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loss of power at high rpm

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the car has coil on plug and gaped spark plug correctly (0.65) , and no fault or restriction in the exhaust its 3 inch free flow , fuel is also perfect 450 lph pump and the car isnt lean or rich its 11.5 afr at 6800rpm i tried everything lean / rich the car advance / retard ignition and nothing affect can u tell me what else should i look at

Hi Moataz,

What would really help us to help you is if you gave us some more information on the engine,

What is it? Is it N/A, turbo or supercharged?

Do you have any other modifications which could affect the VE of the engine? Cams? Head work?

Have you done a compression test? Leak down test?

Is it misfiring or just going flat?

Mechanical issues -- do you have sufficient valve spring pressure (ie, are the valves floating and failing to close). Is your cam timing correct?

Intake restriction ??

You've mentioned COP - are you sure you have sufficient dwell time to charge them, and current capacity in your wiring? What happens to battery voltage at high RPM?

Finally, are there any indications from the ECU sensors that something is changing at 6800 RPM -- could be anything from fuel pressure, inlet air temp, manifold pressure, throttle position? You should look for a correlation in the data with the output you are measuring on the dyno.

Good Luck!

its a bmw m50b28 engine turbo boosting 13-15 psi stock head and cams no mod. and stock timing cams the m50 head with a double spring valves

dwell time is 3.2 ms battery voltage 13.5

no intake restriction at all and no abnormal readings from any sensor

yes i made leak test for the head and valves and every thing was fine

and compression test also fine , no misfire its just noise with no acceleration at the last 500 rpm

Your dwell time could be a cause, normally it causes a misfire type event though. try dropping that to 2.5ms max. What size intercooler pipes and intake are you running?

What ECU are you running? Any chance you could post a copy of your map and a log of the event?

intercooler size 24'*12*3 piping 2.5"

im running megasquirt 3x

I'm still going with insufficient spring pressure. Also, doesn't that engine have hydraulic lifters? If so, I understand that valve float and with hydraulic lifters can lead to pumping up the lifters and then you've got a real power loss as the valve clearance has been reduced too much.

What happens if you reduce the boost level -- does the car still have a power drop at high RPM?

You say , noise without acceleration , maybe clutch is not up to the task.

yes its hydraulic lifters with a dual valve spring i dont think its insufficient spring pressure my friends opens more than 1.5 bar without any problem , i reduced the boost to 9 psi still the problem occurs ,

its not clutch slipping bec. its a new one flywheel , disk and pressure plate and i didnt smell or feel slipping

Do these engine have a variable cam?

no variable cams and everything stock at the head 240 intake 228 exhaust

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