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biggiefl
09-21-2011, 04:01 PM
Does a 1994 454 310hp carbed have a rev limiter? I have heard that some 7.4L have 4600 limiters. Reason for my question is last time out I had almost full fuel, 2 people, into the wind & tide and was doing 59GPS at 4600. Without wind & tide I usually do about 62+ at 4600. Seems like I am in the 4600 mode which is fine but maybe a 25 Mirage would be better if I am hitting the limiter. If no limiter than I am pretty much dialed in I guess. I go through a few slow zones each way so I don't want to waste my fuel getting up on plane cause this thing just pops up with the 23 mirage. Then again it might have been made into a 21 or 22 for all I know.

Tidbart
09-21-2011, 04:49 PM
Thunderbolt V ignition system has a rev-limiter. If that is the ignition system you have.

TB IV has the ignition module mounted on the exhaust elbow and the TB V has is mounted on the distributor body.

B

Tidbart
09-21-2011, 04:58 PM
RPM range for that engine is 4200-4600. If you are at the top of the range, you could try a 25P and see where it gets you.

I have a spare Mirage plus, 25p. If I remember, I will bring it to Sarasota and you can try it if you like.

B

biggiefl
09-21-2011, 08:32 PM
How would I know what ignition I have? I think it is a gen IV. Bring the prop if you ant, I will see if I can try one this weekend and save you the trouble. Thanks!

Tidbart
09-21-2011, 09:22 PM
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One way is to see where the ignition module is mounted, on the ex manifold or the distributor.

See my previous post. I don't think the TB IV has a rev limiter and the V does. Not 100% sure though.

Bob

Tidbart
09-21-2011, 09:34 PM
Just sent you an email. Will help immensely. B

gcarter
09-21-2011, 09:43 PM
This PDF is everything you could ever need to know about Merc ignition systems.

Tidbart
09-21-2011, 10:33 PM
To save you a lot of reading.... from the TB V section.....

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.

B

silverghost
09-22-2011, 12:50 AM
If your engine were really hitting the top rev limit with this type of Merc. ignition system ~
Believe me you would know about it.

The engine would start to randomly miss-fire and make all sorts of strange popping, missing & sputtering noises when the engine hits the ignition's pr-eset upper rev limit.
Almost like a failing ignition system ; or an engine running low on fuel.

The more modern up to date fuel injected engines act a bit differently and it is sometimes very hard to tell you actually hit the engine's upper rev limit.

biggiefl
09-22-2011, 10:36 AM
Thanks...that is what I thought. A limiter would be like in a car. I guess I should have asked if it has a governor but I already know the answer to that.