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Timing Question

2088 Views 15 Replies 5 Participants Last post by  vrooom3440
This may be a dumb question, but, here goes. I'm trying to get 36* total dialed in on my engine. I punched in 36* on my timimg light (vac advance plugged) and reved the engine. Should I see 36* at 0 on the tab?
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Troy,remember,if you just set your TOTAL TIMING to 36 deg without 1st setting your initial timing the initial will very likely be retarded,that looses power,wastes fuel,and causes motor to run a little hotter too.

What happens is if your dist has approx 25 deg mechanical then at 36 total your only left with approx 11 deg initial which is approx 7 deg retarded as most perf cams require approx 16-18 deg initial.

If your running any kind of aftermarket perf cam you need to 1st dial in approx 16-18 deg initial which is done with idle low like 550-600 rpms so mech adv does not start to avtivate and upset the initial setting,vac adv unhooked & plugged too.

After you do that then tighten the dist & recheck timing to ensure it did not move after tightening,if it changed reset & check again.

Then leave the vac adv plugged and now check the total by reving the motor to see what the highest timing reading you get is & at what rpm too.

You may need to get a timing tape to hook on your harm ballencer as your stock timing tap only goes to approx 16 deg for reading initial timing.

With 16-18 initial your total could easily be over 36-38 if your running a stock gm dist and in that case you need to pull the dist and have the mech adv recurved/limited to approx 20 deg to run with 16-18 initial for a 36-38 total.

If you dont do it this way your leaving a lot of perf on table by setting the timing only for a total without 1st getting the initial set correctly and then getting the mech timing curve set correctly to achieve the 36-38 deg total.

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Troy,by going by what your telling me i would say yes,its advancing past 36 deg.

If you are in fact running a non stock aftermarket cam of some kind just do what i outiline in my 1st ans to your post and you should be good to go.

Steve,you state "but I differ a bit with Scott on approaches to timing setup. Too much total timing can damage your motor"

I am wondering how you get that i am suggesting too much total when i suggested he run 16-18 initial(with aftermarket perf cam),then 20 mech,for a total of 36-38 deg ?

36-38 deg total in not too much for a good starting point for dialing in timing for many sbc/bbc perf motors with aftermarket perf cams IMHO.

I agree with you that too much total timing can cause detonation that can break pistons etc but again 36-38 deg total is not out of line at all,it;s a very common setup.

You can run the vac adv off full manifold vacuum at idle if the cam needs more timing at idle or run it off the ported if you dont need any motor timing at diel with a very mild perf cam. Yes somesites the vac adv may need to be limited or changed to get approx 50--52 deg for light load/part throttle cruise.

What i said was after i suggested to set inital timing i said to have the mechanical advance recurved/adj in the dist for approx 20 deg to get a total of 36-38 with 16-18 initial which is very common to do.

You know,its in the mechanicl advance where they replace the coller (older stock points type gm dist) in the mech adv mechanism with a different one to limit/reduce the mech adv. Then they also install lighter springs on the mechanical adv weights so it comes in earlier like at 2,800-3,000 rpms insted of like at 4k rpms like many of the older stock gm dist had.

I think you confused when i said to recurve the mechanical advance with tweaking the the vacuum advance which you sometimes have to do too depending on the setup.

Then he can run a vac adv with approx 12-14 deg adv off intake vacuum if its a hot cam that needs more timing at idle or off the ported vacuum if its a mild cam that doesnt need any more timing at idle.

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