HICKL Posted July 25, 2003 Share Posted July 25, 2003 Hei distributer, vacuum advance un-hooked, how much mechanical advance should I get from idle to 2500-3000 rpm. I have done much reading but get inconsistant or confusing answers. Maybe I'm not smart enough to ask the right questions. Thanks Jeff Quote Link to comment Share on other sites More sharing options...
Guest billy383Z Posted July 25, 2003 Share Posted July 25, 2003 Generally, ALL of your mechanical advance should be in by about 2200 rpm according to all of the Chevy high performance books I have ever read. I have an HEI in my 383 stroker, and all of the mechanical advance is in by about 2000rpm. I have the Mr.Gasket HEI curve kit in mine, and used the heaviest springs in the package and have had really good results. Quote Link to comment Share on other sites More sharing options...
HICKL Posted July 25, 2003 Author Share Posted July 25, 2003 Ya, I'm with you on that, but how much mechanical advance should the stock HEI give me. 5 degrees, 10 degrees, 15 degrees...etc. Quote Link to comment Share on other sites More sharing options...
Guest billy383Z Posted July 25, 2003 Share Posted July 25, 2003 According to my How to Hotrod Your Small Block Chevy book, for street use your ignition curve for street use, you should have a total of 9º (ditributor degrees, not crankshaft degrees) mechanical advance, all in by 1500 rpm. This sounds like a little bit low rpm to me. I put the heavy springs from the curve kit in mine, so my advance is probably in around 2000 rpm. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted July 26, 2003 Share Posted July 26, 2003 DELETE Quote Link to comment Share on other sites More sharing options...
Guest billy383Z Posted July 26, 2003 Share Posted July 26, 2003 If Spiirit is correct in guessing that you are trying ot lock out the vacuum advance and go strictly with the mechanical advance, you would not want to set the mechanical advance at 34º...your TOTAL advance should be in the neighborhood of 34-38º. Depending on your cam/compression ratio/octane rating of your fuel, your inital advance should be somewhere around 8 to 12º BTDC, with the remainder taken up by the mechanical advance. This should be somewhere around 9 to 11º at the distributor (or 18 to 22º measured at the crankshaft). Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted July 26, 2003 Share Posted July 26, 2003 DELETE Quote Link to comment Share on other sites More sharing options...
HICKL Posted July 26, 2003 Author Share Posted July 26, 2003 Thanks guys, I'm only un plugging the the vacuum advance for test purposes. My motor is running porely at high rpm's and when I checked my timing at the crank with a timing lite, it only advances about 8 degrees when the mechanical advance is fully kicked in. So, my base is 10 and it only goes to 18 at 3000 rpm or whatever. From what I have read online, it should have more mechanical advance than that. Just chasing wild geese here. Jeff Quote Link to comment Share on other sites More sharing options...
Guest billy383Z Posted July 26, 2003 Share Posted July 26, 2003 Thanks for the welcome, Spiirit. And, you would be absolutely correct in not making assumptions- that usually leads to trouble! And to Hickl, Yeah you may or may not need more mechanical advance-what is your total advance at 3000 rpm when the vacuum advance is hooked up? Initial advance+mechanical advance+vacuum advance should add up to somewhere between 34 to 38º at the crank, depending on those 3 factors I mentioned in a previous post. If your initial is 10º and your mechanical is 8º, you may not be too far off the mark because most vacuum advance units will provide from 15 to 18º of advance. If your doesn't, look in either the Jeg's or Summit Racing catalogs and order your self an adjustable vacuum advance unit made by Accel (the spark pug wire people). This unit has an adjustable stop to limit the travel to whatever you need, and also the vacuum diaphragm is also adjustable to regulate how fast the timing advances. Nice unit-works great in my car. Quote Link to comment Share on other sites More sharing options...
HICKL Posted July 26, 2003 Author Share Posted July 26, 2003 I think I only have about 24 degrees total advance. around 18 with the vacuum and about 6 to 8 more when mechanical kicks in. Of course my started crapped out last night when I was trying to check all this out so I didn't get very far. Will pick up were I left off today when I get off work if the wife will let me Thanks for ya'lls input. Quote Link to comment Share on other sites More sharing options...
Guest billy383Z Posted July 26, 2003 Share Posted July 26, 2003 Hickl, what kind of car did your 350 engine come out of originally? Not all HEI vacuum advance units from Chevy were created equal. If your engine came out of Granpa's '78 Caprice wagon, it's not the same advance unit that came in the Corvettes. This is something you might want to look into. Have you put a distributor re-curve kit in your HEI? The stock weights and springs also limit the amount of advance that you can get in your distributor. The re-curve kit (weights and springs) should cost around $10 or so, but I haven't priced them lately. I built my 383 engine about 6 years ago, so I'm not sure what they cost now. Also, I'm not sure what your max rpm is, but the stock ignition module and coil in an HEI is only good to about 5000 before they start running out of spark. I have a hig performance coil and ignition module, the Mr.Gasket re-curve kit and the Accel adj. vacuum module in my distributor, and can run my engine up to about 6000rpm (the heads and the cam are what limit my rpm). My car is a daily driver, by the way, not a race car or Saturday Night Special. Quote Link to comment Share on other sites More sharing options...
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