Hi
I’ve been reading old posts from the forum about setting timing as my whole engine needs a tune up. I’ts a 1967 289 2v stock (as far as i know).
The shop manual says timing should be 6 degrees at idle (vacuum line disconnected, i believe this is called initial timing ?)
I pretty much read everywhere (for all engines ford, chevy etc…) that timing should be around 12 at idle and roughly 35 at 3000rpm. It seems to be the generic consensus.
Why was Ford recommending 6 degrees ? is it because of today’s fuel that we need more advance ?
I have done a quick test and my engine seems to be set to 6. Am i right to think it is too retarded and that it is the cause for some backfiring in the exhaust ?
The quality of fuel has improved but often the octane has not.
Also back in the day emissions were an influence, were as modern cars have this built in to their design .
We quickly learned that older cars benefit from a little more initial advance for drivability.
If setting at 12/36 works for you, then run with it.
There are a lot of factors involved with tuning, including vac advance (manifold or ported), and the curve of your distributor’s mechanical advance. The most important of these, in terms of not damaging your engine, is going to be your peak timing at Wide Open Throttle. If you run too much timing for your engine combo and the fuel you’re using, detonation will wreck your pistons, rods, bearings, and damage valves.
If you get a little rattle at part throttle off idle on the way up to highway speeds, it’s not likely to damage anything the first time it happens.
So bottom line: your base mechanical timing on the top end is critical. How your engine runs at cruise is also very important, because running miles and miles with a glowy combustion chamber causes exhaust valve erosion. The rest of it is only important insofar as you want crisp throttle response and smooth, efficient idle.
Modern fuel may not be higher octane than the old Ethyl, but ratings are much more consistent, as is overall fuel quality.
This is a great chance to let Cougar members judge for themselves. I have posted these thoughts on many Ford sites. Todays gasoline is a very slow burning blend. The octane numbers (87,89, &91) do not represent a direct coalition to the octane numbers of the late 1960’s. Where premium was 99 and Chevron white pump custom supreme was rated at 101 octane. The slow burning gas blends of today react very closely to the high lead gas blends of the 1960’s in a high compression engine. I have ran a 12 to 1 extreme build solid roller cammed Weber inducted 289 on todays slow burn gases at 38 degrees of total advance. No pinging and great power. Todays slow burn gasses rated at 91 or 92 octane run great with old school high compression engines and anyone who tells you to reduce compression will help you build a dog motor. Anything lower than 10 to 1 will produce very poor power.
To address the initial timing question, I run as much as 12 to 16 degrees initial timing on all my Ford builds. Now this must be coupled to addressing the vacuum advance curve of a mild build. You need to slow down the vacuum advance and reduce its total. This can be done with springs and shims in a factory style vacuum advance or the use of a newer adjustable advance. To tune out low load pinging under partial throttle operation.
I submit this telling article from the early 2000’s. It was the results of multiple dyno pulls on todays gas and todays gas with octane booster. Also it addresses similar blends prevalent in the late 60’s. it supports that the earlier blends were so much more “explosive” that they had to actually reduce total timing in this Mopar 360 engine build. It display facts that I have experienced in many of my engine builds.
I am currently building a 53 CC Twisted Wedge combustion chamber, flat top 302, with a roller cam. It will run just fine on 91 octane gas with 12 to 16 degrees of total advance and 38 total. Fine tuning the vacuum advance total and start point. Also cam selection can greatly affect pinging as it will blead off static low RPM compression.
Please digest this article to alter your thoughts on todays gas and high compression engines. Yes, old school engines. It is hugely revealing! And don’t get me started on hardened valve seat! What a bunch of baloney!
Rob, you mention the hardened valve seat issue so I’ll post my experience here for whatever it’s worth. Since 2004, I’ve logged nearly 90,000 miles on my 68 (j-code). For about the first three weeks I dutifully added lead substitutes at every fill-up, but soon quit. She’s been fed 91 unleaded ever since and still runs great. I always figured I’d have hardened seats installed whenever the time comes for a rebuild. Are you saying it’s not necessary?
