Where is the hard limiter on a 400

[npark]

Merc Racing says redline at 7k but I read this in another thread in regards to a 250xs so curious if this theory holds true for a 400 too.

The rev limiter on these engines shouldn't be viewed as a "fixed number"- but rather a "window of perhaps 400-500 RPM's".

Depending on various factors (including LOAD), the limiter may kick in earlier, rather than later (in an attempt to avoid a perceived "impending engine overspeed").

Recommended propping RPM is 5500-6000 RPM's. The HARD limiter has varied from 6300-6400 over the years.

In many cases, if propped carefully, and trimmed gradually at WOT, the engine may be cable of reaching 6370, and running there for extended periods.

Provided that you're not activating the limiter... this is acceptable. However, since the engine makes it's PEAK TORQUE and HORSEPOWER in the 5800-6050 range, it would be best to prop it into that range.

[EuropeanAM]

Theory is the same. May limit EARLIER, depending on numerous inputs to the PCM (LOAD and speed at which the engine is approaching WOT range would be two of the most likely to "narrow the WOT RPM window).

[npark]

So then in theory if the engine continues to make power as it builds rpm with little to no fall off up top then it would be benificial to let it carry load and build rpm gradually once close to 6k+. That can be accomplished with a JP, a tall prop and a lot of open water lol.

I know it's an untested engine as compared to the XS but would you say there is a good chance that one could see RPMs north of 7k or is the 7k the threshold that if you do it 'right' the PCM will allow revs to?

[EuropeanAM]

Yes, if approached carefully, under proper load conditions, the 400R is capable of running 6999 RPM's.

Normally would prop it for 6700-6790 under normal running conditions (loaded boat/fuel).