[onebad82z]

Ok I am trying to get the car dialed in (ignition and carb). I have a good understanding of timing and all that's involved. Many threads I have read especially Ignition 101. I was talking to Don @ FBO systems as I was ordering the 10 & 14 degree MSD bushings for my car (MSD Pro Billet 8361). I currently have the MSD 18 degree black bushing in there. I also have vacuum advance (adds 10 by use of a limiter) hooked up to manifold giving my 24 at idle timing. 34 total. Vacuum is "all in" at idle (again using what I learned in Ignition 101).

Not sure why I am not getting 18 initial (I only get 14) as I should with the bushing, part of the reason for ordering the FBO units. Anyway here is my concern. Don stated (he went into more detail, just giving the main idea here) to unplug the vacuum can and turn the distributor a little at a time till I saw no increase in idle RPM. He said to reset the idle speed screws with each increase in RPM. I then would know what the car "wanted" as far as idle timing. I could then use a combo of bushings and vacuum advance to achieve this # and keep the total timing in my desired 34-36 degree range (aluminum headed SBC here).

I did this this morning and find right around 30 degrees it no longer will increase RPM's at idle. So I would like to add this additional 6 degrees over what I have.

Two ways I can do this.

1. UN-limit the vacuum can and add the full 16 degrees it offers. This added to my initial of 14 gives me 30 at idle, 34 total timing. I then should see 50 at cruise...

OR

2. Use the smaller FBO bushing which will give me 20-22 or so at idle and limit the vacuum can further to 8 degrees giving me 30 at idle, 34 total. I then should see 42 at cruise...

Why way is better and why? Or is it the same either way....

I know started kickback MAY come into effect with the 22 initial so that I will chalk up to a con for option 2. I do have a mini starter so it really shouldn't.. but. On the flip side a pro would be the additional timing at cruise...

But is there a larger benefit to running more initial and less vacuum to make up the idle timing? Or performance wise the engine could really care less as long as it is getting it's 30 degrees at idle.

Street/strip car. 95% street driven.

 

[SWHEATON]

JON,1 MORE TIME./LOL !!!!!

* SETUP MECH ADV IN DIST SETUP FOR 18 DEG ADV IN BY APPROX 2600-2800RPMS WITH YOUR SETUP.

* THEN RUN APPROX 18 DEG BASE TIMING WITH THE CAM YOU HAVE FOR 36 TOTAL ,YOU COULD ALSO TRY 20 BASE/38 TOTAL TOO IF IT RESPONDS WELL TO IT.

NOTEON'T FORGTETIDLE MUST BE LOW LIKE 600RPMS WHEN SETTING BASE TIMING OF MECH ADV CAN BECPOME PARTIALLY ACTIVATED UPSETTING BASE TIMING SETTING MAKING IT MORE RETARDED THEN YOU THINK IT IS.

* THEN RUN AND VAC THAT EITHER GIVES ONLY 10-14 DEG ADDITIONAL DEG TIMIG OR A VAC ADV THAT LIMITED TO 10-12 DEG OR SO MAX ADDITIONAL DEG TIMING USING A LIMITER PLATE TO NOT ALOW THE FULL 20-25 DEG SOME VAC ADV HAVE.

WHATEVER VAC ADV YOU USE NEEDS TO ALSO BE FULLY ACTIVATED AT APPROC 2" BELOW THE MOTORS LOWEST IDLE VAC WHEN IN GEAR WITH AUTO TRANS & HOOKED TO FULL INT VACUUM ALL THE TIME TOO.

This a very good inital street perf ign timing curve for your cam/motor setup that will work well right out of the box with olikely nly minimal tweaking of timing later on to find the sweet spot.

SCOTT

 

[RB69SS396Conv]

"Total" timing DOES NOT include vac adv.

Meaning, if you have 24° at high RPMs with no vacuum, your "total" timing is 24° no matter what the vac adv is.

A typical small block will want about 36° "total" (plus at least 10° of vac, most likely more, but genrally not more than 15°), except it will be a couple of ° less than that with Vortec or similar "high swirl" chambers; a typical BB will want about 38°.

I agree largely with Scott's curve suggestion; with the caveat that centrifugal advance MUST NOT start until a couple hundred RPM above idle, wherever that happens to be. Then play around with ported vs hard vacuum to the dist; odds are, it will work better with hard vacuum, but it's a tuning thing. Try it both ways and see.

 

[wildman926]

Hello John,

Yes, you can set it that way, turning the dizzy until no more rpm's are achieved. And Yes, this is what YOUR engine will like as for initial.

You can achieve this setting by using the set screw method that Vince G./69-Chvl came up with. I had this EXACT same setting on my SBC HEI dizzy, using the screw to obtain 26* initial and 36* total. I then used PORTED vacuum to add the extra timing during cruise or NO LOAD. I had a grand total of 52* timing (initial + total + vacuum advance). You have to look at it that way.

