New Aritcle - thoughts on a Mercury Racing 3.4-liter R-series engine

[skialot2]

I found where i saw 4.8" diameter. It's only for the 150R.

The 150R comes with a 4.8" diameter 1.85 ratio no name gearcase. Available in 20" and 25" shaft lengths. Left hand rotation available for twins in 25" shaft only.

The 200R is available with a Torque Master or a Sport Master 1.75 ratio in 20" shaft only.

[Greg G]

Are the new 150 & 200R only available with DTS or can they be hooked up to a non digital system with livorsi gauges and a in-control foot throttle and shifter? I heard the 250R can be purchases in either configuration.

I would think on a smaller offering like this Merc would offer both. The fishing V6 225 might give a tip off?

[Petey]

150 & 200R are DTS only, 250R is mechanical, one model only. The 300R has 50+ different models

[river rocket]

I didn’t know “Speed Control” was a thing until I read your post and looked it up. Damnit. No reason for that to be on an R motor. Or there at least needs to be a way to turn it off. That last thing you want in a small pad v is the computer changing the throttle position without driver input. Ugh

I have spent a lot of time in a single engine 21' V Allison at 100 plus and you don't even notice the speed control. In fact you will love it. Gone are the days of the motor shutting you down up top when bumping the limiter. Now you can just drive the boat on the limiter and enjoy it.

[river rocket]

I'm stumped why they went DTS only on these motors. I'm guessing it is to push the market this way and at some point we will see mechanical disappear. It just seems like a lot of crap that isn't needed along with additional expense for a motor going on a smaller boat that is a more cost sensitive market.

I have DTS on my Allison now with the 450R. I weighed it all. It added 15-20lbs to the boat. DTS offers one advantage that I can see. It allows for dual throttle setups. Currently I can run my 450R with a hand throttle or foot throttle at the push of a button. I would never go fast like that. However, I did use it when idling or when towing tubers. In long no-wakes it's nice to get away from the foot pedal. I could do the same thing with Troll control on the merc monitor. When tubing it was nice to not have to drive with the foot throttle. Aside from that, it only added un-needed weight. I'm switching back to a 300R right now. It will be mechanical. All the DTS junk will sit on my shelf.

[David]

How did the 450R run on the 21 Allison? Why are you going back to the 300?

[Petey]

I'm stumped why they went DTS only on these motors. I'm guessing it is to push the market this way and at some point we will see mechanical disappear. It just seems like a lot of crap that isn't needed along with additional expense for a motor going on a smaller boat that is a more cost sensitive market.

I have DTS on my Allison now with the 450R. I weighed it all. It added 15-20lbs to the boat. DTS offers one advantage that I can see. It allows for dual throttle setups. Currently I can run my 450R with a hand throttle or foot throttle at the push of a button. I would never go fast like that. However, I did use it when idling or when towing tubers. In long no-wakes it's nice to get away from the foot pedal. I could do the same thing with Troll control on the merc monitor. When tubing it was nice to not have to drive with the foot throttle. Aside from that, it only added un-needed weight. I'm switching back to a 300R right now. It will be mechanical. All the DTS junk will sit on my shelf.

To simplify the offering and if you are repowering and want to keep mechanical controls, you can go with a 300R that is only 30-40 lbs heavier than the 200. I think you are referring more to the AMS system which is a mid section and steering system, DTS components alone on a CMS mid section don't add hardly any weight. Here is a Valero I'm rerigging for a 200R, I will take the smoothness and added features of DTS any day of the week:

[river rocket]

Cool setup. Thanks for sharing.

I struggled with DTS vs Mechanical on my 300R which is why I’m asking and writing all this. I'm interested in other points of view on the topic.

I’m referring to dts. The AMS mid section is a tank and is a performance sucker on small single engine performance boats. If the 450R had the CMS midsection it would still be on my boat.

