I have a 79 Bronco that I installed a MSD distributor in not too long ago. I just rebuilt the 400, which only has about 200 miles on it. It’s got 9.5 compression with factory heads, Edelbrock intake & carb, and a comp cams RV cam (designed for torque). It currently has factory exhaust manifolds with dual exhaust, but I have headers that I will be installing soon. According to a website I found, the curb weight of my Bronco is 4718 lbs, but who knows if that’s accurate. I am running 33” BFG A/T tires, which is bigger and heavier than stock tires.

I need some advice on what timing curve to set up in my MSD distributor. I currently have the timing set at 14* at idle, which is the most advance I can run without pinging. I installed the black bushing in the distributor, which allows 18* advance. I also have the two heavy springs installed. My timing curve is hitting 28* at 3000 rpms and 32* at 3500 rpm.

So my question is what timing curve should I be running given my engine specs and vehicle weight? Should I run one heavy spring and one light spring or something different? Should I change the bushing so my total timing is 34* or 36*? Does anyone on here have a similar setup? What timing works best for my 400?

 

Are you going by what's listed or have you checked your timing to verify it ?

most engines run best with the mechanical all in at 2500 in the 32-36 range. it can vary of course.

All in with the vacuum advance should be 50-60 , just have to drive and see. an adjustable can makes getting this right easier.

 

I have verified the timing with a timing light. So from what you said about the timing being all in by 2500, then that means my timing is coming it way too late, which means I need to change my springs....correct? But the weight of the vehicle has a lot to do with how soon you want your timing to be in, that's why I listed the weight. With the weight of my Bronco, do I still want my timing to be all in by 2500 rpm???

 

Typically yes, 3000 rpm at the most in this case. you'll have to drive it and listen for detonation to get it perfected.

I would bring it in a little sooner and then I would drive it hard and keep advancing your distributor a bit at a time until you get pinging and then back it off a little. once you've determined you peaked it out then check it with your dial back and that will give you a target to shoot for. then see how your curve is. once that's in order set your vac advance.

there are too many variables to just use generic numbers. but the numbers discussed are in the ball park. the octane you're running is a big factor and you didn't mention that, if you're not running pump super you probably should be.

 

So maybe I'll change one of the heavy springs for a light spring, which will give me one heavy and one light spring. That should allow it to come in sooner, right? I timed it again today because I had some pinging with it set at 18* at idle, so I backed it down to 16*, took it for a drive and still had some pinging. So I backed it down to 14* and now there's no pinging. So if I bring the timing in sooner by changing a spring, will I be able to run more advance at idle without pinging or does it not work that way? As you can tell I'm not the most knowledgeable about this, so I thank you for your help.

As far as the octane, I'm running the cheap crap. Gas prices keep going up and these old pigs have a drinking addiction....LOL

 

With your compression you're going to lose power with regular gas. and this is why you're hearing pinging at a lower advance than you should.

But you may be able to tune for it okay. if you're pinging that early I wouldn't make it come in much sooner, detonation is the absolute point you cannot cross . so if you think you have the maximum advance you can live with just check your initial and see what it is, probably if it starts and idles okay you won't need to worry about it. you won't hurt an engine at idle with excessive timing it's under load the damage is done.

If you've peaked out your mechanical now it's time to see where your vacuum advance is at. this will not only increase your fuel economy but it will lower your EGT's and run smoother.

 

When setting up a timing curve, I like to find a lonely stretch of road to do time trials. For instance, hit the stop watch at 40 mph and floor it. Click the stop watch as soon as you hit say 65 mph. Repeat. See how your timing adjustments affect the acceleration. And listen for pinging of course.

Since you have a fresh engine build, make sure to read your plugs for air/fuel mix and verify you're not getting oil into the cylinders which will make it tend to ping.

You're on the right track by looking at the entire curve over the rpm range...not just initial. Timing is something you have to play with to your own personal preference and what your particular engine build "wants". Your numbers don't sound whacky to me, btw.

 

65Ford—So with the 40-65 mph time trials, am I correct to assume the timing adjustments I would be making would be with the springs and bushing inside the distributor, not just turning the distributor to advance or retard it? Once I get my idle timing set, then I do these time trial runs and I will be focusing on how quick my timing comes in and what rpms my total timing arrives at…..correct?

