Info. on HEI set-up
07-26-2010, 02:07 PM
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Car: 89 GTA, 80 Chevette
Engine: 350 TPI, 358 Carb
Transmission: 700R4, TH350
Axle/Gears: 9 Bolt, 8.8 with 3.73
Info. on HEI set-up
Well this is my first post but I just want to try to help some people out that are having trouble or don't understand how to set-up a HEI distributor. I don't have one on my trans am but this is how I set up the junk summit distributor on my chevette.
When I first got my distributor, a Summit brand, the instructions said it was capable of 10° of mechanical advance and 10° of vacuum advance. Well, I thought this supposed to be a performance blueprinted unit. Nothing but junk if you ask me. After I got it installed in my Chevette, Yes a Chevette, I checked it with a light. Yes, with the curve on the center plate, this unit only has about 10-12° mechanical advance. The vacuum advance is capable of 20°, not 10° as the instructions state. Yes, it is an adjustable can, but this only adjusts the amount of vacuum it takes to start pulling in the advance, not the amount of advance.
To set up the mechanical advance so you will actually get 20 or more degrees of advance, go by a cheap Mr. Gasket re-curve kit from Autozone. But throw away the center plate and weights. This set along with many others are junk and will also only give you about 10/14° advance. The weights in these kits are to light and require very light springs to make them work. The only thing good in these kits are the springs. With light weights what you will find is you have to use very lights springs to get the advance all in by 2500 RPM, then you end up with timing that bounces all over at idle and also over time if the weights get sticky there will not be enough spring tension to pull them back in and they will stick all the time. I found out from others the best combo is #375 center plate and #41 weights from a late 70’s to early 80’s truck or suburban. This set up along with some medium springs brought me to 22° advance. My Cam as 242° duration and idles happy at 900 RPM. The timing does not bounce around at all with this set-up. So with the base timing set at 14° BTDC I have 36° Total.
Now to set up the vacuum advance which every car should run. All cans, adjustable or not adjustable, are set to give about 20° of advance. This would put your cruise timing up to about 56° or so. This would more than likely cause detonation problems. Advance must be limited to about 10° which can not be done with the screw inside. You need to remove the can from the distributor body and just find a piece of thin metal, I used 14 gauge, cut it to fit on the cans bracket that bolts to the distributor. What you want is to close up the slot so the rod will bottom out sooner and limit the advance. About .088 rod movement = 8° advance, .110 = 10° advance. A vacuum pump is nice to check the movement with. Now to adjust the rate at which it comes in. First off you will have this hooked to manifold vacuum so you want all the advance in under your manifold vacuum at idle. My engine idles about 12” of vacuum so I have my can set to start in about 4” and is all in by 8” of vacuum. If you don’t do this you will have timing that is once again all over at idle, and you will be fighting trying to keep the idle set. I checked 2 stock cans I had around and they also would work perfect, just limit the amount of advance in them.
Before when I was using the distributor as it came from Summit, my initial was at 16° and with 10° advance that gave me 26° total. Vacuum advance was giving me about 10 at idle only because I had the screw backed all the way out. My Chevette ran about 205° cruising down the road. The throttle response also sucked. After all this my throttle response is awesome, but best of all my temps went from 205 to 190 when cruising. Idling I am always at 180°. Hope all this will help somebody.
When I first got my distributor, a Summit brand, the instructions said it was capable of 10° of mechanical advance and 10° of vacuum advance. Well, I thought this supposed to be a performance blueprinted unit. Nothing but junk if you ask me. After I got it installed in my Chevette, Yes a Chevette, I checked it with a light. Yes, with the curve on the center plate, this unit only has about 10-12° mechanical advance. The vacuum advance is capable of 20°, not 10° as the instructions state. Yes, it is an adjustable can, but this only adjusts the amount of vacuum it takes to start pulling in the advance, not the amount of advance.
To set up the mechanical advance so you will actually get 20 or more degrees of advance, go by a cheap Mr. Gasket re-curve kit from Autozone. But throw away the center plate and weights. This set along with many others are junk and will also only give you about 10/14° advance. The weights in these kits are to light and require very light springs to make them work. The only thing good in these kits are the springs. With light weights what you will find is you have to use very lights springs to get the advance all in by 2500 RPM, then you end up with timing that bounces all over at idle and also over time if the weights get sticky there will not be enough spring tension to pull them back in and they will stick all the time. I found out from others the best combo is #375 center plate and #41 weights from a late 70’s to early 80’s truck or suburban. This set up along with some medium springs brought me to 22° advance. My Cam as 242° duration and idles happy at 900 RPM. The timing does not bounce around at all with this set-up. So with the base timing set at 14° BTDC I have 36° Total.
Now to set up the vacuum advance which every car should run. All cans, adjustable or not adjustable, are set to give about 20° of advance. This would put your cruise timing up to about 56° or so. This would more than likely cause detonation problems. Advance must be limited to about 10° which can not be done with the screw inside. You need to remove the can from the distributor body and just find a piece of thin metal, I used 14 gauge, cut it to fit on the cans bracket that bolts to the distributor. What you want is to close up the slot so the rod will bottom out sooner and limit the advance. About .088 rod movement = 8° advance, .110 = 10° advance. A vacuum pump is nice to check the movement with. Now to adjust the rate at which it comes in. First off you will have this hooked to manifold vacuum so you want all the advance in under your manifold vacuum at idle. My engine idles about 12” of vacuum so I have my can set to start in about 4” and is all in by 8” of vacuum. If you don’t do this you will have timing that is once again all over at idle, and you will be fighting trying to keep the idle set. I checked 2 stock cans I had around and they also would work perfect, just limit the amount of advance in them.
Before when I was using the distributor as it came from Summit, my initial was at 16° and with 10° advance that gave me 26° total. Vacuum advance was giving me about 10 at idle only because I had the screw backed all the way out. My Chevette ran about 205° cruising down the road. The throttle response also sucked. After all this my throttle response is awesome, but best of all my temps went from 205 to 190 when cruising. Idling I am always at 180°. Hope all this will help somebody.
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