Idle timing, the hunt for the holy grail

[PotvinGuy]

I was fooling with the engine today and it occurred to me to "optimize" the initial timing; see what makes the engine idle the smoothest, coolest, and highest vacuum. So I cranked it up..and up..and up, to 45 degrees! 700 RPM and it's purring like wifey after a box of wine. Now this is quite a departure from the 10 to 20 I think most folks run. It's just a crate SBC, 9.5CR, nothing special. Any thoughts? Have I made the greatest discovery in automotive history, or should I quit sniffing the brake part cleaner?

 

[bobby6319]

I was fooling with the engine today and it occurred to me to "optimize" the initial timing; see what makes the engine idle the smoothest, coolest, and highest vacuum. So I cranked it up..and up..and up, to 45 degrees! 700 RPM and it's purring like wifey after a box of wine. Now this is quite a departure from the 10 to 20 I think most folks run. It's just a crate SBC, 9.5CR, nothing special. Any thoughts? Have I made the greatest discovery in automotive history, or should I quit sniffing the brake part cleaner?

ya but will it start after you get hot mine will run fine but after you get hot it just drags to slow to start

 

[RPM]

It probably won't start, when it gets hot. Get the motor up to operating temp and play and see how much timing it will take and start. Probably about 18-20. Then limit the curve in the distributor to get that final 38-40. This is where a distributor machine would be real handy. There are some kits out there to limit total advance. Some you just have to weld up the slot and file to fit.

 

[ellis8500]

Let's see, being that I'm 60 and haven't had a carb/regular distributor engine for many years; your question brings me back to the days when we used to do our own tune ups. As I recall, we would set initial timing to what the book said.....8, 10, 12 degrees or so with a timing light and vac advance disconnected. Another way to get really close was to connect vacuum gauge, retard timing until it started to stumble a bit then advance just until it reached max vacuum and smooth idle. When we did that and then checked with a timimg light it would be real close or right on what the book said.

 

[one finger john]

So O.K., what was the highest vacuum you pulled, how cool (or hot) was the engine, describe the cooling system, what was the a/f ratio (and how did you measure it), carb / fuel injection, how efficient is the combustion chamber ( Vortec, fast burn, 60s technology ), steel or aluminum head, EMISSIONS (optimum idle efficiency does not mean optimum emissions efficiency), drivability, ... etc.. I would have to say that with simple, low cost tools available to all mechanics, and an ignition system that allowed instantaneous changes to ignition timing (with all the bells and whistles, temp sensor, knock sensor, humidity sensor, ... etc.), the computer to correlate all the information in real time for ALL driving conditions, You know what I mean, Earl? The Model T had a simple lever that gave the driver manuel control over the ignition advance at any given moment. The general public didn't want to deal with that. As a tool in your own car, it could be quite effective for a while. Then after the newness wore off, the lever would be placed in one position, and probably rust in place.

John

 

[PotvinGuy]

Uh...thanks, John. That was an interesting response, if not exactly on topic.

 

[one finger john]

Your welcome P.G.. It is on topic. You described optimizing YOUR particular combination (C.R, cubic in., and cyl. head) and then asked for any thoughts. Other people voiced concerns about running 45 degrees of advance @ idle and the problem of starting after the engine has reached operating temperature. With some careful modification it IS possibly to run upwards to that amount of timing @ idle by running a starter retard then a locked out advance. This could be done with modern programable electronic ignitions, but you would need to be sensitive to how the engine performance was affected by this. Also octane rating of available fuel and knock sensitivity have to be taken into consideration. All these adjustments can be made manually or sensors and computers can be brought into play. There again, which will you be using, electronic fuel injection or carburetors?. Mechanical (Ala early Porsch, BMW, or Mercedes) injection allows some adjustment thru injection pump rack timing, but not much. Electronics allow infinite injection timing. Which is needed when running bleeding edge ignition settings. Yes, it is nice that you came up with that particular ignition setting, but it is PARTICULAR to YOUR combination. Every single engine is particular to itself. I like the thought of a manual advance lever (like Ts & As), but that would make things rather busy while driving and the public doesn't like or want that.
Also I found that you did not fully explain your methodology and what the standards were for arriving at your conclusions. I can think of three separate instances (not THIS particular situation) where help or thoughts on an engine problem were elicited and information was doled out in dribs and drabs. That is very frustrating. Worse yet, asking for information and not receiving a straight answer, or receiving no answer at all ! Every single person here is more than glad to help someone else out with a problem. Just be willing to give ALL the info, not what you feel is appropriate. Rant over.

