Mercruiser 470, 2 to 4 barrel carb conversion.

[HorizonblueDK]

Yes, it has been debated before, but many threads are quite old now, so I think it's time again

Here is the story. I have a 23 footer with a Mercruiser 470 (2 barrel carb) It goes well, I have a 14.5x19 propeller on it, and it pulls the boat on the plane quite ok, when we are two people in the boat. 19 knots @ 3200 rpm.

A few weeks ago, I had my brother and his family on a trip in the boat, we were six people in total. We were mostly cruising slowly around, but at some time, I decided to see if it was possible to get the boat on the plane, with all those people on board. So I hit the throttle and the 470 engine actually managed to get the heavily loaded boat on the plane

But with six people on board, the limit for the engine has been reached, so I have been wondering if a 4 barrel carb conversion will give the engine a bit more power in the low/mid range ?

I bought two junk engines for spares some time ago, for virtually nothing, and one of them was a 488, so I have a complete kit for the conversion. The 4 barrel carb probably needs a rebuild.

Well, let me hear some input. I would like a little more power in the low/mid range, I have a complete set for the 4 barrel conversion laying in the workshop, so should I do it ?

 

[Scott Danforth]

the 4 barrel will give you about 15 more HP. adding a carb spacer between the 4-barrel and the manifold will help with mid-range.

dropping to a 17P and letting the motor sing on the high end will help with a boat load of people

 

[HorizonblueDK]

I guess that most people would say that I should drop the 470 engine and install a V6 or V8, but the 470 does a decent job, so I will keep it for now. I guess that since I have the parts, for the 4 barrel upgrade laying around anyway, I might as well give it a try. I haven't thought about the carb spacer, but it is an easy upgrade, so I will try that as well.

 

[Scott Danforth]

not going to lie, the 470 looked good on paper, then the execution fell down... the cylinder head should have been aluminum, the block should have had a closed deck, the heat exchanger should have bee larger to begin with.

 

[nola mike]

not going to lie, the 470 looked good on paper, then the execution fell down... the cylinder head should have been aluminum, the block should have had a closed deck, the heat exchanger should have bee larger to begin with.

I liked mine. Never had a 470 specific issue in 12 years. Never had a HG blow, never overheated. Cam shaft seals original. Did have the regulator blow, but the original lasted 25 years. Components more accessible than a vee, and cheaper since you only have to buy one set (assuming they aren't NLA). Original manifolds in brackish water. I'm not looking forward to winterizing this year. Seems very 'final', vs. "hey, nice day in december, throw in the one plug and let's go boating!"

 

[Scott Danforth]

I liked mine. Never had a 470 specific issue in 12 years. Never had a HG blow, never overheated. Cam shaft seals original. Did have the regulator blow, but the original lasted 25 years. Components more accessible than a vee, and cheaper since you only have to buy one set (assuming they aren't NLA). Original manifolds in brackish water. I'm not looking forward to winterizing this year. Seems very 'final', vs. "hey, nice day in december, throw in the one plug and let's go boating!"

you could have installed a HX on your 4.3

 

[nola mike]

you could have installed a HX on your 4.3

I know. Dontcha think I had enough headaches with the install? I still probably can if need be, I have the hx. I'll see how bad winterizing actually is.

 

[Lou C]

I liked mine. Never had a 470 specific issue in 12 years. Never had a HG blow, never overheated. Cam shaft seals original. Did have the regulator blow, but the original lasted 25 years. Components more accessible than a vee, and cheaper since you only have to buy one set (assuming they aren't NLA). Original manifolds in brackish water. I'm not looking forward to winterizing this year. Seems very 'final', vs. "hey, nice day in december, throw in the one plug and let's go boating!"

That’s exactly why I would add closed cooling to any engine that I install to replace my original when the time comes. Ease of rewinterizing you can actually use the winterizing tank instead of pulling out seats bending and stretching etc. Closed cooling + remote oil filter are must haves if I continue owning an I/O.

 

[nola mike]

@Lou C is back! I was pleased with myself that I put in a remote oil filter and drain.

 

[Lou C]

Yep somehow I had another account 18 years ago when I registered and it must have still been active!
As long as my original short block is OK with the reman heads I put on 3 years ago I'll keep running this one, but when its time since it looks like I'm keeping this boat for the near future, I'm thinking of going with a reman pre-vortec non balance shaft engine just like the one I have...why...because I prefer the simpler more reliable mechanical fuel pump, the heated intake allows me to keep using the Quadrajet with the well style choke, and I prefer the adjustable valve train of the earlier models. Yes they have less hp but its good enough. All my old stuff will fit. I have been buying up spare OMC Cobra parts from midwest fresh water vendors on ebay. Just picked up a really clean 4.3 Cobra drive that looks brand new! My old one is still shifting great.