Honda Power Unit Hardware & Software

[Hoffman900]

Sorry, I don't remember who mentioned that it would be hard to measure real time CR.....There was a you tube video with Pat Symonds from 2025 that said that the all F1 ICE used a Pressure sensor to detect knock. That those sensors were very expensive and they wanted to do away with them.

Meaning if they wanted to measure CR real time, they could very easily.

Not entirely, because those are measuring firing engines. Peak combustion pressure is partly a function of geometric compression ratio, but also other things, especially in a Miller Cycle engine. In an Otto Cycle engine you can compare it against an idealized P-V loop, but even then, it depends on other things as well.

We even use these sensors in amatuer racing now (on the dyno). You’re not competitive anymore if you’re not developing with them, and yes they are very expensive, and F1 teams go through them like candy running them in the cars, on every cylinder. They burn up, go out of calibration, etc.

Most sanctioning bodies use these to measure compression ratio (even NASCAR and IMSA): https://katechengines.com/i-30497781-ka ... ester.html . If you fail, then you get torn down and they actually measure them, but again, measuring parts is done at ambient, not hot.

As I said, the only way to fairly do this is assume geometric compression ratio is when the piston to head clearance is zero. Everything else is variable to some degree

[diffuser]

If you change combustion chamber geometry, you’ve now deformed and compromised the valve seats / effect the valve height, it has to work around the TJI unit and in-situ pressure transducer, all of that still has to support 250bar + of cylinder pressure, AND it can’t compromise cylinder sealing.

To even get 16:1 compression requires a very compact chamber to begin with. There just isn’t any room for this and imo is just not a viable theory.

Yeah, I didn't think so either but it doesn't mean that some expert doesn't figure out a way.

The highest heat is in the combustion chamber and anything that comes in contact with it, that is the heads and the pistons. Heads can be made of specific aluminum, which expands twice as fast of any of the steel alloys allowed for piston use.

Not you but I've see alot in this forum of people saying oh you can do this and you can do that to raise the CR and it isn't true. There are very strict rules around building the a ICE and the FIA have taken away as many tricks as they could think of to raise the CR.

[Hoffman900]

If you change combustion chamber geometry, you’ve now deformed and compromised the valve seats / effect the valve height, it has to work around the TJI unit and in-situ pressure transducer, all of that still has to support 250bar + of cylinder pressure, AND it can’t compromise cylinder sealing.

To even get 16:1 compression requires a very compact chamber to begin with. There just isn’t any room for this and imo is just not a viable theory.

Yeah, I didn't think so either but it doesn't mean that some expert doesn't figure out a way.

The highest heat is in the combustion chamber and anything that comes in contact with it, that is the heads and the pistons. Heads can be made of specific aluminum, which expands twice as fast of any of the steel alloys allowed for piston use.

Not you but I've see alot in this forum of people saying oh you can do this and you can do that to raise the CR and it isn't true. There are very strict rules around building the a ICE and the FIA have taken away as many tricks as they could think of to raise the CR.

The problem with expanding materials is as I said, you have two things (TJI) and a pressure sensor threaded in, and the valve seats are cut in / coated. It doesn’t take a lot to distort a valve seat and then your power drops like a rock as they don’t seal (or you hang up a valve). If the seat grows in, you also mess with the valvetrain geometry.

The hottest part in a chamber is the spark plug (in this case the TJI injector) and the valves, all are seeing temperatures well above the piston, especially the exhaust valve and often this is why they’re usually an inconel based alloy.

The combustion chamber is one of those things you want as stiff and inflexible as possible. I worked on an engine where we actually had to drill into the chamber, through a water jacket, and thread in screws that were ground flush with the chamber to support / bridge it, because it was failing.

[AR3-GP]

Not sure how realistic the illustration is, but it implies that one could locate the compressor inside the V. It's possible that this is what Honda was hiding at their PU launch where they didn't show the back of the engine.

[Hoffman900]

To be honest, when you look where the suspension ties in, how slim you want things for aero, where else would you even put it?

