[The Great Detroit Debate]  [25 Bertram Engine Noise]  [Engine Installation] 

Engine Change....471TI

As many of you know, I had planned on running a custom 371TI 225hp Detroit (because I owned it, and it would work) BUT I became really nervous about the engine's ability to handle a super heavy load in rough seas. I knew I wanted the capacity to haul 3-4 fat boys and cruise along at 20 kts, so I felt like I needed a little mo-juice. So what to do?

Based on my budget I basically only had one option,. move up to a Detroit 471TI 325hp. The extra 100 hp will make a big difference when the boat is loaded down with fat boys. The reason this was my only real option is because basically all the parts I have accumulated to build the 371TI will fit & work on the 471TI (thanks Detroit) So here's the list of MY stuff that is now going to be installed on the 471 long block:

1) Coolant tank & exchanger core

2) Raw water pump and drive assemblies

3) Marine gear (Twin Disc MG 5050A)

4) RC configuration tail housing

What! Still A Detroit?

After months of searching and evaluating I had settled on the Detroit 371 series but just couldn't pull the trigger on 225hp....I wanted more. Staying with Detroit basically this means cheap and available parts and it also means that the internal pieces are tough enough to handle 485hp. That's over kill on the bottom end of a 4 cyl 325hp engine. I like over kill.

Here's a few shots of the 3 cyl engine at Stewart & Stevenson, Houston, TX. These photos give you an idea of the physical size of the engine. The short length is a big benefit in a short boat, so I had to do a bunch of measuring to make sure the 471TI would still meet the dimensional needs of the boat, it does...but I will say it's at the max length for the 25 Bert.

The 471TI completely removes any doubt in my mind about having enough power. At 1800-2000lbs and 325hp I now know the boat will be a bull dozer. No guess'in, it will get on with the program and provide one smooth ride. Here's a few pictures of various 471's. Basically this engine is EXACTLY like the 371 + 1 cyl.

This image on the left is a stripped down long block assembly, no accessories are present. The 471 can be configured to anything between 140hp - 325hp.

The 325hp version requires a turbo, intercooler and N90 injectors. Simple formula, I guess that is part of my affection with these engines. They were offered in marine trim by Detroit so part number crossing is not a problem. Go to the books and pick a part number. I am still debating the exact hp I will target. The more you pull out of a given engine, the shorter it lives and the less reliable it is. This rings true for ANY engine.

As you can see by looking at these photos the engines are identical from an accessories stand point. The 371 on the right is shown with the coolant tank / heat exchanger...which will bolt right on the 471! The only thing that won't work is the exhaust manifold, it's missing a hole.

Performance...

Initial performance numbers based on vessel performance simulator software are good. Still  not a rocket, but acceptable in today's world considering the cost of most diesel engines and the rising fuel cost.                             

The 25 Bertram should have cruised between 17 - 20 kts with a WOT of around 23-25 kts. Of course I won't know now. The 471TI should cruise between 22-25kts with a WOT of around 27-29kts. That's big difference in a boat but it's really not about speed, it's about load carrying capacity. If all I wanted was speed, there would be a pair of outboards hanging off the stern!  The economy was a big factor in the selection of a recon, older diesel. The new electronic, 4 cycle stuff get's a lot better economy, but I don't have one sitting in my drive way currently!

Here's a couple of shots of a 471TI industrial or vehicle engine. You can see the intercooler in the air path in the first picture. It sits just above the blower and is fed by the turbo. It's the square box that is bolted in place. That's what keep's the air charge cool enough to keep the engine from burning itself up. Without the intercooler you can't run the big injectors, there would just be too much heat build up in the cylinders.

This is a beautiful example of a 471TI Detroit, clean and everything in it's place...this engine obviously has not been run!

Here is the Detroit diagram on basic 471N dimensions. Sorry for the quality of the image...it's been thought a lot! If your interested in these diamenions, send me an email and I will forward you the original scans. Gear shown is NOt the Twin Disc MG5050A that I am running. It is basically 12" long and has the 10 degree down angle.

Below a sample of the performance calculations from the software on boatdiesel.com, based on the 371TI 225hp Detroit and 8,500lb 25 Bertram, and the second calculation is based on the 471TI 325hp.

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