Can we talk about Small Block ignition timing?

[Rembrant]

I wanted to pick the brains of the experts and BTDT crowd with regards to SBF ignition timing.

After I had my little 302 built, we broke it in on the dyno and then tuned it. The guy that built my engine was really good, but I'll admit that their shop spends most of their time building much bigger (higher compression) performance engines. A lot of BBC's.

Anyway, he set my timing at 12/20, for a total of 32 without vacuum advance. He said that he didn't want to go over 32 for fear of causing problems. He did bump it up to 34 for a pull or two and when it didn't make any difference he put it back at 32 degrees.

So I got the engine home and installed it in the truck, and when I checked the timing it was not at 12/20, at least not according to my timing light. I have to apologize, as I don't remember where it was exactly, but I adjusted it a little bit to put it back to 12/20 (again, according to my timing light).

I have been doing some reading, and the article below caught my attention as it says that SBF's work best between 38-42 total timing.

https://www.fordmuscle.com/archives/2000/03/timing/

My engine is not what one would consider high compression. On the upper end it might be 9:1, but it's probably more like 8.9:1 and even with full vacuum advance I haven't heard the engine ping at all.

Anyway, I guess I'm just curious what you guys with similar engines are running for base timing and centrifugal timing?

I know I need to work on getting my ignition curve smoothed out, but that's a separate issue from where the actual start and finish numbers need to be.

[ArdWrknTrk]

12* is a good start.

With a more efficient engine such as yours you might get away with more, but look out for laboring hot starts.

There's no point in overworking the starter, or drawing so much current.

A lot of factors come into consideration.

Weight.

Gearing.

BMEP. (from your dyno results)

Available fuel (or lack thereof)

if you're on the edge using R+M/2 93 and can only find 91 or even 89 in Podunk, you hopefully have a distributor wrench, and have to deal with the compromised curve.

My heavy truck is all in by 3k and starts just off idle @800, 38* total.

I guess a lot depends on how (and what conditions) you drive it .

Bill Vose is the one who will have the best advice for you, Cory.

 

[Rembrant]

12* is a good start.

With a more efficient engine such as yours you might get away with more, but look out for laboring hot starts.

There's no point in overworking the starter, or drawing so much current.

A lot of factors come into consideration.

Weight.

Gearing.

BMEP. (from your dyno results)

Available fuel (or lack thereof)

if you're on the edge using R+M/2 93 and can only find 91 or even 89 in Podunk, you hopefully have a distributor wrench, and have to deal with the compromised curve.

My heavy truck is all in by 3k and starts just off idle @800, 38* total.

I guess a lot depends on how (and what conditions) you drive it .

Bill Vose is the one who will have the best advice for you, Cory.

No issues with starting currently. The truck might as well be EFI in that department...just a touch of the key hot or cold and it starts instantly.

Three levels of gas here...87, 89, and 91 for premium. There may be higher octanes further west, I'm pretty sure I've seen 93 when traveling, but for the most part it's 87-91 where I live. I've been running nothing but 87 in the truck, pretty much since I put the engine in there last year. I'm not sure on the ethanol content...could be zero or 10%, I'm not really sure. (I drive a diesel VW most of the time, so I haven't really been paying close attention to gasoline.) I did run 91 for a few tanks after I put the engine in, but tried 87 to see if it would be OK and I didn't notice any difference between the two, so I left it at 87.

The Dyno work was really more like a nice addition. My reason at the time was to just have the engine broken in and to have the basic set-up done. I'm working in a single attached garage, so installing the engine was enough work on it's own, and I just wanted to drop it in and hit the key and go. Also, it was just like a small bit of warranty for me that the builder test the engine and make sure it didn't leak or have any problems before I hauled it home to install it.

My main issue now is to get it working better in the lower RPM's. The Peak HP/performance was irrelevant at the dyno time and it's pretty much irrelevant now;).

 

[85lebaront2]

12* is a good start.

With a more efficient engine such as yours you might get away with more, but look out for laboring hot starts.

There's no point in overworking the starter, or drawing so much current.

A lot of factors come into consideration.

Weight.

Gearing.

BMEP. (from your dyno results)

Available fuel (or lack thereof)

if you're on the edge using R+M/2 93 and can only find 91 or even 89 in Podunk, you hopefully have a distributor wrench, and have to deal with the compromised curve.

My heavy truck is all in by 3k and starts just off idle @800, 38* total.

I guess a lot depends on how (and what conditions) you drive it .

Bill Vose is the one who will have the best advice for you, Cory.

Damn, here we go again on ignition timing/advance.

First, the centrifugal (mechanical) advance is tailored to what the engine needs and can use under load, the vacuum advance makes up the difference to what the engine needs for best efficiency (fuel economy).

I found with the older Windsor engines that the high compression ones liked a total mechanical advance of 38-40°, but did not want it all too early. My Cobra 289 had only a mechanical advance dual point distributor, advance curve was most of the way in by 3000 rpm, static timing at 12° BTDC would advance 16° by 3000 rpm, which would be 28° total advance then would continue slower to add another 10° for 38° total at 5000 rpm.

