Finally Decided On a 340/372/416 Six Pack; A Few Questions

[Road_Runner]

OK, here is what I've got and want on this engine build: 73 340 block, supposed to be std bore, we'll see. 73 'J' heads, Original SixPack Intake & Aircleaner, current replacement carbs, 70 HP exhaust manifolds, 340 forged crank if I don't go stroker.

So I'm looking for the most HP/TQ I can get while still keeping this combo very streetable for PB, AC, etc.

I want to use the HP exhaust manifolds but I figured I go with a nice performance 2.5" exhaust so not limiting myself to 'stock' pieces.  Transmission-wise I'll probably stay with an automatic and get a 2800 rpm torque converter, already have shift kit installed.  Rear gearing to be determined.  Thinking about either 3.23 or go with a 3.91 and put a Gear Vendors overdrive on it.  Only other option I'm considering is swapping to a stock 4 speed and stay with a 3.23 rear.

Given my parts is it worthwhile stroking it or will that be too many cubes for the exhaust to handle?  What mods to the J heads?  Cam choices for a 340, 372 and 416 if different for each engine size.  Definitely want hydraulic, would consider roller to allow use of current oils.  Not sure what else but I'm glad I've finally decided on this much.  I guess I'm going for a AAR in Barracuda clothing....

Will probably be listing some parts here including intakes, carbs, air cleaners, etc. that I won't be using now before I list them on Ebay.

Thanks in advance, Jim

[cudabob496]

most hp/tq, while staying streetable, means definitely stroke it.

[Chryco Psycho]

 
 More CI is the answer , it will increase torque everywhere , it will make more power at lower RPM so no need to beat up parts , you will remove 5-6 lbs from the rotating mass so it will rev easier & make the parts seems stronger with less load applied , no down side .
 The manifolds may trim off some power above 5000 rpm no big deal if you have more power all the way up to 5000 & probably beyond that just less than to overall potential .
 The J head mod would be to swap for the 308 swirl heads to the tune of 40 more RWHP , they are both cast iron , look stock  & take shaft rockers , no downside there either .
 Cam choice is difficult , fast ramp high lift but with minimal duration powerband between 2000-6000 stall around 2500 rpm . Roller is a good call to a point , $40 each for lifters or pirate a set when you pull the 308 heads except they will not work in a 340 block only the later roller 360 blocks  , downside is cost , over  1K for hyd roller cam ,  lifters ,  chain springs , retainers, etc + you have block mods generally you need taller lifter bores, maybe bushing the lifter bores  or restricted oiling , the fastest way to get a roller cam block is to use the later 88 -92 roller 360 blocks .
 I love the OD route , typically I use the 833 OD , the 518 is another option

[erat340]

As always, 1st. Ask yourself, and be honest, what RPM and speeds am I going to drive this car most/all of the time? Me? I got stock block, unmolested Eddie 63cc heads, small 256 dur. vodoo, air gap, 750 holley HP, fattened up, and would you believe?, a 2.76. Ive got some serious low end grunt and it will pull on the freeway at WOT until I git skeered and back off. O and 4 speed is justfun.

[Road_Runner]

most hp/tq, while staying streetable, means definitely stroke it.

That's kind of what I figured, but wondered what impact the 'restrictive' exhaust manfolds would have on the decision.

Thanks, Jim

[Road_Runner]

 More CI is the answer , it will increase torque everywhere , it will make more power at lower RPM so no need to beat up parts , you will remove 5-6 lbs from the rotating mass so it will rev easier & make the parts seems stronger with less load applied , no down side .
 The manifolds may trim off some power above 5000 rpm no big deal if you have more power all the way up to 5000 & probably beyond that just less than to overall potential .
 The J head mod would be to swap for the 308 swirl heads to the tune of 40 more RWHP , they are both cast iron , look stock  & take shaft rockers , no downside there either .
 Cam choice is difficult , fast ramp high lift but with minimal duration powerband between 2000-6000 stall around 2500 rpm . Roller is a good call to a point , $40 each for lifters or pirate a set when you pull the 308 heads except they will not work in a 340 block only the later roller 360 blocks  , downside is cost , over  1K for hyd roller cam ,  lifters ,  chain springs , retainers, etc + you have block mods generally you need taller lifter bores, maybe bushing the lifter bores  or restricted oiling , the fastest way to get a roller cam block is to use the later 88 -92 roller 360 blocks .
 I love the OD route , typically I use the 833 OD , the 518 is another option

Are there not some mods that could be made to make the J heads work with this combo?  I already have them and they're date correct for the car (even though it came with a 318 so it still won't be the original motor) and I figured they could be made to work without huge money hopefully?

I definitely want to use the 73 340 block I have unless I get a nasty surprise at the machine shop, and I thought someone came out with a roller cam for these old LA blocks that didn't require much if any mods.  Voodoo maybe? Am I wwong?

