[Squidward]

I wanted to start a thread to discuss tuning strategies for a standard Pontiac motor - nothing exotic, maybe iron heads, mild performance cam. Think of something less than a Ram Air 4 build, but hotter than a smog era 350 stocker. Street motor stuff, not so much a full race build.

How does one set timing curves and AFR for various operating conditions, and how is this validated through data? There is of course the tried and true use of a vacuum gauge and reading plugs, but does any of that change substantially now that many of us run EFI (like me) where we have instant tunability of target AFR via a computer/handheld display? And with drag strips getting swallowed up these days by development, it is tougher and tougher to get track time to see if our tweak gave us an extra MPH, etc. And based on where you live, it might be tough to find a nearby deserted road for extreme testing that wouldn't get you thrown in jail.

So... what are some of your tuning strategies and measurement methods to set timing and mixture for various conditions, like:

- idle tune
- off idle acceleration
- WOT
- part throttle light load cruise

I guess I'm also curious to see how strategies might differ (if at all) on tuning typical carb/distributor combos vs EFI with electronic timing control. My car runs nicely, but it seems like I just emulated electronically what I achieved with a carb and vacuum advance distributor.

Any of you tuning gurus care to share your knowledge with the next generation? Take a whack at one, or maybe all of them.

[PAUL K]

Usually the full throttle A/F is set close, then timing and then wide-open full throttle A/F is fine tuned. Next is the idle circuit and initial timing. After that advance curve and transition circuit and then finally the vacuum advance.


Since the above strategy usually requires a dyno session and or a trip to the track. That's usually not done with a street engine, I'd start with the idle and end with the vacuum advance. Just keeping in mind timing will affect the A/F.


A vacuum gauge visible from the cabin and patience will pay dividends when tuning the timing curve.

[Squidward]

Originally Posted by PAUL K

Usually the full throttle A/F is set close, then timing and then wide-open full throttle A/F is fine tuned. Next is the idle circuit and initial timing. After that advance curve and transition circuit and then finally the vacuum advance.


Since the above strategy usually requires a dyno session and or a trip to the track. That's usually not done with a street engine, I'd start with the idle and end with the vacuum advance. Just keeping in mind timing will affect the A/F.


A vacuum gauge visible from the cabin and patience will pay dividends when tuning the timing curve.

For full throttle, what are your metrics for too much/too little, for either AFR or timing? Do you shoot for best et/mph, but just shy of detonation? Plug color?

I put in a digital gauge cluster/speedo that can measure 0-60's or other parameters, so I can get some feedback on performance. There are other phone apps I've used that can log performance with GPS. Track time is impossible, but some 0-60 or 1/8th pulls on the street are a possibility.

Concerning tuning the timing curve:
For idle I've always used an initial setting that gives best vacuum, but is usually 2 degrees shy of where the engine has trouble cranking. I run manifold advance.

My starter chugs at 18 init, so I ran it at 16 for years. Recently, I moved it back to 14 for a little more margin on the total timing. So my idle timing is 29 (14 init + 15 vac) at 820 rpm. Engine makes best of 15" with this timing, so I think this is a pretty good setting so far.

Sound reasonable?
Would it be worth messing with the idle AFR setting to further get best vacuum? I run FiTech, so that would be pretty easy.

Now, for the WOT timing: Should one shoot for best performance that is shy of detonation? This part gets me a little, because I have thrown a lot of timing at this engine (up to 40 total) before and have never HEARD any detonation. I have 22 mechanical, and IIRC a light-medium spring combo. So total is probably 36 (14+22) by 2500 or so.

For an iron headed Pontiac, is there a well established baseline? I see 34-36 total for many people's tunes.[/I]

WOT AFR: I know this should be richer, because lean causes engine damage.
Would proper settings be evaluated by measured performance and spark plug color?
Should one start out rich, make some pulls, and adjust leaner until proper plug color is reached with best performance results? I see some people like to stay a little on the richer side for safety margin.

I won't overload the discussion asking about cruise timing and AFR right now. Small bites...

Thanks for the help! I'm hoping others might benefit from this thread too. I plan on reporting back with some results to validate what I learn.

[peters23]

I'm no expert on it but installing a wide band O2 sensor and gauge would seem like a good tactic here.

[Formulas]

Stratagies in tuning will vary greatly depending on ones capability whether or not alterations can be made at every point ... For instance if you dont know your way around a distrubutor it would be best to set total timing first rather than setting a specific initial timing number and perhaps be in a detonation pre'ignition state on full throttle

[Formulajones]

Lots of variables. Basically I prefer to set distributor and timing curves first. This makes carb tuning much easier and keeps me from having to go back and revisit the carb more than a few times.

