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Top Dead Center? (TDC)

Old Nov 22, 2008 | 03:40 PM
  #1  
Confuzed1's Avatar
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From: GO PACK GO
Car: 83Z28 HO
Engine: Magnacharged Dart Little M 408
Transmission: G Force 5 speed
Axle/Gears: Moser 9" w/Detroit Trutrac
Top Dead Center? (TDC)

Let's suppose someone didn't use a piston stop or any other means to determine TDC when he built an engine .....let's say that person just "eyeballed it" by setting it as close to number 1 piston at TDC as they could determine and bolted the timing tab up so the balancer read that it was TDC. How many degrees could it theoretically be off either way?? Plus or minus 2.10 or what?

How much movement do you really have in the crank before the piston actually starts to move one way or another? In case you haven't figured it out, that person is me! lol. You see, my engine seems to run on the hot side with my timing set at approx. 14 degrees advanced....and I have a hard time believing it needs more since this isn't a huge duration cam it seems to me....224/236 @ .050 with a 113 LSA....or should I give it as much as it'll take at idle then back off??

EDITL My cooling system seems fine, full of anifreeze, fan runs. I even have a Griffin aluminum rad in it. But it runs at almost 220 degrees and the fan never shuts off....it even boils over a tiny bit when I shut it down....and that's at 45 degrees outside!

Last edited by Confuzed1; Nov 22, 2008 at 03:43 PM.
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Old Nov 22, 2008 | 04:52 PM
  #2  
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From: Northern Utah
Car: seeking '90.5-'92 'bird hardtop
Engine: several
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Axle/Gears: none
Re: Top Dead Center? (TDC)

Okay, try backing off initial. Stock for most SBC is 0 degrees for ESC, and 6 degrees otherwise.
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Old Nov 22, 2008 | 10:19 PM
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Confuzed1's Avatar
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From: GO PACK GO
Car: 83Z28 HO
Engine: Magnacharged Dart Little M 408
Transmission: G Force 5 speed
Axle/Gears: Moser 9" w/Detroit Trutrac
Re: Top Dead Center? (TDC)

Originally Posted by Atilla the Fun
Okay, try backing off initial. Stock for most SBC is 0 degrees for ESC, and 6 degrees otherwise.
The only thing that remains stock on the car is the engine block....see sig.
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Old Nov 22, 2008 | 11:02 PM
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From: Mercedes Norte, Heredia, Costa Rica
Car: 1984 Z28 Hardtop
Engine: 383 Carb
Transmission: 4L60
Axle/Gears: 3.54 Dana 44
Re: Top Dead Center? (TDC)

If you only eyeballed it, you could be a good 10 or 15 degrees off in either direction.
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Old Nov 22, 2008 | 11:05 PM
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Car: 1984 Camaro Z28
Engine: L69 305 H.O.
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Axle/Gears: 3.73
Re: Top Dead Center? (TDC)

Why are you sweating 220 ?
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Old Nov 23, 2008 | 09:52 AM
  #6  
Confuzed1's Avatar
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From: GO PACK GO
Car: 83Z28 HO
Engine: Magnacharged Dart Little M 408
Transmission: G Force 5 speed
Axle/Gears: Moser 9" w/Detroit Trutrac
Re: Top Dead Center? (TDC)

Originally Posted by Apeiron
If you only eyeballed it, you could be a good 10 or 15 degrees off in either direction.
Thanks Apeiron, that answers the actual question I was asking. So I could very well only be a few degrees advanced when I indicate 14 degrees before TDC.
Why are you sweating 220 ?
Because that's 220 at idle, at an outside temp of 45 degrees F., and the fan seems incapable of cooling it down further - that's why. Just think of a summer day when it's 90 degrees outside....I doubt it'll stay at 220 then. It would most likely overheat.

From what I've been reading, timing set too far advanced or retarded can cause an engine to run hot, and perform sub-par. So it seems I need to play more with the timing. I have a bushing installed in the distributor which will only allow 16 degrees of mechanical advance. When I set the timing to 14 degrees initial (so I get 30 degrees total mechanical) - it's running hot.

I'm being conservative because it's a boosted car, but since I could be 10-15 degrees off on the balancer, maybe I'll advance it to 34-36 degrees or higher to see if it likes it better. I have noticed I can advance the timing to 40-plus degrees at idle, and I don't hear any pinging.....I don't know a whole lot about timing a car properly, but I do know 10-15 degrees retarded/advanced can make a world of difference in how it runs.

Last edited by Confuzed1; Nov 23, 2008 at 09:55 AM.
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Old Nov 24, 2008 | 04:52 PM
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From: GO PACK GO
Car: 83Z28 HO
Engine: Magnacharged Dart Little M 408
Transmission: G Force 5 speed
Axle/Gears: Moser 9" w/Detroit Trutrac
Re: Top Dead Center? (TDC)

I decided I'll just get a piston stop and get my timing tab set up right on TDC and go from there....thanks!
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