I have been playing around testing my initial timing. I have found I get the best idle and vacuum with my initial timing at 32-34. This is just at idle. No I am not cruising around with it set up this way. I have had no problems at all with starting the car at 180 degrees engine temp. I have had the initial set at 20 degrees (38 total( A little to high I think)) and the car really seemed to respond to it. No detonations.It doesn't even seem to bring the starter down. I have been talking to Don Gould and am also considering his vacuum advance set up.I have ordered his larger bushings for the dizzy so I can get 24-26 initial. Anyway my engine combination seems to like advance. There must be some real downsides to locking the distributor. I would like to here before I go and do it. 95 street 5 strip
496BB ,10.1-1 ,Msd mechanical,245 solid roller cam @.050 ,650 lift 950 Holley hp

If it starts and drives OK...no reason to worry about it. Have to be careful lugging it under hard pulls at low RPM...but otherwise no issue. These long stroke BBC's really thrive on lots of initial. I have mine idling at 30* with only 8* of centrifugal in it. I don't use a vacuum advance, though I probably could if I limited it to 6* or so max.

Give it a try...won't hurt anything and will be awful responsive!


JIM

Did you fab your own bushing ?

On a 95% street car you need vacuum advance which will bring your total to 50-55 degrees at cruise which is what your engine needs. Otherwise she'll run hotter, get worse mileage, and be less responsive.

Also, I don't see how you are starting your cars with 30+ degrees of initial. I get kick-back at around 20. .

As said above, the downside is potential detonation when loading the engine at low rpm.

The only downside I have found is cranking. I solved that one with a toggle cut out switch. I LOVE locked out timing.

Running 36* locked here, and another 12* ported vac advance. Using a GM crate motor take-off starter. Runs excellent, starter doesnt even blink.

If your starter cant handle more than 20*, you need a better starter, cables, etc.

. Have to be careful lugging it under hard pulls at low RPM...
JIM

As said above, the downside is potential detonation when loading the engine at low rpm.I had mine locked at 36* and it beat the bearings out! I have read where others get away with it but never for me again.

Like said above, if you idle alot or lug it around it is not good. I had great throttle responce and it felt stronger but I did not know the damage that was going on inside of my engine. Cost me a complete rebuild and almost a crankshaft.

I thought 36 was the magic number for total advance. I see you guys running 48 and 55? I assume with WOT the vac advance disingages and at cruise it comes back?
Does anyone run the vac advance system from Don at 4secondsflat.com ?

speedfreak, did you also run vacuum advance? What was your compression ratio? Iron or aluminum heads? Just curious...If locked timing beat the bearings out you must have been on the ragged edge wth detonation any way.

You have to figure that most performance advance curves are in at 3000 or less. Most of you automatic guys are probably driving around at 2500-3000 all the time, so your advance is fully in anyway. I do lug the motor, below 2000. Havent heard any pinging, and I actually drive next to medians/highway dividers trying to listen for detonation...cant hear any, and I have a quiet exh. It works for me, that's all. With the timing locked, I get much smoother engine operation, as the advance weights arent swinging in/out as I go through the gears. Just a stick-shift thing.

The speed the piston gets to TDC on each stroke changes with engine RPM. The speed that the spark gets from the dist cap to the spark plug is fixed. Timing is all about providing the spark at the right time at any rpm. No engine runs efficently at all rpm with locked out timing. Vacuum advance was designed to refine the mechanical advance even further.

The track is all about WOT so locking out the timing eliminates variables that could adversely effect the WOT pass. You don't drive WOT most of the time on the street or even at the same RPM. A functioning mechanical and vacuum advance curve will insure your engine is running efficient which results in increased performance, increased fuel economy, better street manors and most important of all longevity.

All this will surface if you drive your car, I don't mean to the Dairy Queen once a week and to a local show or cruise in a couple times during the summer months. I'm talking putting a couple tanks of gas through the pipes on a Saturday twice a month on top of the DQ and show trips and maybe taking a couple over night trips during the summer... If you really drive your car you will want a proper advance curve including Vacuum advance.

I'm going to swap out my msd billet to a msd billet vacuum advance eventually as well. I'm running 20 initial and 38 total with my 489 and it runs really well. I can't seem to get rid of my tip in hesitation and I'm sure more advance in form of vacuum advance would help tremendously just off idle.

I just got off the phone with MSD tech and they told me not to waste my money. I have a pretty large cam that nets me 8psi at 1000 rpm.

Mine is set identical to Jim's....we didn't confer....but the 496 likes it. I should have gone locked, but for some odd reason I like a little curve in there. Mine is low CR, 9.4:1 so it never drags on the starter (a stock GM HD iron nose deal) My starter is 12 years old, I added brushes once....

I would like to have vacuum advance as well. It helps at cruise rpm, and keeps the plugs cleaner when putting around. But the Dominator doesn't have a ported advance source, and I don't feel like modifying it to have one. The MSD keeps the plugs decent, never black.

BTW...I doubt with that small cam you are near 690 hp.

Ron

If it starts and drives OK...no reason to worry about it. Have to be careful lugging it under hard pulls at low RPM...but otherwise no issue. These long stroke BBC's really thrive on lots of initial. I have mine idling at 30* with only 8* of centrifugal in it. I don't use a vacuum advance, though I probably could if I limited it to 6* or so max.

Give it a try...won't hurt anything and will be awful responsive!


JIM

Big *** battery, big *** cables and a good starter!

Ron

On a 95% street car you need vacuum advance which will bring your total to 50-55 degrees at cruise which is what your engine needs. Otherwise she'll run hotter, get worse mileage, and be less responsive.

Also, I don't see how you are starting your cars with 30+ degrees of initial. I get kick-back at around 20. .

