Timing related question...

[philo_beddoe]

I have a 77 Boinanza, 305 4bbl., all GM parts.  The spec sheet in my shop manual shows this model/year with a 305 2bbl.  When I bought the truck some jerk put a eddlebrock intake and eddlebrock carb on it. So I put it back to the original GM intake and like new fully rebuilt quadrajet 4bbl.  The reason i put the 4bbl is because the primary jets are smaller than the 2bbl. So I'll actually save gas with the 4bbl.  (I won't "get on it" because 305's are not exactly muscle engines)

Here's the problem, the manual (and the sticker under the hood for timing says 8 degrees BTC, @ 500 rmp.  BUT, that's for the origianl 2bbl.   In the Manual,,,,it does show a 4 bbl 305 for the like 82-86 years...and that is 4 degrees BTC. 

Which should I time it to?  8 degrees or the 4 degrees.   (one mechanic said keep it at the original 8 degrees since that is the original 1977 305 engine.   Thanks,,,

[enaberif]

Start at 8 and see how it runs. You might be able to even get 10 or 12 out of it.

[philo_beddoe]

Thanks, I will.   Also, what are the symptoms of an engine when it is set too far advanced, and too far retarded?  How will it run each way?   

[enaberif]

Thanks, I will.   Also, what are the symptoms of an engine when it is set too far advanced, and too far retarded?  How will it run each way?   

Too retarded will make the truck gutless. Too advanced can cause pinging under load.

[philo_beddoe]

Ok, got it. Thanks for the help.  I have an original 1970's sears light and the old dwell tach.  Should be fine..

Will post results.

[philo_beddoe]

Wait, for what reasons would I want to get 10 or 12 degrees BTC out of it???

[enaberif]

Wait, for what reasons would I want to get 10 or 12 degrees BTC out of it???

More power, better response better fuel economy.

[rich weyand]

^^^ x2.  More advance is always better, right up to the point where you get knocking.  This will normally be at low rpms, high load, and high throttle settings, like trying to start from a stop on steep hill and putting your foot in it, so that's how to test for it.  I am running my 350 at 16* BTDC.  The difference in performance is awesome.

BTW, that's what modern computer controlled cars do.  They use the knock sensor to run the ignition timing right at the knock limit.

[philo_beddoe]

Great, that's what i'll do then. Which way advances the timing, turning clockwise or counter c.??  Thanks

[enaberif]

Great, that's what i'll do then. Which way advances the timing, turning clockwise or counter c.??  Thanks

Counter for Advance
Clock for Retard

[philo_beddoe]

Ok, just set idle to factory specs w/dist. vac plugged, put a light on the scale while at 500 rmp and advanced to 10 degrees BTDC. Factory specs calls for 8 degrees, took for test run and she seems very smooth and peppy...(for a 305 anyway).  So, will I be okay having it advanced 2 degrees?   Thanks,,and by the way, what does the pinging or knocking sound like when and engine is too far advanced. Is it very noticeable? Thanks again.

[enaberif]

If it knocks you will hear it. Sounds like it says...

Your perfectly fine +2 degrees probably be ok at 12 but stick with 10 for a bit and see what you think.

[philo_beddoe]

Ok, sounds good. Thanks for all help.  Next project: Valve seals!   

[Stewart G Griffin]

i don't think 4 vs. 2 bbls in and of itself would matter for timing.  Experiment to see which is best for your combo.

Also, based on my research and testing the quadrajet may not necessarily get better mileage than the 2bbl.   Alot depends on how you drive and other factors. 

[philo_beddoe]

Well, i almost never open up the 4 bbls. I only putt around town. No towing or hauling. I have heard from many sources the 4bbl primaries are smaller than the 2bbl jets.  I guess...

As i mentioned, factory it came with a 2bbl setup. I bought it with an edelbrock intake and carb that i believe was too big for the motor. It ran horrible.  Now she runs real smooth, its quieter and has a bit more power.  Big difference.  And does a whole lot better on gas.