Looking for more pep off the line

-
Mattax said:
Let's bring this back to a strategy that I would recommend for this situation.
Limiting the advance shouldn't be needed because 3000+ rpm tuning should be put aside until the foundation is put on solid footing. That said, we know some people just can't resist their urge to floor it.... so this assumes Alecb, you have the patience and interest in solving first problems first.

First problems here are:
a. Some fault in charging system (that can be worked on with the current tune just as it is)

b. Idle and off-idle needs performance tuning and testing. (that can be worked on with the distributor as it is as long as that includes timing vs rpm measurements. Without those, then after making internal changes to the distributor you will be starting from scratch). You can drive it on the local streets, but avoid flooring it or high speed stuff.
Click to expand...
Follow what @Mattax is going to guide you to do with the ignition. He'll show you how to graph it out and actually learn how to do it. My way will give the same result, but leave all that out, because I've done it so damned much, I know "about" where I am with it without all the fancy graph work. You need that though, so you can actually look at it, see what's going on and change things accordingly. You're in great hands with Matt. Just don't get off the rails with somebody else's bullshit, because Matt will get you right.
 
RustyRatRod said:
The cheap Summit headers fit with power steering. Unless you're going to run your front end low and in the weeds, they will work fine. I've run several sets bent like those and the Hedmans and the only thing I had to do was take a pry bar and tweak the two tubes on either side off of the torsion bars, because they rattled against them. All the guys will run them down, but they work well as long as you sit at stock ride height with stock height tires.
Click to expand...
I'm running 225/60/15 tires up front and there is decent ground clearance under the k frame.

IMG_6008.JPG
 
Make sure you follow proper procedures for compression check. Google it or ask around here.
 
Might be on to something with the transmission, when I first put my 340 in my old car it was with a 727 the first test drive I was very disappointed with the take off, but it went really good down the road. It didn’t take long to find out the transmission was starting in second gear and only shifting once into third. Took the valve body out cleaned it and double checked everything. Don’t remember what I had in the wrong place. But it shure took off when I put it back together
 
Let's see if he's actually serious about resolving the issue. 4 pages of generally solid advice. Now time to do the work.
 
I think he fell into the same hole us novices like myself fall into. 73s are heavy freaking cars. Mine is 3480 without me, 3700 with me. fiberglass hood, aluminum heads, bumper reinforcements removed and no heater box. No other options to remove weight unless I acid dip the car which isn't happening. I have a MP 380 hp crate motor, stall and 370 gears. The car is slowwwwwwwwwwwwww and only runs 9s in the 1/8. Going to need a higher hp motor. Put the same motor in a significantly lighter 70 to 72 duster and you are going somewhere.
 
Mean416 said:
Let's see if he's actually serious about resolving the issue. 4 pages of generally solid advice. Now time to do the work.
Click to expand...
I’ve been away camping for a few days, but I made a list! Even on vacation I think about cars. I’ll be getting to work on this once I’m home.

IMG_6023.jpeg
 
Howard1784 said:
I think he fell into the same hole us novices like myself fall into. 73s are heavy freaking cars. Mine is 3480 without me, 3700 with me. fiberglass hood, aluminum heads, bumper reinforcements removed and no heater box. No other options to remove weight unless I acid dip the car which isn't happening. I have a MP 380 hp crate motor, stall and 370 gears. The car is slowwwwwwwwwwwwww and only runs 9s in the 1/8. Going to need a higher hp motor. Put the same motor in a significantly lighter 70 to 72 duster and you are going somewhere.
Click to expand...
Who doesn’t love government mandated safety standards.
 
Mattax said:
There you go. Time to learn.
Chrysler ignition modules still require the ballast resistor. HEI and Capacitive discharge ignitions provide their own control for coil current but that's not what's on your car. So it needs a 0.5 Ohm resistor to protect the coil.

Medium springs have now messed up the advance curve. I can say that even having no idea what brand of spring or what distributor they were intended for. The primary spring provides enough force to keep the timing from advancing until above idle speed. As shown in the link I provided above, minor adjustment to the spring force is available. The factory primary springs all have relatively low spring rate, allowing a very fast advance from off-idle until 1400 to 1800 rpm. There is a lot of off the line performance right in there. The secondary or long looped spring then slows the centrifgal advance because the combustion is getting more efficient with more heat and faster burn rate.

edit:
Link from above: See post 17 for adjustment to initial force (rpm advance begins) Distributor curve help needed
Click to expand...
I went ahead and took apart 4 distributors including the one on the car. Current dist has the gold weights, other one has bigger weights with the long spring. I figure the other distributor would be more of what I’m looking for. I also got 4 vacuum canisters, 2 are adjustable with 11R on the arms, one has 9.5 on the arm, the last has no stamp but a 5 cast on the body. Time to make one good distributor out of 4.

