Lateral-g Forums - Retarding initial timing

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Retarding initial timing

I know retarding initial timing can cause an engine to run hot, has anyone experienced the fuel not burning as well at idle and fouling the plugs.

Sounds like you need a tuner. Where are you?

I enjoy tinkering and learning with my car. In my opinion the whole idea of this hobby is to do your own work.

I agree but you have to start somewhere and its going to take experience. 8 years of high school auto shop didn't do much for me. It wasn't till I was an apprentice with hands on experience that made the difference.

When you say timing...are you referring to ignition timing or cam timing.

Are you having a problem with your car or are you just curious.

Ignition timing. I put my drag engine into a street car. When I was curving the distributor to prevent detonation the plugs suddenly fouled. Prior to this the car ran fine but there was a little black blotch on two plugs as if the rings were rattled and allowed oil to burn onto the porcelain of the plug. Instead of changing distributor springs I changed the bushing which changed my base timing. I'm going to clean the plugs and put original bushing back in to confirm no other problem. Situation made me wonder if base timing could create fouled plugs.

Tell us about this engine, like cubic inch, heads, compression, solid roller, carb, or efi, etc.
What did you change about the combo when you installed you race engine into your street car, in order to cause the detonation, or did you face this issue with this engine in the drag car?

I hope I'm not taking the focus of your thread off track. There is an idle challenge & an idle solution when putting race engines in street cars.

The challenge is, with full on race engines, the duration of the cam is quite large and doesn't want to idle well. This is compounded by trying to run initial timing (meaning the amount of timing advance at idle) in the 8° to 16° range. The lower you try to run the timing, the harder challenge the engine has trying to idle. If the engine is carbureted, the challenge is compounded. If you adjust the throttle blade position open enough to get it to idle ... this is often so far it uncovers the transfer slot ... which adds more fuel ... making the engine run rich & idle poorly ... requiring the throttle blades to be opened even more to stay idling.

With this arrangement, you find the engine is super temperature finicky, hard to keep idling ... and loads up the spark plugs with fuel. So you put in 2-3 steps hotter plugs to prevent that. Now the engine is more susceptible to detonation. So you retard the timing more ... making the situation worse.

The additional PITA is how poorly this combination takes off from a standing start. Automatics aren't too bad, but the manual trans cars have to slip the clutch & rev the engine to get their baby rolling.

:waveflag:

Before we get to the solution, we need to embrace five facts about engines:
1. Engines require a certain amount of power to spin the rotating assembly. How much varies with component weight, friction, valve spring pressure & compression. Let's call this rotating power loss.

2. If the engine doesn't make enough power ... at a given rpm ... to overcome this rotating power loss at that same rpm ... the engine dies.

3. Larger duration cams ... especially the durations in full race engines ... shift the power curve to build more power in upper rpm ranges & reduce the power in lower rpm ranges. The lower the rpm, the less power they make. So idling at 1000-1500 rpm is a challenge.

4. Advancing timing ... to a point ... increases engine power & torque. Reducing timing decreases engine power & torque.

5. We need more power & torque at idle rpm with big cams.

:idea:

The solution is more timing at idle. Not a little more. A lot. Frankly the engine needs more timing at idle that at any point. If an engine builds best power with 36° of timing ... it needs a little more than 36° of timing at idle. But that 's not always feasible.

So why didn't factory engines come with lots of timing? Too hard on the starters. So they used vacuum advance to advance the timing at idle ... to help idle & low speed take offs.

And full timing ... say 36° ... it death on starters. Even if you buy the bad boy, double throw-down, mean, hi-torque, gear reduction starters ... 36° of timing ... when turning the engine over to fire ... will shorten their lifespan.

The starter solution is to utilize a timing retard when turning the engine over to fire. For distributor ignition systems, I LOVE the MSD E-Curve billet distributor. While it has a lot of possible timing curves, it also has the feature we need with these engines ... which is locked timing with a start-retard feature. This is a well designed distributor with billet body, shaft bearing instead of bushing & solid state electronics. No MSD Ignition Control/Amp is required. You can run one or not. You can run a vacuum advance if you desire too, but that's not usually done on race cammed engines.

In my 730HP SBC race engines, we ran the MSD E-Curve with 36° total timing ... locked in all the time ... except when starting. The E-Curve distributor has a built in start/retard option ... that when selected ... allows us to retard the timing up to 30°. So my engines started with 6° timing.

Man ... I'm telling you ... with 6° & a good starter ... they fire instantly. As soon as the rpms exceed 1000, the timing goes to full advance ... which in my case was 36°. The engine purrs at idle. It's crisp & easy to tune. The engine responds amazing when revving off idle. The car takes off easy ... preventing embarrassing moments ... and saves clutches.

There are three easy ways of doing this.
1. Utilizing a distributor with this feature built in, like the E-Curve
2. Adding a starting retard module to your distributor ignition.
3. If you have a distributorless engine, like LS & other modern engines, program this into your timing controller.

:cheers:

BBC 460 cu. in., 950 Holley HP, edelbrock victor jr, edelbrock 355 cnc heads, 10.65:1, .600/ .630 lift solid roller, 245 duration @ .050. Heads are new and raised my compression from 10.25 to 10.65.

Ron,
When I retarded the timing my idle rpm didn't change much so I never raised the idle speed and therefor uncovered the transfer slot. I agree and was originally taught for racing purposes more timing at idle is better but don't you agree for the street you will need a curve in order to prevent detonation during normal driving on the street.

Ron Sutton has a good explanation on basically everything you need, I am thinking of getting one of those distributors or an adjustable ignition box.

Keep in mind that I am no expert.

But another way to help the Idle is to plug vacum advance straight in the manifold, so it pulls advance at idle. It really helps alot. And I like vacuum advance for those situations when the engine likes lots of timing. In leanburn situations and less throttle openings/cruise speed. Since it "adjusts itself" Just watch out for detonation.

And to help some more on the idle transfer slot, could be to run an PCV system, so the engines get some of its air through that, so you can close the butterflies some more. Even though it is not "racey" to have PCV.. HeHe :D

It works for me atleast, I have not needed to drill throttle plates either, but I also only have 236-242@ .050 Hyd. Roller. 461cid. So its a bit more "street friendly" maybe.

On the other hand, I would guess the baseplate on the HP carb does not have so many vacuum outlets maybe?

Really hard to discuss when you haven't stated any of your timing numbers to begin with... more doesn't mean anything and Less doesn't mean anything because it's more from what point or less from what point.

An MSD distributor comes with 3 bushings... the largest diameter BLACK bushing will give you 18* of MECHANICAL advance --- so depending on your total timing desired -- you're initial would be 18* less than that. A BBC should handle 36* of total - so your initial would be 18*.

The TIMING CURVE is set by the springs... and their various combinations will make up what your curve looks like. This depends on gears - and cam - and weight of car and blah blah blah....

What someone would need from you is what is your initial timing - what's the total - what spring combo are you running - vacuum advance? Or not.... etc