John

 

[Northstar T]

"When I was a boy" We use to just keep advancing the timing... go for test drive... repeat as needed until it started pinging. then back it off a couple degrees. of course now we're all rich, can afford timing lights, and set the timing per factory specs........ my jury is still out on which makes it run the best, but I haven't dusted off my timing light for years.

Russ

 

[PotvinGuy]

Rant on, John, if it feels good. As I stated, this is a crate SBC. Straight from GM, no mods, just like you find in 1000's of T buckets. But they run 5 or 10 or 20 degrees initial. Since 45 seems to work so well, why do most folks run so little? Have we all been laboring under bad info? And I really would like to know if anyone has tried unique settings that worked.

 

[PotvinGuy]

Ah, crap, John, I can't stand these unpleasant exchanges. Let me add some info that might help. Maybe my username or thumbnail misled you. That blown EFI is not the motor in question! This motor (crate GM, Gen I 260 HP version, from Summit) is stock. I pulled a head, used a piston stop and degree wheel to set the timing pointer at TDC, so I know it is accurate. It has a Holley 750, Mallory ignition and the usual bucket headers. And I drove it for some months with a typical timing of 20 initial plus 20 speed. As for methodology, I hooked a big mechanics vacuum gauge to the manifold, and twisted the distributor to maximize the vacuum. I got 20". While doing this, the idle increased several hundred RPM, so I turned it down to 700, lower than it's ever idled nicely before. The temperature stabilized about 10 degrees cooler than usual after some minutes of idling. The smooth running is subjective, but it was quite obvious; without audio I don't think I could tell the engine was running. And I used a Flaming River timing light to read the 45 degrees at the damper.

Now several folks have responded with stories of how they set timing; that's not what I'm asking. I'm asking if 45 initial is so good, why do we run so little? And has anyone done anything like this and gone on to run it on the street? How? So far I've just done this idling.

I tend to question the things "everybody just knows". There are a lot of anecdotal stories, technical myths and old rodder's tales that don't advance our knowledge, and, worse yet, lead us to perpetuate bad design. I can't believe people still argue about slowing water flow so it will "cool properly" in the radiator.

If I can add any info that will help in answering my question, ask away. Let's make some automotive history here.

 

[ruggs]

Ah, crap, John, I can't stand these unpleasant exchanges. Let me add some info that might help. Maybe my username or thumbnail misled you. That blown EFI is not the motor in question! This motor (crate GM, Gen I 260 HP version, from Summit) is stock. I pulled a head, used a piston stop and degree wheel to set the timing pointer at TDC, so I know it is accurate. It has a Holley 750, Mallory ignition and the usual bucket headers. And I drove it for some months with a typical timing of 20 initial plus 20 speed. As for methodology, I hooked a big mechanics vacuum gauge to the manifold, and twisted the distributor to maximize the vacuum. I got 20". While doing this, the idle increased several hundred RPM, so I turned it down to 700, lower than it's ever idled nicely before. The temperature stabilized about 10 degrees cooler than usual after some minutes of idling. The smooth running is subjective, but it was quite obvious; without audio I don't think I could tell the engine was running. And I used a Flaming River timing light to read the 45 degrees at the damper.

Now several folks have responded with stories of how they set timing; that's not what I'm asking. I'm asking if 45 initial is so good, why do we run so little? And has anyone done anything like this and gone on to run it on the street? How? So far I've just done this idling.

I tend to question the things "everybody just knows". There are a lot of anecdotal stories, technical myths and old rodder's tales that don't advance our knowledge, and, worse yet, lead us to perpetuate bad design. I can't believe people still argue about slowing water flow so it will "cool properly" in the radiator.

If I can add any info that will help in answering my question, ask away. Let's make some automotive history here.

:thumb: :thumb: :thumb: :thumb:

 

[tnoftsger]

I run that a good deal of timing at idle in a 383 storker motor, of course, with the vacuum advace hooked up to manifold vacuum.

the 8-12 degrees is WITHOUT the vacuum can. The vacuum can pulls in close to 20 for my set up making the idle setting about 32 degrees. As soon as the butterflies open all that extra vacuum advance falls out and we are back to the initial 12 degrees plus centrifical for a total of 32-34.

All that vacuum advance improved my idle a good deal and allow me to get decent fuel milage. Now if you ran 30+ degrees of initial and the plug the vacuum back in.....your looking at 65degrees or so of timing, and idle quality would probably go all to hell......

Tom

 

[RPM]

So at 45 degrees initial timing will it start after it gets hot?

