Q: HEI Upgrade
Thanks for all the input. What I’ve read is that the increased efficiency of electronic ignition will enable the end gases to burn normally, rather than contribute to knock. It seems to me that to reduce knock, I’d have to replace the coil and wires, and regap the plugs, along with replacing the points and/or the whole distributor. Can anyone confirm that knock was reduced/eliminated by installing HEI, or am I setting myself up for disappointment?
A: Installing an HEI is unlikely to reduce/eliminate a knock problem other than by coincedence.The advance curve(s) are what will make the difference.If the HEI you install happens to have a minimal amount of centrifugal advance and/or a vacuum advance unit with a stiffer spring than the original unit then knocking will be reduced. Also the vacuum advance units have differing amounts (in degrees) of advance.
If your only complaint with your points distributor is the knocking problem then you may want to check its advance operation and correct/modify as required.It is not difficult to do but requires some amount of know-how and a few tools such as a accurate tachometer and a timing light (dial-back type) and a dwell meter.For starters make sure the dwell is set correctly and the initial timing is set to spec.Then with the engine warm increase the engine speed while watching the timing mark,when it stops moving as the engine speed increases further dial back the timing light (obviously you will find it easier if a friend works the throttle while you watch and manipulate the timing light) until the mark lines up with the TDC mark on the timing cover.Now read the dial (or display if you are using a digital) on the timing light,this is your TOTAL mechanical (or centrifugal) advance.It should be around 30-36 degrees.
At this point (if the numbers are O.K.) you might try disconnecting (and plugging) the vacuum advance hose,then drive the car and see if the pinging is gone.Be sure and try both hard full blast runs as well as light throttle/lower rpm/higher load situations.If the car works O.K. then you may concentrate your efforts on the vacuum advance.There are a number of ways to go about this including:replace with different unit with less advance and/or stiffer spring,replace with adjustable aftermarket unit or modify your existing unit.By the way,most units have the amount (in degrees) of advance stamped on them (usually 10,15, or 20).You could of course,leave it disconnected but fuel economy and throttle response will suffer.Sorry I’ve been so long-winded about this, of course there are other things to consider like engine temp,combustion chamber deposits,fuel/air mixture.I hope this helps,feel free to email me privately if you have any questions.I don’t have all the answers but I may be able to help.
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Content last modified: January 16, 2014 at 2:30 pm