View Full Version : MCX vs RTP in an X15

02-28-2013, 04:58 PM
I'm looking to buy a used X15. I've mainly been targeting them with the 350 hp MCX. I've heard from more than one dealer that there is very little difference in perfromance on the 310hp RTP and the 350 hp MCX. Since they are both 5.7l the torque curves are similar and the "true hp" on the MCX is overstated. They claim the MCX will just have about 1 mph higher topspeed.

Can anyone confirm or deny this with data? Are the torque curves published anywhere?

Better yet, anyone driven an X15 or similar size boat with the both engine options?

02-28-2013, 05:02 PM
What year are we talking?

02-28-2013, 05:11 PM
What year are we talking?

2007 to 2010 with my ideal being a 2009

Does it make a difference year to year?

02-28-2013, 05:13 PM
I've seen this come up a few times around here when some one is X-2 shopping. I remember reading in those threads that most of the difference between the RTP and MCX was near the top end. I think the right prop will help. It would definitely be worth demoing the boat to see how well it performs. I rarely get my boat above 28 mphs so the ability to do 38 vs 40 mph means very little to me and how I drive. Much more concerned about how well it does pulling some one out of the water on a deep water start with ballast.

02-28-2013, 05:23 PM
I have the MCX engine in my 07 X15 and last season put the Acme 5 blade prop. I can still run over 40 mph but not by much.

We are running 3500 lbs in ballast.

I will say that the Moomba XLV I had with the 340hp motor was WAY stronger than the mcx

02-28-2013, 06:32 PM
That's b/c the Moomba is WAY lighter...

captain planet
03-01-2013, 08:56 PM
I have the MCX engine in my 07 X15 and last season put the Acme 5 blade prop. I can still run over 40 mph but not by much.

We are running 3500 lbs in ballast.

I will say that the Moomba XLV I had with the 340hp motor was WAY stronger than the mcx

That's b/c the Moomba is WAY lighter...

Yea, exactly, the engine in the moomba is pushing around half the boat the MCX is.

03-01-2013, 09:38 PM
I have not been in an RTP powered X-15 to give you the exact answer you are looking for, but I can say that the MCX engine performs very well in the X-15, even when fairly heavily weighted. With the MCX if you put more than maybe 2500 or 3000 lbs of ballast in, you may want to consider a more aggressive prop to get on plane a little faster, but it makes it.

I'm answering your question indirectly by saying the MCX has room to spare, so if the RTP has similar torque to the MCX I would think it would work fine (especially if you're willing to put on a different prop). If you always weight the crap out of your boat, maybe you'd want to stick with the MCX, but I think the advice to get a bigger engine applies to all boats if you're the type that weights them heavily.

03-02-2013, 12:53 AM
I have a 2008 X15 with the MCX. I have been very happy with it. I don't have much to compare to, other than my first boat a bayliner with a V8 mercruiser, but when looking I figure the more HP the better. Anyway it has been a great boat for me and my use. I couldn't ask for more from a boat. That being said if I was in the market now looking for used and found a good deal with a RTP and all else consider, condition of boat, hours, etc. I'm sure I would be happy just because the boat itself, layout, size, etc. is great. If this is one of those purchases that is kinda a big deal for you and won't be doing it again anytime soon I would wait and get exactly what you want. If you don't you will always have that little needling in the back of your mind about it. At least I would. Can you say obsessive much?

03-02-2013, 02:14 AM
I had the 340 in my XLV (23 footer weighing in at 3600lbs) and agree that engine ran that boat great. We would put 2600 in ballast and it was no problem for that motor.

I really believe that the Ilmor 5.7 that I had in my 2012 X-30 was more powerful than the Indmar I had in my XLV though.

Tristar Racing
03-02-2013, 10:29 AM
Is the Rtp-1 Multiport or Throttlebody injected?

03-02-2013, 10:45 AM
Primary difference is the intake- Block, heads, cam, etc are identical between both. Probably a slight advantage with muliport mcx vs. tbi in the rtp on top end but torque and midrange are probably pretty close. I have the rtp predator and it has plenty of power and runs ~ 44mph wih 4 blade SS prop on 205V (original x-star hull). Some say difference is 10~15 hp in reality. Might be more if engine has the aluminum ETX exhaust manifolds as i understand they scavenge the cylinders much better than stock cast iron manifolds to produce a noticable power gain.

03-02-2013, 04:05 PM
There is a difference in years due to the exhaust. The 2009 has a little less power due to the exhaust being more restrictive to make the motor much quieter than the 2008s.