Thunderbolt 4 engineTiming

[84EdH]

[h=2]

Thunderbolt 4 engineTiming[/h]

I have a re-power engine using a 1998 5.7 vortec engine with roller cam. ignition is with thunderbolt 4. when setting the timing, do I just use the thunderbolt 4 instructions? the thunderbolt 4 came off a 1995 mag alpha.

also:

is there a rev limiter in thunderbolt 4 and what does it use as a max wot? is this adjustable?

is there somewhere I can read about the thunderbolt 4, how it works etc. and timing instructions?

if the engine is set to spec, runs good etc. is there any need to confirm advance to match specs, or that just for troubleshooting?

​

 

[FreeBeeTony]

Re: thunderbolt 4 information and timing specs

Re: thunderbolt 4 information and timing specs

As far as I know......

Just set the timing as usual......8* BTDC
No rev limiter on TBIV

Someone else will chime in with timing advance curves........

 

[81 Checkmate]

Re: thunderbolt 4 information and timing specs

Re: thunderbolt 4 information and timing specs

Not positive here...but i think it beeing a 1996 it is a V (5) thunder bolt system not a IV (4) system.

If so than you have to put in base timming mode.

Serial number off old motor will tell the tale?

 

[alldodge]

Re: Thunderbolt 4 engineTiming

8 before sounds right for the 95 model and TB4
Have you gone to Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years! and find the engine? The manual will have all the timming specs for the engine of that year.

 

[84EdH]

Re: Thunderbolt 4 engineTiming

yes, went to manual....but the engine block with newer engine design is 1998, Thunderbolt 4 (for sure is from 1995), so I didn't know if that would effect the timing setting. I have seen threads for thunderbolt 5 (with newer engines) asking for 10 degrees btdc. didn't know if engine changes caused that, or something about thunderbolt 5........a bit confusing to me. also, still after some info. on how thundervolt 4/5 works. I see trouble shooting guide, but just looking to understand system.

thanks!

 

[alldodge]

Re: Thunderbolt 4 engineTiming

My understanding is TBV is adaptive abd TB4 has a steady advance curve based on rpm. 8 degrees initial with 14 degrees advance providing a total of 22 degrees. Found this is one of Don older post for the TB4 advance curve
View attachment 210038

And another place for the curve MT Boats - Mercury Ignition Advance Modules
View attachment 210039View attachment 210040

As for TB5 it has 25 degrees total advance and uses base timming at 10

I'm with you maybe some others will provide some more input

 

[Walt T]

Re: Thunderbolt 4 engineTiming

Yall missing the point, he wants base timing, and is it okay for his engine? Sure, why not. Sometimes you gotta just try and see. Be alert for pinging. Ignition timing is adjusted by rotating the distributor like any other distributors.
He also wants to know how it works.
Its a high energy system works off battery power. Uses a sensor in the distributor to fire as the triggers rotate by. It is not speed sensitive or limited. Ignition coil is specific to this application so you must use that also. I think ignition timing kicks in at 1000 rpm, and totals 24 or something like that. It's controlled by the ignition amplifier. It's a very simple system. Diagnosing no spark is very simple if the tech knows how or can follow Mercruisers simple troubleshooting procedure. I'm sure the guys here have a link to it.

 

[81 Checkmate]

Re: Thunderbolt 4 engineTiming

Yea i seen his point....But we (I) wanted to make sure it was a 4 or 5 system. Becouse they are different.

Serial number off old motor would help alldoge get the right info...becouse he is using the old system for the new motor which should work with no problem.

BTW....Great explanation of how it works.

 

[Walt T]

Re: Thunderbolt 4 engineTiming

Yea they are different. I was referring to the advance curve discussion, while good information our questioner didn't ask about it. But hey you guys are right, the different engines and systems have different curves I suppose because of cam profile and timing being a bit different among some things.

 

[FreeBeeTony]

Re: Thunderbolt 4 engineTiming

The total advance ignition timing of a SBC should be ~32* (including the initial timing).

For example: 8* initial + 24* advance = 32* total........

 

[achris]

Re: Thunderbolt 4 engineTiming

I have a re-power engine using a 1998 5.7 vortec engine with roller cam. ignition is with thunderbolt 4.

