Has anyone swapped out their MEFI3 system successfully with a Holley HP EFI setup using the 500efi intake assembly? I think I'm going to give it a shot this winter.

I have performed the swap on a 502 MPI. Everything plugs right in.

Working on a project at this time 525 EFIs, Holley HP swap, modified TB and upper plenum.

Nice! Have you guys had any hiccups with the system or 02 sensor? I have a fairly mild 502 I'm just finishing up. I have some nice aluminum heads, hyd roller setup, and CMI headers. I'm just trying to figure out if I should stay with this current intake, or go with a complete Holley MPI intake and TB. The 500efi intake that I have has been opened up and I have a mono blade TB on it.

I would imagine the asm style would support more than the mag mpi units , how much more is the question. Would be interested in dyno results

Mark are you doing any before and after dyno pulls. Be interesting to see if there is a power difference between the 2 systems...

I cant give much advice on the intake but can say i have had no hiccups with the Holley system or the O2 sensor. One thing I did that really helped out is install a second O2 sensor. The Holley system runs off the sensor in the Port header. The gauge in my dash runs off the Starboard header. The Gauge has helped me keep an eye on what the computer is reading. Such as a false lean I was getting at idle (sensor too close to open end of exhaust).

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If I was a betting man, I would bet the long runner tpi style of the 500EFI will make a boat load more torque say under 4500 rpm than a Holley Single plane style. However, because of tuninglengths and frequencies, a tall single plane intake with a plenum size and runner CSA to complement the engine of say a 502-540 near 600hp and max rpm of 5800rpm, the Holley style will pull past and beyond from 4500rpm and up.

So................I would love the test and see where it ends up.

BTW: We all know, right ? , that the 454/502MPI intake, 500EFI intake, and 525 Intake are tuned for different level and rpm motors right ? Right.

I think i'm going to stick with the 500efi intake I have and give it an honest try. I hear they're good up to around 600hp? Is there much difference between the 500 and 525 intakes besides the throttle bodies?

We got 641 HP and 649 TQ using a modified 500 EFI intake and throttled body that was machined to a mono plate making them both close to what you get with with the 525 EFI set up from Merc. This was using the 500 EFI computer (remapped) and injectors. This winter we are going to do the same thing with the 525 EFI intake/throttle body as cast but using the Holley HP EFI system on a set of 509's.