Hardened valve seats were a 1970’s solution to using unleaded gas with retarded timing. When timing is retarded this results in still - burning mixture going out the exhaust valve. It certainly doesn’t hurt anything to have them. Many Ford / Mercury products in the 1970’s also used induction hardening of the cylinder head around the valve seats to accomplish the same goal.
However if the car runs OK on available fuel at 34 + degrees of total timing it may not REQUIRE them. Particularly if (for example) you have a compression ration below 10:1 and use 91 octane gas. Other things like lowered compression from using typical rebuilder grade pistons or more aggressive camshaft profiles may also reduce the tendency to have hot exhaust valve seats.
It just doesn’t run right on regular & I’m fairly sure that there’s knocking if I attempt regular.
I could retard timing to see what happens but I’m afraid it’ll really cut into power and make the mileage even worse.
The path of least resistance is to just use high test and be happy.
My engine is a 302 with GT40 heads, performer 289 Edelbrock manifold, 500 cfm AVS2 Edelbrock & I’m not sure what camshaft it is. It’s probably either an Edelbrock camshaft or the GT-40 camshaft that matches the heads.
I’d have to pull the intake to see what it is. Frankly, I think it’s best to just let sleeping dogs lie.
Very interesting. I have always had issues with A code 289 and J code 302 with pre-ignition. Gas in Arizona is different depending on the season, and I have even had to adjust timing depending on the summer / winter gas. My 428 CJ required backing the ignition off just a bit between 93 and 91 octane to avoid pinging. I look forward to hearing more as my professional engine builder nephew also claims to be able to build high compression engines running pump gas (93 octane in Oklahoma) One other thing that is odd about the Hot Rod article is that they talk about MBTE in gas. MTBE has been banned since at least 2006 even earlier in most states. I wonder if they did the same test today how things would turn out?
Bill,
Yup the test was in 2001. Not sure how MBTE would change the results. But I am confident that the gas blends of “yester yore” were a lot more potent than todays gas. I would love to turn back time and get a tank of old 101 Custom Supreme and tune my car to it. My guess is I could get more HP out of that old gas, but it would more than likely take a dyno to prove it.
Royce brings up a good point on cam shafts and low RPM compression bleed off due to the increase in overlap. Anytime I build a J or A code, or even an FE, I recommend at least a mild cam to assist in pinging issues at light throttle. A mild cam coupled to some work on the vacuum advance seems to do the trick to eliminate the light load pinging. And wake up some HP even with stock cast iron exhaust manifolds. A mild cam that will not adversely affect vacuum at idle much.
Royce is also correct on hardened valve seats. Decreased advance increases engine temp and especially exhaust gas exit temperature. In my experience Yorgle example is right on. The driving we do is not nearly as much over a span of time. Yorgle has put on a ton of miles when compared to most of us. Lack of lead in the gas created havoc on RV/Truck engines. And equally on boat engines. Engines that experience a huge work load towing or as a boat “always going up hill”. That is when hardened valve seats are required. Our Sunday driver cars never experience that kind of work and I see no benefit of hardened seats in our cars. And in some cases, the hardened seats can “work out” and cause problems. Another factor to consider.
Timing, octane, and stoichiometric ratios have everything to do with both cylinder, and exhaust temps. Too far retarded dumps unburnt fuel into the exhaust manifolds, raising exhaust and underhood temps, but NOT cylinder temps, because it’s not producing as much heat in the combustion chamber.
Too far advanced means that the piston will be fighting against unnecessary pressure before it reaches TDC, and it will greatly spike peak pressure, causing detonation. That raises engine coolant temps, cylinder temps, oil temps, and reduces power significantly.
Ideally, the spark needs to happen just far enough of TDC that the exploding air/fuel mix reaches peak pressure about 12 degrees after TDC, shoving the piston down.