Mercury XS Powerheads on Older 3.0 Mids

[Stitch King]

So far I have gotten bits and pieces of info on this. Hopefully we can put our heads together and figure out a way to mod the older 3.0 liter EFI plates to work with the Optimax Motors.

If we can keep this thread to a "This is what I know" instead of "It will never work", that would be great.

[Stitch King]

I know that the XS part has solid mounts. I know Simon makes Solid Mount kits that solve that problem.

[Stitch King]

Here's couple of old posts from "Rock" and Simon

You have to change the adapter plate. The compressor needs cooling water and I believe that water exits into the mid thru the adapter plate.
Rock

The 250xs gets cold water from the adapter plate and vent extra air back into the exaust. I would also look for the exaust plate from somthing 2002 or newer.
__________________
Eric Simon
www.simonmotorsports.com

[Stitch King]

The XS tuners are different than regular 3.0 tuners.

Eric has told me personally that the 250 XS tuner is specific to the 250XS.

Wayne Worthy of Hydrotec has made his tuner compatible with XS motors.

[Simon]

You can put a 250xs on any 1997 or newer 3.0 adapter plate. You just have to drill and tap it for the water and air lines. I will post a picture on Monday.

[Stitch King]

Thanks Eric!

[MENNO]

Thanks Eric!

hi stitch no worries about the tuner i think you will not see much difference
in power with normal 3 ltr tuner

or will it cause leaner or richer engine conditions

exhaust adapter plate is important
great that simon can give you the drawings where too tap and put the hoses
on the exhaust adaptor

[Stitch King]

Not sure if the ECU w/factory settings can compensate for tuner differences. I know Eric can reprogram if needed.

Either way, I want the stock tuner. I need the motor to be as quiet as possible. I'm starting to lose some of my hearing and have a constant ring in my ears due to noise exposure over the years. The quieter the better in my case.

[MENNO]

Not sure if the ECU w/factory settings can compensate for tuner differences. I know Eric can reprogram if needed.

Either way, I want the stock tuner. I need the motor to be as quiet as possible. I'm starting to lose some of my hearing and have a constant ring in my ears due to noise exposure over the years. The quieter the better in my case.

don`t expect an 250xs is quiet it is more noisy as an 250efi or carb 3.0ltr
compressor makes lots off noise

[Stitch King]

It's the exhaust screaming like a banshee out of cut cans and drilled mids that wreaks havoc on me. I actually have custom molded earplugs that I use whenever I'm in a performance boat.

As far as the "mechanical" noise, I have access to some of the best NVH test equipment and sound deadening materials in the world. If it's overly noisey I can easily quiet down the offending frequencies.

[Stitch King]

Eric,

Would you please post the pics of the mods to the Exhaust Adapter Plate?

Also what can I expect with using the stock tuner -vs- a 250 XS tuner?

Thanks,

Ken

[MENNO]

Hi stitch King,

Are you already working on your powerhead 250xs

Do you need too rebuild the engine ?

i am asking because i probably get an engine from the same boat yours was on

did you check for compression or leakdown test it ?

open up the compressor too check (i have read something about an bearing that needs too be replaced in the compressor every 300 hrs )


i hope simon can find the pictures for you for the exhaust adaptor drilling and tapping spots

[blkmtrfan]

I can say that without a doubt that a 250xs with the offshore mid is not as loud as a 280 with the sport mid

[Stitch King]

Menno,

I did not do compression readings. I planned to rering the motor and rebuild the compressor from the beginning. Up here we have 6 months of weather that you cannot boat in so I have plenty of time and the parts are only a few hundred dollars.

Ken