GR Yaris Balance of tuning and durability limits

Increasing your rpm redline by 5% increases the Inertia load by 25% (I think). Inertia load squares verse the rpm increase, percentage.
I would have to pull out one of my textbooks to check but that something that seems to have stuck in my mind.

Not quite that much. The load is indeed approximately proportional to the square of engine speed, but going from 7,000 to 7,500 (a 7% increase) would "only" increase the inertial load by about 15%.

I think

It is very early

"I think" ??
I was thinking 7200-7500
I might have to pull out my Corky Bell where talks about increasing engine redline

Your Calc is probably closer to the mark.

RPM Scaling: Inertia forces scale up with the square of the rotational speed (RPM²). Doubling the RPM quadruples the inertial forces trying to tear the connecting rods apart.

Sekred said:

I might have to pull out my Corky Bell…

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So a high reving stroker kit is not a good idea then?
Often thought about doing that if filling up the work van got a little cheaper!

Found this video:

430hp at the hubs on E60. Looks like they revved the stock block to 7700-7800rpm

I've come across the details of the current Japanese sprint champion in the UK


It's a 630hp car running a stock bottom end! Between this and the Motive garage running over 500hp, I'm rapidly forming the opinion that if well tuned the stock block can handle a hell of a lot!

I think there are some things they do to help with achieving that power. The Powertune chap seems to know a fair bit.

Boosted8 said:

I've come across the details of the current Japanese sprint champion in the UK

Fensport GR Yaris 2026

Follow our progress in our Sprint RaceSpec GR Yaris, with 630bhp and 7 speed sequential, can we keep up with the faster cars?

www.fensport.co.uk

It's a 630hp car running a stock bottom end! Between this and the Motive garage running over 500hp, I'm rapidly forming the opinion that if well tuned the stock block can handle a hell of a lot!

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I know a guy with stock bottom end running 500 HP, it hasn't had any block-related issues over a couple of years with lots of track work.

Bottom end, as in crankshaft and OEM connecting rods but forged pistons?

GJR said:

Bottom end, as in crankshaft and OEM connecting rods but forged pistons?

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Stock bottom end (crank, rods, pistons). Hybrid turbo, cams and springs, head studs. Plus all the supporting cooling and fuelling mods required (E85). Lamspeed built it.

The stock rods are forged, but not as strong as aftermarket alternatives.
Toyota Engines - G16E-GTS

The pattern forming is the big power, resilient cars with stock bottom ends use standalone ECU and lots of alcohol. The stock ECU is more variable and unpredictable in exactly what it targets and why for both boost and timing angles. This means the margin for safety gets smaller if you really push the limits, especially so on pump fuel with it's own variability. I think this is why many of the tuners highly recommend you build with 2168 alloy forged pistons and H beam rods for bigger power ECUTEK tunes for example. It only takes a relatively minor knock event to shatter the OE cast pistons.

Altocumulus said:

Stock bottom end (crank, rods, pistons). Hybrid turbo, cams and springs, head studs. Plus all the supporting cooling and fuelling mods required (E85). Lamspeed built it.

The stock rods are forged, but not as strong as aftermarket alternatives.
Toyota Engines - G16E-GTS

Click to expand...

I should have added this is running MoTec ECU.

Boosted8 said:

The pattern forming is the big power, resilient cars with stock bottom ends use standalone ECU and lots of alcohol. The stock ECU is more variable and unpredictable in exactly what it targets and why for both boost and timing angles. This means the margin for safety gets smaller if you really push the limits, especially so on pump fuel with it's own variability. I think this is why many of the tuners highly recommend you build with 2168 alloy forged pistons and H beam rods for bigger power ECUTEK tunes for example. It only takes a relatively minor knock event to shatter the OE cast pistons.

Click to expand...

I spoke to a well regarded tuner who posited that incidents of a major kind with pistons exploding and what not were almost haphazard and down to manufacturing defects. I think there are many things you can do with an engine that will limit things going pop, most of which are a lot cheaper than a built engine.
I think Motive's series is really helpful in producing safe power.

I'm not aware of this. I don't believe there's any helpful data available to prove or pinpoint the presence of a defective piston? I have to assume if it's a genuine problem in your vehicle, you get to find out quite early in your ownership via the first time your fuel quality drops below what the ECU expects due to learnt timing advance or the first time you tune the car and increase the cylinder pressures.

Theres no doubt the OEM pistons are (very?) brittle because of the manufacturing technic.
My theory is very high combustion temps is the likely cause of failure. I am not even going to mention detonation here.
The failure will start somewhere; in a certain area of the piston itself I mean.
Carrying out a failure analysis to find the Root cause would be difficult (and expensive) because there's not much left of the piston when it explodes.
Maybe we could just ask Toyota

Good to keep perspective. 500whp on the wheels is like 650hp on the crank.
That's:
800hp on a 2l
1055hp on a 2,6l
1220hp on a 3l
1625hp on a 4l
2315hp on a 5,7l
3250hp on a 8l

You can fill in what engines fit those capacities.

Of course a piston is highly stressed for combustion chamber pressure, heat and inertia, I find it difficult to say a piston is 'bad' or 'fragile' just because it doesn't hold up to these power levels.

Running E85 fuel burns cooler and prevents a lot of detonation, it also reduces the need for air and boost carrying it's own oxygen molecule in the fuel. They also use massive port injectors that add massive fuel cooling to the cylinder, which direct injectors don't.

And a handful of cars running a few time attack laps per weekend does not equate long term reliability, more like managing immediate engine failure, which is OK for the application. Also we don't always know the backstory, but we know that e.g. the Fensport car isn't on its first engine block.

Bit random but I talked to the owner of JRM here in Sweden that has a long list of TA wins, and he used to run a 900hp Evo6. And he was always afaid it would go bang. Now he runs a half power Supra and he's faster and having way more fun actually driving a lot. Just to say that driveability and reliability go some way too.

I feel more reassured from this research I'm not a total lunatic for possibly having a go at 23psi @ 7500rpm on stock bottom end with 99ron. If it all goes wrong a new short motor ready factory built is £2800.

At the very least a partial lunatic! good luck!!