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Discussion Starter #1
I no longer worry about horsepower but do worry about a clean running engine and good fuel economy. Yes I know 540 blown cubic inches and gas mileage do not belong in the same sentence but I am looking for 18 mpg or so and believe I can eventually get it and I don’t mean just highway mileage. I mean in town with combined driving.
The first thing I did was read everything I could find about vacuum advance. Everything I read said it was a good thing and even dedicated race cars could benefit from in. ALL car idle at some time and it does nothing but improve idle quality. Yes it does increase emissions but I wanted the clean idling motor. One with a 270 @ .050 cam and still idle all day long without loading plugs.
VACUUM ADVANCE seemed to make a big difference in gas mileage, clean idle and taming the big cam.
I run 4 MSD boxes so I naturely bought a MSD billet distributor. But I was running a Mallory and my wiring harness only fit the Mallory so I took the MSD back and bought the Mallory, the billet Mallory with the vacuum advance.
I installed the distributor, set the initial timing at 24 degrees, I have a 20 degree electronic retart for starting. Had to also take the distributor apart and lock the timing curve so I got NO timing out of the distributor. I set the electronic timing curve at 12 degrees all in by about 2800. The nice thing is I can just turn a dial and get any advance curve I want.
I set mine at 12 so with 24 intial I have 38 degrees.
I then hooked up the vacuum line to manifold vacuum and went to 60 plus. Way way too much.
Out came the distributor and after a couple of hours of machining and fabrication I put the distributor back together.
I made a stock, a round aluminum stop with a allen 10-32 cap screw down the center, drilled the plate, taped the hole and with loctite installed the stop.
I then machined an aluminum block to bolt on the side of the distributor, drilled the body, taped it for 2 10/32 cap screws, applied expoxy to the back side and installed the block on the main body and filled in the existing wire hole since it was in a bad location and let the epoxy set up. I then installed the long 10/32 screw with locking nut to act against the stop

This is the completed distributor

I installed the distributor so the adjustment for the total vacuum advance is readily accessible so timing could be set while running and the vacuum pot is in a good spot.
I then marked # 1 plug where I wanted it to be and proceeded to install the plug wires.

I also run a voltage surge protector and keep it high up and cooler running. They are necessary for Mallory distributors.
My original Mallory billet distributor has no vacuum advance but it is a great spare parts distributor or replacement in the even of a failure. Takes me only minutes to change .

Click on this link and read this post. It is one on many I read and am convinced vacuum advance it needed
http://www.chevelles.com/forums/showthread.php?t=186680
How did it run?? Fantanstic. Started right up, idled way too fast, turned the idle all the way down and still idles a bit too fast. Lugs down in 5th below 1500 without bucking, runs I believe cooler, sat below 180 with just one fan running in town.
I set total for all 3 timings at 52 degrees.
The other side effect is that my wide band LM1 oxygen sensor has become very stable at idle. It use to bounce around at idle, that would indicate a miss that I couldn’t find. Now it is steady indicating no more miss in a cylinder at idle.
I highly recommend everyone runs a vacuum advance for a cleaner running motor, again not emission wise but a nice idle, better gas mileage and a cooler running motor.
Read my link and see how with 38 degrees you are still running a retarted ignition as cruising speeds.
I am not looking for advice just telling you what I believe and what it felt like to me.
 

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Discussion Starter #2
Guys I grabbed this from Lar's on Corvette forum. It is worth reading. I already had his paper.

JohnZ and I been advocating the same thing for quite a while. I have a couple of papers on vacuum advance and timing available to Forum members that deals with a lot of the topics adressed above. E-mail me for copies:
[email protected]
Lars
 

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Over the years I have never had much money to do with distributors other than see they were working right, and so have noticed that hooking up vacuum advance at idle is the way to go, smoothed out the engine completely,and with proper curves and initial, ran much better than those stock messed up systems constantly dicking around with the vacuum advance at various speeds/temps/whatevers....

over the years I have found the more that EPA stuff was tossed, the carbs set for the way they were in say '67 or '65 or so, the better off things were, in spite of the unleaded foisted on us....

then there is FI, and I never go back, it's in the chips man....

:cheers:
 

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Discussion Starter #5
Four MSD boxes? What's the story there?
I need the MSD -6AL for the main igniton.
I need the Boost retart for the blower. Boost comes up spark retarts.
I run a computerized timing curve, I found the mechanical wieghts flying out were not consistent enough. If you run light springs for a quick curve when the car returns to idle the weights don't always return so your idle timing is NOT consistent. An electronic curve is always right on.
Finally I have a timing control that allows me to add or subtract timing while driving down the road. If I notice the slightest pinging I can back off the timing a degree or two or up to 15 degrees on the fly. Likewise if cruising for a long time I can add up to 15 degrees from a turn of a knob.
That makes 4 units all biggy backed into each other.
 
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