1.when setting the timing, do I just use the thunderbolt 4 instructions? the thunderbolt 4 came off a 1995 mag alpha.

also:

2.is there a rev limiter in thunderbolt 4 and what does it use as a max wot? is this adjustable?

3.is there somewhere I can read about the thunderbolt 4, how it works etc. and timing instructions?

4.if the engine is set to spec, runs good etc. is there any need to confirm advance to match specs, or that just for troubleshooting?

Always a good question... Quite a few people are making the move from one to the other, and asking the same question.

1. What determines what the initial advance should be, is it the engine characteristics or the ignition system? It's probably a combination of both of those, and the quality/octane of the fuel recommended by the manufacturer... Unfortunately that doesn't answer the question, and it gets harder. TB-IV was on the non-Vortec engines, and only on non-Vortec engines. When the Vortec V8s came out, the new engines were given the new TB-V ignition system. So we don't have either system being run on both engines.... No help there. The TB-IV on the non-Vortec engines was run at 8?BTDC. The new engines are specified to 10?BTDC with the TB-V.. We do however have one document from April 1994 stating the TB-V systems should be set to 10?BTDC. Given that Vortec V8s didn't appear in the Merc line-up until mid1996, one may assume that the 'new' system setting of 10? was also meant for the non-Vortec engine.... This would lead me to think that any engine running the TB-V would be set at 10?, and any engine running TB-IV should be at 8?.... (I think my logic is good :noidea

2. No rev limitier on TB-IV. There is on TB-V, and it is set, on production, at max recommended revs for that engine plus 50, not adjustable. There are 4 different TB-V modules for the SBC... One each for 5.0l Alpha, 5.0l Bravo, 5.7L Alpha and 5.7L Bravo. And there are also two different modules for the V6, one for Alpha, one for Bravo. There will also be a whole bunch of modules for the big blocks too. (haven't done enough research into those just yet... maybe tomorrow )

3. Walt T pretty much nailed how HEI systems work. Inside the module is a high voltage transistor. It's just a very fast electronic switch that acts just as the points would have in the old system. When the timing circuitry requires a spark to be fired, the transistor turns off, collapsing the field inside the coil and generating the spark. For the setting of the timing with a TB-IV system, just do it like you'd do a points system. Idle the engine down to 650, point the timing light at the marks and rotate the distributor until the timing marks are where you want them.

4. Checking the advance curve is a diagnostic tool. I like to do it because it's very quick and simple (and doesn't cost anything), and rules that out as a possible cause of run quality issues. I guess it's a hang-over for the weights and springs era. Weights and springs could break or seize, causing problems... Don't think I've actually seen a TB-IV module (that's working) not advance.... The usual failure mode is ...working, then dead....

Just be aware that there are many different TB-IV modules. This is the list; V6-14, V8-24, V8-22, V8-22A, V8-24S and V8-20R.. Each has a different curve and maximum advance. Also, this advance is the module advance only. If you want to know what advance your engine is running at, add the initial advance to the advance on the curve. So if you have a V8-24 module and have the timing set at 10?BTDC, then at 3600rpm (and above) the advance measured on the engine timing marks should be 34?BTDC...

Service bulletin 95-11 has all the curves for all the system for all Mercruiser engines. There is also a 'generic' TB-V curve on the last page (read the caveat below the graph)....

I haven't seen a write-up on how the TB-IV system works, but it's very simple (and surprisingly good). For a description of what the TB-V system does there is a very good write-up in the newer manuals. I extracted it a little while ago for another member :facepalm: to read... Enjoy

http://forums.iboats.com/attachment.php?attachmentid=209033&d=1377157742

Hope that helps....

Chris.......

 

[84EdH]

Re: Thunderbolt 4 engineTiming

Thanks for all the great information! I do wonder why module differences for V8's with different drives? Why does ignition care whether alpha or bravo is pushing?

Chris I follow your logic but I am tempted to check performance @ 10 degrees too.
Also, how critical do you think base timing is to idle rpm? What I mean is if idle was 750 rpm would that effect performance? Does it matter if timing set on muffs in driveway vs. In water in drive? (I saw a post describing idle speed to be set not in neutral, but in forward gear with no throttle advance)

 

[achris]

Re: Thunderbolt 4 engineTiming

Thanks for all the great information! I do wonder why module differences for V8's with different drives? Why does ignition care whether alpha or bravo is pushing?

