340 Build Questions

I recently Purchased back my dads 73 340 Duster. While im going through it quick replacing stuff from setting i was gonna do a quick once over of the engine to pick up some more power. Currently is a 4spd car with stock rotted exhaust. What he had done to it already in the past from what he can remember is, Put a 340 Steel crank in it, Mopar 474 lift "hemi grind" hyd cam and has a 6pack intake set up on it. I was planning on putting in 10.5 to 1 pistons and a larger cam to wake it up a bit more. I know alot of people try to say stray away with the 6 pack but its how he had it so it will stay with the motor. Not really looking for street manners but just power on pump gas. Ideas??

A small solid cam would give you the best bang for the buck, what heads do you have?

What rear gear?

Low budget. KB 243 pistons on Scat I-beam rods, Port the heads,should be 587 castings. Step up to a racer brown ssh-38 camshaft and headers. More budget add a 4" crank with H-beam rods and forged pistons, a better port job and a st-21 racer brown solid lifter cam and 1 3/4" headers. 3.91/4.10 gears

A cast 4" crank would be the best bang for the buck power and torque you could add if you're already buying pistons.

Might even like that small cam you already have, which would save you $$$

Another vote for a 4" crank. Having driven my 360 and my Dad's 408, both with Eddie heads, the increase in torque is unbelievable.

I like the 4" reciprocating assembly idea too. You can buy a nice kit with pistons etc for under 2$k. Throw on some massaged Eddies and a nice cam from Dwayne Porter, and tune it with a wide band.

Make sure you spend some time tuning the chassis, so it will hook up. It will need it.

Step 1-

-determine the TOTAL budget for the motor upgrades.
More than likely, this will determine the best path to take.

Then double said budget.LOL ask me how I know.


Try the cam you have first.Not a bad little street cam IMO.

This is the best place to start.. dont just
throw money at it.. get a plan of attack..
figure out the HP or ET you are looking for

I pretty much put the buggy in front of the horse on this one. The Budget i thought i had is gone doing repairs on the car to get it back on the road. I do plan on this winter starting a 416 for it with some hefty heads and built for some rpm. But as for now im just gonna be looking at a cam upgrade for the time being. I pulled the heads to see what i had so far and they are 2.02 Mopar J heads, Lifter valley oil sheild, windage tray, and Stock compression pistons. So Just a cam upgrade and new springs at this time is all that i got left in the budget. lol I have a set of hooker headers that would be going on for the mean time till i get the new motor built.

Thanks

Before you can use more cam you need more compression. I'd do that before a cam. That 73 will be is a dog compared to earlier higher compression 340 as you know.

Like said above KB243 pistons worked good for me with a stock bore and a hand hone job. Lighter pistons were noticeable and my true compression was 10.4-1. I CC everything when I rebuilt the motor.
The pistons cost 250 bucks I think, cheaper than a cam swap and safer to install and more bang for the buck.

Lunati Voodoo solid all the way

Crane 691191 FTW!
https://www.summitracing.com/int/parts/crn-691191/overview/

Here's what I'd do:
KB 243 pistons or more expensive/lighter slugs
SCAT SCA26123 forged 4340 rods
Keep the forged 3.31 crank

Here's why: Stock piston/pin is something like 720/165 gram
Stock rod is 758 gram
KB 243 is 597/132 gram
Scat rod is 585 gram

That's 329 grams PER CYLINDER
2632 for all 8, that's 5.8 lb.

That engine will feel like you just added 40 cubic inches because there's so much rotating mass to accelerate now. With no other changes it'll feel like a different engine.

I don't think you need a stroker. I'd use that money for heads with some decent squish.

I'd leave the cam for now, I don't think its holding you back. Wait until you have the engine in its new configuration and then look at changing the cam. Especially as right now it is broken in.

And keep the 6-pack! I think you have most of a very desirable engine there.

R.

Just did a 340 a few months ago with that exact bottom end along with the old solid lifter cam, with ported J heads it pulls hard....

Damm I'm good!

R (top of the world)

If your Dad already put a steel 340 crank in there before, find out what pistons are there n there now. You may not have to change them out. Check how far down in the hole they are and figure out the compression ratio before anything is done!

Keep the 6 pack. Those that say stay away from them because xxxxx more than likely never had one and if they did, never ever learned to tune one. The CAN and WILL make a lot of power. While a rpm air gap and a single 4bbl. will edge it out slightly & be easier to tune, I find little sense in throwing away a super flexable & excellent intake system.

Remember a larger duration cam moves the power band up. More lift directly effects HP.
IMO, a solid cam is probably the best bang for the buck in cam choices. Couple it with adjustable rocker arms from Hughes or Comp Cams. Crower makes anset in Stainless steel. Super durable.

Port your heads and add headers. TTI headers are the best fitting I have used along with there exhaust which needed minor trimming to fit.

I agree as you need to know your budget first. Also how fast are you looking to go and will it be just a street car ?
I built a mild 340 years ago for my girlfriends Dart Sport. The eng was basically stock as I checked it out and freshened the 340 up using the stock pistons and heads as it was a 1970 eng. I did a little mild bowl blending on the heads and used the same cam you have the MP .474 hydraulic flat tappet with stock rockers and shafts. It actually had the 318 Eddy dual plane intake and I used a 650 DP. I recurved the stock dist and added headers and 2.5 dual exh. I used a 904 I had traded for a few years earlier and it had a stock 318 converter. 8-1/4 rear with 4.10's and G/60-15 street tires. The 904 trans was all stock also. I liked that cam as it ran great in that car. We took it to the track and my first pass it blew the tires off and ran a 14.07 at 106 mph. After nursing it out of the gate I got it down to 13.40's @ 105 mph through the exh on street tires. I would power brake it to about 2000 rpm and then just let off the brake to launch and then slowly put it on the floor. I could launch that way and not spin the tires. I feel that car would have run 12's with a good trans , converter and tires as with the 105 mph it had the power to run 12.80's capped up. And the eng was basically stock internally other then the .474 cam. If your only looking for a 13 second street car that cam will work fine. Ron