Hello! I have a 1994 Maxum 2700 scr that had a Gen 4 454 in it. The previous engine was so rust, that I had to break apart the exhaust manifolds to get the engine out of the boat. The new engine that I install is a Gen V 502 MPI and the problem is the exhaust on the 502 didn't have riser spacers. I didn't realize this until I went to put the elbows in and they were to tall. My questions are, is it the boat that needs the spacers because of water line issues? Do I need the spacers with the 502? Can I cut down the elbows? The other problem is I don't think I have enough wire harness slack to raise it up 3 or four inches, because it bolts to the side of the riser. Sorry for the questions all over the place... Thanks in advance

if you need to have the risers higher to reach the the exhaust outlets you need the spacers. And more importantly, if the exhaust is too low water can back into the engine . The risers need to go up above the water line before exiting the boat.
Plus risers that go higher have better chance of protecting the engine from water ingress due to engine cam issues. So if you ever decide to upgrade to a bigger cam the extra height can help.

Seems like my biggest problem now is, I don't have enough slack in wire harness to lift the computer 3 or 4 inches. The computer bolts to the riser.

You running stock Mercruiser exhaust, or the gil-style that came with the 502? I also assume you don't want to cut new holes in the transom for different exhaust location? Your best bet might be to buy the same exhaust you had to cut out of the boat when removing it. You could also cob up a different mount for the ecm with an angle bracket bolted on to bottom of riser. Edit. 502 mpi. Same exhaust as 454. If the spacers were there, they ere necessary. Elbows means thru-prop exhaust. Replace the spacers and either alter the harness or hang the ecm lower so harness reaches.

My comprehension skills must be different than others .
I presume you're meaning to say that your old 454 DID NOT have extensions of the risers but the new 502 does and you didn't realize it until the engine was installed . Is that the case ?
If the old setup didn't have the extensions and you did not have a problem with water ingestion then why would the new setup need them ? If they're stock Merc exhausts it should be a straight swap over , no ?
Having the extensions is a nice safety factor though .

The boat that the engine came from had through the hull exhaust. My original 454 engine had the spacers. I guess I didn't want to wait for them to come in the mail since that is the last piece of the puzzle and I was hoping to put it in the water today.

Actually the other way around, the old had engine had spacer and the new one didn't. I broke the old rusted exhaust apart 2 years ago and forgot that there was spacer. Looked at some old pics on a previous phone and seen the spacers...

Then if you've got through trans exhaust and the original setup had the extensions you're going to have to stick with it . But if it's all stock Merc stuff you're using I fail to see what the confusion is . The Merc manifolds and risers are the same on the 454 and the 502 I believe so there should be no issue with the length of the harness as everything's all going to be in the same place.

Just went out and put a 3" block of wood in place of the spacer and everything lined up perfect. I guess I was hoping someone would say the spacers weren't necessary and I could just cut the elbows 3 inches and have the boat in the water this afternoon... Just ordered the spacers... on or before Friday... Oh well. Thanks for guys help, I appreciate it

Make sure you're absolutely meticulous when it comes to assembling the manifolds and risers/extensions . All surfaces must be spotlessly clean and rust free . Don't forget any gaskets and use some sealer agent as well . Don't be tempted to overtorque either . Many a perfectly good engine has had an early death due to that awful setup leaking .