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 The EFI Dyno Pulling Mercruiser 502 EFI 415hp
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Posted - 03/05/2007 :  18:36:37  Show Profile  Visit B112's Homepage Send B112 a Private Message  Reply with Quote
This post is going to document how to setup a Mercruiser 502 EFI Engine on a Superflow 901 Dyno. Testing of this engine was primarily to insure proper operation and not actually tune the engine for boat performance. The tuning will be done using on water tests along with an O2 and EGT sensor. The dyno used was not consistently being used to simulate marine environments, thus calibrations and comparisons would be difficult if not impossible.

For safely testing the engine, we use VP Race fuel with 103 octane. This was used to insure the engine did not knock or backfire during the testing. The timing was not advanced to the point where it would fail. Additional pulls advancing the timing or increasing the fuel pressure regulator were not performed.

This is the MEFI3 harness ready for reinstallation on the engine:

(Each connector/wire was labeled and tested.)

This is the engine on the stand testing the fuel pressure of the electric fuel pump.

The following video is the first startup of the engine without any timing applied. The timing was set by turning the harmonic balancer with spark plug one out until compression came into cylinder one. Then making sure cylinder one was engaged by the distributer when installing the distributor. The engine started right up with all the EFI hardware without any problems. The engine was put into initial timing mode and the timing was set to 8 BTDC.

Video of the dyno setup:

Notice that in the above video that the electric fuel pump is mounted on the engine stand and not under the dyno heads like the normal setup. The computer is secured to the valve covers and the water pump is only used to keep water in the engine. The dyno circulates water from an external cooling tank, thus the cool fuel sstem is not being cooled by a water source.

The alternator wire was taped off, the starter wires supply the input of the 12Volts from the battery, but the actual starter wire of the dyno was used. The water temp sensor and Knock sensor for the EFI was used. The oil pressure switch and pressure sender were not used in this setup.

Below is a video of the second pull on this engine. The first pull was not able to bring the engine to full throttle because the throttle control needed further adjustment.

Video of the dyno pull of this setup:

The test results were 60 hp less than the prior pulls on a carburator intake setup. While this is disappointing, the improvement on the carburator was 35hp between a serious leakdown on the engine to a freshly rebuilt engine. This 60 hp difference is being attributed to both the current EFI Tune and the intake on the Mercruiser actually cuts off 1/4" of the intake ports on the head. The heads are large port intakes. The real performance test on this engine is being left to water tests to see if the performance stayed the same or improved on the water.

This closes this chapter of the dyno testing of this engine. Hope this helps folks who are tuning up their Mercruiser engines.


Next, it's reassemble engine time:

This is a picture of the engine on the OffShore Mounts Formula uses in the 271 Fastech:

Notice that the mount attaches in front of the L-Brackets mounted on the stringers:

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