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chevy timing advance
OK so i changed my 1991 305 tbi to a 305 with a 500cfm carb. The timing advance for the 305 was 0. Now im wondering what is suggested now that i got rid of the pcm and im using a carb. Any suggestions?
Replies to This Discussion
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Permalink Reply by Octavio Anaya Jr on -
When i had the 305 rebuilt it was bored .040 over and a 5.7r cam was put in. I am using an HEI distributor
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Permalink Reply by Kevin Lee on -
I would set your base timing at 10 degrees before top dead center. You might end up changing it a couple degrees more or less later, but this will get you close to running good
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Permalink Reply by Robb Szwarc on -
you mean 10 degrees, not taking into account that the hei will advance as well? i run 30 to 32 degrees advance on my 350's sometimes as much as 34 or 36.
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Permalink Reply by Gene-0 on -
If I remember my timing procedures correctly Robb you disconnect and plug the vacuum line from the distributer (HEI or points) to set the base time. Kevin can correct me if I'm wrong, but I think that's done because the vac advance will keep moving the timing around. After the base is set then you re-attach the line to measure total advance. I'm sure if Octavio looked up a 305 carbed car, for instance my 85 iroc-z camaro came with a 305 carb and hei to find the spec on timing it would get him into the ball park. I'll have to locate my haynes and I'll post what it calls for as base timing, but I'd bet Kevin is really close.
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Permalink Reply by Octavio Anaya Jr on
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I tried looking up a 1991 carb'd 305, but all i found was tbi or tpi for that year. Im not used to tuning the timing of cars cuz the last time i did this was about 15yrs ago. I have a question regarding the vac advance for the hei as well. whats the procedure and which do i set first after base timing? I already have the base timing set at zero. I currently have the btdc se at 4 degees. this engine was tbi so the base timing was zero. i would like the car to run as good as i can get it. so where do i go from here?
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Permalink Reply by Gene-0 on
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Kevin is the guy to ask, he works on cars for a living if I remember. And he mentioned 10 degrees btdc inital timing. Now if I remember right the only other adjustments you can make to the timing would involve changing your counter-weights and springs (and I'd ask Kevin to be sure here) but you shouldn't need to do that as long as they aren't worn out. From your questions I gather your not planning to drag race so your not looking to squeeze every drop of performance you can get out of the motor. Also you won't find a carbed 305 in 91 you have to look at an older model vehicle with a 305, like I mentioned my 85 iroc-z camaro was one that came with the carb and HEI, I haven't found my haynes book but I will look for it and see what it tells me and pass that along to you. I pulled the factory carb and intake off of mine and swapped in an edlebrock performer carb and intake as well as an earlier model HEI w/o computer control, but I don't remember what the timing was set at.
Octavio Anaya Jr said:I tried looking up a 1991 carb'd 305, but all i found was tbi or tpi for that year. Im not used to tuning the timing of cars cuz the last time i did this was about 15yrs ago. I have a question regarding the vac advance for the hei as well. whats the procedure and which do i set first after base timing? I already have the base timing set at zero. I currently have the btdc se at 4 degees. this engine was tbi so the base timing was zero. i would like the car to run as good as i can get it. so where do i go from here?
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Permalink Reply by Robb Szwarc on
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that is what i was saying 10 degrees without any centrifigual or vacuum advance and i don't disconnect the vacuum lime most of the time, on the near 3 or 4 hundred times i have timed a motor (thats no exageration racing 6 second cars for 10 years means a lot of tuning and timing 3 days a week). i just usually rev it to 3,000+ rpm and time it..........i though that was how it is done. i never even look at the timing at idle because most performance distributors don't even have an external advance, its all internal
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