[Jonsey]

This car used to have the same engine with a much larger cam, TH400 transmission with 3200 RPM converter. It had the stinky idle and not great throttle response at partial opening, but never bucked at low speeds. An auto trans does hide a lot of these issues.

I had a chance to look at the timing this weekend. Warmed up, it had 14 degrees initial timing with 36 total by 3000 rpm. Another 7 degrees was provided by the vacuum advance at idle.

The chart with the MSD Pro Billet directions shows it should be providing 16 degrees of advance at 12 inches of vacuum. I'm not sure why I only get 7.

We swapped out the 23 degree advance bushing for an 18 degree advance bushing and moved the initial timing up to 18 degrees. Idle AFR changed to a 13.5 target. It runs much, much better. Almost no bucking down to 1500 RPM in first gear.

It looks like the MSD Pro Billet uses a GM points style vacuum advance unit. The Crane Cams 99600-1 is out of stock everywhere. Accel has a model 31034 that looks like it will work. The directions with that unit say it can provide between 5 and almost 30 degrees of advance depending on adjustment. I'll order of those and see if we can get a little more timing out of the vacuum advance.

It's amazing how much better it runs with just a little more timing. Thanks for the tips!

[Dlaw455]

Originally Posted by Jonsey

This car used to have the same engine with a much larger cam, TH400 transmission with 3200 RPM converter. It had the stinky idle and not great throttle response at partial opening, but never bucked at low speeds. An auto trans does hide a lot of these issues.

I had a chance to look at the timing this weekend. Warmed up, it had 14 degrees initial timing with 36 total by 3000 rpm. Another 7 degrees was provided by the vacuum advance at idle.

The chart with the MSD Pro Billet directions shows it should be providing 16 degrees of advance at 12 inches of vacuum. I'm not sure why I only get 7.

We swapped out the 23 degree advance bushing for an 18 degree advance bushing and moved the initial timing up to 18 degrees. Idle AFR changed to a 13.5 target. It runs much, much better. Almost no bucking down to 1500 RPM in first gear.

It looks like the MSD Pro Billet uses a GM points style vacuum advance unit. The Crane Cams 99600-1 is out of stock everywhere. Accel has a model 31034 that looks like it will work. The directions with that unit say it can provide between 5 and almost 30 degrees of advance depending on adjustment. I'll order of those and see if we can get a little more timing out of the vacuum advance.

It's amazing how much better it runs with just a little more timing. Thanks for the tips!

Before spending any more on a distributor or cam consider updating the efi to control the timing. Just lockout the distributor and let efi handle it.

[JLMounce]

Originally Posted by Jonsey

This car used to have the same engine with a much larger cam, TH400 transmission with 3200 RPM converter. It had the stinky idle and not great throttle response at partial opening, but never bucked at low speeds. An auto trans does hide a lot of these issues.

I had a chance to look at the timing this weekend. Warmed up, it had 14 degrees initial timing with 36 total by 3000 rpm. Another 7 degrees was provided by the vacuum advance at idle.

The chart with the MSD Pro Billet directions shows it should be providing 16 degrees of advance at 12 inches of vacuum. I'm not sure why I only get 7.

We swapped out the 23 degree advance bushing for an 18 degree advance bushing and moved the initial timing up to 18 degrees. Idle AFR changed to a 13.5 target. It runs much, much better. Almost no bucking down to 1500 RPM in first gear.

It looks like the MSD Pro Billet uses a GM points style vacuum advance unit. The Crane Cams 99600-1 is out of stock everywhere. Accel has a model 31034 that looks like it will work. The directions with that unit say it can provide between 5 and almost 30 degrees of advance depending on adjustment. I'll order of those and see if we can get a little more timing out of the vacuum advance.

It's amazing how much better it runs with just a little more timing. Thanks for the tips!

Is it acceptable now, or does it need further refinement? I would defer back to the addage "don't let perfection get in the way of good enough." It's an older car with a big rowdy engine, some trade-offs are inevitable.

I'm glad those items helped out. Saves you a good bit of money and time!

[Jonsey]

Originally Posted by Dlaw455

Before spending any more on a distributor or cam consider updating the efi to control the timing. Just lockout the distributor and let efi handle it.

I've considered it. A Holley terminator is going to several thousand dollars and quite a bit of time to install. The distributor modifications have cost less than a $100 and a couple of hours.

I want to do an EFI upgrade, but don't mind spending a little time and money to make it a better drive before that.

[Jonsey]

Originally Posted by JLMounce

Is it acceptable now, or does it need further refinement? I would defer back to the addage "don't let perfection get in the way of good enough." It's an older car with a big rowdy engine, some trade-offs are inevitable.

I'm glad those items helped out. Saves you a good bit of money and time!

It's pretty good now. I haven't driven it enough to really say if it's good enough.

Adding the adjustable vacuum advance and tuning in a little more will only take a bit of time.

I'm really curious to out a few tanks of gas through it and see if MPG is affected. It was around 6-7 MPG around town, 13 MPG on the highway. Range isn't great on the narrowed tank that fits between the mini tubs.

