Thunderbolt IV to Mallory

[wca_tim]

Re: Thunderbolt IV to Mallory

Glad you see you got it worked out. How does it run now?

 

[jhilton]

Re: Thunderbolt IV to Mallory

The boat runs great now. The box would not quit advancing. Set at 0 initial and 32 degree at 3200 rpm, I thought it just had a little extra timing in the box. "I thought" cost me 3 motors. This might save sombody from blowing a motor. Thanks for the help.

 

[bruceb58]

Re: Thunderbolt IV to Mallory

Aren't you supposed to set the initial at 8?

 

[Bondo]

Re: Thunderbolt IV to Mallory

Set at 0 initial

Ayuh,... I'd think That's the Problem,....

 

[JustJason]

Re: Thunderbolt IV to Mallory

yep its 8 initially

 

[krisnowicki]

Re: Thunderbolt IV to Mallory

8 before not after, isnt 32 degrees total advance what is normal? so from 8 bdtc to 24 atdc is what the range should be right?

 

[John_S]

Re: Thunderbolt IV to Mallory

8 before not after, isnt 32 degrees total advance what is normal? so from 8 bdtc to 24 atdc is what the range should be right?

No, it is all Before Top Dead Center. Typical SB V8 is 8-10 BTDC at idle and 32-34 BTDC at wot. The modules only add about 22-24 degrees advance.

I don't think the running at idle with zero degree advance wasted his pistons. It sounds like his module was defective and was adding much more advance, which probably caused the damage.

 

[bruceb58]

Re: Thunderbolt IV to Mallory

I don't think the running at idle with zero degree advance wasted his pistons. It sounds like his module was defective and was adding much more advance, which probably caused the damage.

Agreed...0 is too little inital advance.

 

[Apollo75]

Re: Thunderbolt IV to Mallory

Initial advance should be about 8-btdc and max should be 32-34 btdc and the full advance should be in by 3000-RPM-max.

Does the Thunderbolt distributor have advance weights ?

Does the Box ( module ) add more advance ?

I would just like to know incase I find one --- everyone said it is a good unit

Thank You

OFM

 

[John_S]

Re: Thunderbolt IV to Mallory

Initial advance should be about 8-btdc and max should be 32-34 btdc and the full advance should be in by 3000-RPM-max.

Depends on engine and which module is installed.



Does the Thunderbolt distributor have advance weights ?

No



Does the Box ( module ) add more advance ?

Yes



I would just like to know incase I find one --- everyone said it is a good unit

Thank You

OFM

See above.

 

[Apollo75]

Re: Thunderbolt IV to Mallory

It is a 350 chevy --- 4000-to-5000 RPM 32-34 btdc is about max with any configuration I will guarantee that.

So, it is a bad module --- does someone have a picture of this unit with specifications. Or, direct me to one.

Added : Found what I needed Thank You

Thank You

OFM

 

[Apollo75]

Re: Thunderbolt IV to Mallory

Looks like a nice unit --- max advance is in at little over 3000-rpm to 5000-RPM with the big blocks. From what I see here modules run from 20-to-24 degrees advance curves. I am probably not looking at all the modules


OFM

 

[jhilton]

Re: Thunderbolt IV to Mallory

I set the new distributor at 10 intial 33 total with a little modifing. All in at 3100 rpm. Top speed last year was 38mph last year and this is 46.

 

[Apollo75]

Re: Thunderbolt IV to Mallory

Great --- Glad it is running well.

If you notice any detonation or excessive heat I would back total down a couple degrees --- we don't need all that advance at 4500-rpm

Have Fun

OFM

 

[jhilton]

Re: Thunderbolt IV to Mallory

I dont think i will have any detonation, I built it with only 8.3-1 compression ratio with 91 octane (non ethonol gas). I got tired of buildiing 2 motors a year.

 

[Apollo75]

Re: Thunderbolt IV to Mallory

There you go ----

Keep her running rich under load


Best Wishes

OFM

 

[wca_tim]

Re: Thunderbolt IV to Mallory

actually for most small block applications if you have to run more than 33 or 34 degrees advance it means that your compbustion is inefficient - either poor chanmber design, mismatch on components during build, wrong quench height, or running to fat.

the merc advance curves are most 22 or 24 degrees on v-8s but a couple of them are pretty lazy and not in until a bit higher. always worth checking.

When trying to figure out the sweet spot for timing on a new build, you have an advantage in a boat in that as long as you're running under the same conditions, running at wot is like running on a water brake dyno. Start with the timing set at a conservative 30 degrees. walk it up 2 degrees at a time until you start detonating or stop picking up rpms at wot. then back it off a degree. a little more if you detect any signs of detonation.

another thing to watch is the timing line on the spark plug electrode. the electrode on the spark plug will have a line where it has gottten ot enouhg to change the heat treatment adn will color the surface. that color change should be just past the bend in the electrode (moving towards the plug). as you advance timing further it will get closer to the plug.

