tuning

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Hersbird

Hersbird

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anybody feel like giving me a start to finish on basic tuning? I did a search and everybody chases similar problems but I thought somebody making a basic guide with a sticky would be helpful for all.

I got my car up and running but now I'm ready to get this dialed in.
I have a stockish 72 360 with fresh rebuild, the thinner head gaskets and stock magnum heads, probably around 9:1.
a stock 68 340 cam (but a bit more actual lift with the magnum rockers)
has a Apple I-Gap manifold (just kidding, but it is made down the street in China) and a new out of the box edelbrock 1406, stock fuel pump.
and keeping the Chinese theme an ebay hei type distributor. Plugs gapped at .045.
Jegs headers and dual 2.5 exhaust with H pipe.
904 with stock 10.45" converter, new clutches and steels and few other parts.
currently stock 2.74 open 7 1/4 rear but I have a 3.25 open 8 1/4 I need a few parts to get in (big thanks to Idaho for that)

I have it running and driving, did the cam break-in last week and drove around the block a few times over the weekend, and went and got gas tonight. It idles good at 750, drops to about 550 in gear, and starts easy. I set timing but now realize I did it with the vac advance hooked up. It was 12 initial and 35 total and then it seemed idle better with 20 initial but I thought that too much, now I realize I need to go back and see how much the vac is adding. Where it was (the 12-35) it had a pretty good stumble off idle if you didn't ease into the throttle. It stumbled bad enough to kill it in the roundabout and was then hard to restart, I thought I ran out of gas and called my wife. Was with my 7 year old so probably won't hear the end of that soon!

kickdown probably needs some tuning but it is working, I'm pretty much babying the throttle and I have that stumble so it's hard to really check where it's shifting and how easy it is to get kickdown yet.

Looks like I might have a little seepage from the t stat housing and some from my oil filter plate but overall seems tight. Water clean, oil clean, staying cool.
Much better than the 318 even the way it is, and I really can't wait for the new rear end now! I'm so very relieved everything is working as everything (disc brake swap, front end rebuild, motor, and tranny all at once) was out and rebuilt by my always learning hands.
 
First thing you need to do is iron out the timing problems, and sounds like you already chasing yourself. Most of us that use vacuum use "timed" or "ported" vacuum, which means the port on the carb which is "no vacuum" at idle.

Vacuum is "sort of" a non issue with tuning for power, because when you "mash" it, the vacuum goes away with more throttle, anyway. Vacuum can cause spark knock at med/ cruise RPM at light throttle application, so you might have to change the vac. can or maybe adjust it if it is able, but that is LAST

FIRST is to tailer the advance curve so that you can have:

Lots of initial advance for good start, idle, and off idle power, without "over" advancing at WOT at the top end of the mechanical advance. The ONLY WAY to do that is to determine "what the engine wants" at idle, and "what it can handle" at WOT on the top end.

This varies, but 15-20 initial, and 32-36 for total. Even if you are at the "low and high," IE 15---36, that's only about 21* (crank degrees) "in the distributor" and it's unlikely that your factory dist. is that short.



Also understand that what I just said was "crank" degrees---Just about all "specs" are in "distributor" degrees which are HALF that much. Some mopar advance mechanisms are stamped with their mechanical advance figure, so for one that short (20-22) it would have to be stamped 10 or 11.

Frankly, if you can afford it, in my opinion (and that is "new to me") is you might consider investing in a "wide band" O2 sensor / display setup. I bought an Innovate off ebay complete with panel meter for just under 140 bucks. The module / controller can store a log, so you can hook your laptop to it and read the graph after a "run."
 
Its not a stock dizzy but one of those hei style ebay ones. and It may actually have a little more total timing as I wasn't reving it over 3500 when checking. I sort of stopped to find better advice before I broke something.

PS I'm using a timing light with the dial on the back. Is that crank degrees or distributor degrees on there?

and the vac port was the one recommended by edelbrock on the carb.
 
The dial back is used if you don't have a incrementally marked balancer or have timing tape on it. Let's just say for instance you want 18* initial, set the dial to 18 and turn the distributor until the mark on the balancer is line up with the timing tab mark. Make sense?
 