DTS requires a rigging center which is a component mechanical motors do not require. While its not 100lbs it, and the additional parts, when added up come in around 15lbs (based on your configuration). As noted, if you take that weight and add it to the total motor weight you are starting to close the weight gap between a 250R and 300R. In my Allison, the cleanest and shortest wiring was to put all the DTS electronics on the driver side, this meant the weight basically doubled as I need to ballast the weight to offset it. All that makes a difference in a 100mph v bottom. That and the parts are not cheap. If you are re-rigging that is a hidden cost and weight. Since this is a performance boat site and this motor is more than likely replacing a much lighter 2.5's, I think the additional weight is something to know about.

In addition, you add complexity to the trouble shooting process with more cables and the electronics that are part of the rigging center.

I weighted that against what does DTS offer? The capability to use the foot and a hand throttle? Everything else the mechanical motors do. The mechanical 300r converts the cable input to digital anyway. So shifting is smooth on both mechanical and dts. Throttle is the same way.

If you look at my old 2005 Allison XB21 it had a promax, then a 2 different optimax motors, and finally a 300R. The boat was built with smart craft. All that was added when switching motors was a clean power harness for the 300R. That is a really simple upgrade between many generations of motors. The new smaller HP R motors don't offer that luxury. I think that was an error on mercs side. They should have the mechanical capability.

[Greg G]

Comprehensive thoughts and write up RR

[river rocket]

How did the 450R run on the 21 Allison? Why are you going back to the 300?

I will give you the long version as the great thing about this forum is people can search and learn from others. The 450 can be had for cheap right now and I'm sure others are looking at it. This is my experience with a 21ft Allison XB21 450R.

Awesome motor on the LCB but not the Allison. An Allison cannot handle the weight or the power. The acceleration can’t be matched for a boat like mine. It gives the boat a power to weight ratio like a 2002 280. But that is where the fun stops. The motor is simply too heavy and powerful to be usable.

If you follow the Fastbass Marine TV YouTube channel you see I have 100’s of hours running a 300r from a standstill to low 100’s on an XB21 300R. The 300R is the perfect motor for the Allison XB21. I had the 450 on the Allison for a year and could never wrangle the boat into running one 5-80 test (or faster). That was a huge disappointment. I have several videos of that test on the LCB. The boat just couldn’t hold it together. The 450 just got the boat all bound up and out of control. It was super fun from 5-70. The power was so strong it pushed the nose done, and as you came into the 80's the XB21 deep keel became a problem if the nose wasn't up. I tried many props, different setbacks, and all sorts of boat modifications. It was like having a Dodge Demon at the drag strip on street tires. You can get it to hook up and you take all the fun out of it to do so.

That is the main issue on the low end. The only other issue on the low end is it will eat prop shafts. With a 1.6 case you need a 33 or 34 to keep it off the limiter. From a dig those big props you can't let spin up then bite.


On the top end the motor just had too much power as well. On the Allison I was at 60% throttle at 100. You had to be really careful giving it power at 100. Using the analogy of racing, you can chirp the wheels in 3rd. On a boat going 100, you don't want to chirp the wheels or bust the ass loose. So you had to really watch your foot and ease into the speed or you would lose the boat. That wasn't any fun. Candidly, the Allison XB21 is not a 110mph boat. It is a solid 90-100mph boat, but at 105 and more it has a lot of quirks. The LCB on the other hand ate that crap up.


In summary, too much power down low to be fun and too much power up top to be fun. It was awesome from a dig to 70 and then let out. let the nose fly then get in it again to about 90, then slow it up into the 100's.

Add that power to a boat that is loaded down in the rear by motor weight and you bring on handling issues as well. The motor was the tail wagging the dog in waves and rough stuff. The Allison, while not a LCB/Cat can run in bigger water. Not with the weight of the 405R on the tail.

The 450R is also a too smart. It will pull power for a number of reasons. It does it down low until the oil is at temp and it does it up top with water pressure and a few temp readings as well. The minimum water pressure on a 450R is 18psi. That is huge difference from the 300R. You have to have the motor deep and at pressure to not have it pull power. It pulls power when the parameters are yellow not red. Ambient air temps in Minnesota put it in the yellow...... None of that crap is on the 300R. I have had it touch 7-8psi and let me keep it running for a few seconds on the 300R.