If you use manifold vacuum for extra timing at idle, that is ok too, but it will be gone as soon as you take off from a stand still (engine under load), and will come back at cruise (no load). So at idle, you may have your initial at 26*, and say 16* vacuum timing, which would give you a total of 42* at idle (initial + manifold vacuum), but drop down to your initial of 26* once the car takes off.

Here is Vince's pic for reference.

 

[Wooderson]

I always considered that there are two "total timing" specs: Total wide open throttle, and total cruise. You have to know both.

 

[Tom Mobley]

yeah, I don't see how total is total if it doesn't include vacuum advance.

Any new guys that see this: DON'T just advance your timing till it won't idle any faster and figure it's OK. It's not. The method being discussed here involves having a good timing light and a distributor with adjustable mechanical and vacuum advance along with a guy who knows how and why to adjust it. Most distributors have WAY too much advance built into them to use this technique, you'll end up with 60 or more degrees advance and possible engine damage.

 

[onebad82z]

I always considered that there are two "total timing" specs: Total wide open throttle, and total cruise. You have to know both.

Yes. I agree. I seem to have worded wrong. When I state "total" in reference to idle timing I mean initial "base" setting WITH the addition of vacuum advance.

So my "total" idle timing right now is 14 initial along with 10 vacuum = 24 degrees at idle.

When I state my "total" in reference to the timing being fully mechanically advanced as in my 34 degree reference I indeed meant the initial + centrifugal, no additional vacuum added.

My TOTAL timing is 14 initial with 22 centrifugal = 34-36 total

Total cruising degrees is is 14 initial along with 10 vacuum = 24 PLUS 12 centrifugal = 36. Which just happens to be the same as my TOTAL.

 

[onebad82z]

So at idle, you may have your initial at 26*, and say 16* vacuum timing, which would give you a total of 42* at idle (initial + manifold vacuum), but drop down to your initial of 26* once the car takes off.

Exactly what I was trying to say, thank you. Seems I lost my point in too many words.

yeah, I don't see how total is total if it doesn't include vacuum advance.

Any new guys that see this: DON'T just advance your timing till it won't idle any faster and figure it's OK. It's not. The method being discussed here involves having a good timing light and a distributor with adjustable mechanical and vacuum advance along with a guy who knows how and why to adjust it. Most distributors have WAY too much advance built into them to use this technique, you'll end up with 60 or more degrees advance and possible engine damage.

I agree Tom. I have a easily adjusted mechanical advance along with vacuum advance limiting options. You still have to be 100% sure not to go over the recommended TOTAL timing, in my case 36-38 degrees for a SBC. Like Walt said...

So at idle, I have my initial at 14*, and 10* vacuum timing, which would give you a total of 24* at idle (initial + manifold vacuum), but drop down to my TOTAL ( initial of 14* + centrifugal of 22) to 36* once the car takes off.

 

[wildman926]

So at idle, I have my initial at 14*, and 10* vacuum timing, which would give you a total of 24* at idle (initial + manifold vacuum), but drop down to my TOTAL ( initial of 26* + centrifugal of 22) to 36* once the car takes off.

John,

Don't figure in your manifold vacuum at all for what your motor needs. It is "icing on the cake" to help keep plugs clean, etc. Just get your initial where you want it FIRST, then adjust as necessary to get your total (initial + mechanical) anywhere from 32-40 (you just need to take it out and adjust till it pings, see where it is, and back off 2*), THEN connect your vacuum advance, and take it out again and ajust out to see where it pings during cruize, then back off 2* again. This will give you the BEST setup for YOUR motor. It is just a pain in the @ss, but well worth it.

 

[Tom Mobley]

it's called "tuning for maximum performance." It's always been a PITA, but it pays off. WBO2 meters really help, and there's a lot more dyno's around than there used to be.

 

[onebad82z]

it's called "tuning for maximum performance." It's always been a PITA, but it pays off. WBO2 meters really help, and there's a lot more dyno's around than there used to be.

No PITA here. I enjoy getting out and putting the car through its paces! Trying to get it as close as I can just street driving, then I plan to stick it on a dyno just to see what else can be gained with fine tuning. Then the last stage is strip tuning. Well at least for secondaries, I tune the primary side for street driving.

 

[vrooom3440]

John I think you are on the right track... although there is a lot of noise and confusion here.

First to the point Tom Mobley was making: the procedure to advance the distributor until the idle speed stops increasing is a very valid procedure FOR ESTABLISHING WHAT THE ENGINE WANTS FOR IDLE. It is NOT an appropriate procedure for running/driving setup. It will result in overly advanced timing and must be reset before trying to drive the car!

