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Discussion Starter #1
Mabye you guys can help me with this?

Here is my general set up. 385 stroker, zero decked, forged internals, howard solid roller cam 258 intake, 268 exhaust, 605 lift, .023 lash, canfield 195 cc heads, manley severe duty springs, crane rollers, msd 6al, msd 85111 distributer, msd adjustable timing control (add or retard 15 degrees), 750 race demon, victor jr intake,richmond 6 speed 327 first gear, and a 411 rear, so I am pretty much in my power band all the time.

I started and broke the cam in with 8 degrees initial with the stock silver springs and blue bushing in the dist. Eventually raised my initial up to about 12 to 14 degrees initial with about 34 total timing. The problem is that the car runs rich. I started tuning it today and found out the enging idles great with about 24 degrees initial. This way I can back off my butterfly valves on the barry grant, like they recommend and use timing to set the idle where it wants to be. And in turn give me a cleaner burn at idle and a better throttle responce. But with this much initial timing my over all is about 45 which is too much. Even with the largest bushing it is still way to high. So I was wondering if it would be a good idea to lock out the distributor so its always a 35 or 36 degrees and use my msd retarder at start up to back the initial timing to around 20 or 21 so I don't screw my starter or flywheel up. I don't know what do you think?
 

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u should get the timing set to the right specs and then if u worried about blowing ur starter u should buy a high torque starter made for the high performance vette and u shouldnt have to worry about the fly wheel u should be in good shape. so set that thing and u should be good to go.
 

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I have my timing set at 36 degrees mechanical all in by 2800 RPM. With vaccum advance connected my total is 50 degrees. At idle I am around 15. I have no hard start problems, no surging at cruise and car seems to be pretty peppy. I set my timing per Lars paper at Corvette FAQ.
 

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Discussion Starter #4
Thanks, I think I am going to try 18 degrees initial, use the black 18 degree bushing in my msd which will give me 36. I will use the two silver light springs and bring it in early.

Question? If you lock out your distributor does your initial timing even matter. Is it always 36 degrees? Do you have to set your timing marks back to TDC then lock it out.

Because if it was always 36 degrees, at start up I would crank my timing control knob 15 degrees retarded. That would give me 21 initial. I would set my idle at about 900 to 1000. Once I am idling I could crank the timing back up to 36 degrees. Would this work?
 

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robconner said:
Thanks, I think I am going to try 18 degrees initial, use the black 18 degree bushing in my msd which will give me 36. I will use the two silver light springs and bring it in early.

Question? If you lock out your distributor does your initial timing even matter. Is it always 36 degrees? Do you have to set your timing marks back to TDC then lock it out.

When you lock out your distributor, aren't you just disabling the mechanical advance? So your intial timing is all you're going to get. The initial timing has to be in relation to TDC on no. 1 and it's gonna be whatever you set it at (36, 22 , whatever). A locked-out distributor sitting on a shelf has no inherent timing associated with it. It's all in relation to TDC when it's installed.

Because if it was always 36 degrees, at start up I would crank my timing control knob 15 degrees retarded. That would give me 21 initial. I would set my idle at about 900 to 1000. Once I am idling I could crank the timing back up to 36 degrees. Would this work?

You've got to go back to basics...why is there mechanical advance in the first place? In simple terms, at a particular intial timing and 1000rpm, there is X amount of time for the flame front to burn across the cylinder. At 2000 rpm, there is X/2. But the time it takes for the flame to propagate is the same, so you have to start the process sooner to get the peak burn at the right time. Otherwise, the mixture is still burning on the downstroke and a lot of the energy is going into the cooling system, not into pushing the piston down. This would be retarded timing and the reason an engine runs hot with the timing too late. If the process is running way early, you can have the highest cylinder pressure as the piston is still coming up with resulting destructive detonation. At around 3000rpm, the turbulence in the cylinder is high enough to promote the proper burn without the need to advance the timing further. Which is why you are trying to get it all in at 2800. So if you run 36 degrees at 1400rpm, you have too much advance and the chance to burn a hole in a piston in 2 seconds. Besides, you don't really want to be messing with the advance knob everytime you leave from a light or stop sign. You'd need 3 arms.