 

[PotvinGuy]

I run that a good deal of timing at idle in a 383 storker motor, of course, with the vacuum advace hooked up to manifold vacuum.

the 8-12 degrees is WITHOUT the vacuum can. The vacuum can pulls in close to 20 for my set up making the idle setting about 32 degrees. As soon as the butterflies open all that extra vacuum advance falls out and we are back to the initial 12 degrees plus centrifical for a total of 32-34.

All that vacuum advance improved my idle a good deal and allow me to get decent fuel milage. Now if you ran 30+ degrees of initial and the plug the vacuum back in.....your looking at 65degrees or so of timing, and idle quality would probably go all to hell......

Tom

Ah, so the vacuum advance doesn't cause the idle to surge? That is good to know. My next step is to try 20 initial plus 20 manifold vacuum, for a total of 40 at idle. Thanks Tom.

 

[one finger john]

So at 45 degrees initial timing will it start after it gets hot?

P.G., the questions are pertinent and thank you for answering some of them. So, how well does it start? What is the drivability with 45 degrees?
Why would it surge with 20 in. of constant vacuum? The advance can is at it's stop, fully advanced.
Put that set up in a 4500 lb. car with a brain dead soccer mom and see what happens. Put some 87 octane fuel in the tank just to sweeten the knock factor.
G.M. has been playing with timing and ignition advance for small block engines since 1954. They build cars for EVERYBODY, to be driven by ANYBODY. Thus the middle of the road timing.
Ts allow experimentation such as yours because of light weight (under 2000 lbs.) and lack of emissions. Also ease of access to all parts. That is why I like a lever control for the advance or even better a single slide control (like a heater slide bar), with degrees marked or indents to show how much additional advance is dialed in.

You brought up the subject, you invited comment and discussion. This is not high tea at the Ritz. Expect to be challenged. Nothing personal.

John

 

[PotvinGuy]

It does start hot at 45, but it isn't easy, and I have an aftermarket gear-drive high torque starter. And I don't plan to drive it like this. See my reply to Tom above. My plan is to proceed slowly and see if I can come up with better timing than the usual. That is, excellent starting and idling, great performance and fuel mileage, cool running, etc. I just don't think we have explored the territory thoroughly. That might seem presumptuous of me, considering that there are companies that do ignitions for a living. But I've talked to a few of them and some of their advice is obviously more about selling parts than advancing (pun!) the technology. One (no names, but it's one of the biggies) says to use ported vacuum so the boost retard will work! Now THAT is retarded!

Wish me luck. And maybe I'll see you at the Ritz.

 

[PotvinGuy]

Oh, the surge business; that was the same ignition company telling me not to use manifold vacuum or the idle would surge. They must get a kickback from the ported vacuum mafia.

 

[Northstar T]

There are significant HP, mileage, and drivability gains to be made by playing with your timing curves (vacuum and mechanical) as well as initial advance, but there are so many variables in engine, trans, gearing, vehicle weight, your driving style, etc etc, that makes it impossible to say that "[X] timing is the best". that's why I suggested that you try the drive and advance method that I mentioned earlier. ....... but I guess that's "not what [you're] asking"
,
Russ

.

 

[Screaming Metal]

Well, back in he day, they used to have these little gizmos where you could adjust your timing from inside the car. Harley and Indian motorcycles even had them up on their handlebars.

Whenever you'd come to a redlight or had to stop for traffic, you had to adjust your timing ot your engine would start laboring and die, or overheat.
Back in the good ole days of hotrodding, we'd run mech. advance and leave the vaccuum off. Vaccuum is mostly for gas milage anyways.

For pep and performance, run as much advance as you can stand and have your dist. recurved to get it all in by 2500- 3000. I have 4 top dollar timing lights and a dist. machine. Haven't used them ....well, can't remember last time I used them. Anyway, each motor is different and responds diff. to diff cams, timing , carbs....I let the motor tell me what it likes....

 

[roadmonster]

I had your same situation with my small block. It ran great at 42 degrees with good street performance. Total advance was well over 50. BUT I worked my way back to near-stock timing with quick centrifugal advance (yellow springs), early secondary (white spring) and short (14 degree) vacuum can. Although it ran great at 42, it is a real rocket now at 18. Both setups run very cool, in fact I don't use my electric fan unless I'm stuck in traffic. No starter drag either.

At 42 it was running silver advance springs, plain secondary spring, and 20 degree can. If you have a mild cam like I do (Comp 252), get your advance all in by 1800 and your secondaries a tiny bit later. This is for a tall rear end! I have a 3.00 Ford, if yours is higher, this may not apply.

Work your way back to near stock. Just because it runs OK highly advanced doesn't mean that's the best setup. Your carb may be a little big for a mild small block, so your secondaries may be coming in late, if at all. If hot starts are a problem, something is wrong. It should fire instantly.