300XS with incorrect exhaust plate???

[clark rayner]

Guys,

I took my motor in for repair and had the cracked midsection replaced as well as the exhaust plate. My engine was a newer 300XS drop on, on a 250XS mid and plate. These folks had a low hr 225 Optimax that was blown for parts. They claimed it had the correct exhaust plate an mid and put it back together. My research on the Merc parts site shows the two engines run different exhaust plates. This is now installed on my engine, does anyone know if this plate is going to cost me performance?

My research shows 832935A17 for the 225 Optimax and 842777A19 (Solid) or 842777A23 for the 300XS.

I would believe that I may be losing HP with the incorrect plate, just wondering if anyone has any experience here or some input before I go back and get this replaced with the proper one.

Thanks!

[stealthperf]

I noticed that also.... I was going to put a 300 powerhead on mine and was looking up different parts. Nobody could tell me the difference either... Not sure if it has an extra water passage to help cool the exhaust maybe? Possibly machine it in to your plate instead of purchasing a new midplate? Wish I knew.

[rchavis]

I thing they are the same. But one has the soild motor mounts like on my later yr 300X exhaust ?

[clark rayner]

I've run the set up a couple times now, I am playing with engine heights since the set up doesn't seem to be just right. I'd really like to know the difference in the two plates to see if this is something that needs to come off and be replaced. I see the part number with solid and loose mounts listed on the Merc site are different than the exhaust plate listed for the 225 Opti's so there is something different somewhere.

It seems like most parts are interchangeable from motor to motor as long as their 3.0 DFI engines if you are thinking about doing a swap. The exhaust plates do have something different about them, however mine is together and running right now.

[JOE54]

the mtr mounts on standard optis and pxs use a bolt on cover to retain them , the xs plates have cast in mtr mounts that are not removeable and have a much thicker retaining area around mounts for sustained offshore useage (racing) ,bolt have been known to back out of mount covers , and casting on ex plate breaks in frequent rough water useage, I have replaced numbers of pxs plates with xs set up , and would never go the opposite direction on this repair especially if they replaced your plate and used rubber mounts that come on standard optis,TAKE IT BACK DEMAND IT PUT BACK ORIGINAL, ​unless funds dictate other otherwise

[clark rayner]

Thanks for the information. The difference is not in the exhaust, the XS engines were just more solidly mounted. Makes sense.

I may get through the season the way I am set up now and make the swap over winter.

[JOE54]

make sure they used your tuner and not 225 tuner

[EuropeanAM]

make sure they used your tuner and not 225 tuner

Actually, even that will not match the 300XS. 300XS has a completely different tuner from the 225 and 250 models.

This combination should not have happened- period.

[tlt20xd]

I did a 225 pro xs swap to a 300 xs powerhead. The exhaust tuner has completely different exhaust ports and flows differently there is more exhaust gas ported above water and less through the hub. Don helped me with this also and yes it did seam to make a performance difference.

[stealthperf]

I was thinking of doing the same swap... I have a 2006 225 sport xs and it has a different part number exhaust plate.. I figured it would have the good mounts since it's from the race department but the plate is still a different number according to the parts books I found... I figured I would get an aftermarket tuner and a new exhaust plate and a loaded powerhead.. Seems like a fairly economical way to get a 300..

[EuropeanAM]

Personally, I would not recommend anything cut or aftermarket for the tuner- especially if you're pairing it with a fully dressed (warranty covered) powerhead.

[tlt20xd]

Yes mine was a factory 300xs tuner that I went back with.

[stealthperf]

So one pic on the parts diagram shows regular mounts and one doesn't... Is one for the heavy duty mid and one for the standard...... I have the standard mid so would I get the loose mount plate and then get a solid mount kit from someone? I don't do any offshore racing... The plates are pretty spendy so I'd like to get the right one the first time.

[EuropeanAM]

Serial number would definitely help here....

[clark rayner]

So I am in the process of searcing out the correct products for my engine. The tuner is from the 225 and it has cost me top end. These parts are not cheap, especially the exhaust plate. The tuner is specific as mentioned above. I'm trying to locate used low hour parts if I can find them.

Found out that my new mid is OK, the 300XS and 225HP mid are the same.

[EuropeanAM]

Found out that my new mid is OK, the 300XS and 225HP mid are the same.

There are some subtle differences, especially the adapter plate/mount system (depending on WHICH 300XS model is being compared). The driveshaft housing itself is the same, though.

[stealthperf]

Thanks!