Re: Want to convert L72 from ported to full time Advance
'68 OE L-71 with ported vacuum advance has a 15" 201 15 VAC. This will not pass the Two-Inch rule when you convert to full time. Typical L-78/72/71 idle behavior is 14" @ 900 with full time vacuum advance, and about 25 degrees total idle spark advance, so a 12" B26 is right on the money.
What are are your engine's OE centrifugal advance specs. Check your CSM and AMA specs and post? Has it been modified from OE?
What about the camshaft. Is it OE or bubba? You can get an idea by checking idle vacuum at 900. It should be at least 13" even with the ported vacuum advance and OE initial timing. If it's a lot less you have a bubba cam and need a different VAC.
I can't say how many times someone has posted a question about setting up an OE engine spark advance, then ten posts later we find out the engine isn't anywhere near OE, and the biggest violation is usually a bubba cam with so much overlap that the engine won't idle anywhere near like OE and needs a completely different spark advance map setup than a real OE engine to run even half decent.
Duke
'68 OE L-71 with ported vacuum advance has a 15" 201 15 VAC. This will not pass the Two-Inch rule when you convert to full time. Typical L-78/72/71 idle behavior is 14" @ 900 with full time vacuum advance, and about 25 degrees total idle spark advance, so a 12" B26 is right on the money.
What are are your engine's OE centrifugal advance specs. Check your CSM and AMA specs and post? Has it been modified from OE?
What about the camshaft. Is it OE or bubba? You can get an idea by checking idle vacuum at 900. It should be at least 13" even with the ported vacuum advance and OE initial timing. If it's a lot less you have a bubba cam and need a different VAC.
I can't say how many times someone has posted a question about setting up an OE engine spark advance, then ten posts later we find out the engine isn't anywhere near OE, and the biggest violation is usually a bubba cam with so much overlap that the engine won't idle anywhere near like OE and needs a completely different spark advance map setup than a real OE engine to run even half decent.
Duke
Comment