Depends on the combo but I'll shoot for an initial and total timing combo. I dyno all my stuff before it goes in the car so this is relatively easy. Total timing is found on the dyno where it makes best power and then I'll design the curve around that for the street. There is really no good substitute for this. You either need a dyno or some track time to find what the engine likes for a total number. It's the safest way to do it taking the guess work out.

Carb tuning is straight forward. Having the timing done with enough initial and idle timing mixed with enough vacuum advance makes tuning the transition circuits much easier. WOT afr again needs to be done on a dyno or track if you're looking for best performance. Engines are so different in what they want in this area too it's hard to suggest a number per say other than a safe number to start with, much like total timing. Some sort of testing has to be done.

A conservative start would be 32 total, maybe 14-ish initial, and another 10-12 degrees of vacuum advance. AFR at wot in the low or mid 12's won't hurt anything and is plenty safe. I then make timing swings before I lean things out and just sneak up on it.

[PAUL K]

Originally Posted by Squidward

For full throttle, what are your metrics for too much/too little, for either AFR or timing? Do you shoot for best et/mph, but just shy of detonation? Plug color?

Best MPH or HP cross checked with A/F & plug reading

Originally Posted by Squidward

I put in a digital gauge cluster/speedo that can measure 0-60's or other parameters, so I can get some feedback on performance. There are other phone apps I've used that can log performance with GPS. Track time is impossible, but some 0-60 or 1/8th pulls on the street are a possibility.

It might be easier to test 30-60 mph times or another range that you're comfortable with. It will eliminate traction and transmission shift inconsistency. Forty to seventy in second gear works well on my daily.

Originally Posted by Squidward

Concerning tuning the timing curve:
For idle I've always used an initial setting that gives best vacuum, but is usually 2 degrees shy of where the engine has trouble cranking. I run manifold advance.

My starter chugs at 18 init, so I ran it at 16 for years. Recently, I moved it back to 14 for a little more margin on the total timing. So my idle timing is 29 (14 init + 15 vac) at 820 rpm. Engine makes best of 15" with this timing, so I think this is a pretty good setting so far.

[I]Sound reasonable?

Yes, but usually less initial timing works better on milder combinations.

Originally Posted by Squidward

Would it be worth messing with the idle AFR setting to further get best vacuum? I run FiTech, so that would be pretty easy.

Probably, I like a lean idle setting with as little initial as the engine is happy with.

Originally Posted by Squidward

Now, for the WOT timing: Should one shoot for best performance that is shy of detonation? This part gets me a little, because I have thrown a lot of timing at this engine (up to 40 total) before and have never HEARD any detonation. I have 22 mechanical, and IIRC a light-medium spring combo. So total is probably 36 (14+22) by 2500 or so.

Some engines will be hard to time with the "hear detonation and back it off two degrees" deal. That strategy was popular when engines requiring high octane were run on lower octane fuel.

Unleaded fuel generally likes less timing. Most of our race gas 455's work best at 36 but the pump gas combos prefer 32-34. That's for factory iron head builds. A 3.75 stroke engine usually wants a little more timing.

Originally Posted by Squidward

WOT AFR: I know this should be richer, because lean causes engine damage.
Would proper settings be evaluated by measured performance and spark plug color?
Should one start out rich, make some pulls, and adjust leaner until proper plug color is reached with best performance results? I see some people like to stay a little on the richer side for safety margin.

Start rich and go lean. Best performance/power sets the WOT tune but remember A/F will effect timing. After the A/F is set, dial in the timing and go back and fine tune the A/F

Originally Posted by Squidward

I won't overload the discussion asking about cruise timing and AFR right Small bites...

Cruise timing can be set with a vacuum gauge.

Originally Posted by Squidward

Thanks for the help! I'm hoping others might benefit from this thread too. I plan on reporting back with some results to validate what I learn.

You're welcome, I hope others share their input. We're all trying to learn.

[Cliff R]

Engine parts choices really help with this particular topic.

The better job you do making choices in terms of static compression and cam events, the easier it is to come up with timing and fuel curves that will work with your particular set-up.

These engines all operate pretty much in the same "range" for timing and fuel delivery, which is a blessing when it comes to this topic. What takes us out of the "normal" range are "low" static and dynamic compression resulting from too much overlap or late intake closing from the camshaft based on the CID and compression ratio.

For engines with optimum compression and very well chosen camshaft setting up timing and fuel delivery is relative easy. The vast majority of those engines will be fine with about 8-12 degrees initial timing, another 10-12 mechanical (20-24 at the crank), and 10-15 degrees from the VA.

IF you have "low" compression and or a tight LSA or "hefty" camshaft with a lot of overlap you may very well need a LOT more initial timing to make the engine happy. A lot of squish area combined with a lot of overlap my require quite a bit of total timing plus quite a bit from the VA as well.

