Does anyone know if a Thunderbolt IV ign. set-up has a built in rev-limiter. Part no. on the module is IG25A-V8-24S. And if so, what is it? Thx.

I'm pretty sure it dosn't.

correct, Thunderbolt IV ignition has no rev limiter, took mine up to 5800 to find out!!! (stupid, i know, but if my 4.3 blows up it is good reason for a new 350)

Sorry, but yes they can. My T-IV does have a limiter. Also is shown in my Merc manual. Not sure what the limit is, but I also have seen 5800 with it at times. Maybe not working??? BTW, the limiter is not in the module, it's a separater componant.

I've got one laying around here somwhere that I know doesn't have a limiter. Had it way up there a couple of times in years past.

Thanks all for the info.

US1-are you sure you don't have a Tbolt-5? The stock 4's did not come with a limiter.

100%
In fact, I just went out to double check and make sure that it did have IV on my module just to be sure. And, here is the ignition parts breakdown from my motor. Item #43
T-bolt IV ignition

Maybe this only applies to the HP series motors?

To my recent surprise, some Tb IV's DO HAVE rev limiters.

My '93 454mag does not have one and my '96 525SC does. I've hit it(5300rpm) on the 525SC trying a smaller prop. Both are TB IV's. My Merc Manual for High Performance Engines says that the HP425, HP450, HP465, HP500, 525SC, 600SC, and 800SC are all equipped with TB IV's and rev limiters. There is nothing in the manual, that I have found, that shows anything about the actual limits or where the limiter is located.

Hmmmm....so maybe it's just the black motors that didn't come with a limiter. That would make sense...sorta....