If you look at the advance mechanism on a Ford distributor, there are 2 curved weights riding against the upper portion of the distributor shaft, there is a slot in each end of the "advance cam" with a number stamped next to each. The number is the distributor advance in degrees, crank advance is double this number. Example, if the slot has 10 stamped next to it, it will give 20° crank degrees of advance. Originally there would be a small rubber or plastic sleeve over the tab to limit this to the marked amount. These crumble with age and loss of it is roughly 2° crank degrees.

There are two springs on the advance mechanism, a light one and a heavy one, light controls the initial stage, the heavy one serves two purposes, it limits the initial advance, then allows the higher rpm advance to occur.

Most newer electronic ignition systems produce a much hotter spark than the older breaker point systems, that being said, they will fire a leaner mixture by virtue of a wider plug gap (.035 on the Cobra engine, .042 on Darth's 460 with DS-II) the vacuum advance will pull the breaker or pickup plate against the direction of rotation to increase the total advance at cruising speed (light load, high vacuum) this is what helps your gas mileage. Many newer engines can handle as much as 60° advance at 2500-3500 rpm light load conditions. The best way to arrive at that in fine tuning yours is to drive the truck on the highway, and very gently increase the throttle opening, if you get some spark "rattle" that goes away with more throttle, then you have too much vacuum advance. One of the ways Detroit engineers cured this was the EGR system, it weakens the mixture and slows the burn rate in the cylinders. If you eliminate the EGR, then sometimes the vacuum advance will need to be decreased or at least the rate will need adjusting.

Older Ford distributors allowed this adjustment with different springs, shims and a stop sleeve that could be done by removing the end cap on the advance diaphragm, newer ones generally have a hexagonal housing and a 18" Allen wrench inserted in the vacuum tube engages a screw through a plate in the hexagonal portion. Adjustment is: clockwise = more and quicker advance, counter clockwise = less and slower advance. Short of having a distributor machine, this part becomes a trial and error process.

Ford balancers have a dual direction scale from 10° ATDC to 30° BTDC, so a certain amount of the mechanical advance can be checked with a standard timing light, if you have an adjustable advance timing light, you can check it all the way. One warning, do a "sanity check" of one of these by locking it at 0° at run the engine up (use the fast idle cam so it is consistent) and read the scale, then using the adjustment bring the 0 TDC mark in line with the pointer and see if the reading on the light's advance scale matches. I have seen one (a Snap-On) that was way off when checked this way, and it was at idle!

[Gary Lewis]

No issues with starting currently. The truck might as well be EFI in that department...just a touch of the key hot or cold and it starts instantly.

Three levels of gas here...87, 89, and 91 for premium. There may be higher octanes further west, I'm pretty sure I've seen 93 when traveling, but for the most part it's 87-91 where I live. I've been running nothing but 87 in the truck, pretty much since I put the engine in there last year. I'm not sure on the ethanol content...could be zero or 10%, I'm not really sure. (I drive a diesel VW most of the time, so I haven't really been paying close attention to gasoline.) I did run 91 for a few tanks after I put the engine in, but tried 87 to see if it would be OK and I didn't notice any difference between the two, so I left it at 87.

The Dyno work was really more like a nice addition. My reason at the time was to just have the engine broken in and to have the basic set-up done. I'm working in a single attached garage, so installing the engine was enough work on it's own, and I just wanted to drop it in and hit the key and go. Also, it was just like a small bit of warranty for me that the builder test the engine and make sure it didn't leak or have any problems before I hauled it home to install it.

My main issue now is to get it working better in the lower RPM's. The Peak HP/performance was irrelevant at the dyno time and it's pretty much irrelevant now;).

Cory - My reading, and very limited experience, shows that 38 - 42 degrees is about right on a small-block Ford - for the initial and centrifugal together. But, as Jim said, Bill's the guru on this.

But if what you are looking for is more low-end torque and a bit better MPG, then it isn't really the total advance that needs to change, but the rate at which it comes in. I say that because most systems will have the total in by something like 2600 R's. But that's not "low-end". So what you want is to have it come in faster - and maybe farther. However, the Ford dizzy is a pain to change the advance curve on, so if you are in there changing anything, change both the rate as well as the total.

Jim's favorite instructions, and mine as well, are these from Crane. They show you the order in which to dial in your advance, meaning intial/centrifugal/vacuum, as well as how to do it. And they have some suggestions on how much and how fast.

[Rembrant]

Cory - My reading, and very limited experience, shows that 38 - 42 degrees is about right on a small-block Ford - for the initial and centrifugal together. But, as Jim said, Bill's the guru on this.