You haven't said anything about vacuum advance and I assume this distributor doesn't have it or you have it plugged. For a street engine, the high initial timing that you want at idle (around 20 degrees) for a good clean burn is easy with the vacuum plugged into manifold vacuum. As soon as you open the throttle the vacuum-induced advance is gone.
 

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Discussion Starter #6
I have no vacuum advance, pretty much no vacuum left. I have to rev up the engine to put the headlights up and down. Thats pretty much all I use vacuum for.

My problem is that I can't get 20 degrees initial without too much total. With the black bushing I will get 18 mechanical so I will be able to set my initial at 18. Hopefully this will clean up the idle and lean out my mixture alittle. I am also going to put in the two light silver springs to bring it in quicker. I am also considering opening up my gap on my plugs .005 to give me alittle hotter spark. I haven't had time to try any of these changes yet, run it and check the plugs. Hopefully I will this weekend. I dosen't sound like locking the distributor will help me. Thanks for the input.
 

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Rob,

What if you made your own bushing? But instead of a round one, you made an oblong one. I'm not looking at the distributor now, but if you used the diameter of the biggest bushing as the width and made the length a little longer, you could limit the maximum mechanical advance. Just by trial and error, you ought to be able to dial it in. Better yet, mike the different bushings, you know what amount of advance the different diameters/colors represent. You should be able to figure out what length you need. If you can't make this oblong bushing work, try to limit the length of the slot the bushing rides in by adding a spacer that limits the bushing travel. Again, I'm not looking at the mechanism, so I'm maybe not giving you the right specific idea, but I think the way to go is to set it at 20 initial (if that's what you want) and then limit the mechanical advance to 16 by a mechanical means.
 

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Discussion Starter #8
Why don't I think of these things.:thud:
Thats right it would make to much sense. I appreciate your time and advice, I will let you know how it works if I ever get back to my car.
 

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I just looked at the illustration on the MSD box. I'm not suggesting that this would be permanent or the right size, but in 2 seconds, you could make a spacer out of a crimp-on ring lug terminal. The thing is shaped like a donut with a tail on it. Pick one that has the same ID as any of the bushings. Bend the tail 90 degrees to the donut and put the terminal on the pin between the bushing and the nut that holds the bushing in place. The tail should be sitting in the slot facing the direction the bushing travels when the mechanism is advancing. The tail is now a spacer that keeps the bushing from traveling all the way up the slot. Obviously, the right piece is needed to fit with the big bushing. Just a way of illustrating what I am talking about.

Got to thinking about the "big picture" just now. We're setting everything up to have a load of advance at low engine RPM when it might not tolerate it.
 

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Discussion Starter #10
Beats the hell out of me, know I'm really confused. The guys at Barry Grant told me that once I set the butterflys to original specs then I keep advancing the timing until the engine idles at the desired rpm. They said let the engine tell you how timing it needs. Then you can adjust the four corner idle to smooth it out. They said with my cam and engine combo I will probably need at least 20 initial and mabye more. I ended up needing around 24. He said you might need more than 20 and end up locking the distributor. Thats where I arrived with this idea in the first place. Since putting the motor in last spring I have only been able to put mabye 2000 miles on it. So I still haven't had enough time to find the perfect tune up combos. Anyway how can you find out you have to much initial timing without finding out the hard way.
 

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Rob, I was hoping Grumpy or Olddog would chime in as I think they have a ton more practical experience with hot engines than I do. With the large cam and steep gears you're running, you might zip right through the "danger zone" without a problem. A big cam is more tolerant of a lot of timing at low rpm because the cylinder pressure is low as the intake closes so late. But, I don't know how you can figure what will work before trying it.
 

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Discussion Starter #12
I ended up using the black 18 degree msd bushing. So I have 18 initial and 18 mechanical with 36 total. I backed the msd adjustable timing control down 2 degrees for a total of 34. I think the car runs better. I did two full runs first through fifth, one with nitrous, both felt strong. After each run I pulled over immediatly and checked a couple of plugs they were a dark brown with a few black splotches. They looked the same after the nitrous run. Since then I have screwed with the carb alittle. It still needs some adjustment. I am going to the local track tonight for a test and tune. Hopefully I will figure something out, and take some good video. I still think it is too rich at idle.
 
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