To the case in point, cruising will want 50-52* of advance. So you can easily add more vacuum advance than 6*. But be sure that 6* is crankshaft and not distributor advance, because vacuum cans are often specified the *other* way.

So I guess I would mess with the mechanical until you can get 16-18* at idle and around 36* total timing. No vacuum advance for that part of the tuning.

Then hook up 14* or so of vacuum advance all in at idle and connected to manifold vacuum.

Call it done unless you want to go dyno optimize it.

 

[onebad82z]

So I guess I would mess with the mechanical until you can get 16-18* at idle and around 36* total timing. No vacuum advance for that part of the tuning.

Then hook up 14* or so of vacuum advance all in at idle and connected to manifold vacuum.

Call it done unless you want to go dyno optimize it.

I have exactly that right now. Well close as I can get with the largest MSD bushing.

14 initial (with 22 mechanical) giving me 36 total. I than have the vacuum can limited to 10 crankshaft degrees (verified with a timing light) by use of a limiter. I can pretty much nail the vacuum limiter amount with the use of a very small scale I made and a Mityvac hand pump. You suggest use of a Mityvac in several posts and it works great!

So I guess my original question of which is better...

OPTION 1: More initial with less vacuum

* My TOTAL timing can be 22 initial with 14 centrifugal = 34-36 TOTAL

.. which then could give me...

* Total cruising timing degrees could be 22 initial PLUS 8 vacuum = 30 idle PLUS 14 centrifugal = 44 cruise degrees. (Obviously less than the 50-52 optimal most suggest).

OR

OPTION 2: Less initial with more vacuum

* My TOTAL timing is 14 initial with 22 centrifugal = 34-36 TOTAL

.. which then gives me...

* Total cruising timing degrees is 14 initial PLUS 16 vacuum = 30 idle PLUS 22 centrifugal = 52 cruise degrees.

Again both options I am using vacuum to get me as close to 30 idle timing degrees I can get as that is what MY motor seems to like best.

SO...

My vote goes to OPTION 2: Less initial with more vacuum and the added vacuum will help get the cruise timing closer to the 50-52 most see as best? Option 1 will only net me 44. Option 2 nets me 52. Either option is 30 idle timing degrees and 36 total degrees (no vacuum addition).

I can set it up either way and just want to be sure to pick the best method.

 

[SWHEATON]

Your cam would really like approx 18 base timing,then add 18 deg mech in dist by 2600ish + approx 14 deg from vac adv and you get 50 deg timing at cruise,its that simple.

All you have to do is have someone/a dist shop(or your) setup the mech adv for 18 deg and vac adv for 14 deg max. Then you simply install the dist ,set it to 36 or 38 deg total at lke 3k rpm to ensure mech adv is fully actrivated when setting total timing and your good to go. Dont forget to plug vac adv when setting total timing. You will have 18 or 20 deg base tiiming and 50-52 deg with all timing in at cruise depending on if you run 36 or 38 total,but your good to go after doing that,no fuss no muss/LOL!!!!!

Use at least 93 oct fuel for this street perf ign timing curve.

Thats how to correctly setup a good starting point for dialing in setup but it will run very well there,trust me on that,could try tweaking the timing a deg or 2 up/dn from there to see howit responds.

But the cam your running 20 deg base may be even better so that would inc total from 36 deg to 38 deg total + approx 14 deg fronm vac adv now = 52 deg at cruise.

I have found over the yrs its not as good to depend on the vac adv for the addiitonal base timing and or additonal timing at cruise like you want to do.

Thats why i keep suggesting the setup listed above because its a good initial setup for a street perf ign timing curve that will work very well right out of the box if done right.

Someone stated above they thought your making this harder then it needs to be and i tend to agree with that statement at this point.

JMHO.

Good luck.

Scott

 

[Tom Mobley]

more noise, or info. many cars today have OD trannys and cruise at around 2000 RPM. That won't get your mechanical advance all in. So, observe your cruise RPM, adjust accordingly. Your engine may not want all the advance at that low RPM, or it may.

Also, use the Mighty-Vac to see what the tip-in and all-in points are for the vacuum advance are. hook up a vacuum gauge inside the car and drive with it a couple weeks.

If the carb is lean at cruise as it should be for a street car it can stand a LOT of vacuum advance. Out of this deal comes gas mileage. There's guys out there getting mileage you wouldn't think possible with big engines and OD.

My own car is a daily driver 406 with iron aftermarket heads, hydraulic roller short duration cam, Q-jet and 200-4R with 3.73.

legal freeway cruise is at 16.5 A/F and 56° timing at 2100. I had to screw around with it a lot but it gets over 22 on the freeway. Every time gas goes up I feel better about the time I put in getting right.

I'm just sayin' is all.

 

[onebad82z]

Scott... Tom... I find no noise here myself. I appreciate everyone's input as it all has helped me understand which way is better and for what reasons. This is what I wanted to know. I need to understand how and why along with that what.

