My Experiments with Ignition Timing on an '83 Ford 460

[Big O Dave]

I have an '83 F250 4x4 with a 460. It has 108,000 miles on the original engine. It has 4.10 gears, a C6 automatic and the compression ratio for that vintage was pretty low, I'm not sure exactly what it is. The engine burns no discernable oil.

In December 2005 I replaced the timing set and the water pump... the timing gear I used was spec'd for a 1970 Lincoln 460, and is thus "straight up," versus the 8deg retarded original timing set. Because of this, I had to adjust the ignition timing, since after the timing set install, the ignition was advanced 8deg over its pre-install setting.

Anyway, here are my findings (all numbers are BTDC):

30 - Hard to start, pings a lot even with premium fuel
25 - Not as hard to start, not as much pinging, almost liveable, good power & mpg
15 - No hard starting, no pinging on premium, excellent power, best mpg (almost 11 mpg!

)
6 - Easy starting, no pinging with any gas, gutless, 2mpg less than 15BTDC

I keep it at 15BTDC now, all the time. Even on regular fuel, it very seldom pings.

It's amazing how ignition timing can affect an engine. Set at the stock 6BTDC it feels like it needs an engine rebuild, compared to 15BTDC.

 

[surfstar]

Since I've been using FP, I upped my timing from 8* to ~11* to see if I can get any more MPG. So far no MPG difference, but it *may* accelerate better.

Last fall, in warmer weather, I noticed some pinging with 12* and put it down to 8*. I've read that people who use FP can run 89 octane instead of premium, so figured I could up my timing with FP.

 

[Oldmoparguy1]

When you changed the timing gear to one with a different index, you very likely changed the cam timing. Based on the figures you posted, it sounds like you have retarded the cam. This would hurt your low end power. I'm not a Ford guy, so I don't know that engine, but that is what I would expect from my mopars. You might try to recurve the distributor advance to improve drivability.

 

[johnd]

Sounds like my experiments on my 1962 Ponitac 389. By the time you advanced the timing enough to give it power, it got really hard to start. I put an MSD external timer on it and then I could retard it 6 degrees to start and run 6 deg. adv running. On static timing of 12, that gave me a total advance of 18 deg and it ran smooth as a top. I finally got that thing up to 15 mpg by the time I sold it which was really amazing for a 4000 lb carb. vehicle with that sized engine.

 

[mechtech]

That 8 degrees sounds like chain stretch.
I never hear of stock gears being that much retarded, especially in an engine that needs low end power.

 

[Jimbo]

Do you pass smog checks at 15? The 87 Dodge is gutless at 10, but fails with high HC readings at 15, where it runs much better, but pings a little. The reason for retarded timing is for emissions.

When I had access to a smog testing machine in college, I experimented with carb jetting and timing on my VW. Small timing changes made a huge difference in CO at idle.

 

[Big O Dave]

To answer some of your questions:

1. The OEM timing set for a post-1971 Ford 460 is retarded 8 degrees from a "straight-up" (TDC) position. The first 460/429 (Series 385) Ford engines ('68-'71) were built with timing sets configured to "straight-up" (TDC) cam timing.

2. Installing a '68-'71 spec timing set in a 460 built after 1971 advances the timing for the cam and the ignition by 8 degrees, because it moves both cam and ignition timing, since the distributor gear is turned by the cam.

3. The 8 degrees were not a result of chain stretch, although I have no doubt that the original timing chain had seen much better days.

4. For more information on Ford Series 385 cam timing, go to this forum at Ford Truck Enthusiasts and do a search on "timing set."

5. Regarding smog checks, I set the ignition timing to the OEM spec for smog checks, and then back to 15 afterward.

 

[Big O Dave]

I agree, unDummy, that's not the way to mess with ignition timing.

However, when I installed the new timing set, the ignition timing was advanced along with the cam timing, so I had to back off on the ignition timing by the same amount the new timing set advanced it. I did this by turning the distributor.

