timing and tuning basics

[AmadeusCharger500]

Can someone tell me how to set the timing correctly.

I have 383, enlge mild cam, FBO distributor with MSD box, headers. The distributor slots are welded, I ditched the rest of the FBO system and went with MSD. Somehow my timing changed from 15@900 rpm to 35@900, after the ignition change over. Engine has been running hot. I was going to just move it back to 15BTDC but it the rpms decreased and sounded like the engine was starving. How do you tell what timing the engine likes best?

[is_it_EVER_done?]

First of all you are trying to run a race only modified distributor in a street car. It simply won't work no matter how much you tray to adjust the carb or timing.

Get yourself a Mopar Performance electronic distributor w/vacuum advance. This will give you the best all around performance, and give you about double the gas mileage that you are currently getting (if you can even drive it as it now is). Hook the vacuum advance to the ported (not manifold) vacuum port of your carburetor.

Next, I would suggest you go to your local bookstore and buy or read up on ignition systems, their design, theory, and implementation. You will learn that for a mild cammed, relatively small displacement engine, heavy street car, that a near stock vacuum advance ignition is going to be near ideal.

Keep in mind that the vacuum and centrifugal advance mechanisms are "analog" computers. Any benefit to eliminating one or both is only going to be found in a pure race car at a lightend race weight, operating in a very narrow high RPM range, with every other power modification already implemented. Otherwise you will go slower and kill drivability.

[AmadeusCharger500]

Really?
I was told by more than a few people that a mopar engine with even a mild cam would run better at 15 initial and 30 to 35 all in around 2500.

I was also told several times to plug the vacuum advance

If someone could please enlighten me about the radical difference in opinions, that would be great.

I'm all for hearing you out and may try your suggestions, but I put this combo together with a lot of thought and help from people on this board. It would help if I got a consensus before I start sidestepping all the things I've done up to this point.

[firefighter3931]

Really?
I was told by more than a few people that a mopar engine with even a mild cam would run better at 15 initial and 30 to 35 all in around 2500.

I was also told several times to plug the vacuum advance

Yep, that's where i like to set them up. Vac advance is a pollution thing....plug it and forget it !


Here's a good thread for you to read.....the engine is a 383 very similar to yours. Once properly tuned it went from a pooch to an animal ! 


http://1970chargerregistry.com/70messageboard/viewtopic.php?t=1207&postdays=0&postorder=asc&start=0




Ron

[is_it_EVER_done?]

Really?
I was told by more than a few people that a mopar engine with even a mild cam would run better at 15 initial and 30 to 35 all in around 2500.

I was also told several times to plug the vacuum advance

If someone could please enlighten me about the radical difference in opinions, that would be great.

I'm all for hearing you out and may try your suggestions, but I put this combo together with a lot of thought and help from people on this board. It would help if I got a consensus before I start sidestepping all the things I've done up to this point.

based on what you are saying, I have to ask if this original portion of your post is correct?

The distributor slots are welded

If the slots are welded, it is a locked distributor that has no advance curve. This is a race only modification that is used with a very high stall converter or 4 speed, and is designed to be used in a very narrow/high RPM operation. This is a big difference from a modified advance curve.

In any event, I strongly urge you to read up on ignitions. One book I can recommend is by Christopher Jacobs. He has a PHD and EE degrees, as well as more ignition related patents than anyone else. his book is offered in three different titles (revisions) that I am aware of, and is straight forward and to the point in understandable terms. He also lays out a simple method of calculating the ideal advance curve your car needs, not an approximation. I have one of the first editions and it's titled "The Doctors Guide To Optimizing Your Ignition System". This was revised under the same title, and is currently titled "Performance ignition systems". It is available from Jegs or most other book vendors.

Purchase and read this book, then determine the advance curve your cars weight and combination needs and you will wonder where the ignition advice that is available all over the internet ever came from. Plus, you can dramatically improve gas mileage, and drivability.

Firefighter3931: you state that

Vac advance is a pollution thing....plug it and forget it !

 
Since vacuum advance was introduced in the 20's and continued until digital computers replaced all advance methods in the late 80's/early 90's, it is evident that vacuum advance had nothing to do with emissions whatsoever (since emissions were never considered until the mid 60's). It's true that the vacuum advance was tweaked through the 70's/80's to reduce emissions but mostly by reducing or eliminating it (NOX device) which was so detrimental to performance, drivability, engine longevity, and gas millage, that it was changed back even before the computerized cars came about. I strongly suggest you also get the book I mentioned.

