Rev Range + Limited RPM

Hello guys, new on this forum, I thought I’d dive deep into the forum community where fans of the sport and knowledgeable motorcyclists hang out. Context: Currently writing an assignment and the brief is to develop a MotoGp engine, while considering the maximum rpm and calculate the MPS if there are rev limiters.

Can someone help me on this topic, as I’m finding either conflict info or inconclusive data and really struggling to get past this hurdle. So my question to you is, what is the maximum rev range of the current MotoGP bikes (need reliable sources so I can reference it, will reference the forum as well) and do the MotoGP bikes have a rev limiter.

That’s all I need and it would be a massive help. Plus it adds credibility to my assignment.

Thank you lads and lasses

Hi, and welcome! Always nice to see people interested in the technical side as I am.

What I will say is I write this not knowing how much you already know and how long you have been a MotoGP fan. I'm guessing you are doing some sort of Automotive or Motorsport Engineering degree in the UK such as I did.

For a bit of background. Early MotoGP bikes were ~990cc 4 strokes with a variety of cylinder configurations. V5, V4, Inline 4 and even an inline 3. In 2007, in an effort to reduce speeds, the governing body introduced a rule of 800cc to reduce power. What happened in reality, was revs went up and pneumatic valve systems were introduced to keep engines reliable (at great expense). Due to a number of factors, most notably the 2008 financial crisis, it was clear that costs had to come down. This started with reducing number of engines per yr allowed, and fuel restrictions (hence power).

So for the 2012 season, one major factor in keeping costs down was the agreement of retaining the current 800cc heads by freezing the bore to that size on 1000cc engines. They also limited all engines to 4 cylinders so as I'm sure you know, if you limit the bore, displacement, and number of cylinders, you dictate your stroke! Short stroke, very oversquare 800cc engines were revving to 20,000rpm +. With the information above (81mm bore, 4 cylinders and 1000cc max displacement), your stroke would be 48.5mm. With the fuel limitation of 22 litres for a race, these are all extremely restrictive conditions on your ultimate engine speed and power.

Some of my engineering notes are a bit rusty, but from memory, ~27m/s is about the limit for piston speed if you want reliability. Taking that number into account for the engine specifications above gives 16,700rpm. I did find this article which may be of use to you:

Piston Motion: The Obvious and not-so-Obvious, by EPI, Inc.

What I would say, is go and buy the book "MotoGP Technology" By Neil Spalding (3rd edition). It has a LOT of information regarding engines design in there and would be invaluable to you.

If you want me to elaborate more, feel free to ask!

From what I know the KTM engine operates between 8,000 and the rev limit of 18,000

Tough question because the manufacturers don’t say much, and when they do make a disclosure to the press, the performance figures seem to be malarkey.

I agree with #22 regarding the theoretical performance threshold. It’s difficult to say how the engines actually run in race trim to meet the fuel restrictions and engine life restrictions. Plus, the ECU and software are supplied to Dorna’s spec.

The best we can do is guess. My personal guess is that the engines are running lower than theoretical cylinder pressure for reliability. They make around 16,000 rpm on the throttle and produce around 240-250bhp. The series has been paranoid about engine performance since the day the 990s took to the track. I don’t think the GP Commission will tolerate much more engine performance than that.

Geonerd back in the day made multiple posts about this by analysing the sound from the exhaust. From what I recall he could diagnose firing order, revs and probably some other pieces of info. Use the search function on the forum. Good luck.

Barbedwirebikerr said:

Geonerd back in the day made multiple posts about this by analysing the sound from the exhaust. From what I recall he could diagnose firing order, revs and probably some other pieces of info. Use the search function on the forum. Good luck.

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There was also the ability to tell how fast the seamless gearboxes could change gears thru sound analysis

mylexicon said:

Tough question because the manufacturers don’t say much, and when they do make a disclosure to the press, the performance figures seem to be malarkey.

I agree with #22 regarding the theoretical performance threshold. It’s difficult to say how the engines actually run in race trim to meet the fuel restrictions and engine life restrictions. Plus, the ECU and software are supplied to Dorna’s spec.

The best we can do is guess. My personal guess is that the engines are running lower than theoretical cylinder pressure for reliability. They make around 16,000 rpm on the throttle and produce around 240-250bhp. The series has been paranoid about engine performance since the day the 990s took to the track. I don’t think the GP Commission will tolerate much more engine performance than that.

Click to expand...

Exactly this in a nutshell. Simply put, the engines could rev higher and put out more power but the FIM controls the engine configuration and size (crucially, bore), along with fuel limits and electronic hardware/software.

I don't know where its documented. The FIM originally proposed a rev limit and the manufactures rejected it so the FIM responded with rules that resulted in a longer stroke