That's only for the TB-V. Main difference between Alpha and Bravo is the shift interrupt switch (there isn't one on Bravos )

Chris I follow your logic but I am tempted to check performance @ 10 degrees too.

Not a bad idea... Just be aware that if you're running a slightly lower grade of fuel, or it's been in the tank a little while, with the more advance, less tolerance for detonation.

Also, how critical do you think base timing is to idle rpm? What I mean is if idle was 750 rpm would that effect performance?

Have a look at the curves. Although the 'nominal' pick-up point is 1000rpm, it might be as early as 700 on a module (that's within tolerance). I always idle an engine down as low as possible to set timing (I try for about 600-650)....

Does it matter if timing set on muffs in driveway vs. In water in drive? (I saw a post describing idle speed to be set not in neutral, but in forward gear with no throttle advance)

Timing can be set on the trailer on the muffs, no problem (just get the engine speed down to 650ish), but idle speed does need to be in the water (in gear) for TB-IV...

Chris.....

 

[84EdH]

Re: Thunderbolt 4 engineTiming

Ok i get. it timing at 650 but idle speed done in water in gear. Also different tb4 modules just different versions over time I presume.
Nice tb 5 link. Now I see what alldodge meant by calling tb 5 adaptive.

Thanks!

 

[achris]

Re: Thunderbolt 4 engineTiming

Ok i get. it timing at 650 but idle speed done in water in gear. Also different tb4 modules just different versions over time I presume.
Nice tb 5 link. Now I see what alldodge meant by calling tb 5 adaptive.

Thanks!

Different TB-IV modules are for different curves. Have a look at that service bulletin... The different modules have different numbers for the curves..... not just different versions...



sent from my Samsung.

 

[84EdH]

Re: Thunderbolt 4 engineTiming

I checked the different curves and see specific modules, with their own curves for specific engines.

Here is the new puzzler: I built the engine I have now from a 1998 5.7 vortec long block that came in an OMC crate. (new, old stock). I was converting from old style 2pc rear seal, low ps pump, log manifolds etc. to the "new stuff".

I found an excellent 1995 Mag Alpha 350 Serial # OF295214 350 MAG Alpha with a cracked block, from freezing. I scavenged all the brackets, starter, alt, and Thunderbolt 4 ignition. I put a cast iron dual plane, high rise vortec manifold and an edelbrock 1409 on with new center rise style exhaust manifolds.

It seems to run fine. So my question now is this: Is the module in tb4 from that 1995 mag 350, the right module for the 1998 longblock it ended up on?

 

[FreeBeeTony]

Re: Thunderbolt 4 engineTiming

What numbers are stamped on the module?

 

[84EdH]

Re: Thunderbolt 4 engineTiming

Tony, I don't know, will have to check. from the service bulletin its looks like that 1995 serial # mag 350 alpha calls for 821125A or 8095361T6. not sure which engine moving forward would be most like what I have.

 

[FreeBeeTony]

Re: Thunderbolt 4 engineTiming

I have a 350Mag and it has a V8-24S stamped on it = 24* of advance.........

 

[achris]

Re: Thunderbolt 4 engineTiming

I checked the different curves and see specific modules, with their own curves for specific engines.

Here is the new puzzler: I built the engine I have now from a 1998 5.7 vortec long block that came in an OMC crate. (new, old stock). I was converting from old style 2pc rear seal, low ps pump, log manifolds etc. to the "new stuff".

I found an excellent 1995 Mag Alpha 350 Serial # OF295214 350 MAG Alpha with a cracked block, from freezing. I scavenged all the brackets, starter, alt, and Thunderbolt 4 ignition. I put a cast iron dual plane, high rise vortec manifold and an edelbrock 1409 on with new center rise style exhaust manifolds.

It seems to run fine. So my question now is this: Is the module in tb4 from that 1995 mag 350, the right module for the 1998 longblock it ended up on?

The main problem we have is that we don't know the best curve specified for the Vortec. They only came out with TB-V, there was no TB-IV on them....

So, with that in mind, I looked at the V8-24S curve (the one from the 350 Mag) and the V8-24 (one that would possibly best suit the Vortec) and the V8-24S is slightly more conservative in the 2000 to 4500 rpm range, so that will be less likely to detonate. Given those curves, 10 BTDC might be the best initial advance.