Will these headers fit?
 

Hey guys. Checking to see if anyone can tell me if these will fit a 502 mpi. Stock bravo location. I'm worried about the shift brackets and such. Thanks for your help.

http://cgi.ebay.com/ebaymotors/mercr...8#ht_500wt_948

I would guess that the real problem will be with the location of the exhaust tips in your transom.
Will the tips need to be located/installed where your swim step is? Above or below the swim step?
Do you have thru-the-transom exhaust now?
If so, are the tips going to be in the correct location for the new exhaust?
Do you realize the engine will need to be removed to install the "Y" pipe?
Anything that bolts to the stock risers (the EFI box and the remote oil filter) will probably have to be relocated. Not a simple job depending on the year of the 502 MPI.
Dennis Moore

It's a 2001 checkmate convincor. Already has silent choice and tips exit under the platform. Thanks for the reply. Hate to buy not knowing if they will work. But I can relocate the filter and efi box if needed.

The 502 MPI engine will not respond with a horsepower increase from a better flowing exhaust.

An engine with a carburetor will flow more fuel if the engine vacuum pulls harder on the carburetor from a less restrictive exhaust system (The carb jets will flow more fuel with higher engine vacuum).

It doesn't matter how much harder the engine vacuum pulls on the injectors, they will not flow more fuel. The flow of the injectors is controlled by the computer and the fuel rail pressure.
No extra fuel will enter the engine and the improved exhaust system will scavenge the exhaust gasses faster. This will create a lean condition.
It won't hurt the engine but it will not result in any horsepower improvement. You will need to increase fuel rail pressure with an adjustable fuel pressure regulator.
Dennis Moore

I disagree with your statement as most 502 mpi's are excessively rich stock, although I doubt he will see much of a gain though as the exhuast isn't the only thing restricting a mpi and stock cam kills these motors.
Those look like ( I am sure they are) lightning headers that have been painted purple, I used to have the same set on my 272 Baja and my Bud-"oldnavy" on here bought them and installed them on his 1995 Checkmate 28 Convincor so I think they will fit without too much bs. I mounted my shift linkage on my transom when I had mine and had to mount the ecm on its own bracket, Smitty

X2

Leaning out an engine that is set up rich will make more power.
They will not lean it out enough to hurt the engine either. I have CMI headers on my 502mpi's.

Well, I must say from first hand experience, (matthewr) your 502mpi will most definitely respond positively from the exhaust upgrade. Those stock manifolds you have now are very restrictive, not to mention weigh a ton. I have done this very same thing with my 454 magnum mpi with very pleasing results. I have the Dana Flow Torque exhaust system and my engine is completely stock. I could tell immediately my engine ran better, much smoother and much better acceleration all through the RPM range. The boat pops up and planes out much quicker with less effort than before. My boat is only a 21’ and maybe that’s why I can feel such an improvement.

Although I completely agree with (Dennis Moore) in theory, (re-calibrating air fuel mixture) I was told by the manufacture this was not of concern with just the exhaust upgrade. Now, if you were changing cam etc. then definitely.

I also tend to agree with (articfriends) that these engines are set up on the rich side from the factory.

If you don’t end up with the purple headers, look into the Danas, they also have the brackets needed for relocating the shift linkage, remote oil filter and EFI box.

They are very nice, you will like them.

Good luck!

Thanks for the reply guys. Now just bidding to win. I really appreciate the info.

Well, if they don't fit, I may be interested, depending on the price you end up paying. I have lightnings on my boat right now, but would like to get them hooked up to my Silent Choice Y-Pipe. These look to be the factory Lightning switchable exhaust setup.