[firefighter3931]

If the slots are welded, it is a locked distributor that has no advance curve. This is a race only modification that is used with a very high stall converter or 4 speed, and is designed to be used in a very narrow/high RPM operation. This is a big difference from a modified advance curve.

Firefighter3931: you state that

Vac advance is a pollution thing....plug it and forget it !

 
Since vacuum advance was introduced in the 20's and continued until digital computers replaced all advance methods in the late 80's/early 90's, it is evident that vacuum advance had nothing to do with emissions whatsoever (since emissions were never considered until the mid 60's). It's true that the vacuum advance was tweaked through the 70's/80's to reduce emissions but mostly by reducing or eliminating it (NOX device) which was so detrimental to performance, drivability, engine longevity, and gas millage, that it was changed back even before the computerized cars came about. I strongly suggest you also get the book I mentioned.

Welding the slots doesn't mean that the distributor is locked completely.....this modification is done to shorten the mechanical advance so that the tuner can dial in more base timing and not go into detonation. I don't need to read any books on how it should work because i know this way does work....been doing them this way for years. 

Bottom line is BB mopars like lots of base timing and respond well to this mod. The bigger the cam, the more spark lead it wants. 


Here's a quote from a member with a 70 Charger, 440-6 pack (all stock) with a reworked timing curve :

"Got my timing curve tuned approx like you adviced yesterday
G*D D*NM!! did that make a difference!! The motor pulled so hard it felt like the car was made of cardboard instead of steel!!  I realize now that I really didn´t know how the 440 (+6)
is supposed to pull until now even though I´ve had the car for almost 2 yrs now....  Lot´s of fun driving it now. Thanks for the advice Ron"


Another happy 440 6-pack owner :

" Ron
After fighting the Vacuum advance issue I tried your way.. holy s#$t I have another gear almost...@15 degrees initial it pings occasionally but just breifly.I'll see how this goes for awhile I might try alittle more advance and mix some octane booster and see. We only have 90 up here. The rough idle was smoothed out by adjusting the two airbleeds screws on the bottom front of the carbs. It's getting speedy...Alan"


Ron

[oldcarnut]

This is a really old thread I know but I couldn't find a topic on my question and I thought it would fit. 

Sooo the question concerns setting the idle rpm and initial advance.  I'm under the impression from other posts to set about 15-16 initial at about 800 rpm.  Sounds simple enough but where do you find that sweet spot where the rpm and timing are where it needs to be for either to set?  Adjusting either changes the other so which gets set first and how do you know when to leave it alone and just the other to fit ?  Take me to school please.

[AmadeusCharger500]

1st decide on rpm setting, 700 to 800 is pretty good range. Then hook up a vacuum gauge and move the distributor until you get the highest vacuum, you can also hear this change as it will change rpms. You may have to readjust the rpm once you find the sweet spot.

[myk]

What sort of a distributor do you have?  Does it have an adjustable mechanical advance?  Do you run vacuum advance, and if so, is that adjustable also?  

Here are the steps that I performed with my new Firecore setup:

1. set idle speed to desired RPM

2. disconnect vacuum advance and plug the vacuum port

3. check to see where, and then set your initial timing.  16-18* is the typical range for our cars

Now this is where it depends on what sort of a timing light you have.  You should have a dial-back timing light or some timing tape set on your damper.

4. raise idle speed to 2500-3000 RPM.  Check your timing number now, is it 36* like many of us?  Then, take this number and subtract your initial timing number from it.  What do you get ?  This number will be your mechanical advance timing.  It's important to know this because you don't want to have too much timing dialed in.  That will lead to a hot running engine and possibly driveability problems as well.  Some guys here like Coonhunter Joe are running 40* or so total timing, but that isn't for everyone.  Typically, you want to keep it in the 34-38* range.

5.  The best way to figure out your ideal timing is what Amadeus suggested, which is to hook up a vacuum gauge to your manifold vacuum and then add initial timing until you reach the highest vacuum.  For me, this put the car at 40* total timing.  Now, once you've dialed in timing to your highest vacuum, you should take this number and add it to your mechanical advance number.  Where is it at?  How close is it to the ideal 36-38* range?  If it's too high then hopefully you have a distributor with adjustable mechanical advance, like the Firecore units.  If that is the case you can raise or lower your mechanical advance to where you need it to be.

