I have no intention of removing the limiter as the tyres are only speed rated to 112mph, but I do find it funny that with the speedo pegged at 180kmh, and feeling the limiter cutting in and out, the engine is only turning over at about 3500rpm.

I just wondered what the natural 'terminal velocity' was, approximately. It seems like about 130-140mph but that is only a guess.

That would probably have to do with internals as well and airflow, is my guess. Valve float at higher rpm could happen since this is a fairly large v6. I wonder if oiling keeps up well at that speed?

It's bucket and shim valves so I believe (But don't quote me) valve float is less of a problem. High-revving motorcycle engines (11000rpm use them too), and it only revs to 6000 approx, as you say, because of the reciprocating mass of the pistons.

As for the oiling, I wouldn't be worried. You guys don't get the little tiny Toyotas like the Aygo. Those things will run flat out all day.

I dont trust mine over 85. I had a '95 and towards then end, it wouldnt make it over 55 mph.

Ive got the accelerator pedal to the floor and it goes 0-60 in about 10 seconds, shaking and really seems to be working hard at high speeds.

My 4runner has lots of strengths, high speed is not one of them. When I lived in the south, one of the thing some of the 4x4 clubs would do is day at the nascar track - did not really seem that appealing to me

Interesting thought, but im content keeping mine at 75 max

I have hit my speed limiter more than once on aggressive freeway passing episodes and it's always entertaining. The speed limiter is there for good reason on these vehicles though, and I doubt it would go too much faster without it.

With all above mentioned, it's also a JDM thing: most speed gauges are limited to 180km/h (112mph) because they somehow think doing this would deter speed racers. 5th gen is not sold in Japan anymore (4th gen was somehow popular in Japan, regarded as a stripped down Land Cruiser Prado, the Hilux Surf), so 5th gen speedo goes to 120mph.

I just noticed your name is SurferUK... so disregard the last sentence lmao. And yes you can see Suzuki hayabusa having 180kmh speedo, and everybody knows they can go well over 300.

your valves don't care if you're going 40mph in 1st gear, or 130mph in 4th gear, engine RPM is engine RPM. You can easily rev the motor up past the 3500rmp the OP is seeing while hitting the speedo cut. There's no issue with valve float on a factory setup operating within its limits (unless, of course, you have a manual transmission and go for the money shift and ramp the engine RPM significantly quicker than it naturally would under it's own power).

I would find it hard to imagine these things getting up past your estimated 130-140 mph. If we had some numbers for your speed ramp (say from 70-110 mph) it could be a little bit easier to guess how much more "go" is left, but regardless, I just don't think there's enough power to overcome the drag nearing the 130mph mark.

Edit**

For reference I wanted to compare some numbers to my old 1993 4cyl Toyota Camry I had that I remember topping out somewhere between 120-130mph (not speed limited.. .just ran out of juice).

Here is what it looks like..

4runner power to weight ratio is slightly higher, at .0442 vs the Camry at .0425, but the coefficient of drag is increased, .36 for the 4runner vs .28 for the Camry. Just using that as a base for comparison.. I stand by estimate of 130 for the 4runner lol.

Probably limited by one of two things, either gearing or horsepower. If you can't reach "top speed" as calculated, in top gear then you don't have enough horsepower to pull that gear. If you can't reach calculated top speed but are able to reach redline in top gear, then you are gear bound.

MPH= RPM x 60/tire rev per mile x overall gear ratio