changing from 6cyl to 4cyl

[brother chris]

Okay, I have a 23' Fiberform with an inline 6 and need to replace it cause the engine is hooped. My friend ran an idea by me and I am not sure if it is feasable. Any input would help. <br />His idea was to use my 4cyl engine I have in my mini van and put it in the boat. How much hp/speed will I lose if I use a 4 cyl instead of a 6 cyl? The boat weighs in around 3000lbs and the mini van is around 2000lbs. <br />I know the starter and alternator would have to be changed to a marine kind. <br />What is the difference between a regular engine and a marine engine? Just the thinkness of the wires?<br />I know this sounds crazy, but I will never know for sure unless I ask. Any input is appreciated. <br />I'm just a backyard mechanic. 5-6 beers, I can fix anything. Yeah right!

 

[ZmOz]

Re: changing from 6cyl to 4cyl

I don't mean to be rude, but the fact that you're even asking this question proves that it would be an extremely difficult thing for you to do. First of all, I don't know what engine is in your van but most likely it's not going to just "fit". It's not like a lawnmower where you can just bolt down any old thing. You would loose a significant amount of speed and hole shot as well. Weight has nothing to do with it...water vs land makes it seem like your boat weighs about 20,000lbs. Marine engines have different carbs, exhaust, distributors, water pumps, alternators, starters, cams, etc. To get any kind of performance what so ever you would need a different cam, which is easily available for most marine engines, but I doubt there are very many marine cams out there for 4 cyl. van engines.<br /><br />Now, with that said, yes it's possible. So is building a space ship and flying to mars. Myself, I'm currently working on turning a '66 mustang into an amphibious vehicle.

 

[Butch Ammon]

Re: changing from 6cyl to 4cyl

I agree.... DON'T do it. <br /><br />I too have an inline 6 (165hp Mercruiser) on my 1975 Sea Star 17' trihull runabout. Mine still runs great after all these years (knock on wood).<br /><br />My 165hp inline 6 is essentially a small block 250 Chevy straight 6 that you would see in a small Chevy Nova or a Chevy C-10 pickup from back in the 70's. BUT..... the only thing in common is probably the main engine block. The heads, intakes, exhaust, valves, lifters, and most importantly the carb and about 90% of the engine is converted to marine from automobile. i.e... it looks like a small block Chevy straight 6, but it is way different.<br /><br />Just as well, I couldn't take this engine out of the boat and try to put it in an old 1975 Chevy Nova.<br /><br />Check it out.... Does your boat's engine look like this?<br /><br />

<br /><br />I hope this helps. I'd look at used boat engines and get another inline 6 engine, or try to repair the one that's in the boat right now.<br /><br />Butch

 

[John Carpenter]

Re: changing from 6cyl to 4cyl

That inline 6 cyl Chevy is as good an engine as you can get...but is probably marginal powerwise for your setup. If you are going to re-power, the 4 cyl is the wrong way to go. Best and cheapest way to go here would be to buy a long block replacement for your current engine.

 

[brother chris]

Re: changing from 6cyl to 4cyl

Hey Butch, that is the exact same engine I have in my boat. The only problem is that when the boat was given to me the engine compartment cover was left off, so it has been rained on for over 6 months now. <br />The motor won't turn either, so I have to repower it. I just thought that since I have an extra engine, I could have used it for this. I guess not. <br />I don't know how to rebuild an engine, so I guess it is time to go to Ebay and look for a used inline 6. <br />Thanks for the replies.

 

[Butch Ammon]

Re: changing from 6cyl to 4cyl

Originally posted by brother chris:<br />Hey Butch, that is the exact same engine I have in my boat.

Cool! As far as the Mercruiser 165 I-6, they are a dime a dozen. You could visit any marina or used boat dealer and I guarantee you someone will have a used Mercruiser inline 6.<br /><br />Good luck!<br /><br />Butch A.