While I was at it, I decided to experiment with the ignition timing to see how it would change power, response and fuel economy. That's what I'm reporting above, my findings.

The purpose for using a '68-'71 timing set, compared to a '72 and later one, was two-fold:

1. Better throttle response.
2. Advancing the cam timing 8 degrees, to the TDC position, moves the hp and torque peaks down 600 rpm in the powerband with this particular engine. Since I've never had the engine over 3,500 rpm, I didn't need a hp peak at 3,600 rpm, for example. Now it's at 3,000 rpm and the torque peaks at 2100 rpm, both of which are much more useable for me. My fuel economy went up about 1 mpg in my normal usage, too. Downside? The engine runs out of breath before 3,500 rpm (with the stock cam), but I couldn't care less, since I never go over 3,500 rpm and very seldom go that high.

One more benefit: cruising at 65 mph on the freeway, when I come to steep grades the engine maintains speed with no additional throttle. That's nice, and kinda fun.

Regarding distinguishing between ignition and cam timing, the title of this thread is My Experiments with Ignition Timing on an '83 Ford 460

[ February 01, 2006, 02:42 PM: Message edited by: Big O Dave ]

 

[punisher]

mechtech
Member # 4768
posted January 30, 2006 04:46 PM
--------------------------------------------------------------------------------
That 8 degrees sounds like chain stretch.
I never hear of stock gears being that much retarded, especially in an engine that needs low end power.
--------------------------------------------------------------------------------

Trust me, FoMoCo did it on most of their smog engines. The timing gears were purposely cut "retarded". It was done to reduce N2O emissions and it did indeed kill torque.

 

[unDummy]

So it advances the cam in relation to the crank and in turn affects the ignition timing.
IMO, thats not the way to play with ignition timing. Use the distributor for that.
Cams should be installed with correct gear straight up, or degreed with any adjustable gear.
If the cam specs, or any other variables like head castings, intakes, emissions..., are different from the years(1983 vs 1970), then you should swap those parts too.
Put the correct timing gear in and be rewarded with a better running engine. Or, swap the carb/intake/heads/exhaust/cam/....from the pre 1970 motor and enjoy your 1970 cam gear!

I wish that everyone would distinguish between ignition timing and cam timing.

 

[Big O Dave]

Just to give you an example of how ignition

timing affects this engine, I just did a tank with the timing set at the factory 6BTDC (measured as per the emissions sticker on the engine) and got 7.6 mpg.

With the ignition timing set at 15BTDC (measured the same way as above) and on the same route as the tank above, it got an even 10 mpg.

The only difference was the ignition timing.

 

[TheTanSedan]

Glad to see someone get around that lousy FORD "fix".

Have you set total timing, or only the base? Considering the changes in fuel (zero lead, nowadays), I found some extra pep and mpg on my late 1971 Chrysler 383. Changing the advance curve was a big help! Since mine was worn (piston seal) I found that more initial timing and less totalwas the key.

The car weighed 4,700-lbs with driver, full fuel and truck junk; had 29" tires and a 2.76 rear . . . I needed all the pep I could get (and ran a 195F thermostat to boot).

 

[tom slick]

what is your total timing? mechanical advance? vacuum advance? these numbers are actually more important then base timing.

 

[Big O Dave]

The truck still has the original vacuum advance distributor (and the original Duraspark module with the blue grommet), and it has not been re-curved (yet!

). To be honest, I don't know what the total ignition timing is... all I've done is experiment with the base timing.

I update you guys after I find out about the total timing, and then with my experience with re-curving the distributor.

 

[TheTanSedan]

Chris Jacobs book on PERFORMANCE IGNITION has some great pre-dyno suggestions on the how-to's for us DIY types.

A GTech or other meter would be my second purchase.

Graphing the performance (on paper, for us oldtimers) is the key to finding the curve you want.

 

[TheTanSedan]

http://www.amazon.com/gp/product/sitb-next/1557883068/104-5957167-0097521

 

[Big O Dave]

Thanks SO MUCH for the link... it appears to be a "must read." I gonna get a copy!