A lot of times people run more advance at wot because they percieve it'll give more power, when in fact it doesn't. it's about matching the timing to the burn characteristics of the engins set-up.

ps. the advance curves for the engine modules are shown in the service manuals in the adults section I believe. also, if contemplating changing ignitions or an ignition upgrade, I would highly recommend a crane Hi-6m ignition module and using the merc distributer with it. it gives you multiple spark at lower rpms, a built in rev limiter and a number of options on preprogrammed advance curves. great set-up.

 

[JustJason]

Re: Thunderbolt IV to Mallory

if you have to run more than 33 or 34 degrees advance it means that your compbustion is inefficient

????

the merc advance curves are most 22 or 24 degrees on v-8s but a couple of them are pretty lazy and not in until a bit higher

Yes thats true, but keep in mind its 22 to 24 degrees of advance ON TOP OF the original 8. Which would bring total advance to 30-32. People always forget about the original 8.

When trying to figure out the sweet spot for timing on a new build, you have an advantage in a boat in that as long as you're running under the same conditions, running at wot is like running on a water brake dyno. Start with the timing set at a conservative 30 degrees. walk it up 2 degrees at a time until you start detonating or stop picking up rpms at wot. then back it off a degree. a little more if you detect any signs of detonation.

Eagh.... thats a little dangerous and this is why. We (humans) cannot always detect spark knock. Especially on big bad boat motor, a throaty 350 with esentially an open exhaust. Its not just us... engines that use a spark knock detector such as TB5's and up don't always detect it either. If you try and do it by ear, or anything outside of factory specs, you are brewin a recipe for a cooked motor.

 

[wca_tim]

Re: Thunderbolt IV to Mallory

unless you're running fuel that isn't up to the compression ratio of the engine, it'll just about always stop increasing power long before it'll start pinging... many people have their timing past the max safe advance needed for max power at wot.

timing required at a given rpm is a function of the intake, combustion chamber geometry, and compression - factors that control the rate of burn front travel. for example in an engine with a fairly wide duration camshaft, it'll idle a lot better with a good bit more initial advance because of the poor fuel atomization, incomplete cylinder evaclaution, etc, etc, etc... present at lower rpms for an engine designed to make bigger power at higher rpms.

for the standard small block chevy with an efficient combustion chamber design, good unifrom fuel atomization and an optimized air fuel mixture, 32 or 33 degrees total timing (or even less) should be plenty for max power. When components are mismatched or you're talking aobut less efficient head designs, it'll take more timing advance to put the max cylinder pressure at the optimum approximately 10 degrees after top dead center.

The more efficient combustion is, the more of the fuel that burns at the same time, the less time before tdc you need to light it off...

 

[Apollo75]

Re: Thunderbolt IV to Mallory

Here fellas, work on this applied to boats running under full load and tell me what you think

"The idea that lean mixtures at high loads burns holes in pistons is correct, but it is for a different reason than some people think.

The exhaust gases are always hot, to different degrees. However, with a lean mixture, there is extra oxygen left over in the combustion products (by the very definition of lean).

Combining very hot oxygen with hot aluminum results in the aluminum (the piston) burning (the aluminum chemically combines with the left-over oxygen), just like if it had been hit with an oxy-acetylene gas cutting torch! The burning of the aluminum adds further heat, and the process gets catastrophically destructive in a hurry.

The chemical equation is: 4 Al + 3 O2 → 2 Al2O3

Note that at low loads there isn't enough heat in the combustion products to raise the piston temperature enough to initiate burning of the aluminum, so lean mixtures at low loads are safe (and save fuel).

With rich mixtures, the aluminum can't burn (there's no oxygen left after combustion, and it's too cool in the chamber before combustion), it has to melt instead, and this harder to do (the endothermic phase change absorbs a fair bit of energy, unlike the exothermic burning of a lean mix which gives off energy).

Detonation can also be caused by lean mixtures, which is another reason to avoid running lean at high loads. It *will* cause huge spikes in the cylinder pressure (that is audible as 'knock'), that can damage the pistons and even the cylinders by over stressing them with mechanical loads. It must be avoided at all costs.

Rich mixtures burn more slowly (because there's not enough oxygen for the amount of fuel) than lean mixtures (for which an excess of oxygen ensures quick combustion), and this can result in detonation as the unburned portion of the chamber is compressed and heated by the still combusting portion. At low loads, the cylinder combustion speed is much slower (because the air fuel density is much lower), making detonation less likely, so lean mixtures are again okay. "


Full Article: http://www.megamanual.com/ms2/tune.htm#ve

OFM