Trojan Boat Forum

I've been thinking in an academic sense (hopefully) about replacing the Chrysler 318 with a GM 4.3L MPI V6. The Marine Power 4.3L MPI V6 makes 230 hp at 4,000 rpm which is basically equivalent to the 225 hp at 4,000 rpm that the Chrysler 318 makes. I see two advantages when compared to repowering with a GM V8. First, the V6 will be lighter. Second, the V6 is shorter in length. The engine on a F25 or F26 is angled. The GM V8 engines tend to be too tall requiring modification to the engine hatches. With the V6 being shorter in length, it's possible that it might clear the engine hatches and not be too tall.

I also see two disadvantages. The first is that the V6 is only available in LH rotation. This would require changing props, etc. I also don't know if the V6 would have enough torque to push a 6,000 lbs. boat around. The torque of the 4.3L MPI V6 is 267 ft.-lbs. Does anyone know what the torque of the Chrysler 318 is?

Any thoughts on the idea would be greatly appreciated.

Better check your specs that engine makes its rated HP at 4800 rpm not 4000 . You will have to down size on the prop .

You could put a lower gear in the new transmission and achieve the torque you want. I do recall a truck we had with a 4.3 and it was a beast for a V-6. I thought the 4.3 was a 5.7 Liter minus 2 cylinders. I bet it does have a wot of over 4000 though.

The Michigan Motorz website lists 4,000 - 4,400 WOT (http://www.michiganmotorz.com/complete- ... p-330.html). I just checked the Marine Power website and it lists 4,800 WOT (http://marineenginedepot.com/20056/0/Ma ... e-Package/), so it looks like the Michigan Motorz website is wrong. 4,800 divided by 4,000 is equal to 1.2, so using a transmission with a 1.2 ratio should let me use the same prop dimensions. Are there any 1.2 ratio transmissions that also switch the direction of rotation (LH to RH)?

It looks like the ZF 45-1 IV might be a good fit for this application. It's available in a 1.2:1 ratio and has a 20 degree angle like the Paragon PV V drive. It is 4 inches shorter in length than the Paragon PV V drive, but I think the engine room has enough space to move the engine back 4 inches. It does not offer an option to reverse the shaft rotation, so a change from RH to LH rotation for the propeller would be required. I'm not sure if this would adversely affect the boat handling or not.

What effect would the prop walk have on your maneuvering

So cruise with the V6 will be 3820 rpms instead of 3200. Do you feel comfortable running the engine that hard?

obeejr wrote:So cruise with the V6 will be 3820 rpms instead of 3200. Do you feel comfortable running the engine that hard?

If you set your gearing to the desired RPM you should not have to run it that hard. I think the 4.3s have a good track record, and in truth will probably be more economical with the right set up. If they could run 454s in a 25,000 lbs 12 Meter, you should have no problem running a modern 4.3 in a 9000 lbs f 26.

Correct that...6000 lbs

obeejr wrote:So cruise with the V6 will be 3820 rpms instead of 3200. Do you feel comfortable running the engine that hard?

I currently cruise at 21 mph at 3,000 rpm. With the V6 I would cruise at 21 mph at 3,600 rpm. If I ever do make the switch I would probably in reality cruise at 20 mph at 3,500 rpm. I think a Vortec 4.3L V6 should be able to cruise comfortably at 3,500 rpm without any harm.

would like to see how this plays out , how soon are you planning this? Would be interested in the results as if it worked I'd probably follow suit. lol of course you pull the trigger first ok. keep us posted

trojanmanXSagain wrote:would like to see how this plays out , how soon are you planning this? Would be interested in the results as if it worked I'd probably follow suit. lol of course you pull the trigger first ok. keep us posted

Hopefully my current engine/transmission package will last another 10 years, so I won't be doing this anytime soon. What made me think of it is the fact that the GM V8 engines tend to be too tall and the Trojan hatches typically need to be modified. The idea just came to me one day that the hatches might not need to be modified if a GM V6 is used. I find with a major change like this that it's best to take a long time to think things through.

Try searching 'Repower" and my screen name, I went outside of the norm on our previous F-32, and installed inline 6 165 hp Mercruisers, turned out to be beautiful installation and cruising around the bay at 10-12 knots, they sipped fuel 3-4 gal an hour.

Maybe you should consider a transmission change in lieu of a whole engine swap, and use transmissions with an angled output shaft so your engines sit level. that would solve the clearance issue?

At this point engines are changing drastically with technology. Who knows what 10 years will bring. One of the most interesting power set-ups today is fords eco-boost V6 and how much torque it produces at such low RPM, even surpassing Ford's largest V8. Maybe diesels will be more common, and hence cheaper by then too.

ok I found your post , nice job btw, now here come the questions. you stated with the smaller engines you were still able to get on plane? how fast were you able to go with that set up? What would one expect for speed if a 6 was installed into an f26? The ans is beyond my math.engine skills...