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Last year, FCP Euro Video Editor Stephen Coppola and I discussed power delivery problems with his SpecE46 (an E46 330i built to an agreed standard) and how he was down on power and speed relative to other cars that should be more or less identical. The engine from his race car is original to the chassis and has accrued some decent mileage with ~120,000 miles in total and ~25,000 miles as a race engine. Maintained well or not, engines will always wear out, and that wear will be accelerated if the engine is used in high-stress applications (such as a race car). 

The M54B30 engine is robust and inexpensive, making it an excellent choice for powering a race car. It’s relatively simple, lightweight, makes decent power + torque, and they are easily sourced as replacement engines since it powered a lot of BMWs in the early to mid-2000s.


In the case of the engine in question, it had inconclusive results last year as to where it was losing its power. The intake manifold had a bad DISA valve, but after replacing that, the engine still lacked the punch it used to have. The butt dyno never lies. After a compression test where all of the cylinders were relatively close in spec, a leak-down test provided conflicting results.  

In order to finish the season last year, Stephen swapped the original engine with a used one. Unfortunately, that used engine did not survive NJMP due to a money shift (we have a full tear-down video on that carnage), so rebuilding the original was the best way to prepare the car for the 2023 season. Circling back to the original engine to see where the power loss was coming from is where this gets interesting. 

Valve Seats Are Wear Items, Too

All engines are air pumps, and for an engine to make power, it needs to be able to seal its combustion chambers. Piston rings, valves, valve seats, head gaskets, the engine block, and cylinder head all play a part in this. Assuming no engine damage and the engine is in time, very little air should escape the combustion chamber when the valves are closed. Any air escaping the combustion chamber should go past the piston rings and into the crankcase. 


Before tearing down this M54 for a refresh, we performed another leak-down test. It was easier with the engine out and on a stand since we’d already removed the intake and exhaust manifolds. Immediately, the problem became clear. Many of the intake valves had excessive leakage. The intake and exhaust valves need to be closed to perform a leak-down test. No air should leak past the valve or valve seat with the intake and exhaust valves closed. With upwards of 60% leakage coming out of many of the intake ports, we knew we had found the problem.

After removing the cylinder head from the engine, we investigated further to determine if this leakage resulted from bent valves, valve seat wear, or carbon buildup. We flipped the cylinder head upside down on a stand and filled the combustion chamber with water to visually confirm the leakage. We found that not only was a substantial amount of water able to leak past the valve seats, but other valves were also leaking on the exhaust side. In total, we found valves to be leaking on every combustion chamber we tested (we stopped at four because that was already very conclusive).

At this point, the cylinder head needed to go to a machine shop to be flattened, crack checked, and for a valve job. It’s always nice to drop off a deconstructed cylinder head to your local machinist as it makes their job easier, and the turnaround time is generally faster. We pulled the valves out of the cylinder head and found many of the valve seats on the cylinder head to be pitted and also found the corresponding seat on the valves to be pitted as well.


It may not look like much, but this deformation/wear is more than enough for air to escape the combustion chamber. And this excessive leakage through the cylinder head will always produce power/performance problems. An issue like this would not be that noticeable on a car driven on the street. However, the lack of performance is painfully obvious when you’re on a race track getting chased down by almost identical cars. 

Everything else in this engine looks great, and we’re satisfied a cleaned-up cylinder head with reground valve seats will fix the performance problem. When diagnosing a performance problem, remember that the engine is nothing more than a fancy air pump. If it’s not sealing correctly, you will lose power. It really can be that simple sometimes. 

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Written by :
Gareth Foley

Gareth is the BMW Make Level Marketer for FCP Euro and has been with the company since 2012. Gareth's BMW obsession started with a hand me down E39 528i when he was 17. From this car he learned how to do his own repair work while also learning more about BMW. When Gareth was at CCSU studying Marketing he had the opportunity to go to SEMA with the college car club. This is where he developed his love of the automotive industry. Since joining FCP in 2012 Gareth has sought out to develop one of the broadest and most accurate BMW replacement parts catalog. he can be reached at

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