I've installed a 305 engine from a 1986 El Camino into my 53 chevy 210 coupe. I am using the stock HEI type distributor but I cannot locate a vaccuum advance port. Is there one? Is it electronically controlled by the mysterious wire loom that I see hanging from the passenger side of the distibutor base? What are those wires for anyway? Also, the instructions for my replacement Edelbrock carburator asks to determine if I have a timed vaccuum system and to connect the corresponding vaccuum port on the carburator to the vaccuum advance port on the distributor. How should I set this up? Thanks.
the GM cars got computer controls about 1981, so the distributor you have will not work for you without an engine computer to control the ignition timing. You need to find a 1975-1980 Chevy HEI that has a vacuum can, and does NOT have the 4 wire harness hanging out the side of it.
You also want manifold vacuum for the vacuum advance. Ported vacuum on a SBC will make it heat up idling.
Will any 1975-1980 GM HEI unit work as a replacement for a 305 engine? Or do I need a 305 specific unit?
Mostly any 75-80 Chevy (but not all GM) HEI will work, there were some different advance curves but usually that's not as big a problem as finding one with a good working centrifugal advance unit...the weights and pivot pins tend to wear out, so inspect carefully before buying. Ported vacuum is the same thing as timed vacuum.
You want to pull the vacuum off the carb above the throttle plates off a port that has "NO" vacuum at idle!!! If you pull it off the manifold That'll have the distributor advanced at idle!!When you pull vacuum from the carb above the throttle plates, when you step on the pedal the butterflies open & advance the dist.!! tranny vacuum is the opposite, that you pull off the manifold. jimV
All of the old SBCs that I worked on had to have manifold vacuum. You remove and plug the vac line to set the initial timing. When you plug it back in the timing light would jump up off the scale. That is the way it's supposed to be. (you could also tell if the vac advance was working)
Tommy got it ..... You actually want 25 degrees of advance AT IDLE with the vacuum hooked up to MANIFOLD vacuum...( usually about 10 degrees inital and about 15 in the can)...this will also INCREASE gas mileage while helping the engine to run cool .....I think C9 did a BIG write-up about this ...check the archives.... Jersey Skip
I did, but it got lost somewhere along the line. I can post it again if you like as well as add some comparative test info between manifold and ported vacuum that I've done since then.
I have to disagree with ya, You set your timing at a idle at 8o(?) BTDC , with the vacuum advanced hooked up above the throttle plates when you step on the gas pedal the butterflies open , draw vacuum & advance the spark!!!!when your moving faster the centrifical advance takes over.The vac advance is just to get it going.( quick advance) If the timing is set with the vac at full advance at a idle when you stepped on the gas the vac. would fall off after awhile & retard the timing.If you set the timing with the vac advanced advanced why would you need it!!! jimV
Bone stock with no modifications on my 350 the vacuum advance is connected to the front of the carb, its a quadrajet does that make a difference? its around a 1975 or so my transmission vacuum is connected to the manifold between the distributor and carb, brake booster is connected to the rear base of the carb
Search the Tech archives. Enjenjo is right, C9 is right. The post you are looking for is by burndup. My browser isnt letting me link?
I just posted the timing article. Titled, "A reprise on 'Got Time'." Hope it lasts longer than the usual two hours....
You need vacuum advance at idle. At high RPM, you don't need much advance, Jacob's makes a high RPM advance retard box. On drag cars, I have used vacuum advance, and installed a lock out switch so the vacuum advance won't work in high gear. It's good for nearly a tenth in the quarter.
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