Crank degrees are exactly what it says--degrees measured at the crank.

The only time "distributor degrees" comes into play is in the spec books and shop manuals, and depending on how "you think" if using a distributor machine.

It's important, thought to understand the terminology, because if you buy a distributor which someone says "is 15 degrees" that MIGHT be 30 crank degrees and is way too long.
 
Lots of RPM drop putting it in gear. Make sure it's not dropping timing when put in gear. It shouldn't at such a low RPM.

I prefer ported vacuum to manifold.

my 2 cents, set initial around 16-18 minimum, especially if it starts easily when set at least at that point. Then curve the rest. I believe those distributors require you to bend a tab to adjust mechanical.

Find out where it stops advancing. You may need to look into some micro springs at Ace Hardware or find some springs that will work from other distributor set ups.

Fuel pressure can be an issue with ede carbs. Look down carb to see if fuel is dripping off the boosters. If you see fuel dripping, you have issues!
 
Also, I would not trust your "dial up" timing light until "you know you can." There are lots of cheap timing lights around, garage sales, craigslist. I've bought two perfectly serviceable lights for less than 10 bucks in the last couple of years. That way you can check timing with a "standard light" then compare it against your dial up unit.
 
I'd do what is suggested above. When messing with dist, do all initial set ups without vac. adv.

The initial timing is set by determining the point at which the rpms continue to increase and then drop off while at idle. Disconnect and plug the vac adv line on the carb. Check and increase the timing by bumping up a few degrees at a time until it noses over and then back off a few degrees, that should be your base line. And as mentioned above, it is going to fall into the 14-20 * range. Set the timing at the new position and bolt it down.

From there, recurving the mechanical advance to get the best response from the engine is whats needed. You need to limit the mechanical advance. You have to figure out where you are first. Run the engine in park or neutral and increase the rpm, while checking the timing, continue to inc rpm until the timing maxes out, record the reading. That is your total - initial plus mechanical adv timing, this needs to be limited to around 34*. I'd go to the manufacturer and look at their tuning info on how to adjust this.

For changing the mechanical advance rate, what kind of curve is determined by trial and error, too many variables to give a formulated reply - vehicle weight, axle ratio, auto vs manual trans etc etc. Look at the dist manufacturers site and see if they offer parts to change the curve. Something faster than stock adv is what is needed. Changing the springs inside the distibutor or changing the adv weights will be whats needed. Trial and error again, change one thing at a time and evaluate by driving it.

After that, hook up the vac adv., and drive it under different conditions noting any spark knock. Usually you can adjust these using an allen key that fits into the vac port of the canister. My guess is you wont need to - with a pretty stock set up like you have.

For the carb, its going to be trial and error again, determined by driving it. Knowing what the base line set up is for the carb is important. Write down the baseline info, like: jet size, metering rod number, shooter size. This way you can always revert back to the baseline if the motor's tuning goes out of whack. Change one thing at a time and test drive it.

Start by installing a larger accel pump shooter to see if it increases the response, you can also move the pump arm to different positions to change the rate at which the shot is delivered. Usually the hole closest to the fulcrum is the right position. If you are using headers, you might want to look at increasing the primary jets by one size, alternatively you can adjust this by changing the metering rods to a smaller diameter.

The whole process is trial and error, there are no set parameters except for the total timing limitation.

Good luck with it.
 
What distributor? I'd like to read the manual for it just out of curiosity.
 
Yes the skip white one on ebay. No manual there, I'll look and see what came with it but I don't think much. Mine was the "pro" model and even had an "-R" at the end of the part number so you know this is good stuff! LOL.
Thanks for the great tips, I will disconnect the vac, time it by idle speed, and then see what the light says the timing is. The light is 20 years old but a craftsman and only used a few times, the dial does seem to match the marks on the tab for the few degrees available there.
 
You have to reset the idle speed every time you feed more timing in.

Sometimes you end up in an area beyond where the starter will handle timing set this way. That's why I like the kickback method, find where it strains the starter and back off a couple degrees. Starter may be your limiting factor.
 
Besides the things like leaks, Igntion timing is a good place to start.
Get it in the ballpark, and then you may come back if you're into fine tuning.