Squish area and squish distance are pretty big "players" here. With modern thinking in those areas, in other words tight squish and modern combustion chamber shapes you'll find more times than not that your engine woln't need a lot of timing anyplace. It will also be able to burn leaner mixtures for optimum power over the entire load/speed range.

What I've found over the years that every single engine is it's own deal so to speak and we typically have to "adjust" the timing and fuel curves accordingly. Still most fall well within the range provided above, unless you made some really poor choices for it.

Sort of a "rule of thumb" here that I use is how much initial timing the engine wants to be happy cranking up well heat soaked and providing plenty of vacuum at idle and good idle qualities. Anytime I see an engine that needs, likes or wants much past about 14 degrees initial timing and doesn't knock the nose off the starter on a hot restart well heat soaked it just doesn't have optimum compression for the camshaft being used. Doesn't mean that you can't "crutch" tune it with a BUTTLOAD of timing, or even come up with a decent running engine either. It just tells me a little more "squeeze" or a little less overlap would have delivered a much better result........FWIW.......

[Squidward]

Thanks all.

I've been wanting to take a more data driven, but practical approach to tuning. Track time and dyno time are tough to come by, so I was trying to learn how to do this on the street.

I like the suggestion for some 30-70 pulls on the street to measure WOT afr. I will have to come up with a test plan to minimize variability while I run timing and afr up and down to find the peak.

Concerning WOT AFR and timing: is the ideal performance peak easily discernible?
I will likely start with 32 total, and work up to 34, 36, and maybe 38 if it is still on the upswing.

For afr, I think I will start out safely rich, and make some pulls to log performance and check plugs while going progressively leaner. I will hope that the performance peak and the proper plug color happen around the same afr setting.

[Cliff R]

Reading plugs on this new fuel is useless.

Using A/F meters to measure full throttle runs next to useless.

Why?

This new fuel doesn't leave much behind and almost always the plugs show "lean" by visual observation, and by the time you figure out you are really too lean you will have pounded the rod bearings pretty hard, broken a few rings, or put a couple of pistons in the oil pan!

What A/F would you be shooting for? A very well thought out engine build will be a LOT more efficient than one with poorly chosen components, so VE is better, and BSFC is less, so it would require less fuel and leaner A/F ratios at WOT.

GOOD plan to er rich at WOT and full engine load, also wise to keep total timing retarded a degree or two as well. A tad rich hurts nothing, lowers EGT's, and LESS chance for detonation, all else being equal. Contrary to popular belief you aren't giving up enough vehicle performance to measure either, especially with a "butt meter".

I used to tune to the brink of extinction at the track with WOT A/F, swapping secondary metering rods and going from "pig" rich to where the engine was "huffing" out a little black smoke to so lean it started to "surge" a bit mid-track. Guess what, after dozens of private track rentals and test & tune nights playing around with that deal I found that the entire spread of ET was seldom much more than .5 seconds and under 2mph, with most runs being much closer. So I ended up in later years just leaving the carb a tad "fat", and timing a couple of degrees less than where the engine made best power or quickest runs. Being well within safe limits vs pushing the envelope isn't costing enough in vehicle performance to risk damaging a very EXPENSIVE engine........FWIW......

[chiphead]

Ideal WOT AFR is hard to determine without a dyno or a dragstrip. On the street, I shoot for 12.2-12.6 AFR WOT without detonation. Like Cliff says, richer is safer and you're not giving up much power. My engine like cruise AFRs in the mid 13s at 70F. The E10 really doesn't color the plugs. I've kept adding fuel and the plugs stay bone white. After 100 miles they may get some color, but if they're quickly getting brown/black, you're pig rich.

For max timing at WOT, I've found the edge of detonation and then slowed the timing curve down to come in later.. In my case, I heard the popcorn about 3200 RPM at about 3/4 throttle, when the AFR suddenly spiked into the mid 15s. I read the plugs and confirmed pepper on the plugs. I had about 34* at that RPM. So I put in the heavy springs in the distributor and removed 1* of base timing, so total timing comes in at about 3500 RPM. I also went up 1 jet size front and back and used 1 HG higher power valve. That fuels it more and earlier as throttle opens. The changes got rid of the detonation and the car feels very responsive.

The difference here is tuning a carb with a ARF gauge is open loop. The carb does its thing and the gauge just tells you. With FI, the computer is going to drive the AFR to the commanded value. Keep an eye on injector pulsewidth at a given PSI to judge how much fuel you're actually giving. That's sorta like judging carb jetting. If your jetting is way out of line, its a clue something else is going on.