For those reasons I made the switch. I looked at the V10 400R. It is a little heavier, but based on the manual didn't have the 450R smarts (which I liked). I was heading down that path until a friend let me drive his 2002 280. It really sunk in how the weight was an issue still so I went 300R.

[HydroSkreamin]

Cool setup. Thanks for sharing.

I struggled with DTS vs Mechanical on my 300R which is why I’m asking and writing all this. I'm interested in other points of view on the topic.

I’m referring to dts. The AMS mid section is a tank and is a performance sucker on small single engine performance boats. If the 450R had the CMS midsection it would still be on my boat.

DTS requires a rigging center which is a component mechanical motors do not require. While its not 100lbs it, and the additional parts, when added up come in around 15lbs (based on your configuration). As noted, if you take that weight and add it to the total motor weight you are starting to close the weight gap between a 250R and 300R. In my Allison, the cleanest and shortest wiring was to put all the DTS electronics on the driver side, this meant the weight basically doubled as I need to ballast the weight to offset it. All that makes a difference in a 100mph v bottom. That and the parts are not cheap. If you are re-rigging that is a hidden cost and weight. Since this is a performance boat site and this motor is more than likely replacing a much lighter 2.5's, I think the additional weight is something to know about.

In addition, you add complexity to the trouble shooting process with more cables and the electronics that are part of the rigging center.

I weighted that against what does DTS offer? The capability to use the foot and a hand throttle? Everything else the mechanical motors do. The mechanical 300r converts the cable input to digital anyway. So shifting is smooth on both mechanical and dts. Throttle is the same way.

If you look at my old 2005 Allison XB21 it had a promax, then a 2 different optimax motors, and finally a 300R. The boat was built with smart craft. All that was added when switching motors was a clean power harness for the 300R. That is a really simple upgrade between many generations of motors. The new smaller HP R motors don't offer that luxury. I think that was an error on mercs side. They should have the mechanical capability.

DTS offers a lot of idle/shift/driveability that simply cannot be accomplished as smoothly if at all with a cable throttle and IAC.

Just realize that even the cable engines are DTS, you are just adding the DTS weight directly on the engine and operating it remotely with a cable. It's still DTS at the engine.

As far as AMS goes, I do prefer stiffer mounts than what Merc offered in the 450R, but have driven plenty of cats over 130 with the system and if set up properly, are rock solid. The 500R's are even stiffer and nicer to drive.

As far as 450R water requirements vs the 300R, it just makes sense that putting out more than 50% more power inside the combustion chamber is going to produce more heat and require more cooling. Overall airflow through the engine/exhaust is up, hence the exhaust cooling requirements going up as well.

[DangerNewb]

I had twin 300r with the HD mids and cable operated controls. No complaints with driveability or any other issues other than having to manually sync rpm between the engines while underway. Seems the lighter weight of the engines was worth it. The controls were super smooth.

[David]

Thanks very much for the explanation of the 450R on the 21 Allison. I can't say that I am surprised. The 450R is a lot more weight and HP than Mr Allison ever expected when he designed the boat. And he has been clear about big motors on the smaller Allisons. Even Tuff don't recommend more than 470 lb on their 20 (which is 21'10")

[David]

I had twin 300r with the HD mids and cable operated controls. No complaints with driveability or any other issues other than having to manually sync rpm between the engines while underway. Seems the lighter weight of the engines was worth it. The controls were super smooth.

You sold the Liberator already? Not what you were hoping for?

[DangerNewb]

You sold the Liberator already? Not what you were hoping for?

I'm building a house on Kerr lake and decided the extra money was more helpful than the boat. Particularly with insurance and property taxes on the boat it had a lot of carrying cost. Boat was fine overall. I was able to enjoy it for 3 summers and got most of my money out of it.