I need help with 2 issues. Correct timing for my engine. I have been told several different answers from people who you would think would know. The most experienced person who owns a speed shop says small blocks like 35 to 38 degrees of advance. Also, 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 (Pep Boys cheapies) that are on this engine. Any advice greatly appreciated. Dave 350 small block bored and stroked to 383 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 MSD PRO-BILLET DISTRIBUTOR. ACCEL SUPERSTOCK HIGH TEMP PLUG WIRES. EDELBROCK PERFORMANCE HEADERS. FLOWMASTER DUAL EXHAUST. TCI “STREET FIGHTER” HIGH PERFORMANCE 3600 STALL CONVERTER. T400 Trans & shift kit B&M PERFORMANCE MEGA SHIFTER. 3.73:1 REAR GEAR.

Around 34-36 degrees all in as soon as possible without getting detonation at WOT.

If you're timing it by best performance, it doesn't really matter that the timing marks are perfectly accurate. If it matters to you though, use a piston stop and make a new TDC mark.

Actually, it could be anywhere from 32-42 degrees although the 34-38 is normally the best range. One degree off can mean as much as 20 HP. Where an engine likes it's timing depends on the engine. Timing that works good on one engine may not be the best for another. The only real way to find the best timing for "your" engine is to put it on an engine dyno and do pulls at different timing settings. Once the best timing is found, no other tuning adjustment will change where the engine likes it's timing.

You'll need a piston stop and a degree wheel to see if the timing marks are accurate. Years ago I had an engine that kept making more power as I kept advancing the timing. At 45* advanced I decided to double check the timing marks. The pointer was out 8* so the 45* was actually 37*. I was starting out in the high 20's. No wonder it made more power as the timing was advanced.

Even if your marks are out, it won't really matter. If you make the most power at 45*, it doesn't matter if it really is 45* or something else due to incorrect timing marks as long as you know those marks at 45* make the most power.

Tuning at the dragstrip, adjust timing 2* at a time and watch the MPH. If MPH goes up, you're making more power. You can get within a couple of degrees to the best timing.

What heads?

Stock heads.

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)?
Thanks
Dave