It's better starting with the low speed circuits and timing, and that shouldn't be an issue with your setup.
For initial:
The ol' guideline published by Barry Grant will put you in the ballpark.
It's based on duration at 0.050 and displacement.
http://www.demoncarbs.com/Tech/DemonSelectionGuide.asp

Set initial with vacuum advance hose plugged!
- and at this point, you can take one of two approaches. Do all your mechanical advance tuning and come back to the vacuum later, or work with them both. For a more radical cam, I'd really encourage the first. But your cam is so close to stock 340 that you could use a stock curve as a starting point.

If you chose to use the stock timing curves as the starting point, then you would probably do better with the manifold vacuum. Using 1968 as the example:
Timing around 500 rpm set at 5*
Centrifical Advance at 500 = zero
If Manifold Vacuum advance at 500rpm is 11", then vac advance = 10*
Therefore under normal idle conditions, timing will be 15*

An engine with poor idle vacuum or emmissions is usually not able to do this. So in those cases, set timing at 500 (or more typically 750 or higher rpm) at 15*, and hook the vacuum advance to ported vacuum.

After you have the idle and off idle timing in the ball park, then you can set the curb idle fuel mix. But there is a catch - as mentioned, changing the advance will change the engine speed. So while setting the timing, you will have adjusted the initial throttle position (idle stop screw) to get the idle rpm you want.

The really correct thing to do at this point is take the carb off and check the position of the throttle blade relative to the idle and transition holes or slots. There should just be a bit of the transition slot visible below the throttle plate.

If there is too much timing the throttle will start too closed and the mix will be usually be set too lean. It may seem great in Neutral, but won't develop enough power when dropped in gear, hence the common rpm drop.
So the real idle tuning is not in N but how it runs when put in gear.

If you set the idle mix in N (most of us do) for highest vacuum and best rpm or both, then make it 1/8 to 1/4 turn richer.

If you're really into tuning, I suggest making a graph of the timing curves - right up 3500. It should stop climbing by then. if not, you can keep going - it gets a bit scary with the fan and belts spinning but engine itself should be OK (assuming oil is warmed up) as there is no load on it.
 
all sounds like great advice. I agree with 67Dart273, don't rely solely on your dial back timing light. I used mine and at idle it was correct but when I degreed the balancer it seemed the timing light was off at higher RPM. I suggest degreeing the balancer with timing tape, don't paste it on there (it will fly off) just put some marks at 15, 35 and 55 BTDC, (which are good settings for initial timing, total initial+mechanical advance, and all in initial+mechanical+vacuum advance), then buy a nice static light from ebay and check the timing. My timing numbers on my 360 are 18 initial, 36 total and 55 all-in (or 50, I'm not sure I'd have to check LOL)
 
My light must be off. I checked the TDC marks and they were on so I don't think its the marks, but I got it running awesome now. It was slightly wet on the road today but it flat snaps now. I did it by ear, and then checked the starter and it was just wanting to kick back a bit so I backed off some all with the vac disconnected. The light says this was 30 degrees, so that's why I think the light is snafu. The vac was hooked up to the manifold port as edelbrock recommends this for pre emissions, I tried the timed port but it doesn't seem as good. So the Vac adds another 10 degrees up to 40 (again my light must be off). Then the mechanical with no vac hooked up was adding another 20 degrees total. Idle is at 750 and it's dropping to 600 in gear now.

I then moved the pin on the arm of the accelerator pump of the carb out one notch. The throttle with not stumble or bog no matter how hard and fast I hit it. My converter is brake stalling right at 2000 rpm. It does upshift early at 3500 with full throttle so I need to put more pressure on the rod although I'm maxed out with what the threads allow there. I need a longer kickdown rod. Don't worry I know that's a must.

Like I said, it was a bit wet out, but even just some 0-45 mph runs on the 2.74 gears this is the fastest car I have ever owned. I can't wait for the 3.25s but now think I'm going to need that limited slip! My RT short cab Dakota with it's 3.92s and magnum 360 was pretty fun to drive as well but early butt dyno says this is quicker.

Now I need to find an accurate light and see what I'm really looking at for timing.
 
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