Initially I had an Edelbrock 750 carb on it, but yesterday I swapped an Edelbrock 600 onto it and it seems more snappy off the line and I’m hoping I get a little better fuel mileage with the smaller carb. When I did this carb swap, that’s when I adjusted the timing down to 14*; just on the edge of pinging.

440 Sixpack—I’m not sure if my vacuum advance canister is adjustable or not. I’ll have to look into that. And I don’t have a dial back timing light, just a regular timing light. But basically I want the most advance from the vacuum canister that I can get without pinging….is that correct? But I don’t want my total timing to be over 60*???? Is that right?

I agree with you that using the cheaper gas makes it more susceptible to pinging. Case in point, I have the exact same distributor in my 460 in my 78 F150 Super Cab and I have the exact same timing curve setup (black bushing & 2 heavy springs). The only difference is I use supreme gas with no ethanol and it allows me to set my idle timing at 18* rather than 14* or lower. So my timing curve is 32* at 3000 and 36* at 3500.

I use my truck for towing my travel trailer. My truck is about 5500 lbs and the travel trailer is 8200 lbs empty. So there are a couple reasons I have the timing curve set very conservative.

1) When I built my 460 a few years ago, I bought a duraspark distributor from an engine builder who recurved it for me to match my setup. Well there was a bad spring inside the distributor and it allowed it to advance way too far and I melted 3 pistons pulling a hill with my trailer behind me. Funny thing is I couldn’t hear the engine pinging, probably because the truck is so loud. So I had to rebuild the engine again because of a bad spring in the distributor. Since that time, I have upgraded to the MSD distributor.

2) I don’t want a repeat of having to rebuild my engine because my timing curve isn’t right. With the timing set the way I have it, I can pull a 6% hill with my trailer behind me with the pedal wide open on the floor and I have no pinging and the temp doesn’t get above 197* even in the summer.

Question……With that said, if swap out one of the heavy springs for a light spring so I have one heavy and one light spring and allow the timing to come in sooner, how would it affect my pulling power, water temp, etc…??? Would I gain any performance pulling so much weight by bringing in the timing sooner? Like I said, I’m scared to put too much advance in it too soon because I don’t want to lose my engine again. But if I can advance it a little by changing a spring and gain some performance or power pulling a hill without pinging or the water temp going crazy hot, then I’m all for making the change. But I wanted to get your thoughts about doing this before I did it.

 

If you plan on doing serious towing you really might consider tuning for super . your compression isn't that high but it's much higher than stock and that comes at a price.

I'm not a timing tape fan but it's better than nothing , are you using that or are you just guessing at your mechanical advance ?

 

I am using a timing tape on the dampener. What's your thoughts about my timing curve setup considering I use it for towing? Is the timing still coming in way too late or leave it as is? Compression on my 460 is right at 10:1 with aluminum super cobra jet heads.

 

Hard to answer your questions concretely. I'd say start with initial (vacuum disconnected and plugged) of around 10-14. You want it advanced enough to prevent overheating and have strong idle but not so much it's hard to start. Then find out how much and how soon you can advance timing without pinging or until you see no more power being made(your stopwatch time stops decreasing). And like you said, it's about adjusting the bushings and springs at that point to optimize the curve. If your engine is pretty much factory, then factory timing will be close though a little conservative. If you've changed cams or modified heads then performance may benefit from a timing curve adjustment.

Vacuum advance is a personal choice in my opinion. Some guys like it and some don't. Some guys like ported and some like full vacuum. I like to nail down the mechanical advance curve and then play with vacuum (ported, full, or none at all) and see what the engine and I like.

 

Aluminum heads will help some. but at 10.1 you really need super especially since the cam you have isn't going to help you any. if you're going to burn regular I'd probably leave it coming in later you need to keep it toned down . try it and see .

The vacuum advance isn't really a matter of debate for those who understand ignition timing. there are many advantages to it and no downside unless you don't know what you're doing. there are valid arguments for running manifold vacuum but ported is usually what works best . since your mechanical advance is going to be et a little wimpy to account for your octane you need to run a healthy amount of vacuum advance. the beauty of vacuum advance is as the throttle plates open and drop the vacuum it retards your timing and protects your engine. mechanical just holds in there . you can have too much of course that's why it needs limited sometimes.

