ignition timing/super charged
 

I'm looking for a second opinion on ignition timing specs for a GM 350 engine with a Mercury Thunderbolt IV(v-6) ignition and a roots type supercharger.

what did the first opinon have to say?

What boost, compression, heads, plugs, intercooled or not? Injected or carb?

Here is the set-up:
GM 350 ,162 b&m blower(6-7 pounds of boost),holly 4150 750cfm carb,lunati cam for super charger(custom built for marine use), mercury thunderbolt IV ignition(6-12 degrees timing),standard plugs for mercruiser 260

set your total timing at 34,blower motors like advance even at low rpm,i always use msd distributor and lock it out.

What is the compression ratio????

30-34* total depending on CR.

8:5-1

initial timing
 

What would the initial or idle timing want to set at for the above engine set up

In my opinion 34 is too much with a non intercooled little blower putting out 7 pounds of boost with no knock protection. If it where mine and I was not going to set it up on a dyno it would not have but 30 degrees total as it just not worth the chances.
Allen

That would depend on how much advance his module gives. It looks like he is running a V6 module which will give about 10* of advance. Initial timing is really not that important.

I would set it at 30-32* total. Also I would change the spark plugs to 2 heat ranges cooler.

At 7 lbs with that little heat pump, I would not run more than 28 degrees total. Especially with the crap pump gas of today.

I spent a lot of time with B&M blown small blocks. Blown up countless ones until I dialed the timing back so they would live. BUT it's a double edge sword, at 28 total, exhaust gas temps are high. You'll need good quality valves and seats to get any decent life out of that combo.

Good luck,

Kurt

As for the V6 module, disregard initial timing altogether. That module starts advancing at 650rpm. Although technically it provides 14degrees (when on a 6 cyl) when fitted to an 8 cyl with an idle of 1000 or so, you will only see 8-10 degrees of advance.

I'm a big fan of the V6 module for blower motors, they are stone reliable (unlike MSD) and if you did ever have a problem, you can find ign parts anywhere.

Kurt

Here's how the shakedown run went-
The engine ran great from cruising speed(3000 rpm) all the way to full speed(4900 rpm) then 15 minutes later(at cruising speed 2800 rpm) the engine a made snap-snap-snap noise and shut down. This is the same noise it made the past two times the engine failed. The failure resulted in tuliping the exhaust valve in #1 cylinder(= compression loss) and melting the spark plug electrode. I don't think this happened this time because the engined fired up and I was able to run the boat at cruising speed all the way back to the ramp.
Tomorrow I'm going to look at the plugs and do a compression test and see whats up. Hopefully everything is finest kind. Any thoughts on that snap noise?

I run Weiand 174s on BBCs with MSD Distributors (85551) and 6a boxes. Initials are 16 with 10 degree stop bushings made by a company in Idaho(?) specifically for miniblower apps. Total 26 using weakest dist springs, all timing in by 2500. Use 93 octane treated with Turbo 108. Carbs are speed demon 850s. CR about 7.8 with flattop forged pistons, open chamber GM rect HP heads . No detonation, no high exhaust temps (Gils with 4" stainless pipes), water and oil temps stabilize low, motors run and sound great. Sounds like the above ignition setup might work better for you. What's your exhaust setup?

Is your gas fresh and good quality 93 octane? I've had a pop pop pop misfire at full throttle when my gas isn't fresh. Maybe some water made it to the carb. A compression check is always a good idea when you don't know the cause of a problem. Rule out anything being broken. You really have to be at the top of your game to tune in a supercharger. Make sure you have the proper fuel mixture at all rpms, high octane fuel, 28-30 deg. ignition timing. Make sure all of your plug wires are good, run cooler plugs than stock, run a 120 deg. thermostat or none at all, large oil cooler enough to keep oil temps below 250 wide open. A lot of things to check. Good luck.

this is why i sugested 34 total,when u run 30 or less the exhaust temp is way to hot,hence the tuliping if exhaust valves,after you pull the heads,if u dont have any burnt pistons,install inconel exhaust valves and start at 32 total.use 93 octane fuel &put bigger jets all the way around:party-smiley-004: