Vacuum Tuning

[duaneo]

Gents,

My truck has a remanufactured 360, and my mechanic and I are having a disagreement. He is a firm believer of timing "by the book" If it's supposed to be at 12 degrees btdc, then that's what we puts it at. When I drive it, it feels like I'm pulling a trailer. Just sluggish. When I step on the gas, it doesn't want to go.

When I put a vacuum gage on the manifold, pull the vacuum advance and plug the hose, and adjust timing for maximum vacuum, the vacuum at idle goes from 15 to like 21. Driving it with the advanced timing is like the sun came out from behind the clouds. I step on the gas and it GOES. I'm not hearing any strange sounds, it's not behaving strangely. If I put the timing light on it, It's not even on the marks, it's so far advanced.

When I put the balancer on (new from LMC) 0 degrees was exactly at TDC. My Mechanic also confirmed that the balancer is on correctly.

So talk to me. Am I asking for trouble? For all intents and purposes, it drives a LOT better with the way advanced timing. I watched a couple of youtube videos with examples of engine knock. I didn't hear any when I drove around the neighborhood, and out on the freeway.

Thanks in advance for your feedback!

Cheers,
Duane

[sargentrs]

If it's not pinging or clattering at acceleration or WOT, don't sweat it. Suspect your timing light may be a little tweaky. Did he replace the balancer with an OEM or aftermarket with a different diameter? I'm a firm believer in timing by what the engine wants. 20-21Hg vacuum is where it should be. I also prefer to time an engine to max advance at 2500rpm at let the initial fall where it wants to. On my 302, I swapped in a Duraspark ignition and set the timing to 10*. She ran like crap. I hooked everything up and timed it to 38* at 2500 rpm and she ran great. Initial fell in at a crazy 22* although I suspect something might have been off with my light, my balancer, my timing pointer or my old blind eyes.

[hazelnut]

What's the condition of the mechanical advance inside of the distributer ?

Sounds like the advance is corroded inside and not letting the advance work like it should or the advance needs to be reworked to get the advance to be where it needs to be in full advance.

Advance should be at 38* when its in full mechanical advance.

[duaneo]

It's got a shiny new MSD distributor in it. I put the balancer on myself, and it was an identical match for the one from the old engine. Other than a little dieseling when I shut the engine off, it ran fine for my commute this morning, and compared to the last time I drove it to work (it backfired a couple of times in the intake and was generally gutless) it ran like a top! I'll keep and eye and and ear on it, and watch for a possible increase in MPG. Currently I'm getting around 8 mpg.

Cheers,
Duane

[TNIceWolf]

If its dieseling at shutdown I myself would consider backing the timing off just a bit. Its possible to have too much of a good thing. It is also possible for the dieseling to cause some unwanted damage to the engine. Backing the timing off just a bit could save you some future headaches without actually reducing the performance of the engine, Vacum timing can be a tricky beast as it is dependant on any known or unknown vacum leaks. You may think you have no leaks because certain parts or gaskets have been replaced....but until you check and verify that the vacum gauge can lie to you. Also it is good to remember that the 360 engine is built for torque and not high performance. its not going to be a race car unless you invest in changing it to say a 390 or a 410 stroker. If you are getting around 8 mpg you arent getting the mpg I get out of an F350 dually with the same engine in worn condition and with a NP 435 manual trans and 4:10 rear gearset.