Hidden Secrets of a Formula 1 Piston

[matthewgrant71]

I'm new to this forum, so please forgive me if I break any rules!

I was a Formula 1 engine designer, project manager and ops manager at Cosworth for a number of years, and I now run my own company Modatek, selling new Cosworth engine parts plus race-used F1 engine parts.

I also write about some of the details behind the F1 engine parts, including this one on the CA2010 piston:

https://modatek.co.uk/the-hidden-secret ... -1-piston/

Happy to answer any questions.

[hollus]

Couldn't fit better in this forum!

[SmallSoldier]

Really enjoyed the article! Thanks for sharing

[gruntguru]

Hi Matthew. Nice article. Thank you for posting.

Could you describe the function of the "accumulator groove"?

[matthewgrant71]

Sure, I wrote a blog post about it here: https://modatek.co.uk/piston-accumulator-groove-tech/

Here's an extract from the post that explains how the accumulator groove works:

"It is inevitable that some combustion gases will escape past the top compression ring. This might be due to oversize ring gaps. Another reason is the unsettling of the top ring when the piston rapidly changes direction at TDC at high engine speeds. To combat this, the small additional volume in the accumulator groove reduces the pressure on the underside of the top ring.

"This reduction in pressure is an effective method to reduce or eliminate unwanted ring flutter. This is a phenomenon that can have an adverse effect on engine performance and can potentially lead to high levels of blow-by. (Blow-by is the escape of combustion gases past the ring).

"The reduction in pressure in the accumulator groove also has a beneficial reduction in pressure above the second compression ring. Stabilising both compression rings will improve the sealing performance of the rings."

[Hoffman900]

That little bit of extra volume is enough to drop pressure a worthwhile amount? re: accumulator groove

[SiLo]

Certainly a welcome addition to the forum!

[matthewgrant71]

That little bit of extra volume is enough to drop pressure a worthwhile enough? re: accumulator groove

Yes, it's a small volume but the time to pressurise or depressurise is incredibly short.

[saviour stivala]

That little bit of extra volume is enough to drop pressure a worthwhile enough? re: accumulator groove

Yes, it's a small volume but the time to pressurise or depressurise is incredibly short.

Yes. The time is incredibly short indeed, On the CA it, the pressure/depressure changes over 600 times per munite at 20K RPM.

[vorticism]

I was a Formula 1 engine designer, project manager and ops manager at Cosworth for a number of years...

Since you were an insider, and if you were there circa 2013:

--What was the atmosphere at Cosworth like around that time? The FIA/FOTA had decided with the turbo-hybrid formula that engine supplying in F1 was to be the domain of big OEMs only, by demanding development, on a short schedule, of large power-dense batteries and high speed electrical devices on top of a challenging combustion specification. Yet Cosworth had been with F1 for fifty years, a pumping heart in the sport for decades.

--Do you or your colleagues have a general sense of how much is cost to supply one year’s worth of V10 engines vs one year of V8 engines vs one year of V6 hybrid power units? Factoring in allotment rules and inflation.

--How important was F1 for Cosworth relative to Cosworth’s other markets?

--What’s your assessment of Cosworth’s V10 and V8 competitiveness across the NA era? A Cosworth V8 once beat both V10s and V12s in 1994 with Benetton at the hands of Michael Schumacher. If Cosworth had been partnered with Mclaren or Williams or Red Bull or Brawn (other successful non-works constructors, garage teams), the 90s, 00s, and 10s might have looked different for them.

[matthewgrant71]

2010 to 2013 was actually a great time to be at Cosworth (at least it was for me). We were the last of the independents, and we really thrived on making an engine that we felt was on a par with the big manufacturers.

It was difficult to make any improvements in power because the engine was homologated, so we focused on reliability and cost effectiveness, and I think we really excelled in doing that. I don't think we had a single failure or stoppage due to engine issues in the last couple of years, and we came in under budget with our engine build costs.

It's hard to put a price on what all of the alternative configurations would cost. Most of the cost under today's regulation comes from designing and developing an engine that will meet the required reliability levels. Back in 2010 we had to make sure that we could get to 2,400km on an engine, and that was for the 8 engines per driver regulation ... now it's down to just 3 engines, so the mileage requirement is even higher, probably around 6,000 km per engine.

When you consider that 20 years ago we didn't have to reuse engines, the mileage requirement was only 500 km (and we struggled to get engines to last that long!), so we spent all the budget chasing performance.

To answer your last question, and obviously I'm very biased, I would say that from 1999 onwards we had one of the lightest engines on the grid, and we were near the top in terms of power, probably not right at the top. But then outright power wasn't always the target. Things like packaging, thermal efficiency, driveability, etc were equally important.

[vorticism]

Thank you for the insight. Were you involved in any blown diffuser mapping? Did EBD tuning influence the design of the internals at all, or was that all down to the ECU?

In addition to achieving higher mileage, the latter high endurance 2.4 V8s were making about the same hp/L (I find 750 hp for the 2013 Renault engine) as the 3.0 V10s. So, hats off to you there. With another few years of dev, do you think they could have been made to go to 6k km like the V6s? Or does having 2/3 of the redline offer too great of an advantage in terms of reliability.