IMG_6029.jpeg


IMG_6030.jpeg


IMG_6031.jpeg
 
Top one was made by Mallory, and while some people like the adjustability, its geometry isn't well thought out.

The others are chrysler made. On the governer, the part with the slots for the weights, the max advance is stamped.
Just take a note of what is there and if the slots are in line, or slightly angled.

Not knowing how much initial the engine will work best with, its sortof a crapshoot as to which governer to use. Nothing over 13 if that's a choice. Most secondary springs on the on the early 70s cars will have a very long loop. I'd start with the shortest overall length if there's a choice. Those were for engine with initial timing around 0 or 5* BTC. You want to have at least 10 or 12 initial.
Same with the primary spring. Make sure whichever one you choose, there is some tension on it when installed with the governer. Don't want the timing to advance below idle rpm. You may be able to add some tension with the eccentric. Photos of that in the linked thread.
 
Mattax said:
Top one was made by Mallory, and while some people like the adjustability, its geometry isn't well thought out.

The others are chrysler made. On the governer, the part with the slots for the weights, the max advance is stamped.
Just take a note of what is there and if the slots are in line, or slightly angled.

Not knowing how much initial the engine will work best with, its sortof a crapshoot as to which governer to use. Nothing over 13 if that's a choice. Most secondary springs on the on the early 70s cars will have a very long loop. I'd start with the shortest overall length if there's a choice. Those were for engine with initial timing around 0 or 5* BTC. You want to have at least 10 or 12 initial.
Same with the primary spring. Make sure whichever one you choose, there is some tension on it when installed with the governer. Don't want the timing to advance below idle rpm. You may be able to add some tension with the eccentric. Photos of that in the linked thread.
Click to expand...
So I put the chrysler distributor together and set initial at 16-17 degrees. Total mechanical advance is about 35-37. Now when I attach the vacuum canister and rev it up, it goes past 40 degrees and starts detonating. So my vacuum and mechanical advance systems need work. I made a few laps around my neighborhood and also discovered that the car does not shift down into 1st automatically. It likes to start in 2nd gear which explains why it’s a dog off the line. If I manually shift into first it pulls a bit harder when accelerating. Cruising around it bounces between 2nd and 3rd when starting and cruising.
 
One more time. initial means nothing without rpm. "total" means next to nothing without rpm.
Don't go wide open throttle until the baseline is established. The one way that the engine can be damaged is detonation uner heavy load (heavy acceleration in upper gears). Pull the spark plugs and see if there are aluminum specs on them. If so, that's from the piston.

You can't use a little of one procedure and mix it with a little of another procedure.

If you want to start with WOT, then you have to approach it the other way. Set up timing at a high rpm, like 2800. Then work back to other conditions.
 
The governor on the transmission, it would b a place to start. Pull the tail shaft off and remove the governor and clean it up make shure it’s moving easily. And meybe adjust the bands. Put new fluid and filter in it. Do not flush it. All that does is break up varnish in the case that will plug everything up. The next course of action would be to rebuild it
 
Could clean up valve body also before a full rebuild. If it’s not the governor and it’s not the valves, you have some leaky seals in the trans. But I would start with the tail shaft
 