I honestly don't see the advantage to locking out the timing if you have a distributor that works properly.

Do any of you guys with locked out timing have back to back testing (locked vs non locked) at the track proving the gain in performance? I just wonder if the perception of better performance is due to the seat dyno being uncalibrated.

Personally I run all mechanical advance no vacuum, but I don't see the advantage of not have a timing curve.

I thought 36 was the magic number for total advance. I see you guys running 48 and 55? I assume with WOT the vac advance disingages and at cruise it comes back?
Does anyone run the vac advance system from Don at www.4secondsflat.com ? I am running a custom built distributor from www.4secondflat.com and love it these BBC want alot of timing.

We have it at 22* at idle with vacuum plug off. With vacuum plugged into manifold vacuum at idle its at 32* and no problem starting, at cruise 50* and wide open is 36*... This is a BBC 498 @ 10.5.1 compression pump gas motor and no detonation.

I just got off the phone with MSD tech and they told me not to waste my money. I have a pretty large cam that nets me 8psi at 1000 rpm. Todd you can buy a custom bushing from www.4secondsflat.com that will get you at i think 26* initial. Give Don a call.

Thanks skip....I have a clean idle now but may give it a shot.:thumbsup: I ordered a new set of metering blocks with adjustable idle feed restrictors so I can fatten up the transition a tad.

Thanks skip....I have a clean idle now but may give it a shot.:thumbsup: I ordered a new set of metering blocks with adjustable idle feed restrictors so I can fatten up the transition a tad. When i had my carb built from Pro-Systems they drilled a tiny hole in both metering blocks to help out with the transition. I have had a lean spike right when i released the clutch, i can see that it was lean from my Innovate AFR meter. Hope that works for you and if not try more initial.

speedfreak, did you also run vacuum advance? What was your compression ratio? Iron or aluminum heads? Just curious...If locked timing beat the bearings out you must have been on the ragged edge wth detonation any way.
No vac can. Engine is in sig. It was a 383, no more than 10.5:1cr and alum heads. Something deff happened. All upper bearings were wasted if I remember correctly and the balancer was quality with timing marks on it. Happened around 3k miles.

I honestly don't see the advantage to locking out the timing if you have a distributor that works properly.

Do any of you guys with locked out timing have back to back testing (locked vs non locked) at the track proving the gain in performance? I just wonder if the perception of better performance is due to the seat dyno being uncalibrated.

Personally I run all mechanical advance no vacuum, but I don't see the advantage of not have a timing curve.

I was running some advance on the new blower combo until now. I had always run it locked NA but tried to kill a little bottom end under boost.:D I should have some decent back to back numbers after this weekend. The air will be MUCH better but I can correct for that in the data.

I spoke to Calvert this week and they said lock it out to hit the tires harder, but the reality is I like it locked because a) it makes a big ole cam idle like a champ and b) there is no worrry of creep as RPMs get really high.

Your right it doesn't make 690. It makes 691. Mark Jones know how to make an engine. I have it locked out right now at 32 degrees and it seems to really like it. I talked to Don at 4secondsflat and I am going to try his bigger bushing so my initial will be around 22 maybe 24. I need 1 more hot day to see how it reacts to that. Might be tough here to get that!

Dan that is amazing and yes Mark dose know how to build a motor.

Skeeter, Looks like I'm going thru all the pains you have experienced just 5 or 6 months behind. I follow a lot of your posts.

Skeeter, Looks like I'm going thru all the pains you have experienced just 5 or 6 months behind. I follow a lot of your posts. I would get as much initial timing as possible, but i realy like running the vacuum advance from www.4secondsflat (http://www.4secondsflat) at 32* with manifold vacuum, 50* cruise and 36* WOT. My problem 1st was my MSD module went out and 2nd my coil went out 3rd sucking oil down my PCV and 4th my carb was out of the T-slots. But now its all good and about 95% tunned.

That bushing will help for sure.

I was running some advance on the new blower combo until now. I had always run it locked NA but tried to kill a little bottom end under boost.:D I should have some decent back to back numbers after this weekend. The air will be MUCH better but I can correct for that in the data.

I spoke to Calvert this week and they said lock it out to hit the tires harder, but the reality is I like it locked because a) it makes a big ole cam idle like a champ and b) there is no worrry of creep as RPMs get really high.

I can understand killing some low end with a blower. What I don't understand is how are you going to hit the tires any harder. If you have a 3500 Stall and total timing all in by 3000, then your timing is for all intents and purposes locked out at your launch RPM. Also if you are killing bottom end how is that going to help hit the tires harder?

I'm not trying to argue I am just trying to make sense of it, so I can understand the advantages better.

I run 20* initial and 32* total all mechanical, I then retard from there with a Crane boost retard. I have a 3500 stall, no trans brake, so if I smash it from idle the converter is going to flash and my timing will be all in. If I foot brake it and hold it against the converter (approx 3000RPM) then smash it from there my tining will still be all in.

For a blown application I don't like vacuum advance, actually I don't care for it on any of my performance stuff.

Royce, Well, my converter only flashes to 3,000 and I foot brake at 2,200 off the line so I think I will get some benefit but not a whole lot.

Like I said, for me the higher RPM stability is the bigger issue. You tend to get some bounce with the weights no matter what you do. With the boost I want to make certain of what the timing is. It's certainly not for everyone but I have liked running it that way.

Royce, Well, my converter only flashes to 3,000 and I foot brake at 2,200 off the line so I think I will get some benefit but not a whole lot.

Like I said, for me the higher RPM stability is the bigger issue. You tend to get some bounce with the weights no matter what you do. With the boost I want to make certain of what the timing is. It's certainly not for everyone but I have liked running it that way.

Fair enough, I will be interested to see the results of your testing.