CheezMoe

I have XE268h in 383 with 10:1 and have had similar issues this summer. Had to back initial down from 16 - ~12, and I cant run any vacuum advance without low rpm high load detonation. I consistently pull 15* of vac at 900 RPM. Im thinking about trying a few gallons of AV gas, I know this motor can do so much more!

bobs77vet

maybe the local additives in the gas for emissions are screwing with us....i didnt get close to 15" though..... i tapped off of the power brake cannister for the vacuum gauge, i wonder if that somehow reduced the vacuum pull?

LancePearson

a job for mad dogs and Englishmen! I live in River's Bend. The land here is a penninsula with the Appommattox R. on the S. and the James on the N. I'm on the north side of the penninsula and Pt. of Rocks Road is on the south side of the penninsula. We were the high ground the last year of the Civil War and Grant's headquarters were where the two rivers joined at City Pt. in Hopewell.

Lots of history here.

Lance

LancePearson

In many areas of the country the gas mix in summer changes by epa regulation to include more ethanol than the winter to reduce air pollution. I suspect that the more ethanol they put in the less our engines run well. Hate that stuff. It has much less fuel content and screws up seals and gaskets over time and mileage drops as well. If ethanol is cheaper than gasoline then you'd expect some distributor to be loading up with more ethanol in the gas being sold as well to line his already fat pockets.

Don't know what ethanol costs right now but do know that the ethanol plant built last year in Hopewell, Va. to put out 65 million gallons of it never opened as the economics went to heck. Its fermentation base was the grain, Barley. A huge place that somebody called something like Osage Bio Energy put something like $160mm into and is now for sale without ever producing commercial ethanol. It was near the rivers as it takes 23 gallons of water to distill 1 gallon of ethanol they say.

Only plant in the state according to the media at the time.

Lance

gkull

Well it is obvious that you need a better starter.

I've said this many times......... your distributer total mechanical advance determines what your initial timing is. So you rev your motor to 3500 rpm and set your timing at say 38 degrees (no vac assist)

Whether your timing when you check initial is 4 or 24 before TDC the only way to change it is to vary the mechanical stop.

Lars is a smart guy, but I don't buy into his ridged BS. If you have wimpy stock motor that has low compression. By all means get full timing in faster. But once you get rid of EGR or start to really fill the cylinders with cams, intakes, headers. You need to bring in max timing at a higher rpm.

All my motors have if I bothered to check would be 18 -22 initial and all in by 3200 rpm. Where Lars has you all in at 2800 or less, I have less timing because I still don't have max advance. So on a hot day I don't have to back the timing down

As to how far to turn the cap to change the timing in degrees. It's all math. 360 degrees in a circle...... Right? Lets just say the outside dia is 4 inches In simple math dropping the end off of the numbers you have 12 inches around the circle.

12/360 = .033 inches. So 10 degrees is only .33 or about a 1/3inch. You have 8 cylinders and 360 degrees. How many degrees do you have between each cap spark plug wire? 45 degrees between firing.

This is a prime example of somebody that doesn't understand timing. Not only ignition, but also cam. His answer is AV gas They make variable vac advance pots and his timing is all screwed up. probably all in at less than 2800 rpm

Originally Posted by dosoctaves

I have XE268h in 383 with 10:1 and have had similar issues this summer. Had to back initial down from 16 - ~12, and I cant run any vacuum advance without low rpm high load detonation. I consistently pull 15* of vac at 900 RPM. Im thinking about trying a few gallons of AV gas, I know this motor can do so much more!



I should just give up on this. You can't argue with morons and you can't explain the truth. They will beat you down with stupid! But happy 4th to all of you that understand how timing is supposed to work

bobs77vet

i was looking at the distributor and i came up with the same conclusion....not much movement for 5-6* i couldnt really figure out a formula for it though

LancePearson

I owned a 35' sailboat for years. You would be surprised what a small change on a compass 3-5 degrees is for the same reason...360 degrees in every circle. The 5" referred to above diameter is approx. the dist. head you hold but the actual shaft down below that goes into the engine is what, 1"? Takes very little down there to move 5 degrees on a 1" diameter circle!

I don't have any expertise but you'd think a separate timing circuit box where you simply adjust some type of dial to modify the output of a chip would be far more precise. i guess that's what modern distributors probably do in some fashion though I've never looked at mine on my 2008 Trailblazer. It has a coil on each spark plug, fuel injection and tons of sensors and smart stuff. it's also the smoothest engine I've ever driven. About the same technological change in timing and managing spark and ignition as a set of magnetic shock fluids are to old spring and oil loaded shocks.

Lance

CheezMoe

Excuse Me?! Why dont you explain to us smart guy, the real scientific "truth" to what seems to be a common issue in this part, and how adding some unaltered higher octane gasoline should not be expected to mitigate the problem. Please do!? : ...and what would we all do without all these expert : s on the board looking for us helpless morons to berate! Get a life, azzwipe!

LancePearson

dosoctaves...that's a really sharp looking '73. Do you have a gallery of several photos of it? I looked at your public site and only saw one in the "garage."

Lance