How much initial timing and where to put the vac. hose - Team Camaro Tech
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post #1 of 3 (permalink) Old Mar 4th, 07, 09:43 AM Thread Starter
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Location: Bend, OR
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How much initial timing and where to put the vac. hose

2 questions:

I'm getting ready to fire my BBC and I'm curious when it first fires to break in the came, I'm guessing I'll be close to total advance on the motor. After bringing the idle down, what would be a good timing mark for a not-too-radical 460 with a comp 280H, headers, Perf. RPM intake, ect????

Next: I always though that when running a Holley, you always hook the vac hose from the dist to the port that's in the primary metering block. I read a couple of posts awhile back that had me thinking that's not ness the case. Does that not pull enough vac when you punch it? Where is a good place to stick that hose......and don't say up my butt!!


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post #2 of 3 (permalink) Old Mar 4th, 07, 09:55 AM
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Re: How much initial timing and where to put the vac. hose

Before you fire the engine, have your timing light hooked up and ready to go. When it fires, immediately set the timing to 35-40 degrees advanced at your break-in rpm so the headers will not get hot. After you get the break-in procedure finished, set your total timing in the high 30's, you best setting depends on the specific engine.
Next, when you 'punch it' the intake vacuum goes to zero so having your vacuum advance on the ported or constant source will make no difference. The difference comes at idle where the ported vacuum goes away.
After that you need to consider whether or not your vacuum advance can is right for the engine you have modified. Guys seem to understand that a stock mechanical advance curve probably won't work with a modified motor but try to use a stock VA can on the same engine with less than stellar results.
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post #3 of 3 (permalink) Old Mar 4th, 07, 10:25 AM
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Re: How much initial timing and where to put the vac. hose

What he said. Assuming you have to break in a new flat tappet cam, we want LOTS of advance. I usually preset the throttle idle stop to give me 2000 rpm plus (ballpark on the top step of the fast idle cam) preset the initial to around 20 degrees, and preset the idle mixture screws to a turn and a hlaf out. As soon as she fires (have a helper turn the key) just pull the vac can toward the carb until she stabilizes, then set the idle stop for 2500 rpm and let her run.

For that cam to live, you need 30 minutes, smooth and cool.

Until the cam breakin is completed, just don't worry about tuning. Advance till she sounds good and let her run.

Once your cam breaking is done, let her cool, then refire and worry about fine tuning.





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