340 build

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scot73swinger

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I have been buying parts for my 340 build for a while and not sure if i have a workable setup. I have a 68' 340 with "X" heads. The block has been bored 30 over, the heads have been ported and polished and have stock valves and rockers. Has chromoly pushrods and Isky double valve springs, stock crank that has been balanced and the oil galleys chromed. Stock connecting rods with KB flat top pistons. Has Comp cam and hydro lifters (cam is 292 duration and 509 lift), 4150 Holly Street HP 750cfm carburetor on top of an Edlebrock RPM air gap manifold duel plane. The heads have been milled and block been decked. I believe it will have 10:1 or 10.5:1 compression. Any and all opinions welcomed.
 
Looks liken great street stripper combo to me!
I did the same with a 360 a d the MoPar 292/.509 cam. It was backed by 4.10's and a 4spd. You can do mid 12's in an A body. If it is light, low 12's are doable.
 
Pay attention to the top piston ring gap. And if you have not done so already have a good local shop balance it. Replacing stock rods with Scat I-beams will shave weight off allowing engine to rev faster and reducing stress on the crank. If you stay with the stock rods get them resized or at least have a good local shop look them over. Stock rods are plenty strong just not as strong as the Scat I-beams and heavier. Get crank checked over by a machine shop for run out and taper. Overall sounds like a great build.
 
Double springs and stock rockers might cause a problem.
 
sr71mopar said:
Double springs and stock rockers might cause a problem.
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X2

Stock stamped rockers are very flimsy. Get a set of the HD stamped rockers, if you're running a hyd. cam. Mancini has them as MRE-9742. $99 A lot less than the typical $400+ roller rockers.
 
Are the sprngs two sepreately wound round wire springs with a flat dampener in between them, or are the springs a single round wire spring with a flat wound dampener inside it?
It should have the 995-16s for either "292" cam Comp makes. You should have the shop verify the Isky springs will work properly with the Comp camshaft if they were bought seperate. If the springs are true doubles - you cannot use factory retainers, and the spring seats and guides should have been cut to allow use of them and the positive valve seals.
Post a picture of the installed springs and we can tell you if it's right.
 
The engine was my dads that he had in his 64 1/2 GT Dart. I am reusing the valve springs and pushrods but everything else that's aftermarket I have replaced. So I know that the valve springs are going to work, I did all of the head work myself while in school and checked all parts and flow tested the heads on the flow bench. I will probably go with some after market rockers and connecting rods. Thank you for the comments. I would also appreciate opinions about ignition systems to use as well as oil pump and a carb spacer.
 
I think he has a single spring and damper set up rather than dual springs which would possibly include a damper.
A regular oil pump will do fine at this level for sure. Just keep the RPM's under 6600.
Should the future provide extra money, Hugesengines has a nice roller rocker set up in that 400 or so dollor range. Well worth the money.
 
I think so too, Rob. What concerns me is the cam requires true duals.
Scott- Do you recall cutting the spring seats or having to use the smaller, hard-plastic valve seals?
 
The springs are duel with a damper, two round springs and flat damper. I didn't do any cutting on the spring seats. Like I said its the same setup as when my dad had them in his car. All I did was port and polish the runners, do a valve job, check the spring tension, check the pushrods and valve stems for trueness and wear. Not 100% sure about the seals but i believe they were a hard plastic style. After listening to everyone I will spend the money for some rockers. If I plan to go higher in RPM what would be a good oil pump to use? I plan to stay around the 6500-7000 range.
 
Your Pop probably had the spring seats machined for the when he did it.

It is not the oil pump but rather the oil passages that need work to move and flow enough oil at the desired RPM. The pump and main it sits on should be modified itself with some porting and smoothing out of the passage.

Look up "Guitarjones" and is oiling mod thread. The MoPar performance books will detail this as well. The stock oiling system (in total, not any one part) is good for 6000 RPM if the engine is loose and old. At 6500, it gets a little thin to say for sure if the passages are up to par for the chore.

I have take. 1 LA to 6800 a lot without issue for years while another took less RPM to make it unhappy at only 6500. My last 360 went to 6600 no problems. I pushed another 200 out of it and I paid the price.
 
I assume its a 4 speed car with that cam? and some 390s or more in the butt, I like your build and have had three very close to what you are putting together . That cam loves gears oh ya and zinc lol
 
If you go with a high volume pump make sure you get the strong intermediate shaft. A standard shaft will snap.
 
Planning on building a 727 I got out of a 76 dodge van. Still need to get ahold of an 8 3/4 rear end. With the rockers is there a particular ratio to go with or is it specific to the engine?
 
highly recommend if you run a hv oil pump...use the billet shaft from MP..or other places...the pump could round out the hex end..
 
For ignition I use trailblazers hei conversion for 100 dollars it really works well and Im 100% happy especially on hot restarts.
 
I would say fit the car is going to see more street time and you can afford it change the cam.You can still have a bad *** idle and maintain decent vaccum/throttle response while making as much power over a more usable range by going with a newer cam design.
 
scot73swinger said:
Planning on building a 727 I got out of a 76 dodge van. Still need to get ahold of an 8 3/4 rear end. With the rockers is there a particular ratio to go with or is it specific to the engine?
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Thats fine dont skimp on your convertor 3200 stall and 391 rear gear that is a hot set up for the street but so is your motor set up. on the rocker ratio 1.5 hd mopar hyd bolt them on and rock and roll if you have any more questions I would say read mopar magazine cheep as dirt BY steve dulcich
 
moper said:
Are the sprngs two sepreately wound round wire springs with a flat dampener in between them, or are the springs a single round wire spring with a flat wound dampener inside it?
It should have the 995-16s for either "292" cam Comp makes. You should have the shop verify the Isky springs will work properly with the Comp camshaft if they were bought seperate. If the springs are true doubles - you cannot use factory retainers, and the spring seats and guides should have been cut to allow use of them and the positive valve seals.
Post a picture of the installed springs and we can tell you if it's right.
Click to expand...

Not fully put together but a picture of the springs installed.
 

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Make sure that you have some converter. I put a 292 cam in my 340 back in the 80's, sounded great, but wouldn't spin a tire. Went to a old Crane HMV278 (I know, a CHEBBY grind, and it will smokem at will.
 
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