SN17

I need help with 2 issues. Correct timing for my engine and what is the best/most accurate aftermarket timing mark or wheel or method of measuring timing. I have an adjustable timing light, but I don't trust the aftermarket marks that are on the engine. Any advice greatly appreciated.
Dave

350 small block bored and stroked to 383
SMALL BLOCK CHEVY BORED AND STROKED TO 383ci
PISTONS: 9.7:1 KIETH BLACK.
EAGLE CRANK & RODS.
CRANE CAM 113141 STREET/STRIP
Intake; 109 lift, 238 degrees
Exhaust; 119 lift, 248 degrees
ROLLER ROCKERS.
MELLING HIGH OUTPUT OIL PUMP.
EDELBROCK DUAL PLANE HIGH RISE MANIFOLD.
HOLLEY 750cfm DOUBLE PUMP CARB.
NITROUS OXIDE SYSTEMS, SUPER POWERSHOT 150.
MSD DIGITAL 6 IGNITION, 6 degrees of retard on nitrous servo
MSD PRO-BILLET DISTRIBUTOR.
ACCEL SUPERSTOCK HIGH TEMP PLUG WIRES.
EDELBROCK PERFORMANCE HEADERS.
FLOWMASTER DUAL EXHAUST.
TCI “STREET FIGHTER” HIGH PERFORMANCE 3600 STALL CONVERTER.
TCI UNIVERSAL LOCK UP KIT.
B&M PERFORMANCE MEGA SHIFTER.
700R4 TRANSMISSION AUTOMATIC TRANSMISSION.
3.73:1 REAR GEAR.
Cam Specs:

cnorton

I begin every project by making sure that I have a harmonic damper that includes etched or engraved marks at least every two degrees from 50 degrees BTDC to 10 degrees ATDC plus marks at 90 degrees, 180 degrees, and 270 degrees. The mail order catalogs provide a variety of these. My personal preference is ATI. It includes marks at one degree intervals around the circumference.

For a first generation block, the next item is an adjustable timing pointer that attaches to the block by indexing off two of the timing cover cap screws. For LTx blocks or other applications, I fabricate a positively indexed, adjustable pointer.

Using a piston stop and a degree wheel (the instructions for this procedure are found just about anywhere on the Internet) locate the precise TDC point of the rotating assembly. Make sure that the harmonic damper and adjustable pointer are installed with the pointer precisely aligned with the 0 point on the damper when you have confirmed the location of true TDC.

Assemble the rest of the engine according to your usual procedure.

When the engine is ready to fire, rotate the engine to about 25 degrees BTDC on the compression stroke as indicated on the pointer and rotate the distributor by hand to bring the rotor into alignment with the #1 post on the cap. Install the cap and tighten the clamp on the distributor.

Procedure from this point is basically your option. My work is mostly done on race engines that are timed by using locked timing curves and total ignition advance. I fire the motor, bring the engine RPM to the point that all the centrifugal advance is engaged and use the light to check and set the total timing figure. Loosen the clamp and rotate the distributor by hand until the preferred total advance is indicated on the damper. Most Stock eliminator motors get between 36 and 38 degrees of total advance. Super Stock motors like less timing, usually between 32 and 34 degrees. The actual "sweet spot" is determined by track or dyno testing.

If you have a vacuum advance distributor and a street engine, be sure to disconnect and plug the vacuum port before checking initial timing. Check factory specs and set the initial timing according to the book for your application. Road test or dyno test to determine the optimum final timing setting. It's helpful to know where the timing is at idle and also at maximum advance in case there are issues with the vacuum advance system or centrifugal advance weights. Some after-market vacuum systems are adjustable and there are centrifugal kits available to permit tailoring the advance curve to your needs.

Some professionals like to use adjustable lights but I'm a gnarly old guy who has experienced systems that do not like adjustable lights. Some race ignitions (particularly some MSD boxes) don't seem to respond well to adjustable lights. I would set an adjustable to zero and forget it. If you experience misfire while using such a light, try an old-fashioned, not adjustable one. It's a matter of preference.

Good luck.

redneckgames

just curious what heads you are running and the cam specs.

SN17

Thanks cnorton. I completely understand your guidence. makes perfect sense. I am off to locate a good dampner, piston stop and degree wheel.

I suspect my timing marks are about 4 to 6 degrees off. When my Son drives at the track and sprays 150 shot he gets a backfire in third gear up through the carb. I imediately stopped the run for fear of toasting the engine. Now I think I am pretty close to knowing where zero is and I discovered he had 42 degrees in it and when the nitrous selonoid comes on the MSD box retards 4 degrees, meaning he was spraying 150 at 38 degrees. I have re- adjusted the timing to 36 (on motor) with 6 degrees of retard on the MSD box when nitrois is activated. This may not be optimal, but it makes me feel a bit more comfortable. We have not run the car at the track yet to test this since I made these adjustments.

Let me ask this hypothetical; Assuming 36 degrees is the sweet spot, how much retard would you start with when spraying 150 (NOS PowerShot)?

Lastly I have an MSD Billet Distributor. The speed shop I bought it from spun it up and adjusted the advance/springs for 38 total. They said I did not need to use the vacume advance or hose pluged in. The vacume advance nipple on the distributo should be plugged, right?

Thanks
Dave

Oh yeah, I have stock 350 heads.

Thanks
Dave

cnorton

Dave,

Glad the description made sense. I re-read it several times to make sure that the critical elements were covered. If you have questions about that, don't hesitate to ask.

I am the least knowledgeable source available in terms of power in a blue bottle. My kind of racing doesn't use it and I have no experience with it. Sorry.

I do know, as a rule of thumb, along a continuum from stone stock to highly prepped, as the heads and manifold combination become more efficient, the motor needs less timing and less jet. That's why the Super Stock motor only wants about 34 degrees of timing while a Stocker might run better with 38 or 40. Jetting becomes leaner on Super Stock motors as well.

Good luck,

c





The nipple on the distributor is inconsequential however, as you know, it is critical to block off the vacuum source at the carburetor end. I'm sure that you've done that.