[Squidward]

Cliff, thank you. I didn't know that wot afr changes didn't make really big changes. It sounds like high risk/low reward when you get into the lean space. And concerning plugs, I've never been good at reading them, and didn't know the impact of today's fuels. So I like the conservative strategy you propose. I'm not racing anymore.

This engine is still the 40 over 350, forged/forged, with 702 Voodoo cam, degreed, and ported #12's. FiTech feeds it, so I will have afr and timing control available as soon as I swap some parts around. I hope my combo was well thought out, it seemed like it at the time.

Ultimate plan is to pull the 350 into reserve status, and run a 400 forged/forged combo with big valve 47's, and a 703 Voodoo cam. Time and my body pain become limiters to that adventure.

[Squidward]

Chiphead, also thank you for that input. I can glean from your experience, especially with the timing adjustments.

[VCho455]

Originally Posted by Cliff R

Reading plugs on this new fuel is useless.

.....

Thank you for speaking out against eyeballing plugs. I've been arguing against it for years. Any time you get fuel from some place other than a drum you have no guarantee the additives or octane in the fuel is the same as the last time you filled the tank. All those chemicals and contaminants from the fuel tanks at the station will not allow you to consistently read plugs from one tank fill up to the next to tank fill up. Are you actually seeing the results of how the fuel was burned or are you seeing the deposits left from the chemicals in the fuel?

In my experience only times I've been able to accurately read plugs was on the dyno, running AV gas, using a loupe and bright lighting to see deep into the plug. Any other method has been a waste of time.

Just my opinion which along with a sawbuck will buy you a steaming hot cup of Joe just about anywhere.

[Cliff R]

"The E10 really doesn't color the plugs. I've kept adding fuel and the plugs stay bone white."

Very accurate statement there, and really NONE of this new fuel even Marine or Rec fuel colors them up much either. Every single time I'd pull a plug from my 455 it was very very light tan to almost white. Anyone looking at them would immediately cry "LEAN" and want to start fattening things up to color the plugs darker when in fact the tune on my engine was perfect in all areas. I was also using a very efficient carburetor, 1977 Q-jet with the APT feature. I used to mess with that a bit, and play around with how much timing the VA was adding at light engine load. I found that tuning lean in that area did NOT produce the results one would expect. Lean with part throttle mixtures didn't use less fuel for normal driving.

This happens for several reasons. First and foremost it's impossible to get past the basic laws of physics.....it takes a specific amount of energy to do a specific amount of work. Also, when you start going lean at part throttle to a point where power and efficiency suffer more downward force with the right foot is REQUIRED to maintain engine speed and work load in that area. In other words when you start hurting efficiency with overly lean mixtures the carburetor compensates with more fuel from the increased throttle angle to maintain speed. That's sort of a hard one to get your head wrapped around and nearly everyone in this hobby associates "lean" with improved efficiency and less fuel consumption, but that's just not the case.

The correct A/F, combined with the most ideal ignition timing provided by the VA at light engine load delivers improved economy over trying to run an overly lean mixture, simple as that. So in layman's terms being a tad richer that when the engine starts to show negative symptoms from too lean requires LESS throttle angle to do the work, and less overall fuel consumption.

Same thing with timing added by the VA. Once you hit the correct value(s) for timing at light engine load adding more timing very quickly causes the engine to produce negative symptoms in protest. This may be slight "miss-fire" in the exhaust note, very light detonation, surging, or just lack of power and you have to move the right foot down further to compensate.

One last note and I'll sit down. Despite the fact that it is now 2025 and we should all be using Vacuum Advance on these engines there are still a BUTTLOAD of folks who don't use it. Even some very skilled, experienced and well educated folks, and I will never understand why as it's a load sensing device, costs NOTHING in terms of lost power anywhere in the load/speed range, and only offers benefits for the end user in terms of improved fuel economy, less carbon build-up, and if nothing else less money extracted from your wallet while you enjoy your pride and joy running to car shows, cruises, drag strips or just taking your significant other out for some ice cream on a nice warm summer day........FWIW.......

[turbo69bird]

Back into the tune, especially on turbo cars it’ll punish you if you don’t . I set up every car FAT (rich) and lazy ( retarded timing ). Then I back into it by going leaner and more advanced as I go. Irreversible damage can be done being LEAN but being RICH never hurt anything !

[Cliff R]

I actually have considerable experience tuning turbo set-ups, and absolutely and for sure you seldom if ever get second chances if you aren't adding enough fuel and pulling out enough timing in correct proportions as engine load and boost increase. If you are lucky you'll just breach the head gasket(s) and have some coolant running out the tail pipes. Not lucky was usually the case here and we've caved in ring lands and even pushed a few pistons into the oil pan when the tune was off some......