Help on rebuilding a 73 340

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Do you know how to do a stall test? Give us an idea as to the current TC.If the teener is sluggish off the line with 3.55s,I would first look to the compression test, and then to the stall.If compression is down around 135,the low rpm torque will be soft and you will need a higher stall, to get the Rs up to where the happy zone is. But if compression is 165 or better, then perhaps the timing is late or slow. Most teeners I have worked on have a generous amount of low RPM torque, even with compression down at 150.So I think those are the three areas you need to respond to; compression test. stall, and timing. Timing includes the idle number,as well as at what rpm its finished advancing,and what that power timing is.
If the idle timing is 10* and the PowerTiming is 35*,That doesnt sound too bad. But if it doesnt get to that 35* until 4000rpm, that would be horrible.And if it lingers at 10* til 2000rpm, well thats even worse.
What I do is make a timing map.I disconnect the vacuum advance and I set the initial,idle timing to TDC. Then I rev it to 2000rpm and record the timing. Then 3000 and record the number.And 4000 as well. Then I go back, and fill in the numbers at 1500,2500, and 3500.Then I get some graph paper and plot the numbers;rpm across the bottom and *advance on the vertical.If the line thus generated has a kink in it, I sometimes go back and check the timings around the kinked area, to fine tune exactly where it is.This graph can be a huge help in tuning.I sometimes generate curves as fine as every 200rpm.
When finished I put the timing back where I found it and hook the vacuum advance back up.Then its time to analyze the results and make a plan.
 
back to balance - the 318 is internally balanced - no weights on harmonic damper or flexplate or torque converter. a 1973 340 with a 1973 crankshaft is externally balanced - the harmonic damper is counterweighted and the converter has counterweights on it. b & m makes a counterweighted flexplate for the 340, with it u can use the converter u have or any non weighted converter
 
If you want to get an idea of the Scr of your 340, now is the best time to do it.
You need to roll the engine over and get any one cylinder to have its spark plug be the highest point of the chamber. Then you put the piston for that cylinder at TDC/compression stroke. Next measure out 100cc 0f oil into a graduated container. Could be a measuring cup from the wifes kitchen, or my favorite is a veterinarians syringe. Then start filling up that chamber, to the bottom of the plughole. I usually shuttle the piston back and forth a few degrees to prove its at TDC. Then figure out how much oil went in there. Which should be 100cc less whats left in the container.After that its simple math: ( Swept + cv)/cv : where swept is( bore sz/2) squared,x Pi x stroke, x16.387. and cv is chamber volume. Heres an example for a stock bore 340.
Swept = (4.04/2) x (4.04/2) x 3.1416 x 3.31 x 16.387 = 695.3cc
So (swept+cv)/cv =(695.3swept +90.5cv)/90.5cv = 8.68Scr. Badaboom!

Well I suppose theres a slim chance that more than 100 ccs goes into that chamber! Just suck up another 50cc into the syringe and carry on.
This method is only as accurate as the tools you use and the care you take in the set-up, and the ring/valve seal. If you spill some oil,stop.Set up a new chamber.Use a thick single viscosity oil, like 50 wt.If the oil is too thin it will run down the piston and through the ring gaps. If the oil level in the chamber does not remain stable try a different cylinder. Do not use any cylinder more than once.Just one cc of oil remaining in the chamber will skew the results.I like this method and have used it many times, to help estimate what to expect from a loose motor.
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This method can be dead accurate.
 
dancinwulf said:
First let me say I am 67 years old a retired farmer pretty fair diesel mechanic , welder, electrician but as to tuning still trying to learn my 318 with the 3.55 gears is slow off the line but works well at higher speeds....but just trying to figure out what would be a good cam choice so that it will idle yet have some good juice in the lower end. I really am not concerned about the best milage but hate to waste fuel, not into racing but enjoy having some hp when you want to romp on it. I have plenty of free time but hate to waste it by doing the same job twice. In my area the speed limit is usually 65-70 most places I drive which was why I used the 3.55 gears. So I really appreciate all the input from all of you not quite sure how to do the thank you on this but THANK YOU ALL FOR THE ADVICE IT IS GREATLY APPRECIATED
Click to expand...

From this description, I cannot stress post #6 more. Good luck.
 
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