GR Yaris Why limit boost on warm up

[Mintmansam]

I thought I’d ask this question as I think I see the reason why, but wanted to throw some more thought into it

The car limits BHP output on warm up, like other performance cars, however these appear to be limited by rpm and not load. I understand this faster moving valve train, pistons etc would need thinner oil.

Why does the GR limit on Load, surely 7,000 rpm at low load or high load is the same frictional effect on the valve train?

Now here’s my thought. Is it load restricted to limit differential of the heat within the block? Higher mechanical BHP/kW output will produce higher heat output. Are Toyota limiting heat output to minimise heat differenatail in the engine?

I’m thinking it’s an open deck, small displacement engine so perhaps it’s “prone” to higher expansion rates ? Or could it be an emissions thing?

Thoughts please

Or it could be something completely different , just wanted to get other peoples take

 

[Onehp]

It's indeed thermal expansion rates of the engine on warmup. Put too much load=heat in a cold engine, the pistons will 'grow' too fast relative the higher mass engine block, causing excessive wear, maybe even scoring, if you're an utter nutter one could even seize an engine.
It's also a matter of lubrication, cold viscous oil not flowing quick enough in the right places and high load is also a recipe for breaking the lubrication film. Higher rpm without high load actually helps shear and thin/heat the oil (but not 7000rpm obviously, I mean not labouring the engine on low rpm with boost).

Really it applies on all engines but it becomes worse with an engine with very high specific output capable of generating a lot of heat quickly, and the smaller gaps and tighter tolerances one wants to run with modern thin oils.

This is all generally speaking, I don't know the exact design intent of the engine designers, nor the material choices or other design choices for performance that could possibly warrant extra caution.

 

[Kaxe]

Don't you just love it when the car has warmed up and the car comes alive!! ...what an animal when you start booting it!!

 

[Mintmansam]

Don't you just love it when the car has warmed up and the car comes alive!! ...what an animal when you start booting it!!

Yer you certainly tell the difference, you realise the length of each gear.

These cold winter days means you have to wait longer, though I like to wait a few mins more as well

 

[Smoothound]

Yer you certainly tell the difference, you realise the length of each gear.

These cold winter days means you have to wait longer, though I like to wait a few mins more as well

I generally wait till the oil temp is around 70 degrees before I start going for it...

 

[leviGRY]

What @Onehp said.

I also wanted to mention the turbo, it goes from sat still at ambient temperature to spinning at a 6 figure RPM and 400+C exhaust gases flowing through it. That initial warm up process needs to be managed, ie not putting too much stress on it and heat into it quickly.

 

[Jip]

The biggest wear on an engine is during warm up. So a car that doesn’t do many miles, and has a stop start life, will in theory have more detrimental wear than one that is warmed gently and then used all day.

 

[Michael Knight]

I'm actually glad it has this feature - its so easy to just forget that car is still warming up. Really well thought (again!) at Toyota. No wonder terrorists use their vehicles as they last.