonable mods, correct? Is this not a concern because the Magnum rocker system is fine? -OR-
Magnum rockers suck IMO. Not from a performance standpoint, but from a cost standpoint. LA based heads and intakes are most cost efficient in my experience. It doesn't really matter as long as your builder knows what he's doing and you accept the fact that you will spend on the rockers. Using the roller block and stock type lifters could offset that cost tho.
5. Do I need to figure on MAX heads & upgrade the valve train? At that point have I reached the balance point of having gone the roller cam in the LA 340 route instead?
You will have to upgrade the valve train regardless of what head you choose.
I am not worried about originality, but I want a somewhat period correct look, so if I go Magnum, I will be using LA pulleys, valve covers, etc. Already have the headers though, so no hunting the elusive manifolds. I also know this hinges on whether the 340 cylinders can/need to be bored etc.
Almost any head when painted orange or red (or blue) will look stock to almost anybody not into Mopars. That being said - you should be looking at a mild setup. Not worrying about horsepower numbers. Mild compression, cam around 250* at .050", 5500 or so power peak. I've built several of these, and they run great and have plenty of power. Going for max HP will lead you to spend more than you have to in order to hit a number. Also - disregard engine dyno figures. They are for the most part smoke and mirrors.
Click to expand...
 
Thank you for your responses so far. You noticed I didn't say anything like Aluminum heads, how many Hp will this make etc. I think I misused duration when I meant more under the curve.
 
Right. But inevitably that will come up...lol
Area under the curve is determined by the lift over various duration figures throughout a given lift cycle. So you were right. Duration, advertised (total) anyways is just another way to describe it.
 
how much power do you want?
If cost matters an LA flat tappet 360 can be built economically and
be very quick in an A body...
 
If I build an LA motor, barring any problems with inspection, I would probably stay with the 340 I already have.
 
most will tell you sell the 340,buy a cheaper 360 and take a profit.
me....i'm a 340 fan, and through all my builds have never owned or wanted a 360.
 
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