01-08-2021, 05:30 PM | #26 |
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Re: Engine Timing Help
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Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3 |
01-09-2021, 12:16 PM | #27 |
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Re: Engine Timing Help
With the piston stop what method did you use to rotate the engine all the way back around?
With a bar, hand grip on the belt and pulles or something else. |
01-09-2021, 01:23 PM | #28 | |
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Re: Engine Timing Help
Quote:
FYI, I'm now seeing that my issue is probably carb-related and not mechanical/electrical/timing at all. I'll follow up with details when I can be sure of what I'm seeing.
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Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3 |
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01-09-2021, 05:25 PM | #29 | |
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Re: Engine Timing Help
While the cam timing will definitely make a difference in how the engine runs, it has nothing to do with ignition timing. Sure, the distributor is driven buy the cam, but that "link" is just turning it. The ignition timing itself is in relation to the piston. So either can happen independently. The cam could be off and the ignition correct or the reverse where the cam is right and the distributor off. Of course neither is good, but the point being that the cam being off doesn't automatically mean the distributor is off too.
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01-10-2021, 07:49 AM | #30 |
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Re: Engine Timing Help
wait what? we still haven't tried manifold vacuum yet? It costs nothing and is easy peasy.
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01-10-2021, 11:50 AM | #31 | ||
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Re: Engine Timing Help
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An engine with any kind of performance mods should be running with full manifold vacuum to the distributor, but it has to be the right distributor too.
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01-10-2021, 01:14 PM | #32 |
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Re: Engine Timing Help
Hi Al, I’m thinking my engine problems lie elsewhere. I think the question I’m trying to answer is something more like “Why does my engine die when I set base timing to a reasonable range?” All my testing has been done without any vac advance, so introducing it would muddy the waters, no? Easy, but what would it prove if it ran better or worse?
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Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3 |
01-13-2021, 10:14 PM | #33 |
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Re: Engine Timing Help
It was a good weather day here so I got the '68 out on the road and did some tuning and test driving. Having an exhaust makes a big difference when you're listening for pings! Apparently the engine was pinging a lot when I had it at the 40-something advanced timing position, but my exhaust was too loud for me to hear it. Obviously it needed to be retarded quite a bit from there, but it always chugged and died when I got close to 12-10 degBTC. That was my head scratcher...until I realized my curb idle was probably the reason that was happening. It was backed off all the way so that the throttle linkage was bottoming out without touching the screw. I hadn't realized it got that far. I arrived at the position because I was tuning the carb + timing for max vac and max idle speed. Sounds like the instructions I was reading needed a little more detail--needed some boundaries I should stay within.
Runs pretty darn good now, real strong. My timing is advanced somewhere beyond the tab and my gun doesn't allow me to tell for sure where I am, but I get no pings when I'm going uphill under hard acceleration. Problem solved, I think? Can anyone take a stab at explaining why this happens? I understand why it wouldn't run at normal timing, I'm more curious about why it does run with advanced timing.
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Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3 |
01-14-2021, 05:57 PM | #34 | |
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Re: Engine Timing Help
I just saw this thread and I'm very impressed with the detailed troubleshooting you all have done, both in clearly laying out what has been done and all of the thoughtful guidance. It's all stuff I think about and have tried in my own cars and in the engine lab. I'm an engines guy. I just love the internal combustion engine.
One thing I have experienced is that extra timing is great at helping to compensate for other problems. Even though you can run an engine on a bigger carb (and I do that, too), I'm wondering if the carb is having other issues. If it runs too lean it will need extra timing to run best. I may have missed it in the thread, but are you sure the idle mixture, accelerator pump, and main fuel circuits are ok and delivering the right air-fuel ratio? Also at a really low idle speed, all bets are off on how well it's managing the AF. Quote:
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(Very) Slow-Going Build Thread: Stock 1970 Short Step with Stock 1970 LT-1 http://67-72chevytrucks.com/vboard/s...d.php?t=567340 |
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01-14-2021, 07:24 PM | #35 |
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Re: Engine Timing Help
I’m completely unsure! I have followed some YouTube advice on how to initially set up my Holley and I have it running pretty well now, but I’d like to know how to be sure I’ve tuned it well. BTW, I have a QJ ordered and expected to arrive in March, which is about when i can really hit the road again with this pickup, so it’s not critical to get this Holley tuned. That said, I’d like to win this fight and add to my (scant) carb knowledge.
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Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3 |
01-18-2021, 10:22 PM | #36 | |
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Re: Engine Timing Help
I'm in learning mode with my Holley. Mine wouldn't idle very well because of a massive vacuum leak (forgot to connect PCV, as the hose barb was hiding under the carb when I reassembled things after a rebuild).
Then I had an issue with ethanol gas, too much sitting, and corrosion that stopped up my accelerator pump circuits. It's running better now. When I get roadworthy front tires for it and start taking it on longer distances I'd like to do a more systematic tune, like the Hot Rod (Roadkill Garage) guys did in their "Tater Truck" episode. For Holley guys it's a great tutorial on how to properly tune their classic 4bbl. Quote:
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(Very) Slow-Going Build Thread: Stock 1970 Short Step with Stock 1970 LT-1 http://67-72chevytrucks.com/vboard/s...d.php?t=567340 |
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01-25-2021, 08:18 PM | #37 |
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Re: Engine Timing Help
My experience with high performance 327s is probably beyond the scope of this discussion but here goes..
Back in the early '70s during my racing days I ran 327s (bored to 331 - .030 over and 339 - .060 over) exclusively.. 64cc production heads (camel hump).. 2.02 intake valves and 1.70 exhaust valves.. Fully ported and combustion chambers polished to chrome like finish.. Domed pistons that produced > 12.5:1 compression ratio.. 110 octane race gas and 38 -39* total advance timing, all in at 2200 - 2500 RPM.. Turned those little bastards 7800 - 8000 RPM all night long.. I never lost an engine to detonation or preignition... 327s inherently like lots of timing advance... |
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