[diffuser]

Not sure how realistic the illustration is, but it implies that one could locate the compressor inside the V. It's possible that this is what Honda was hiding at their PU launch where they didn't show the back of the engine.

https://i.postimg.cc/6p2VBZTx/image.png

Honda started out with the compressor in the V in 2014.My understanding is it later became a problem cause they were limited in space and ran into sizing problems. They then moved the compressor to the front of the ICE in the 2017 complete ICE redesign. That being said, the regs nolonger allow a MGU-H and my understanding is that will reduce the compressor's sizing needs. So that might be were it ends up.

I expect there to be more distance between the compressor and the turbine. That doesn't look like the 175mm allowed.

[Bence]

Can you add some room/distance to the fixed 175mm by elongating the housing/blade shapes?

[diffuser]

Can you add some room/distance to the fixed 175mm by elongating the housing/blade shapes?

From Article 5.5.5 of the 2026 F1 Power Unit Technical Regulations:
The compressor and turbine of the turbocharger must meet these dimensional constraints:
Compressor exducer diameter (A): between 100 mm and 110 mm.
Compressor axial length (B): from inducer diam edge to rear of exducer must be between 30 mm and 35 mm.
Turbine inducer diameter (C): between 90 mm and 100 mm.
Turbine axial length (D): from exducer edge to front of inducer must be between 35 mm and 40 mm.
Maximum distance between compressor and turbine (E):
no more than 175 mm from the rear face of the compressor exducer to the front face of the turbine inducer.

   ┌───────────────┐                     ┌───────────────┐
   │   COMPRESSOR  │                     │    TURBINE    │
   │               │                     │               │
   │  Inducer   →  │                     │  ←   Exducer  │
   │               │                     │               │
   │  Exducer  ←───┼───── E ≤ 175 mm ────┼──→ Inducer    │
   │               │                     │               │
   └───────────────┘                     └───────────────┘
            ↑                                       ↑
            │                                       │
   Rear face of compressor                 Front face of turbine
       exducer plane                          inducer plane

[AR3-GP]

Can you add some room/distance to the fixed 175mm by elongating the housing/blade shapes?

From Article 5.5.5 of the 2026 F1 Power Unit Technical Regulations:
The compressor and turbine of the turbocharger must meet these dimensional constraints:
Compressor exducer diameter (A): between 100 mm and 110 mm.
Compressor axial length (B): from inducer diam edge to rear of exducer must be between 30 mm and 35 mm.
Turbine inducer diameter (C): between 90 mm and 100 mm.
Turbine axial length (D): from exducer edge to front of inducer must be between 35 mm and 40 mm.
Maximum distance between compressor and turbine (E):
no more than 175 mm from the rear face of the compressor exducer to the front face of the turbine inducer.

   ┌───────────────┐                     ┌───────────────┐
   │   COMPRESSOR  │                     │    TURBINE    │
   │               │                     │               │
   │  Inducer   →  │                     │  ←   Exducer  │
   │               │                     │               │
   │  Exducer  ←───┼───── E ≤ 175 mm ────┼──→ Inducer    │
   │               │                     │               │
   └───────────────┘                     └───────────────┘
            ↑                                       ↑
            │                                       │
   Rear face of compressor                 Front face of turbine
       exducer plane                          inducer plane

I noticed you are posting a lot of AI lately. In the case that you do this, can you please put a disclaimer?

[diffuser]

Can you add some room/distance to the fixed 175mm by elongating the housing/blade shapes?

From Article 5.5.5 of the 2026 F1 Power Unit Technical Regulations:
The compressor and turbine of the turbocharger must meet these dimensional constraints:
Compressor exducer diameter (A): between 100 mm and 110 mm.
Compressor axial length (B): from inducer diam edge to rear of exducer must be between 30 mm and 35 mm.
Turbine inducer diameter (C): between 90 mm and 100 mm.
Turbine axial length (D): from exducer edge to front of inducer must be between 35 mm and 40 mm.
Maximum distance between compressor and turbine (E):
no more than 175 mm from the rear face of the compressor exducer to the front face of the turbine inducer.

