This question is mostly about my timing on a 489 BBC. Been running 91 and 93 octane with a some run on if the motor is over 180 or so when shut off. I had about 4 or 5 gals in the tank and added 5 gal 101 octane and now the motor shuts off fine even after a long drive. Compression is about 10 to 1. 489 small dome SRP, deck was just surfaced clean about .010 with a.039 gasket. Timing is at 18 intial 36 total mech adv with a 850 demon and untouched 119cc gm 310 aluminum heads. Cam is hyd roller .242 .248 540 560Should I change my intial timing lower and run more advance bushing like 14 intial 21 advance to run the lower octane. Thanks for any suggestions or comments.

Sounds like you have it figured out.
I'd start with initial @ 10° and total around the 36° you have.

I'd just give it what it wants. I like to tune my junk for best performance.
Pulling timing out to run cheaper gas is not on my radar.

Have you tried shutting if off in gear?

Mine has 10.6-1 comp. timing locked at 38* and shuts off every time. Sounds like your idle might be too fast, mine idles at 1200 rpm.

Thanks for the input, It shuts off in drive and it dies fine. The 101 is at the race fuel supplier and a little troublesome to get it in 5 gal every few days. I would like to stay with the pump gas 93 being 4 different locations around the OKC area. I have idle at 950-1000 and can try lower, it will idle down to 800 nuetral 750 gear but it seems low to me. Should nt a cam like I have idle at around 1000 in nuetral. I should get to mess with it some this evening. Thanks

am i missing something here... when ya turn off the key it really does not matter what your timing was set at since there is no juice in the ignition system at that point anyway... Right? timing will affect how the engine behaves when it is running. if a lower idle does not solve it, what about setting up a switch to shut off the fuel pump (if it is electric) before you kill the ignition. that'll kill it fo sho.

No scuba, you're spot on. Its typically the idle curcuit being "too open" that causes dieseling. Mixing in less volatile high octane fuel mitigates the gasoline's ability to fire without spark.

My idles a bit on the hoigh side right now,. and it will diesel for a second. It's all about idle circuit.

If you're not running a vacuum advance, then you should consider running at least 24* initial timing (with no change in total). This will help the engine run cooler by having more combustion complete by the time the exhaust valve opens. So it doesn't heat the exhaust valve/port/head as much. Plus the additional timing will make the engine idle higher, allowing you to close the throttle plates back down some to get back to your original idle speed (I came back later to edit, and put this sentence in, but I see Jim beat me to it below. Great minds think alike I guess. Hey Jim, check your personal emails, I sent you a couple).With cooler combustion chamber components, and the throttle plates closed more, that should be all you need to put this problem behind you.

Kicking initial up will also allow you to get the idle speed up with the throttle plates closed a little more. That will also help.

If nothing else you could use one of the old Idle kicker solenoids.

JIM

540Hotrod That may be exactly what I need. I dont know how to get the 24 intial and keep the 36 total with the MSD mech I have. I have the smallest bushing (18 adv) in now. Was going to drop the timing a few degrees and timing light went south. Just went on a 30 minute drive to town, its well over90 deg, temp got to 205 some but mostly 190-195. Should I try locking at 36 and see how it runs.

You want the largest bushing you can get in there. Someone I saw the other day was even making larger ones to limit it even more.

I just have the large bushing on mine...one of these days I'll get a larger one or may even just try locking it out. I use the lightest springs and with my idle speed around 1000-1100 or so it is just starting to advance a little. It idles around 31* or so. Then total is 36-38* depending on my mood that day.

You want as much initial as it can stand then limit centrifugal. It really wakes things up. There is even a place for a limited vaccum advance in situations like this to help out.


JIM

To answer your timing question this guy

Quote:
www.4secondsflat.com". His telephone number is 541-942-5920

can supply you with 10 and 14 degree bushing kits for relatively cheap. I am using the 10 myself for 26-28 initial.

Thanks goes to Tokyo Torquer for that find though


Shawn,
And thanks to Shawn for setting me up with it.:)
I just got mine yesterday......
This will allow you 22&36 or 26&36 you get the idea.

Brian

Blue66 thanks for the reply. I will get those soon. My 4.11 26" tires are not helping matters at the 50 + speeds. Yes 540 my throttle plates are opened a bit much.

if your plates are opened up too much then try drilling a small hole in each one on the same side as the idle transfer slot. find the right amount of throttle opening and increase the size of the hole install steps until you achieve the target idle speed. This is of course after the timing and idle mixture is where you want it.
This will make your idle circuit more effective and easier to adjust.

The run-on can be affected by your timing settings.

Ultimately you may want to go with the idle kicker solenoid, works great and very easy to install and setup.

My $.02