Timing and Octane blues- HELP!

YodaFan1138 · 01-01-2003

Hey Guys,

When I went to set the timing on my 1969 Mach I 351W/FMX auto, I looked up in my owners manual the stock setting. The chart in the book said timing should be set at 6*. Does this mean BTDC or ATDC? Also, if my harmonic balancer looks like the diagram below, am I set at 5* BTDC or ATDC?

Passenger side of car
-10
-
-
-
-
-5(where my timing is set)
-
-
-
-
-(Unreadable)
Driver's side of car

My owners manual (keep in mind this was printed in late 1968) recommends an octane rating of 99.8 (premium fuel) for my 351w-factory 4 barrel carb. Any idea how I can achieve this type of octane in my gas without spending upwards of $5/gallon? I tried a bottle of Pennzoil outlaw octane booster but was only able to raise my timing one degree without detonation. Will a one degree difference boost my power and fuel economy any (give me a ballpark figure, please)?

Thank you all very much for your help.

YodaFan1138 · 01-01-2003

Hey guys,
I realized that, as I've been having this problem for awhile and have posted it on many sites that I've messed up and posted the same question (although the octane problem is still there).

NoSlow5oh wrote (in reply to my previous post from a week or so ago): "Yodafan1138, from my understanding in your post you have the wrong idea on the timing. When you advance the timing, you would move to a higher number BTDC. So if you had 6* BTDC and you advanced it 1* then you would have 7* BTDC. If you had 6* BTDC and you retarded it 1* then you would have 5* BTDC. You are right though when you say that an engine will perform better with the highest number of timing BTDC right before it detonates. If it was pinging at 6 and at 5 it doesn't ping anymore then 5 would be your best bet."

IS THIS RIGHT? Wouldn't you make more power if your timing was at TDC, with all the firepower going towards pushing the piston downwards rather than 5* BTDC, with a portion of the power going towards slowing the piston down? It was my understanding that achieving timing closer to TDC would increase the horsepower, gas mileage, and overall performanc of my engine. So confused....

GT50 · 01-01-2003

All timing references are at BTDC ( what someone will correct me ) If it calls for 6* and it pings then back it off a couple. It will hurt performance yes, but not really that much. Your manual suggests that you use 99 octane or higher and that was leaded fuel back then. So I guess you have to use current premium fuel and a octane booster or back off the timing.

How is the temp of the engine? Does it run hot? This could amplify pinging as well. Also carbon build up behind the valves is another culprit. Only way to tell is to remove the intake and exhaust manifolds and have a peek at the valves. If this engine is still original then, you probably have worn valve guides and need to freshen things up a bit.

Sometimes a pinging issue can be a real bear to resolve..

YodaFan1138 · 01-02-2003

351w-4bbl was completely rebuilt before I bought it, so valves should have been replaced, heads magnafluxed, etc. I shouldn't have carbon buildup with only about 3,000 miles on the rebuild, should I? Also, do you recommend an octane booster that will definitely kick 92 or 91 octane up to about 100 (and can I get away with adding this miracle liquid to 89 or 87 octane?)-please keep in mind that I want to stay away from the $5/gal stuff

So if my timing is set at 5* btdc and I move it to 6* btdc, I have advanced the timing, correct? (Conversely, if I move timing from 5* btdc to 4* btdc, I have retarded ignition timing, correct?)

Essentially, to make the most power I will need to retard the engine timing as much as possible (with my understanding this would be timing closest to 0* btdc or tdc, with all power working on pushing piston down rather than slowing it down first, then using whatever's left to push the piston down in the power stroke.)

NoSlow5oh · 01-03-2003

YodaFan1138, I have checked with 7 different auto companies and the information I gave you is correct. It takes a certain amount of time for the fuel to burn in a cylinder so if you gave it a spark right at TDC then the piston would already be on its way down in the power stroke before the explosion could expand and push the piston down. Therefore, you give it a spark before it reaches TDC and the explosion and expansion occures at about TDC. Ever wondered what a mechanical advance was? It uses the centrifugal force of your distributor shaft to shoot the spark sooner BTDC as the RPMs increase because the piston is traveling faster and will reach TDC faster. The fuel will burn about the same rate at all RPMs so you want the expansion to happen at TDC. This is the EASIEST way I can explain it to you. And if you have doubts, call someone.

YodaFan1138 · 01-05-2003

Hey guys,

I (accidentally) lied about my harmonic balancer layout- sorry! Trying to See what the rotten thing says with a timing light in broad daylight is kind of hard, this is what the HB actually looks like (after having a partner get in and bump the starter a few times so I could copy down a diagram):

(Passenger side) (Driver's Side)
*
H8 | | | | | | | | | | | | | | | | | | | | | BTC
ATC 10 TC 10 20 30
0

Believe it or not, the * is where the indicator says my timing is set without pinging (2* ATC), 92 octane with a can of Better-n-led lead additive. Freaky, huh? Does the H8 mean that this HB is meant for a specific engine, do I have the wrong HB, is my timing mark simply in the wrong bolt hole on the head/block, etc.?

Also, will it hurt my performance at all if I start using 87 octane and adjust timing accordingly? Thanks for the help.

EZBNME · 01-05-2003

You need to check your vaccum advance rate, total advance with no vaccum and rate. 2 degrees intial is just not enough. You need to get someone to check out what i'm telling you and get your distributor recurved for todays fuels and to allow more intial timing.