Alecb said:
Hey all,
I've got a 73 Duster with a 360 LA and 727 that I rebuilt myself, and I'm looking for suggestions to make more power down low. The engine is bored over 0.040, has KB 107 pistons, 9.6:1 compression ratio, stock crank and rods, Summit K6901 camshaft 218/228 0.441 lift, stock J heads, stock cast iron intake, Holley 600 cfm vacuum secondaries, TCI 141500 converter, 3.23 rear gears, timing set at 12-15 degrees BTC. My build is meant to be a street machine on a budget, it runs well but it feels a little lacking off the line. Any suggestions for making better power would be much appreciated.
Click to expand...
I concur with rumblefish post #6. With your displacement and intake valve size, the tighter the LSA the better. 105° would be good if you can get a cam grinder to do one that tight. 108° would be sortof acceptable.
Richard Holdener did a youtube video comparing on the dyno three LS cams on a 6.0l, I believe. He had Crane grind four cams, all with the same lobe profiles. The difference was LSA; 108°, 112°, 116° and 120°. Note that the General uses a cam with 122.5° LSA to keep a smooth idle. That wide LSA also flattens the torque curve and extends it, at the expense of the bottom end.
Richard dynoed the 120° LSA cam first. When they installed and dynoed the 112° LSA cam, the engine picked up about 35lb/ft torque between 3500 and 4500 RPM but lost a few above 5500 RPM. When the 108° LSA cam was installed it picked up just a few lb/ft over the 112° cam. Now this engine was built with LS3 heads that flow real well. Your heads do not flow anywhere close.
I do agree with the guys stating tuning is required, and will get this engine performing. The wide LSA tends to flatten the torque curve, so it will never have the snap a shorter LSA will give.
Another thing to consider is valve lift. At 0.441" it is mediocure these days. I would check intake valve to piston clearance and consider stepping up .1 on the rocker ratio. This will get the valve off the seat quicker which helps. In addition you would pick up probably 0.025" lift. I expect your heads flow would top out around 0.500", so getting the valve lift closer would benefit getting air/fuel into the cylinders.
Mattax said:
I generally discourage relying on voltage measurements at the coil because they will vary depending on conditions.
For example, Engine off, key in run.
Power supply voltage will be roughly 12 if the battery is in good shape.
Current at coil will be much under. How much so depends on the connections and the alterator field draw.
Also with the ECU ignition, its like the points are closed all the time when key is in run, engine off. So current flows thorugh the resistor full time, making it hotter (and higher resistance) than when running.

When driving, power is supplied at roughly 14 Volts, current flows through the resistor on/off. So running there is a higher voltage supplied to the system plus cooler resistor - and more so at higher speeds.

Some things to check.
Engine off. Resistor should be .5 to .6 ohms
Engine running. Voltage supplied to resistor compared to overall system voltage should nearly the same. Alternator output voltage should be around 14 V, and the voltage at the resistor should be within a 1/2 volt of that.

Its best to do these measurements when the battery fully charged. The ammeter will show whether its recharged or not. It should be finished recharging within a few minutes of starting. If not, charge the battery on a charger and try again.
Click to expand...
 
I do agree with the cam swap but on a budget the trans and the tune would be first then some gears in the rear end, then definitely a cam. Some head work and an intake would be great to but as time and money allows eventually it will be a great car, your definitely getting good advise and heading in the right direction
 
Low stall torque converter, second gear starts and super tall tires on those 3.23 gears are a recipe for being doggy off the line. Fixing those things will matter more right now than messing with cam and distributor.

JMHO
 
Make sure your kickdown linkage is properly adjusted. Also make sure the shifter itself is properly adjusted and not binding. These things can be off and it won't shift right. Worse yet, you can damage the transmission.
 
Something not everyone realizes is that tire diameter can effectively change gear ratio. I.e., if the rear tires are 30 inches tall, then compared to the 26 inch height of your front tires, your effective gear ratio is 26/30 times 3.23, or 2.80.

With the right combination of torque converter and tire diameter, 3.23 gears can be pretty quick off the line. The mild 360 in my 67 Barracuda would burn rubber most of the way through low gear with street tires and 3.23 gears (not to mention OEM springs in the distributor, a cam that was just installed dot to dot, and pistons that sat .100 below deck at TDC). (Nitto drag radials fixed that, even when I switched to 3.55 gears.) With enough traction, 3.91's will be quicker, but there's a definite trade-off of high rpm's at cruising speed and loss of top speed. Shoot, these days, even 3.23 gears will have you buzzing at highway speeds compared to today's cars, which can turn less than 2,000 rpm's at 70 mph. Of course, they get by with that because they have many more transmission gears than our old three-speed Torqueflites. With the latter, rear gearing is always a compromise.
 
Last edited:
I think the camshaft is the damn last place he should start, UNLESS he's going to check and or change its position. Some of yall love spending other people's money. Yall have fun.
 
65 Cuda 340 said:
Something not everyone realizes is that tire diameter can effectively change gear ratio. I.e., if the rear tires are 30 inches tall, then compared to the 26 inch height of your front tires, your effective gear ratio is 26/30 times 3.23, or 2.80.
Click to expand...
I might not be understanding you right but what do you front tires have to do with gear ratio.

A 24" rear tire has a one to one ratio so tq at axle and road is the same any tire larger, tq at the road will be lesser depending ratio from 24", eg.. 24/30= 0.8 .8x 3.23 = 2.58 , 24/26=0.92 .92 x 3.23 = 2.97, so 2.58 and 2.97 would be the effective gear ratio .
 
You must log in or register to reply here.
-

Back
Top