But if what you are looking for is more low-end torque and a bit better MPG, then it isn't really the total advance that needs to change, but the rate at which it comes in. I say that because most systems will have the total in by something like 2600 R's. But that's not "low-end". So what you want is to have it come in faster - and maybe farther. However, the Ford dizzy is a pain to change the advance curve on, so if you are in there changing anything, change both the rate as well as the total.

Jim's favorite instructions, and mine as well, are these from Crane. They show you the order in which to dial in your advance, meaning intial/centrifugal/vacuum, as well as how to do it. And they have some suggestions on how much and how fast.

Thanks for the replies gentlemen,

I will be back with more questions later, but first I have a quick question slightly off the topic of this thread, but still related...

What is the max spark plug gap my stock DSII ignition can handle?

[ArdWrknTrk]

Thanks for the replies gentlemen,

I will be back with more questions later, but first I have a quick question slightly off the topic of this thread, but still related...

What is the max spark plug gap my stock DSII ignition can handle?

Try .048"

There's no point in huge gaps. It just has to ignite the charge.

Atomization and swirl or turbulence determine that.

If you get over 50 the charge is going to start breaking down the insulation on even good plug wires.

Scotty's site used to have a GREAT article on recurving the DSII distributors. Including how the notch related to the stamped numbers on the arm (weight)

I'm not sure about his pages now, but a lot of my bookmarks are broken

[LARIAT 85]

If your timing is late, it will show on a vacuum gauge. Unless you have a wild cam, you should have 18 - 22 inches of engine vacuum.

My distributor was calibrated very similar to yours: 12 degrees initial and 20 degrees mechanical/centrifugal @ 3000 RPM. When I installed it in my truck, I adjusted the initial by using a vacuum gauge. I loosened the hold down bolt and slightly turned it (by the vacuum canister) until I reached the highest reading on the vacuum gauge. Then I took it for a test drive and listened for pinging. It pinged only a little, so I retarded it back by about two degrees. Then I checked for kick-back on a hot re-start.

I ended up at 16 degrees initial. It is noticeably quicker on the bottom end here than when it was set at 12 degrees.

My normal vacuum reading is 21 degrees at idle in PARK.

[Rembrant]

If your timing is late, it will show on a vacuum gauge. Unless you have a wild cam, you should have 18 - 22 inches of engine vacuum.

My distributor was calibrated very similar to yours: 12 degrees initial and 20 degrees mechanical/centrifugal @ 3000 RPM. When I installed it in my truck, I adjusted the initial by using a vacuum gauge. I loosened the hold down bolt and slightly turned it (by the vacuum canister) until I reached the highest reading on the vacuum gauge. Then I took it for a test drive and listened for pinging. It pinged only a little, so I retarded it back by about two degrees. Then I checked for kick-back on a hot re-start.

I ended up at 16 degrees initial. It is noticeably quicker on the bottom end here than when it was set at 12 degrees.

My normal vacuum reading is 21 degrees at idle in PARK.

Thanks for the replies here guys. I am going to adjust the timing and get it dialed in better than it is, but I'm starting to realize here that (I think) I am chasing several issues at the same time.

My timing, whether it is set at an optimal point or not has still been pretty consistent.

The truck definitely has a miss, and I need to take a step back and give things the KISS treatment...keep it simple stupid...

Up until this point I have been totally ignoring the plugs, wires, cap, and button because they're all fairly new and don't have many miles on them (3500 miles maybe?). I'm going to replace a bunch of this stuff before going any further.

Something I'm curious about however...along the same topic of this thread, is the upper advance shaft in the distributor? How much play/wiggle is OK here? I pulled the rotor button off last night and noticed it has some wiggle.

 

[ArdWrknTrk]

Thanks for the replies here guys. I am going to adjust the timing and get it dialed in better than it is, but I'm starting to realize here that (I think) I am chasing several issues at the same time.

My timing, whether it is set at an optimal point or not has still been pretty consistent.

The truck definitely has a miss, and I need to take a step back and give things the KISS treatment...keep it simple stupid...

Up until this point I have been totally ignoring the plugs, wires, cap, and button because they're all fairly new and don't have many miles on them (3500 miles maybe?). I'm going to replace a bunch of this stuff before going any further.

Something I'm curious about however...along the same topic of this thread, is the upper advance shaft in the distributor? How much play/wiggle is OK here? I pulled the rotor button off last night and noticed it has some wiggle.

I would always start with a 'tune up'.

3500 miles seems like nothing though.

Although a tune up with Autolite plugs is what put me off them.

Changed plugs, rotor and cap.

Had a miss that wasn't there before.

Changed the rotor back. Still there.

Changed the cap back. Still there.

Pulled the plugs and TWO insulators were not crimped tightly.

So NEW is not necessarily GOOD.

I'm sticking with NGK until they bite me too.

Axial play, or torsional play?

Any side to side wiggle of the shaft is a problem.

This was mentioned in reference to a DUI dizzy recently, where the guy went to an old points distributor and a Pertronix unit because poor oiling ate the shaft bushings.