One of the things Ron suggests that you do is to turn the car off, and then try to start it.  If the car is difficult to start you will need to back off the timing until the hard-start problem goes away.  Also, check your driveability to make sure you don't have any issues.  You may want to read my thread about my Firecore distributor installation, because we discussed timing in it quite a bit:

http://www.dodgecharger.com/forum/index.php/topic,119680.0.html

[oldcarnut]

Thanks guys.  I'll try the vacuum setting first then adjust rpms and see what I get.  Bought some timing tape too as I only have a basic timing light. I don't know what's in this temporary motor other than it has a wieand intake, aftermarket adjustable rockers and big pushrods, had a complete MSD setup, 850 Holley, sounds like some cam installed, and some other bolt on upgrades.  The headers were removed and stock hp manifolds back on and I replaced the MSD with a complete Firecore system because I had already ordered it for the 440-6 to be built.  The carb was switched to a Holley 3310-4  (750 dual feed-vac sec with a couple mods).  I lost all it was initially set at with the part switching but don't think it was tuned good to start with when it was in the Challenger I bought and sold.  Hopefully get it done today

[myk]

If you've got the Firecore that's good news, as you can set your mechanical advance where you need it to be.  I just got rid of my Mopar Performance distributor that was non-adjustable.  I love Mopar products and all, but that ignition kit was JUNK...

[oldcarnut]

Tried to get a good vacuum but best I could get was 13.  I advanced it way forward expecting things to drop off but it just ran a little worse. Idles fumes bout stunk me out garage even with fans blowing.  Decided to check the carb settings out.  Found this guide http://www.corvette-restoration.com/resources/technical_papers/Holley_Carb_Tuning.pdf   My secondary throttle plates were closed off with the primary open too much (by the tune file) and one side mixture screw almost closed and the other bout 4 turns.  Looks like I need to get that straight first.  I need to get a hex set screw for the 2nd plates adj. so I can make any adjustments with Allen wrench while it's bolted down. 

[myk]

Don't let the fuel issue distract you from the timing.  Ron says to get the timing squared away, then move onto the fuel.  Where's the timing at now?

[oldcarnut]

Got the carb back on.  After a few adjustments this is what I found.
At about 800 rpm with the timing to 18 the vacuum is at 10 1/2.  Vacuum adv plugged on carb.
At 2500 It looked to get at about 38*  2000 got me at 30.
Vacuum would get to 15-16.  It would spike jump to a little more and drop back.  
At idle I could rotate the dist to 48* give or take and get 15 vacuum.  A 100 idle rpm drop or couple deg drop below 18 would made the cam start sounding noticeably more lumpy out the stock/quite exhaust.  Seemed to like 18 smoothing out but did good in low 20's
At the 18* setting cranks up fine.   So what is all this telling me?

[myk]

You didn't get the 15" of vacuum until you reached 48* of timing at idle?  My vacuum did not improve at idle past 24*...

[oldcarnut]

If I idled it up more and rotated I'd get to 14-15 after the 40*  Started maxing out after 40*  But leaving idle 750-800 and rotated at 30 Id have 12.5 but get 13ish close to 40 and after that 14 but start running rougher.  I only would get a good 15 with rpm running higher.

[myk]

And that's at idle speed right, around 800 RPM?

[oldcarnut]

I clarified it one post up lol.  Guess I'm gonna have to open up exhaust some.  I don't know what the cam is.

[oldcarnut]

Too bad its not street ready to take it for a test drive.  I'm just glad I got it to a point I can move it out the garage on its own power instead of pushing

[myk]

I clarified it one post up lol.  Guess I'm gonna have to open up exhaust some.  I don't know what the cam is.

Just making sure I understood you properly.  I hope you get to road test it soon...

[oldcarnut]

I clarified it one post up lol.  Guess I'm gonna have to open up exhaust some.  I don't know what the cam is.

Just making sure I understood you properly.

I was actually editing while you posted.  Anyway what ya think?  Leave it at 18*?

[myk]

I clarified it one post up lol.  Guess I'm gonna have to open up exhaust some.  I don't know what the cam is.

Just making sure I understood you properly.

I was actually editing while you posted.  Anyway what ya think?  Leave it at 18*?

If that was the best you could get it to then leave it.  With my car, it pulled up to 19" of vacuum and 24* of initial, but I felt it was better at 20* and 17" to live with.  Does your car start up easily with your current setting?

[oldcarnut]

Fires right up

[myk]

Sounds good to me, then.  What more is left until you get it on the road?

[oldcarnut]

Body interior needs painted and interior put in not to mention the outside body work plus fenders and rear window plug welded in..  In other words many months