 

65 Ford—The 400 in my Bronco is kind of stock and kind of modified. I’m running higher compression (9.5) flat top pistons from TMeyer, Edelbrock intake & carb, and a flat tappet comp cams RV cam (for torque). Other than that everything else is stock. I will be installing headers soon, but want to get my mufflers first since I’m going bigger on the exhaust tubing size.

Regarding the vacuum advance (ported vs manifold); I’m using ported vacuum. There seems to be a lot of debate on which one is better to use and there’s valid arguments for and against, but I figured I’d use the ported vacuum because that’s how the factory designed it to be used.

440 Sixpack—I think there’s a little confusion on which engine I’m talking about so let me clarify. This post was initially referring to the 400 in my 79 Bronco, which has 9.5 compression and I’m using the parts as explained to 65 Ford above. Then I started asking about my 460 in my 78 F150 Super Cab, which has the aluminum cobra jet heads, 10:1 compression, roller cam, headers, and other after market goodies. Both engines are running the exact same distributor, only the 400 in the Bronco has a flat tappet RV cam (for torque) and the 460 has a roller RV cam (for torque). I use my truck to tow my travel trailer, but I have both distributors set up with the exact same way (black bushing & 2 heavy springs). The only difference in timing is the 400 in the Bronco is set at 14* at idle (using cheap gas) and the 460 in my truck is set at 18* (using supreme w/no ethanol).

You made a comment “you really need super, especially since the cam you have isn’t going to help you any”. What do you mean when you say “super”? Are you talking about using supreme gas instead of regular gas? Since I’m using supreme in my 460, do you think I can get away with adding 1 light spring instead of using 2 heavy springs? Would it help to bring the timing in sooner knowing I tow a trailer with it? Currently, the mechanical timing is all in by 3500 rpm. Would it help with towing power if it was all in by 3000 rpm? I know I’d have to test it out to know for sure, but just wanted to get an opinion to see if it would help at all.

Regarding ignition timing in general….I have a general understanding of it, but as you can tell I’m not very knowledgeable regarding the fine tuning aspects of it. I’m not sure which adjustments to make given a certain engine & vehicle setup. All I basically know is that you want as much idle advance as possible without pinging and you don’t want more than 36* total mechanical advance (and some engines require less timing). Regarding adjusting the vacuum advance canister to give you total advance, I have never messed with that and have no idea what it should be set at. I also have no idea what the best timing curve should look like nor do I know what the benefits of having my timing come in sooner rather than later. Am I leaving power on the table by having my timing coming in so late? What benefits would I see if I brought the timing in sooner rather than later? I’ve been turning wrenches for many many years (32 years), but I’ve never really understood the fine tuning aspects of ignition timing, nor have I really dove in and tried to learn it until recently. So please forgive me for all the questions, I’m trying to learn by asking you guys these detailed questions. Thank you for your patients.

 

My 351m with Performer 400 intake, Crane torque grind (Fireball) cam straight up, 600 carb runs great with quick advance kit that sees all mechanical advance in by 2,000 rpm, to set it I pull vac advance loose, plug it, set total timing at 35* btc, at about 2k to 2500 rpms, then lock her down and reconnect vac tube. Edelbrock carb and a Holley FPR set at 5.5 psi. Otherwise, all stock including that "easy turn starter saving" low compression option.

 

I was wondering if we were talking about the same engine.

I'm old enough it used to be called super now it's supreme. back when there was no unleaded.

Your cam grind can bleed off some compression. for instance the 428 CJ that was in my high boy when I bought it has TRW's and a compression ratio higher than I wanted for the pump non ethanol super I can easily get. so when I freshened it up I put a custom grind roller cam in it that is not only ground for my exact build and vehicle but I had Brent do what he could to bring me down a notch on compression. it came out perfect in all respects. your cam isn't going to do this, and that's ok you just have to work accordingly.

A cam isn't the ideal way to set your compression ratio and there is a limit to it's efficiency and effect but it is always a factor in a build and a way to cheat a little.

As far as when to bring it all in , at what rpm and at what degree of advance are you at where you aren't getting any pinging ? normally you want it in by 3000 . most of the time 2500.