Performance Difference?

25thmustang

Lieutenant Commander
Joined
Mar 20, 2008
Messages
1,849
With spring rolling in, I will be getting back into working on the boat. The plan is to tackle the cabin in the next month or so, and then time for the motors. My question comes up regarding the boats power.

The boat is a 27' IMP with twin 3.7LXs. 4bbl carbs, 4" Heat Exchangers, aluminum manifolds etc... The short blocks are trashed on these motors from the PO. I purchased a 25'er with twin 470s. These are the 2bbl carb, 3" HEs, cast iron manifold motors. The 3.7LXs were rated at 190 hp, and the 470s, at 170 hp. My question remains, should I put the 470s in as they sit, and live with the performance being a little lower than it should. Or should I buy the gaskets, and have all the old parts checked to make sure they are true, and turn these 470s into 3.7s?

My idea now, to save some time and money (new homeowner, money is a good thing to save :D) is to put the heat exchangers on and call it a day. I know the power might be a little off (to the tune of 340 hp vs 380hp), but with claims of this, and other similar boats toping in the 40+ mph range, I can't see suffering all that much?

Let me know your guys opinion, and take this into consideration. I bought the boat over a year ago, and it spent 0 hours on the water last year. I have the good parts off the 3.7s, sitting in the shop, but also have two perfect running 470s which could technically bolt right in.

What would you do? Risk waisting another year, trying to get all the right gaskets lined up, have the parts checked over and cleaned and then putting them on, or put the two motors in, and take the boat out on the water?

Thanks in advance.
 

Bondo

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Apr 17, 2002
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71,082
Re: Performance Difference?

What would you do? Risk waisting another year, trying to get all the right gaskets lined up, have the parts checked over and cleaned and then putting them on, or put the two motors in, and take the boat out on the water?

Ayuh,.... I'd install the 2 running motors,+ SELL the barge, buying anything Without 470s(or OMCs) for power...
 

oops!

Supreme Mariner
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Oct 18, 2007
Messages
12,932
Re: Performance Difference?

just to elaborate on bondos comment.....the 470 are notorious for being a troublesome engine...
 

haulnazz15

Captain
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Mar 9, 2009
Messages
3,720
Re: Performance Difference?

I'd be looking at twin 4.3L v6's if you could fit them in there. The 470's would be a bad idea.
 

25thmustang

Lieutenant Commander
Joined
Mar 20, 2008
Messages
1,849
Re: Performance Difference?

I know and have done a lot of research on 470s and have seen first hand the problems associated with them. I looked into a repower, but due to the engine compartment size, there was no option but to find some 3.0s, which I did not want to do. I'm stuck with the 470/3.7 for the time being. I will do what I can to keep track of the cam seal, and make sure I take care of the good motors in there. My saving grace is the motors I have are fresh with no hours on them, which should give me some time to enjoy it.

With that said, other than having the "cursed" motors, what would you guys do?
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: Performance Difference?

If the 190s planed her easily and she ran in the 40s then the power question is probably a non-issue. This assumes all other things are equal to those "claims". I never believe anybody's speed claims that are not:

a) GPS or radar, no current and
b) Loaded up with all of the typical stuff. Important things like beer and ice and those that are less so like fuel :eek: :D
 

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: Performance Difference?

I would expect that you would lose 3-4 mph.... if you wanna run the boat then drop them in and go with it.... if you are gonna put much more into it... save that effort for your next boat.
 

25thmustang

Lieutenant Commander
Joined
Mar 20, 2008
Messages
1,849
Re: Performance Difference?

My thoughts are to run the motors as they sit, but to see about changing from the 3" to 4" heat exchangers. I have heard this is a smart move to make.

I understand that these motors are less than desirable, and even considered pure junk to most. I plan to run them out of sheer necessity, seeing as I have them, I have the boat, and I want to get on the water. If they seize on me in the first summer on the water, I will have learned my expensive lesson and move on. If they last, I might be inclined to sell it and count my blessings. If they last, I might even decide to keep the boat around and enjoy it till they go (of course doing what I can to help prolong this enjoyment).

I think the idea of bolt them in and go seems to make the most sense. Not wasting hours and dollars for slightly better parts and slightly better performance.

BTW: the performance I mention was mentioned by the previous owner, as claimed by his GPS. I have spoken with other IMP owners with the same motors and they to had claimed top end in the middle 40s. Not sure on exactly what the set ups were, but the PO of my boat had two friends, fishing and day cruising gear on board.
 
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