Timing question.

[6Stang7]

I just set the timing on the stang @ 10 degrees BTDC. However, it ran a lot smoother at a higher advancment....much higher. It looked like it was at 15-20 degrees!!!! What gives? Shouldn't the motor be pining like mad by then? I have low compression (I am assuming around 8.4:1 tp 9:1), but that shouldn't make that much of a difference...should it? The engine is a 1978 302.

-Shaun

 

[rbohm]

more than compression ratio, cylinder pressure is the key here. a low compression engine can tolerate, and usually needs, more timing than a high compression engine does. most engines like timing between 10 and 14 degrees initial and 34-38 degrees total. that said, perhaps your balancer has slipped and is giving you erronious readings. as long as you are not getting any spark knock, or have a hard time starting the engine, especially when hot, push the timing back to 15 degrees indicated.

 

[Ozsum67]

Why not just time the engine without a light usinf a tach or vacumm gauge? That is the only true way to get optimum performance.

 

[brianj5600]

How do you set timing with a vacuum gauge? I always though that timing had to do with combustion chamber and piston top design as well as fuel type.

 

[jesserose17]

Mine runs great at 16 BTC, so I wouldn't worry too much. Most performance engines are set around 12-18 BTC.

 

[Ozsum67]

How do you set timing with a vacuum gauge? I always though that timing had to do with combustion chamber and piston top design as well as fuel type.

You simply advance the timing until you aquire the greatest amount of vacumm without pinging at WOT.

 

[67GTA-FB429]

I have my timing at 10-12. and I have adjusted the mixture screws until the vaccum gauge is almost steady, there is a 1-2" bounce. I am going to try the vaccum gauge timing adjustment and see how that works on smothing out the idle. Yeah I know, I have a really big cam and it will be lumpy.

 

[Ozsum67]

I have my timing at 10-12. and I have adjusted the mixture screws until the vaccum gauge is almost steady, there is a 1-2" bounce. I am going to try the vaccum gauge timing adjustment and see how that works on smothing out the idle. Yeah I know, I have a really big cam and it will be lumpy.

Good luck with it. As you know, a lump cam will make for lower than normal vac gauge readings and fluctuations on the needle. For a stock engine, a steady needle is desired. Anything less may indicate valve train problems or other internal wear.

 

[67GTA-FB429]

it is an experiment....see if I can smooth it out a little more...and yeah, it is real lumpy.