Hard Popping sound in the exhaust

here is what I have 383 sbc on methanol. I have timing fixed 20 and marked the 36-1 with mark at 20 BTDC because too much stuff around the timing marks. This mark line up with the center of the hall sensor. 122 BTDC in tuner studio. 20-degree mark lines up to center Hall sensor with timing light while running. I did verify distributor wiring order, checked the valves ok. It looks like from under the car it is an explosion in the headers when it does it on both sides. First time with EFI stand alone. I can't find a way to send the project file it won't let me attach MSQ file

Bit of a long shot, but do you have the correct firing order for the camshaft? IIRC, the early 1-8-4-3-6-5-7-2 was changed out to (checks) 1-8-7-3-6-5-4-2 in some applications* as it was thought to give a better firing characteristic for something(?). If so, then 4&7 will be only firing on their exhaust strokes, igniting through the valves into the exhaust? They're different from the LS's 1-8-7-2-6-5-4-3.

You don't say if the engine actually runs with the exhaust 'explosions', or if it won't start at all and just ignites in the exhaust? If the latter, it may be a brain-fart with the firing set 360 degrees out - we've all done this at one time or another, no biggie.

Oh, what do you mean by "hard"? I'm not familiar with methanol fuels, but normally a rich mixture has more of a bang with a lower tone, but lean has more of a sharp crack with a higher tone - could you just have way too rich or lean of a mixture for the methanol, and so it's having issues being ignited?

*Sometimes referred to as the 4-7 swop.

The engine ran before with the 18436572 order the Heads and intake were changed to support EFI. Made a couple changes set AFR to 6.5-1 from 5-1, change from fall to rising then recheck time which is at 20 fixed. Problem still there. Engine does run with the popping going on, starts right up. I start it again to record the sound but it is so loud you can't here it on the recording so I moved the laptop out of thee garage to the drive way and did it again the popping is less and not as loud. The car is almost out of fuel. But you still can't here it on the recording I have not seen in tuner studio any place to put in what kind of fuel I'm using. I put the file there anyway you may have better audio then me.

Bear in mind that, as already mentioned, methanol isn't my thing, so you may wish to consider these discussion/thinking points...

That sounds like a bad misfire, with the unburned charge being ignited in the exhaust.

Methanol can be significantly harder to ignite than other fuels, so making sure the ignition and plug gaps are up to the job might be worth checking, especially if the mixture is 'off'.

You say you have the AFR changed from 5:1 to 6.5:1 - that may be where the issue lies, depending on how it's done?

If it's based of the lambda value, as all AFRs normally are*, without having some means to correct that from the normal petrol/gasoline fuel, it's going to be the equivalent of what that would be on a "gas'"engine, which will be around double the fuelling actually required - that's bad enough, but as the lambda reads the presence of oxygen in the exhaust gases, incomplete ignition may leave some unused oxygen in the exhaust and the ECU will try adding fuel to compensate, making it worse.

If possible, use a lambda value, as this is the raw data all the AFRs are based on, with somewhere around 0.85 probably being a good starting point. Personally, I'd recommend everyone learn to use lambda values, as it's consistent across ALL fuels, whereas AFR will be different for every fuel type and blend.

IE, lambda 1.0 is stoichiometric, or chemically balanced where all the fuel and oxygen is used up, for methanol this is ~ 6.4:1 compared to ~ 14.7: for petrol/gasoline, or ~9.0:1 for ethanol.

This may help make sense of it - https://i0.wp.com/ls1tech.com/forums/attachments/forced-induction/349083d1334238324-e85-afr-procharged-car-11psi-lambda-sclae.jpg

* it may be possible some ECUs directly compare the air mass taken in against the fuel flow - and/or injector size and duty - to calculate the nominal AFR.