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Old 12-16-2011, 04:06 AM
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Total advance showing 60-70 deg, what is it really?

Build: 305 stock bottom end, crower 00980 supercharger cam, procomp 210 heads 2.05/1.65 70cc (not positive on that exhaust valve), .064 copper head gaskets, 7.8-8.0 CR, true flat top pistons (no valve reliefs at all), weiand 144 blower with pulleys calculated for around 7 psi boost although with the bigger heads it's probably less (my gauge just came in so I'll have exact numbers tomorrow), Holley 780 DP no power valve jetted way up ( I think 84), Accel HEI dizzy unmodded dropped in vac advance hooked up to partial on carb, 3500 stall, th350, 3.73 rear in a 1951 dodge pickup.

Issue: First of all the thing absolutely rips!!! It's awesome, seems faster every time I drive it, but according to my timing light/ balancer tab I'm running 40 degrees initial and like 70 degrees total after i time it by ear. I know this isn't right and I know I should limit the mechanical advance and I know too much advance is a nightmare for a blower but it seems to want the more the better. Right now I have a very slight amount of starter kick back, where do you guys think that puts my initial timing really at? After knowing that how much should I limit the mech advance?

Any other comments on the build are welcome, I'm not sensitive. It was sold to me as a 350, during the build I learned otherwise but I have no regrets, more boost from the same pulleys, and this thing revs!!

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Old 12-16-2011, 05:27 AM
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Sounds like you have the wrong harmonic balance and/or timing tab on it.
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Old 12-16-2011, 06:01 AM
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Quote:
Originally Posted by poncho62
Sounds like you have the wrong harmonic balance and/or timing tab on it.
I think you're right, it's what it came with. The tab is correct i believe because it's at 12o'clock, but the balancer must be wrong.

Any way to closely figure initial?
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Old 12-16-2011, 06:04 AM
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You can put the engine at top dead center on #1 cylinder and remark your balancer. Easier to do with the tab that sits at the 2 oclock position.
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Old 12-16-2011, 06:29 AM
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Quote:
Originally Posted by poncho62
You can put the engine at top dead center on #1 cylinder and remark your balancer. Easier to do with the tab that sits at the 2 oclock position.
Come to think of it, I did that during the cam install. It was spot on, or at least real close? This is even wierder now that I think of that.

Any other ideas?
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Old 12-16-2011, 08:09 AM
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You need to get a handle on the correct timing ASAP- the engine you save may be your own!

The following is from another post I made on this:

Quote:
There are several different dampers and timing tabs. Both the diameter, thickness and the placement of the line on the outer ring of the damper can differ, as well as how the timing tab is positioned. So you need to know what damper you have, to know what tab to use.

The three most common locations for the timing mark on the damper:

The exact years of the type of damper timing marks overlap one another, depending on the exact application.

The pre-'69 damper has the TDC line on the outer ring at the 2:30 o’clock position- or 2º before- (i.e. to the LEFT of the keyway, looking at the front of the engine) the keyway centerline. The keyway is seen in the ID of the damper.

The damper used from '69 to about ‘84 has the TDC line at the 2 o’clock position- or 10º before the keyway. You'll find that aftermarket dampers are the 10º type, as are the bolt-on tabs sold in the aftermarket, unless they're adjustable.

A third timing mark was used from about 1978 to about 1995. It is at the 12 o’clock position- or 40º before the keyway. This damper uses a timing cover that has the tab welded on at about the 12 o'clock position. Professional Products lists the years for this type damper line as being ‘84-’95 and is a 6-3/4” diameter damper.

If you're unsure, or just want to check the accuracy of the tab/mark for TDC, DETERMINE TDC and MAKE A TIMING TAPE will help you to see for yourself.
It is good to hear how much you're enjoying the engine, though. But seriously- get the timing under control now, not later. One mistake can and will cost you big-time.