Speaking of the V10s, I assume that circa 2005-2006 it was a simpler, less costly solution for all the engine suppliers to reduce cylinder count by 20% than to reduce displacement alone by ~20% (maybe closer to 15% factoring in frictional and pumping losses, combustion side effects from downsizes, etc). Although it would have been nice to retain the cylinder count and sound, and would have been interesting to see what the limits were for ever smaller cylinders, and how fast a ~260 cc piston could reciprocate (Ferrari had 250 cc pistons running 17k RPM circa 1996), it would have entailed major redesign of the heads, valves, pistons, etc. Or at least, that is the assumption. Can any case be made that scaling the V10 to ~80% size would have been not cost-prohibitive vs the removal of two cylinders and the redesign of a crank? We’re in the age of CAD (easy parametric scaling) and I can’t imagine the manufacturing changes that drastically at 80% scale. The fluid dynamics may change significantly as you scale down, but then again, year on year, the engine devs would have already been doing CFD work and reshaping ports and coolant channels anyway. So I guess the question is: was scaling truly cost prohibitive? Maybe there were additional concerns, such as stressed member rigidity as you scale down.

To your last point, indeed some customers would probably take a hit on peak HP in exchange for smaller radiators. And durability. No chance of points if you don't finish. Although you also list packaging in general in terms of deliverables, in the context of these NA V8s. As independents, was that compromising? Not having both the chassis and engine designers under the same corporate umbrella.

[gruntguru]

Sure, I wrote a blog post about it here: https://modatek.co.uk/piston-accumulator-groove-tech/
. . .

Once combustion pressure drops again, does the accumulator groove discharge back to the top ring groove, down to the lower rings or both.

[saviour stivala]

Qouting from motor trand:- The science behind piston ring and grooves explained. ''The accumulator groove is machined into the piston between the top and second ring. Its purpose is to provide additional relief space for pressure ascaping past the top ring to build up before attemts to pass the second ring. It supports top ring sealing by relieving pressure and it helps reduce ring flutter due to pressure changes. Accumulator grooves have proved most effective and are common feature on many, if not most racing pistons''. Having qouted all that, it must be said that it, the first use of accumulator grooves in pistons ring design is attributed to drag racer Bill ''Grompy'' Jenkins.

[matthewgrant71]

Thank you for the insight. Were you involved in any blown diffuser mapping? Did EBD tuning influence the design of the internals at all, or was that all down to the ECU?

In addition to achieving higher mileage, the latter high endurance 2.4 V8s were making about the same hp/L (I find 750 hp for the 2013 Renault engine) as the 3.0 V10s. So, hats off to you there. With another few years of dev, do you think they could have been made to go to 6k km like the V6s? Or does having 2/3 of the redline offer too great of an advantage in terms of reliability.

Speaking of the V10s, I assume that circa 2005-2006 it was a simpler, less costly solution for all the engine suppliers to reduce cylinder count by 20% than to reduce displacement alone by ~20% (maybe closer to 15% factoring in frictional and pumping losses, combustion side effects from downsizes, etc). Although it would have been nice to retain the cylinder count and sound, and would have been interesting to see what the limits were for ever smaller cylinders, and how fast a ~260 cc piston could reciprocate (Ferrari had 250 cc pistons running 17k RPM circa 1996), it would have entailed major redesign of the heads, valves, pistons, etc. Or at least, that is the assumption. Can any case be made that scaling the V10 to ~80% size would have been not cost-prohibitive vs the removal of two cylinders and the redesign of a crank? We’re in the age of CAD (easy parametric scaling) and I can’t imagine the manufacturing changes that drastically at 80% scale. The fluid dynamics may change significantly as you scale down, but then again, year on year, the engine devs would have already been doing CFD work and reshaping ports and coolant channels anyway. So I guess the question is: was scaling truly cost prohibitive? Maybe there were additional concerns, such as stressed member rigidity as you scale down.

To your last point, indeed some customers would probably take a hit on peak HP in exchange for smaller radiators. And durability. No chance of points if you don't finish. Although you also list packaging in general in terms of deliverables, in the context of these NA V8s. As independents, was that compromising? Not having both the chassis and engine designers under the same corporate umbrella.

I didn't personally get involved with hot blown diffusers, but I do know that it caused a lot of grief with exhaust valve temperatures. I heard it running at the track once during a private test session at Silverstone with no other cars running, and it was so loud! You could hear the car going round the entire track and know exactly where it was.

With regards to extending the mileage on the V8, then yes it would be entirely possible, it would just mean compromising the performance. We (Modatek) have several customers who can get to 5,000 km on their V10 and V8 engines.

You are right in that going from V10 to V8 was much cheaper than trying to scale down a V10. I saw an interview somewhere with Bruce Wood (Cosworth MD) where he explains that the 300cc cylinder with the bore to stroke ratio that we were all running was about optimal. It would have been great to keep the V10 (and maybe V12 too) but it wouldn't be as simple as just changing the scale, it would end up being a complete redesign of just about every component, starting from scratch.

Your last point about not being able to work alongside the chassis designers is a good one, and its true that it works better if engine and chassis designers are under one roof. But nowadays, with better communication technology and fixed rules for things like engine mounting points, it's less of a concern.