[JLMounce]

I would bet it helped a little. My 580hp 465 with a slightly larger cam is doing better in town than you're getting on the highway, with a less efficient automatic behind it.

I provide fueling with a FiTech that controls timing as well.

A batch fire system like yours is never going to be a big winner in the fuel economy game, there's too much fuel wasted to that batch process and inefficient fuel burn due to liquid fuel puddling on the back of the intake valves. The additional timing is likely helping to light that off more efficiently though.

[TheSilverBuick]

A few post back people were talking about injector timing. Last fall I put bigger injectors in my Buick 455 (replacing 12 year old ones that two were leaking during a clean and flow test), and decided to play with the injector timing. I swept it in 10º increments 200º and for the most part the response was unchanged until I hit this spot and it dramatically dropped the AFR one full point in a 20º change. Same pulsewidth/duty cycle, so exactly the same amount of fuel going in but more of it was being burned and less fresh air passing through.

Buick 455, roller cam around 215º duration, 0.570" lift and I forget the LSA but low overlap.

https://youtube.com/shorts/E4NuHJmPmcQ

[Jonsey]

Originally Posted by JLMounce

I would bet it helped a little. My 580hp 465 with a slightly larger cam is doing better in town than you're getting on the highway, with a less efficient automatic behind it.

I provide fueling with a FiTech that controls timing as well.

A batch fire system like yours is never going to be a big winner in the fuel economy game, there's too much fuel wasted to that batch process and inefficient fuel burn due to liquid fuel puddling on the back of the intake valves. The additional timing is likely helping to light that off more efficiently though.

What MPG are you getting highway?

[Jonsey]

Originally Posted by TheSilverBuick

A few post back people were talking about injector timing. Last fall I put bigger injectors in my Buick 455 (replacing 12 year old ones that two were leaking during a clean and flow test), and decided to play with the injector timing. I swept it in 10º increments 200º and for the most part the response was unchanged until I hit this spot and it dramatically dropped the AFR one full point in a 20º change. Same pulsewidth/duty cycle, so exactly the same amount of fuel going in but more of it was being burned and less fresh air passing through.

Buick 455, roller cam around 215º duration, 0.570" lift and I forget the LSA but low overlap.

https://youtube.com/shorts/E4NuHJmPmcQ

I can't wrap my head around what the dropping AFR means. Does it indicate a more efficient combustion cycle?

[TheSilverBuick]

It means less raw fuel is leaving the cylinder during overlap and more is getting burned in combustion.

[JLMounce]

Originally Posted by Jonsey

What MPG are you getting highway?

Around 18mpg. The car does it's best around 75mph at 2400 rpm. Below that the cam is not in it's efficiency zone and I waste fuel to overlap.

[Jonsey]

I wanted to report back with results.

I installed an adjustable vacuum advance can, but couldn't get any more than the 7° of vacuum it had with the existing can. It turned out the issue was the prior owner had installed some kind of vacuum advance limit plate. It's visible in the picture on top of the vacuum advance. I installed the limit plate back on with the adjustable vacuum can without realizing what it was. Worse, when I couldn't get more advance, I adjusted the vacuum can too far and ruined it (too many turns and the screw comes out inside the diaphragm.)

The prior owner had two advance limit plates and a few different bushings that go on that stud that limit vacuum advance. I put the old vacuum can back on and a different plate with no bushing. Immediately had 30° of vacuum advance. None of the existing bushings got the right amount vacuum advance, so I made a couple out of 1/8" plate, trial and error until it was where I wanted.

So far, it runs best at 16 initial, 12 vacuum, 18 mechanical, very close to what JLMounce recommended. It might run a little better up top with just a bit more mechanical advance (36° vs 34°) but I don't have the right bushing for that. AFR targets are 13.5 idle, 14.0 cruise.

At these settings, it can run down to about 1500 RPM in first gear before it bucks. It can do 1800 RPM in 6th on the highway as well. It still smells a little at idle, but better than before. Probably can't do much better without less intake/exhaust overlap or sequential injection.

After making these changes, it did develop a little flat spot when transitioning from the idle circuit to cruise at gradual acceleration. I could see the AFR go all the way to 15.9 in those instances. On this setup, the IAC needs to be set to almost closed at idle, as close to 5 as possible. With the timing and AFR changes, the IAC was closer to 35-45 at idle. After readjusting the throttle blades to get the IAC closed a bit more, the flat spot is mostly gone. It still goes lean in transition, but I can't feel it.

I can see the advantage of digital timing. I must have had the distributor cap off a dozen times messing with it.

All this really makes me want to upgrade the EFI. Terminator is looking really tempting!

Thanks to everyone for all their help.

[JLMounce]

Glad to hear you're continuing to make improvements. It sounds like you need to add some accelerator pump enrichment. I'm not sure how that's handled on your system, but it should be a parameter you can tweak.

[grivera]

Great to hear you're getting it dialed in. A Progression Ignition would make all the timing changes easy-peasy! https://progressionignition.com/prod...gories/pontiac