Good luck.
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Old 12-17-2011, 08:43 PM
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ok, so I made a timing tape today. Sure enough, I was at 38 initial and 60 total!! I ditched the vacuum advance (ported) and twisted back to 17 initial and 34 total with no vacuum because these numbers are almost by the book. The test drive definatly lacked a little of the previous low end power and after letting first gear ride for a bit I had a nasty backfire through the carb and it stalled the truck. Then the truck started and idled fine but stuttered home as if it was out of gas (91 octane by the way)?

I also installed my vacuum/boost gauge I have 10hg at idle 20hg cruising and 6psi boost at 3500 rpm (which I was pleased with). Normal driving and slightly aggressive driving were similar to before. Any suggestions for adjustments tomorrow would be appreciated.
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Old 12-17-2011, 08:59 PM
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You definitely have a low static CR, and actually I'm surprised the 2.05" intakes fit the 305 bore. But in any event, this combo seems like it wants a lot of timing. Just watch out for detonation! One bad case and those stock pistons will fail. Why they haven't already is a testament to just how low the static cr really is.

FWIW, using a stock 305 bore and stroke, piston down the hole 0.025", a 12cc dished piston (common to many 305's, they also had true FT IIRC in some engines) and a 0.041" head gasket along w/a 70cc chamber, the SCR is barely 7.5:1. Likely this is what has saved you from detonation, but the wide quench takes some of that leeway back from you- w/o good turbulence/quench, the detonation potential increases.

You might do best just locking the timing at as much as you can use w/o detonation under boost.
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Old 12-17-2011, 09:23 PM
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The .064 copper head gaskets are 4.2" bore, that's what gives those 2.05's the clearance. They are definitely true flat tops. So the low compression allows me more timing? Cool, thanks man! I've got a 120 gallon fuel pump coming next week, anyone think that's why the engine stumbled on me after running it WOT for a while?
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Old 12-18-2011, 05:11 AM
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Quote:
Originally Posted by hogan23
The .064 copper head gaskets are 4.2" bore, that's what gives those 2.05's the clearance. They are definitely true flat tops. So the low compression allows me more timing? Cool, thanks man! I've got a 120 gallon fuel pump coming next week, anyone think that's why the engine stumbled on me after running it WOT for a while?
That head gasket and piston combo puts the SCR around 7.6:1, w/all else being as I stated above.

The amount of timing isn't just related to the SCR, the amount of boost will define the total timing before detonation just as much, if not more, than the SCR. Do you know what the boost is? You can get an idea by the pulley ratio if you don't have a gauge.

The stumbling could be ignition, carb tuning, fuel pressure/volume (you do not want excessive fuel pressure- you'll likely need a pressure regulator to keep it to around 5psi at WOT) or even the ground electrodes being burned off the plugs- so sort out the timing before any more WOT blasts. A BTM would be a wise investment for any blown application, IMO. It will allow more timing off boost and less timing as the boost increases.
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Old 12-18-2011, 11:20 AM
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I did just put a boost gauge in, I'm getting 6psi at around 3500 rpms. I'm definately laying off the WOT pulls (but they are so fun), I'm gonna go add the vacuum advance back but turn it down to around 5. Was I right to build this engine as low compression as I did? I thought for the 6-8 psi boost on pump gas I needed to. I've done ALOT of reading but this is my first full build.
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Old 12-18-2011, 08:13 PM
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What type of ignition system are you using ? I have seen a 2 wire magnetic pickup distributor with the wires crossed going to a msd ignition system . the car would run pretty good timed by ear but the timing was way off using a timing light and it was difficult to get a steady reading .
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Old 12-18-2011, 09:30 PM
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Quote:
Originally Posted by smokin63
What type of ignition system are you using ? I have seen a 2 wire magnetic pickup distributor with the wires crossed going to a msd ignition system . the car would run pretty good timed by ear but the timing was way off using a timing light and it was difficult to get a steady reading .
Accel HEI, no 6al or anything. I plugged the vacuum advance back in and it runs very good. Still lacks a little from what it was off the line, but I think I'll bump it up a little more tomorrow. I think you guys are right, with the compression as low as I made it, I can get away with more than normal advance.
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