A combo such as yours Tom that gets 22 on the freeway is reason for this post. Others may as well, but Tom gave details hence my using his as an example. Anyway, right now the car is getting 9.... 9 MPG. I know it can do better. How much is yet to be known, but I want to think at least 15. Now this is combined driving... freeway, city/town, and a fair share of back road blasts through the gears. I cruise the car generally around 2500 in 4th unless on the freeway where it seems to like 2500 in 5th. Anything under that it gets "cranky" to say it best. May be due to the timing being off and the carb is not dialed in yet either. That post will come after I sort the timing out... stay tuned! Or it may just be the nature of the beast with the new cam. I have 6th but until I put a 4.10 in the car I have to greatly exceed posted speed limits to use it so for now I don't even look for it.

Back to the main topic.

I have my TOTAL timing all in by 2900 or so. Would I be better to have it all in under my cruise RPM?

I do have a vacuum gauge permanently mounted in the dash. I made a custom Autometer dash cluster years ago and put that in right away.

As far as the vacuum can goes... it starts to pull in at 3" vacuum and is all in by 7.5" vacuum. Right now it is limited to 10*. It offers 16*. This is crankshaft degrees. My idle vacuum is 9" at 950.

Scott... you say...

"I have found over the yrs its not as good to depend on the vac adv for the addiitonal base timing and or additonal timing at cruise like you want to do."

This is exactly my reason for this post. See my post from 9:40 last night with the 2 options. Problem is as I see and understand it is that I need the additional vacuum to get my cruise timing in range of optimal. To have more initial and less vacuum leaves me short in the cruise range.

 

[onebad82z]

And I do want to reiterate what others have already said in this thread for newcombers to it and timing. (And I agree with 100%).

DO NOT SET YOUR TIMING TO THE HIGHEST RPM AND RUN WITH IT. 99.9% CHANCES ARE YOU WILL DAMAGE YOUR ENGINE AS THE TOTAL TIMING WILL MORE THAN LIKELY BE REALLY HIGH. YOU NEED TO FACTOR IN TOTAL AS WELL BEFORE RUNNING IT IN SUCH A TUNE.

 

[onebad82z]

Ok guys got an update here.

Since it was the easiest of my available options right now I decided to pull the limiter out allowing the vacuum can to add its full contents of 16 crankshaft degrees. So right now my timing goes like this..

14 initial plus 22 centrifugal gives me 36 total degrees. This is how I have been running the car for the last few weeks and it likes this so far.

14 initial plus 16 vacuum can added degrees (before it was limited to only add 10 degrees) now gives me 30 @ idle. This is what I determined that MY car and combo liked best AT IDLE. This now gives me AT MAX a cruise timing of 52 degrees. Only difference was removing the limiter, did not touch the distributor position.

I warmed it up and took a ride. WOW what a difference that additional 6 degrees made. The car before would not pull down any lower than 2000. Any lower and it would buck and stumble. Take off and in town cruise 100% improved. A weird dead spot I had between idle cruise and getting into the mains is now gone. Now with the added 6 degrees it will pull down to 1500!

I took it on the freeway and was able to cruise rather easily at 2000. Before I needed to be at least at 2500 for it to be civil. I was also able to close up idle mixture screws 1/8 turn to achieve best idle. I can almost smell more MPG..:thumbsup:

No pinging anywhere and it is pretty hot out today... 85-90 degrees.

So right now the game plan is to run it like this for a few days/weeks and see how it acts in the long run. If I am still not happy I will swap it all around to have more initial with less vacuum and see how it likes that.

Overall a plus for the day!:hurray:

Did manage one back road romp to see how the 2 step was working with my latest rewire. Car screams off a 4k rpm launch to the rev limiter at 7k without a hint of laying down! Guess I may need to re-evaluate that 6400 shift light pill.

 

[Tom Mobley]

That's what I'm talkin about.....

only one way to find out, get out there and do it.

I'll bet you just increased your gas mileage by 50% and there's probably more in there. Lean mixtures burn slow and can stand a lot of advance. Have a WBO2 or know somebody who does?

 

[onebad82z]

That's what I'm talkin about.....

only one way to find out, get out there and do it.

I'll bet you just increased your gas mileage by 50% and there's probably more in there. Lean mixtures burn slow and can stand a lot of advance. Have a WBO2 or know somebody who does?

Hell yeah. Built to beat on and I do on any given chance..

No wideband of my own nor anyone I know. I broke down last winter and bought an OBD 2 scanner to chase some problems in my DD. Thought I made a good buy and then see the new Innovative LM-2 is nearly the same price and I can use it to tune the camaro. Damn lost that one! Anyway.

I hope to get a LM-2 this winter. For now it is the ole butt-o-meter tuning while watching MPG!