timing question

[drivehard]

I had a 1995 Mercruiser 5.0L with a 2bbl carb ~190hp

I did not properly winterize the boat and cracked the block. I rebuilt it...well

I dropped in a 355 with 10:1 compression, edelbrock intake, 4bbl edelbrock marine carb, new performance marine exhaust manifolds...I transferred all the accessories over from the 5.0L to the new engine, including the ignition system.

I can't remember the exact name for the ignition, I think its thunderbolt IV?

Anyways, I know there is a timing difference between what was on the 305 and the 350 for that model year...the 305 is slightly advanced in the higher revs.

Now to my question...I understand this ignition has a rev limiter of 5000 rpms. I'm cool with that. It limits rpms by pulling timing. At what RPM does this start?

I can easily take her right up to 5000 rpms...I know I need a new prop. Right now I have a 21". I can't decide to try a 23, or a 25. Mostly just do 2 people cruising, and speed

If it starts pulling timing at 4600 and I can still pull up to the 5000 rpm redline, then I think I will try the 25". If it doesn't start pulling timing until right at 5000...well then I don't know yet.

 

[Bondo]

Re: timing question

I can't remember the exact name for the ignition, I think its thunderbolt IV?
I understand this ignition has a rev limiter of 5000 rpms.

Ayuh,....

The T-Bolt IV will Rev to the Moon if you want,.....

I'm not sure about the T-Bolt Vs.....

 

[Don S]

Re: timing question

The Thunderbolt IV does not have a rev limiter, that is a feature of the Thunderbolt V system. One not, it doesn't "Pull Timing" to prevent overrev, it stops the spark.
Here is a copy and paste out of the OEM service manual for the TBV.

This is for Thunderbolt V only

Over-Speed Control
The ignition module will prevent the engine speed
from exceeding a preset limit by stopping the spark.
This feature has an RPM range that varies from model
to model. The over-speed limit for a particular engine
is set slightly higher than the top end of the RPM
range for that model. For example, if the recommended
range is 4600-5000 RPM, the over-speed
limit would be set at 5100 RPM. When RPM reaches
this limit, spark is turned-off until engine RPM drops
down to a ?Reset RPM?, which would be approximately
4750 RPM for this example. At this point,
spark comes back on.