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Old 04/18/2007, 08:46 PM   #11
miller511
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Location: Livermore, CA
Joined: Feb 04
Posts: 552

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Quote:
Originally Posted by robert campbell View Post
Hello,
This is a subject right up my alley. I tune and assist people in starting new engines in the Seattle area.

Jeff,
A couple questions and then some thoughts.

I assume it starts hard when it is cold.
I assume you used the distributor from the 302.
What year was the 302 or better yet what year is the distributor?
I assume you have a vacuum advance on the distributor.

I do not think it is a starter problem, but it does sound like you need a new starter. Using your starter for anything longer than 10 or 15-second bursts is not advised. Engines, as you want this one to do, should light right off.

With the cam you are running, I assume you are looking for horsepower. I would recommend at least a 650 or 750 carb for this combination. A 600 could work on a 347, but I would cam it more mild and would work in a 5,000 RPM peak or less. This engine could make good torque with a 600-CFM and a milder cam.

I did not see a mention of what heads are on it or its estimated compression ratio.

Lets talk timing. A stock distributor works with a stock cam at about 6 degrees before. That is what I call "initial" advance. The centrifugal advance and the vacuum advance add to this number. Regardless of the distributor most 10 to 1 engines work best at 38 degrees to 40 degrees of "total" advance. I would recommend that you put a degree tape on an engine that has this must potential and you are looking for performance. You may have a "fluid" damper or a similar performance damper that already is 360 degreed.

So I want you to get it started and hold the rpm up to about 2,500 to 3,000. This will ensure that you have all of the centrifugal in and with no load the entire vacuum in. Ensure if you have vacuum advance that the hose to the carb is plugged in. You want to see what the "total” advance is. If it is not 38 to 40 degrees before then you need to increase the initial. Hopefully you are not using a smog distributor with 2 vacuum diaphragms. Get rid of that thing. Very common in 1968 or 69.

Now it gets more complex. I would assume that if you have a single diaphragm distributor from the 67 and older or non-California car, you should see 38 degrees of total advance.

You motor will more than likely run much better with more "initial" advance. Somewhere near 12 to 15 degrees before. If you dial that in it will have way too much "total" advance and ping like hell. So for your motor I would recommend either a MSD or Mallory distributor with "adjustable" centrifugal advance. I would shorten up the "centrifugal" amount of advance so you can run more "initial" advance. Whew!!! Following all that. The goal is enough initial advance to make the motor happy at idle with enough total to make HP!!! But we have flat spots and crab adjustments to talk about.

I agree with David, you may want to seek his professional tuner. The advice on spark plug gap with a stock coil is spot on. Do not open the gap with a stock coil.

You did not say what tranny you have. Auto get vacuum secondary. Manual you can use mechanical. The 4779 holley would be perfect for this cam and engine if you have performance heads, 10 to 1 or more and short gears (3:50 or lower) and are looking to go fast. I am unsure what you what you want to do. Go fast or mild motor. With a 347, I think you want to go fast.

Remember... " There is more to life than gas mileage"

Give me all the info on you cars components and whether burying pukes driving Chevy's is your goal!!!

Rob

Holy cow Rob!!!

OK. Here goes-

Heads are Edelbrock Performer RPM w/60cc chambers
Compression ratio is 10.47:1
Distributor is vacuum advance and I believe is original 1968 vintage, but not completely sure. It does have two vacuum ports, although the one closest to the distributor body has always been capped off.
Damper is not 360 degree marked or fluid. it is marked zero to 40 degrees.
Rear end gears are 2.79
Tranny is auto C-4

So, it's sounding like the 600cfm carb simply isn't getting enough fuel to the engine?
What about my newer stock mechanical fuel pump? Could it be not pumping enough fuel? It worked fine on the 302.

And the second issue is a distributor that I should upgrade to one with adjustable cetrifugal springs?

Thanks for your help, Jeff

Jeff Miller-
1968 Tahoe Turquoise GT/CS
2007 Black GT/CS Coupe
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