Transmission-wise the car has a recently rebuilt 904 in it now, I've got a low mileage 70 E Body 833 so I'd like to use that if I end up going the manual route.  But for now I'm going to stay with the auto since I'm going to be converting the Roadrunner to a 4/5 speed. 

Thanks for your input, Jim

[Road_Runner]

As always, 1st. Ask yourself, and be honest, what RPM and speeds am I going to drive this car most/all of the time? Me? I got stock block, unmolested Eddie 63cc heads, small 256 dur. vodoo, air gap, 750 holley HP, fattened up, and would you believe?, a 2.76. Ive got some serious low end grunt and it will pull on the freeway at WOT until I git skeered and back off. O and 4 speed is justfun.

 That's kind of why I still haven't settled on a rear gear.  It's got the same 2.76 rear in it now and depending on how the motor works with it around town will determine what gear I change it to if any.  This is not going to be a race car I just want it to be reasonably fast to back up the look even though I'm keeping the mist green/white combo which hardly screams performance.  I got jumped by a newer Shelby last week and I had to laugh, I'm sure he thought I had more in it than just a 318 2 bbl!! 

Thanks, Jim

[Chryco Psycho]

you have to be careful with lift on the cam & the oiling groove , talk to the cam companies & machine shops that have installed hyd rollers in older blocks , I am not positive what can or needs to be done , even Lunati may not have the answers , I ran into a problem with a low base circle cam & Lunati lifters , all of the oil pressure bled out of the oil groove as the lifters sat too low in the bores with the valves closed , new set of rod & main brgs 
 Yes you can make J heads work , the problem is they just don't work , change the chamber shape shape weld up the port floors , & alter the intake port for swirl & you are good tyo go , the reality is the Js will work but will also leave a buch of power missing , no solution , a local wrecker Should have a set of 308s for $50 or so if there are a lot of trucks in your area

[Road_Runner]

you have to be careful with lift on the cam & the oiling groove , talk to the cam companies & machine shops that have installed hyd rollers in older blocks , I am not positive what can or needs to be done , even Lunati may not have the answers , I ran into a problem with a low base circle cam & Lunati lifters , all of the oil pressure bled out of the oil groove as the lifters sat too low in the bores with the valves closed , new set of rod & main brgs 
 Yes you can make J heads work , the problem is they just don't work , change the chamber shape shape weld up the port floors , & alter the intake port for swirl & you are good tyo go , the reality is the Js will work but will also leave a buch of power missing , no solution , a local wrecker Should have a set of 308s for $50 or so if there are a lot of trucks in your area

For me, the main reason with going with a roller cam would be the ability to run normal oil and making it less likely to have an oil related cam failure, but if its really as iffy as you say I'm not sure its worth the risk.  Kind of defeats the whole purpose.  So the 308's would still be as big a benefit even with the HP exhaust?  I could definitely go with the 308 heads if its going to be that big a difference which I know you've pointed out before.  I do want to run as reasonably fast as it can or I'd just leave the 318 in it.

Thanks, Jim

[blown motor]

I'm no motorhead but why not go with X heads for the larger intake size.

I have a 904 behind a 340 bored 60 over, X heads, Lunati cam, 650 Eddy, TTI headers and 2.5" Magnaflow exhaust. The 904 handles it fine.

Where is most of your driving? 3.23 gears will give you a lot better gas mileage than 3.91. Just something to think about.

[Chryco Psycho]

the X heads were used from 68-69 , the J were used from 70-72 but are virtually identical heads , on the last year had smaller intake valves .so no gain using X over J castings .

[cudabob496]

I'm no motorhead but why not go with X heads for the larger intake size.

I have a 904 behind a 340 bored 60 over, X heads, Lunati cam, 650 Eddy, TTI headers and 2.5" Magnaflow exhaust. The 904 handles it fine.

Where is most of your driving? 3.23 gears will give you a lot better gas mileage than 3.91. Just something to think about.

As far as rear gears go, since its not a daily driver, I have built my Cuda to be as fast as possible when I smash the pedal, because I want
people to know what its like to mess with a Cuda. I'm getting challenged all the time, especially by all the new Camaros, Mustangs, and newer
Challengers. If you have a great looking car like a Cuda or Challenger, then I would build it so some little Subaru won't get any bragging rights for beating you. I have 3.91 rear gears, with a 3500 stall converter.

Also, having had 3:23s in the Cuda, going to 3:91s made it a lot more fun to drive. I now consider 3.23s boring in comparison.  I also just took
the 2.72s out of my 99 Trans Am, and went to 3.73s. Man, what a difference in quickness!

[Road_Runner]

Hi Guys, not getting spanked by the modern cars is definitely part of this.  Right now a V6 Accord would run away from me, but I'd only go with a 3.91 or steeper gear if I also went with some kind of overdrive.  That's why I'm going to go ahead and start building the motor and then drive it some to be sure I'm staying with the automatic before deciding to change the rear gear and adding an overdrive if necessary.  I know  there's always going to be faster cars out there, this is more about backing up the look of these cars and just making the car more fun to drive.

Thanks, Jim