   ┌───────────────┐                     ┌───────────────┐
   │   COMPRESSOR  │                     │    TURBINE    │
   │               │                     │               │
   │  Inducer   →  │                     │  ←   Exducer  │
   │               │                     │               │
   │  Exducer  ←───┼───── E ≤ 175 mm ────┼──→ Inducer    │
   │               │                     │               │
   └───────────────┘                     └───────────────┘
            ↑                                       ↑
            │                                       │
   Rear face of compressor                 Front face of turbine
       exducer plane                          inducer plane

I noticed you are posting a lot of AI lately. In the case that you do this, can you please put a disclaimer?

https://www.fia.com/sites/default/files ... -08-16.pdf

Page 15 if you don't trust my quote.

[Vappy]

From Article 5.5.5 of the 2026 F1 Power Unit Technical Regulations:
The compressor and turbine of the turbocharger must meet these dimensional constraints:
Compressor exducer diameter (A): between 100 mm and 110 mm.
Compressor axial length (B): from inducer diam edge to rear of exducer must be between 30 mm and 35 mm.
Turbine inducer diameter (C): between 90 mm and 100 mm.
Turbine axial length (D): from exducer edge to front of inducer must be between 35 mm and 40 mm.
Maximum distance between compressor and turbine (E):
no more than 175 mm from the rear face of the compressor exducer to the front face of the turbine inducer.

   ┌───────────────┐                     ┌───────────────┐
   │   COMPRESSOR  │                     │    TURBINE    │
   │               │                     │               │
   │  Inducer   →  │                     │  ←   Exducer  │
   │               │                     │               │
   │  Exducer  ←───┼───── E ≤ 175 mm ────┼──→ Inducer    │
   │               │                     │               │
   └───────────────┘                     └───────────────┘
            ↑                                       ↑
            │                                       │
   Rear face of compressor                 Front face of turbine
       exducer plane                          inducer plane

I noticed you are posting a lot of AI lately. In the case that you do this, can you please put a disclaimer?

https://www.fia.com/sites/default/files ... -08-16.pdf

Page 15 if you don't trust my quote.

Oof

[Craigy]

Not much to gain much past 18:1 CRs, the additional frictional forces reduce engine life and wipe out the extra power gain. This wasn’t happening before because there was no big advantage.

It’s happening now because the rule was written badly before (they just changed the 18 to 16 for the new rules and then added the temperature measurement later), some teams were looking for marginal gains and going back to 18 was a low hanging fruit and the rule was conveniently written if FIA was corrupt enough, and I mean… they knew the answer to that last question.

Some teams thought the challenge was to get as close as possible to 16:1 in working conditions, others thought start at 16 and see if you get to 18. Amateur rule making.

When Pat Symonds presented his lecture at IMechE in Cambridge Uni in 2019, he mentioned powertrain engineers discussing going well past 18:1. I'm not sure if there's video of it, but he said this right in front of me.
This is why the FIA specified a limit in the 2017 version of the technical regulations -- from 2014 until then there was no static compression limit in the rules at all; the word "compression" doesn't exist in them.

[collindsilva]

Dear Wazari San,

Hope you are doing well, concerning the recent controversy on the CR ratio, what is your take on it, how do you think Merc achieved it, being an engine guy you would have far better knowledge and expertise on this subject.

[lio007]

Dear Wazari San,

Hope you are doing well, concerning the recent controversy on the CR ratio, what is your take on it, how do you think Merc achieved it, being an engine guy you would have far better knowledge and expertise on this subject.

I don't know if I would even call it a loophole. Compression ratio is measured one way and what happens outside of that parameter is up to each PU supplier. There are many ways "to skin a cat" as the saying goes. I personally have no concerns about it and using metal compositions in the piston to maximize power should be each manufacturer's goal IMO.

[collindsilva]

Dear Wazari San,

Hope you are doing well, concerning the recent controversy on the CR ratio, what is your take on it, how do you think Merc achieved it, being an engine guy you would have far better knowledge and expertise on this subject.

I don't know if I would even call it a loophole. Compression ratio is measured one way and what happens outside of that parameter is up to each PU supplier. There are many ways "to skin a cat" as the saying goes. I personally have no concerns about it and using metal compositions in the piston to maximize power should be each manufacturer's goal IMO.

Had read that post, it was more than a month ago, i am afraid maybe Honda has missed the trick since they and Audi are looking for protest, Wazari San may be knowing the actual status, just trying to get some insider info