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Old 03-11-2010, 08:27 PM
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How do I advance timing 25 degrees?

Sbc 5.7 350 bored .40over
Timing needs to be advanced 25 degrees for good power curve I was told with my cam. Timing chain is at TDC, BALANCER is stock, balancer mark is also at zero mark on timing cover. Please help, what should I do when I have a computer controlled HEI?

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Old 03-11-2010, 09:21 PM
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timing

Get an earlier HEI with vacuum advance and no computer hook-up. Buy and HEI curve kit and install it using a light and medium spring. Buy and ACCEL or MSD rotor and cap. and install the distributor.

Measure the diameter of your balancer. Multiply the diameter by .309" . This will give the length between 0 and 36 degrees on your balancer. Borrow a set of vernier or dial calipers. Set the distance on your calipers and scribe a line on your balancer on the right side of your stock 0 groove, using the groove for your guide. Use a marker to hi-lite your scribed line - now you have 36 degrees BTDC. (example: 8" balancer x .309 = 2.472")

Plug the vacuum advance, start the engine with a timing light hooked up.
It's best to have someone to control the throttle while you use the timing light. Slowly open the throttle while watching your timing marks with the light. Some where between 2800 and 3500 rpm your marks should quit moving (advancing). You want to line up your new 36 degree mark with 0 on the timing cover.

When you have 36 lined up with 0, tighten your distributor and double check your timing. What you have accomplished is power timing your engine.

Your cam manufacturer said to advance your timing 25 degrees. Most 350's
have 10 degrees initial timing, set at idle. 25 + 10 = 35 degrees. You already have your timing set at 36 which is a very good starting point.

I'd leave your vacuum advance plugged. Once your sure you have 36 degrees total advance. you can also check your timing at idle and record this reading. You might find that your engine might like + or - 4 degrees.

Try to run the coldest heat range plugs as possible without fouling. this will help prevent detonation and let you run a little more timing.

Good luck
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Old 03-12-2010, 03:16 AM
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But I have a Tpi motor with 1227730 ecm. Does that matter since the computer controls timing also?
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Old 03-12-2010, 05:50 AM
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Timing

Sorry moneyman, for some reason I thought you had TBI.If I were you I would call MSD. Their tech line may be able to aim you in the right direction with their timing controls. MSD can be found at <www.msdignition.com> .

If you're the patient type call 915-857-5200 and ask for tech help. Do yourself a favor and make a cheat sheet with your make and model vehicle,
VIN number, engine, trans, fuel system and ignition system. Also list any component changes you have made to the drivetrain.


Different companies sell proms or programmers that can change your computer settings. MSD is only 1 of them

A somewhat sly thing I have done when I was younger was to hang where the nice rods were and ask about their tuneups. This forum is a good start because you will get a lot of information.

Good luck
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Old 03-12-2010, 07:32 AM
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These are my mods and current problem

350 TPI/L98 corvette
Speed Density
Bored .40
H-beam rods
Forged 1pc crankshaft
Srp domes
Ported aluminum heads
58mm throttle body
Ported intake manifold and plenum big tube runners
Underdrive pulley/crank pulley only
30lb injectors brand new
Adjustable regulator(pressure at 50psi)
Custom programed chip from harrisperformance
Heated 3 wire o2 sensor
700r4 performance built
3400 stall
HEI Computer controlled
Timing fluctuate from 8 degrees advance to zero mark on the balancer at idle. When given alittle throttle the power drops or shall I say it don't sound like is hittng like it should. Then say at 2000 rpm the power picks up and and the balancer mark shows on the 10 degree retarded mark on the timing cover tab. The car also runs very rich and when I thump the throttle it pops out the exhuast
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Old 04-10-2010, 10:16 AM
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Problem was fixed somewhat lol.....I took the distributor out and advanced the crankshaft damper mark by 4 degrees then I re-sat the distributor back in and reset the EST wire. All works fine now.
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