IzzysAuto

This is an old thread but I have some input to it. By what definition are you talking about by the strength? Amount of boost an engine makes? Amount of horsepower and torque it puts to the wheels on the same dyno same locations same day and weather conditions? there are many ways to determine the strength of an engine? The true measurement of strength also include durability and drivability too. Having owned a BPU GTR and a big single turbo Supra I can tell you between those 2 which were crazy fast but the way the power is delivered was totally different. Through all the years and all the fast cars I can here is my opinion of the strongest engines made from the factory that are available here in the use by size. Keep in mind these numbers i am giving you are from a mustang dyno and on 93 octane gas.

4 cylinder = 4G63 Evolution motor will safely handle 450 WHP and 450 WTQ

5 cylinder = 2.5 used in the US spec Audi TTRS can safely and reliably make 500 WHP and 500 WTQ on 93. ( Clutch will not last that long same goes for EVO lol )

6 cylinder = 2JZGTE Supra engine can safely make 650 WHP and mid 500s WTQ if you got the right size turbo. problem is power band is very narrow due to size of turbo. These things like a quick spooling smaller turbo and keep it in the 500s for a very fun car i had to learn the hard expensive way with this platform.

8 cylinder = this is difficult to answer normally aspirated on pump gas the AMG 6.3 engines are hard to beat. On OEM supercharged applications the Trinity Engine from the 2013-2014 Shelby GT500 is a beast and so is Chryslers Hellcat engine.

As for the V-10 and V-12 application i do not have any first hand experience with them to comment on other than from what I have read

Helicoptah

for petrol - 5th gen Viper. older, forged release of the 8.4l viper can make 3000+ hp on a pair of turbos. it can take 30 ish psi of boost. but why are you even talking about pressure? you can make a lot of pressure on a tiny turbo, and have little amount of airflow, thus stressing the engine less. you should probably talk about CFM. or, battel the most output power from a production motor.

for diesel - Audi Q7 V12 TDI. 39psi of boost stock! and thats a diesel. i am sure that engine can handel double.
another possibility is duramax (forgot which one, but used a lot for super high performance builds) max rated ia 35, can go upto 40, and absolute peak before blowing the **** up is 44.