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Old 01-06-2018, 10:09 PM   #1
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Location: Winslow, Az
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82 Chevy SWB 355 timing issues!!!

I'm having timing issues I'm thinking it's to do with vacuum advance but it could be the distributor too was kinda cheap and thinking it was a mistake but it does have an adjustable vacuum advance so I'll tell you what I'm working with and let you guys decide.
I'm trying to tune a 355 SBC simple right well I'm struggling I know my way around a stock build this is my first performance build 26 years young so I got alot to learn and I'm learning the hard way performance doesn't tune like a stocker.
I ripped a 350 out of an 1982 RV it was a 4 bolt main, had a blown head gasket and a pitted cylinder so I took it straight to machine shop said he could sleeve it and said he could square it with a .030 bore job so I did the machine work and had the bore match my 12cc dish valve relief piston and had it decked to the .025 in the hole it was close already to that (keeping pump gas in mind) I'm running the stock crank he polished it up for me said it was a desired crankshaft to have (if someone could tell me why I'd like the info don't have any numbers off of it but maybe I should) running the stock rods as well had the surfaces reconditioned. Plasti-guaged as i installed to stock clearances. I'm running a comp roller cam setup @ .050 lift intake duration 235 exaust duration 249. intake lift is .522 exaust lift .509 on a 107 love see running the "kit" so everything is comp. I topped the valve train with a set of Dart Aluminum heads 64cc chambers and 180cc intake runners and a 75cc exaust 2.02 intake valves 1.60 exaust valves. On top of that is a Holley strip Dominator single plane intake and stacked on that is a 4160 vac sec Holley 750 CFM carb. 73pri/75sec jets 2.5 power valve (produces about 5.5-6hg vacuum) the distributor I'm running is an assualt racing 65k coil HEI w/adjustable vacuum advance I got a cheap Mr gasket mechanical curve kit with on soft and one med spring = about 18 seems to like it there but maybe that's where I'm wrong I've bench set my carb so that the plates are correct in the idle circuit is working properly but when I hook up my vacuum advance to "ported" (no vac at idle I checked) and soon as I start to accelerate timing jumps to some where in the 40s and my cherry bombs start sounding like the are launching artillery shells I know tuning over the web is almost impossible but hoping someone can tell me where I went wrong. Do I need an MSD box or can I make my setup work as is or do I need to change somethings up?
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Old 01-07-2018, 12:16 AM   #2
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Re: 82 Chevy SWB 355 timing issues!!!

sounds like you started with the new weights & springs so now you didn't get a baseline & your engine don't like that much advance. Try this- put some stiffer springs or heavier weights in the mechanical advance 1st, then if it still pops you may have to mechanically limit the vacuum advance either by adjustment or stopping or limit the module plate from moving.
It COULD be a bad distributor so throw a stock HEI in there & see how it runs. Heck go drive it without the vacuum hooked up before you deal with the weights & springs & see how it does just so you know.
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Old 01-07-2018, 04:49 AM   #3
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Re: 82 Chevy SWB 355 timing issues!!!

I have been driving without it hooked up drives great at wide open a little slow on the take off and I get a pretty good jerk late like my secondarys are opening up a little late (could be a fuel issue I'm running a stock pump but seems to do alright with keeping fuel in the bowls in the driveway my friend has one on his 383 does fine). I have a stock HEI laying around that came off it originally I could try. Got a full assortment of jets, pump cams, and secondary springs to play with my carb but want to get my timing dialed in first. I'll be back to it tomorrow spent most the day replacing the heater core that filled my ducts up with antifreeze was quite the mess but got to clean,seal and repair it right. Would the low manifold vacuum affect the vac advance? Or vacuum secondarys? I know it had a dramatic affect on my brakes.
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Old 01-07-2018, 08:30 AM   #4
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Re: 82 Chevy SWB 355 timing issues!!!

Low vacuum will play with the vacuum advance. Check the docs on that aftermarket unit to see when it comes in and how much. Also, check what you are adjusting with the adjustment screw. The Accell unit I have comes in, IIRC, at 11". The adjustment changes how much advance, but not when it comes in.

Might check what the vacuum secondaries are expecting for vacuum.
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Old 01-07-2018, 10:48 AM   #5
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Location: Bowser
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Re: 82 Chevy SWB 355 timing issues!!!

Here’s a link on setting your timing.

I had a similar built motor to yours and lived at higher elevation like you do.
My motor ran best with 22 initial, 12 in the mechanical and 10 from vac advance. Had 12 hg of vacuum. I ran a modded Hei.
At higher elevation you need to start the fire way earlier, hence the much higher initial. You also need to run your carb slightly leaner. And your tranny gear ratios or torque converter stall are somewhat critical.
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distributor, sbc, timing, timing adjustment

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