Moparts

340 build help

Posted By: 71GoMango

340 build help - 05/09/23 07:51 PM

I’ve tried searching before posting so I apologize for asking possibly a redundant question.

I feel like I try to finish this thing about every 5 years, it’s crazy how time flies…Here’s the build, I had an issue and spun a bearing had a friend helping with the rebuild and life happened and I moved to a new home and just never could get back and finish this but I have another good friend who is helping motivate me to finally finish this thing and get my car on the road after probably 20 years of sitting.

So here’s what it have, my buddy thinks I need a single plane intake and a 750 double pumper carb possibly (he is not a fan of the avenger 770) and he is recommending a better torque converter. So my questions what don you guys think the best intake and torque converter would be for this combo.

71 Challenger RT/Formal roof option(SE):

- 340-4bbl 727-auto
- Holley Avenger 770 carb
- Edelbrock Performer RPM dual plane intake
- 1-5/8" ceramic coated headers
- 8-3/4 sure grip 4.10:1 rear end (489 case)
- X-Heads machined & assembled by Herb McCandliss
- Mild port work
- 2.02-1.60
- Mopar Perf hydraulic rocker arms & springs
- Stainless steel valves
- Bored .030 over
- Steel crank
- Mopar Perf purple shaft cam 284/484
- Keith Black Sylvolite pistons (11:1 compression)
- Standard rods (shot-peened)
- Speed pro rings (file fitted)
- Double roller timing chain
- Miloden high volume oil pump
- Electronic ignition
- Light springs in distributor
- 8mm Morroso plug wires
- High fire Mopar Perf coil
- Fairbanks 11” street action torque converter

Thanks for your help in advance!
Posted By: topside

Re: 340 build help - 05/09/23 09:29 PM

What are the plans for the car ?
Street use, I'd stick with your existing intake & carb.
Drag strip, maybe the friend's idea, but I'd test them both back to back.
I'm guessing that converter has probably around 2500 stall; might be a bit low for the old 284/484 cam @ 340-ish CI.
Way better cams than that on the market in the last 30 years, but may not be in your plans to change.
11.0:1 - was that measured ? That's a lot for pump gas with iron heads.
Posted By: 71GoMango

Re: 340 build help - 05/09/23 11:18 PM

I should have also mentioned the reason I feel something in this combo is off, when we did have it together we couldn’t get it to light the tires like had no umph, but the motor when idling and revving sounded like a beast! No the pistons weren’t measured im assuming that’s the way we bought them, this list was something my dad had written up. He passed away in 2004 so this was my way of knowing what all the car had. It will mainly be a street cruiser but would love to be able to hit a drag strip every once in a while. I really don’t want to spend more money than I have to lol, but I want to be able to light this thing up when I want to and make a descent pass if I do take it to the strip.
Posted By: dvw

Re: 340 build help - 05/09/23 11:48 PM

This actually sounds like a decent combo. I have a similar 360 in my Challenger. Ported 360 heads w/2.02, 220@.050 hyd roller, LD 340, 9-1 true comp, 650 DP Holley, TTI headers and 2 1/2 TTI exhaust. The biggest difference is the cam, my lower compression, and a smaller carb. It has a 3.55 with the factory 2.47 1st gear 4 speed. It's been 12.7@108 thru the exhaust with 275 drag radials. 12.50@110 with a 4.30 and slicks with exh and air cleaner in place. It 'll rip the 275 radialT/As on the street from any rolling speed in 1st gear by just flooring the throttle. Runs on 87 octane to boot. By all rights yours should run pretty close. If anything the cam selection could be a little better. But that cam isn't terrible. I check cranking pressure and check the cam installed C/L.
Doug
Posted By: crackedback

Re: 340 build help - 05/10/23 01:22 AM

The ignition tune up/settings makes a big difference when running the 284 and 292 mopar cams. Plenty of initial and limit mechanical to hit your desired total number.

If the engine doesn't have somewhere at least in the 16-20 range for idle timing, it's likely not going to be "snappy" or clean off idle.
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