2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

[jmlloar]

Thinking of swapping the 4 out for a 6<br /><br />how much does the 4cyl weigh?<br />and how about the 6cyl?

 

[paulie0735]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

john you will need to provide some more info than that.

 

[KaGee]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

John, <br /><br />Regardless of brand, gear ratios in the drive vary between motors. Some will argue that can be overcome with prop changes. Best performance will never be achieved unless the the drive is properly matched to the motor.<br /><br />I prefer Bondo's way... buying a "donor" boat and transplanting the complete power plant. Of course, that said, your existing hull must be able to physically accept the transplant. Some boat configurations are such, that you could not install anything other than what came in it.

 

[Bondo]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

I'm Just Guessing here,......<br /><br />Would the 3.8l be a 250cid Chevy,..???....<br />And,...<br />Would the 4.1l be the 292cid Chevy,..???...<br /><br />I'd Guess that there's About 100lbs. difference between the 4 cylinders,+ the 6 cylinders.......<br /><br />And,.... What Keith says is So True........ <br /><br />Btw,...... Keith,... I FINALLY got those manifolds mounted,.....Yesterday......<br />Today the drive goes on,+ Hopefully,.... I'll Splash It,+ do alittle Fishing this afternoon............

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

I am talking about the chevy engines

 

[KaGee]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

Without exhaust manifolds my 3.8, 229cid weighs in at around 375, so add another 100 with the manifolds and another 35 with alternator, carb and oil.<br /><br />Go for a 4.3 though... shouldn't weigh much if any more and there is a bunch of them out there.

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

I was thinking of the 4.3, but the 6 is gona be cheaper. also the engine is longer so weight added is foward of where its at now, where as the 4.3 will weigh more than the 4 and all be added at the transom

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

With the gear ratio thing and I know I'm opening a can of worms with this but, no matter which engine I use keeping the same outdrive ratio<br /><br />now correct me if I'm wrong but all the engines at lets say 4,000 rpm would all be turning the prop at the exact same speed, the only reason for the drive ratio change is the higher HP engine can more easily turn the prop at a higher rpm than the smaller engine so greater fuel economy can be acheived.<br /><br />Does this sound correct?<br /><br />So say this, if I swap out only my trashed 2.5 for a easier to find straight 6 my boat should run just as well as it did with the 4, but probably not as well as it would with the correct outdrive ratio . with only a slight increase in fuel usage. Then factoring in the increased weight it will sit lower in the water but it should come up to plane quicker. <br /><br />i understand the mechanical part, but hydrodynamics is new to me, althuogh I understand aerodynamics and it seams similar.<br /><br />Any thoughts? or flaws in my idea?<br /><br />my only goal at this time is to be able to put the thing in the water as quickly and cheaply as possible. And I can get my hands on a few 6's realy cheap and realy easily.

 

[cobra 3.0]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

You'll cetainly will want to increase prop pitch with that six.

 

[ron7000]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

i pondered the idea of swapping out the 3L 4-cylinder in my 2002 bayliner 19'. First thought was go to the 4.3L v-6 then I thought why not the 5.7L v-8. Weights according to mercury's website are 635-848-946. That's total weight all with an alpha outdrive. It may not be close to what your setup actually weighs but you can see there's a 213 lb difference from the 4cyl to a v-6, and only another 100 lb difference between the v-6 and v-8. I can understand if you can get the 4.3L cheap and easily, but also know the 5.7L chevy is very common and can be cheap.<br /><br />Funny thing with the 3L, 4.3, and 5.7, is the inline-4 is as long as a 5.7 and the 4.3 is as wide as the 5.7, so if you can fit in a 4.3L you hopefully should be able to fit in a 5.7 <br />I don't know how different the transom plates are between the three, and you would have to fab up front motor mounts.<br /><br />With the drive ratio, going from a 4 to a 6 you are correct in that if you change nothing else your top end speed will be no higher, unless you let the motor over-rev which it probably will since you have more power. You may be able to get away with a higher pitch prop if it's available.<br />the 4-cylinders usually have a 2:1 ratio and a 19-21" pitch prop. Changing the drive ratio is only matter of changing the upper set of gears, not a big deal. If you go to a 5.7 then a drive ratio change is a must unless your goal is to get to 30mph as fast as possible. In the case of a 5.7L or even a 4.3L I would think fuel use would be the same if you're geared right to take advantage of the extra torque available.<br /><br />biggest thing to worry about the extra weight is how low the aft end sits in the water and how bad the wash over would be when you slow down. That can cause water to backflow into your manifolds and cylinders and hydrolock the engine. You can easily simulate the weight with 2 or 3 people sitting on the transom.

 

[horsefly38425]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

when you say 6 do you mean stright or v it may work better with a v6 /not as long . I put a v6 in 4 pullout many yr's ago inline6 would not fit, but even with the v6 had lots of trouble

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

The inline 6 is the way I'll go if I do the swap. other than the fact that its longer everything off the 4 fits except the distributor and the manifold. all brackets and motormount is the same as is the bell housing and flywheel. Even the pistons are the same. And yes the 4.3 isnt to hard to find here either but the 4 cyl is pretty wide in this little boat as it is (its a 68 MFG CorvetteII and at 15' X 5'it's tiny) also buying one manifold and being able to use my elbow is alot cheaper than buy 2 and a Y-pipe for the 4.3. Plus I can get the inline's for $50- $100 bucks running and the 4.3's are more in the $300 range lengthening the dog house is no problem and moving the mount forward is no problem either since i have all the stringers removed for floor replacement.

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

Also for bondo<br /><br />the 3.8 is a 230ci chevy<br />the 4.1 is a 250ci <br /><br />most people think of the 250ci when they see a inline chevy but the 230 was actually more common in the cars than the 250 until the 70's<br />and the 292 chevy was truck only<br /><br />as far as auto's go when it comes to boats I'm new

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

and for kagee<br />although the 3.8L came as a 229ci engine I'm not sure if it was in a boat It's a V-6 and looks identicle to the 4.3L<br /><br />and the 3.8L inline is 230ci's

 

[fendersfender]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

Yep...3.8's were put in boats...i have twins...and yes they are almost identical to 4.3's....even the exhaust manifolds are interchangeable.....I'll use 4.3's when I decide to repower

 

[KaGee]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

I thought i made it obvious I had one too... guess not. Hystat has one also. They were only made for 4 or 5 years. The 3.8 evolved from the 5.0 305. They share a lot of parts.<br /><br />The 4.3 came out sometime in late '85 and is a close relative of the 5.7 350.

 

[lilmandavis]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

worms anybody?!

 

[jmlloar]

Re: 2.5 - 3.0 4cyl vs 3.8 - 4.1 6cyl

in the car it started as a 3.3L V-6 started in the 78 malibu. then was punched out to 3.8 V-6, then 4.3L. all of them are basically the same just like all small block chevy V-8 are. I'm surprised any of them have survived. In the car the smaller ci ones were trash. They blew up really easy<br /><br />I didnt mean to offend anybody, Like I said the marine side of these engines is new to me. But the auto side I cut my teeth on