21' w/ blown 4.3l engine... swap options?

[dr.fowler]

Re: 21' w/ blown 4.3l engine... swap options?

Well, I know that there's room for the 5.7litre, as it came stock in that very boat, just as an upgrade option.

I guess I don't understand why it would be so little gain. I think it would be a big deal to go from a pansy 140hp or whatever, to 100hp or more jump by adding a v8. Wouldn't that give the boat added hole-shot power? Wouldn't that make the boat more responsive to the throttle? Wouldn't that make it more fun to drive? I know I'm gonna spend some money on the motor, but I really like the boat, and I would rather spend 8grand and keep it than spend 25grand and buy a new boat. either way, I'm not going to put in the same dumb motor and end up with a still-disapppointing amount of power. What kind of power do the vortec heads give? It can't be more than a handful.... I just need to know where to buy the motor at. Any good sources to be recommended?

 

[Bondo]

Re: 21' w/ blown 4.3l engine... swap options?

Mercruiser will Gladly sell you a Complete Drop-in 5.7l,..........

With a 4bbl. Carb or EFI, or even MPI..........

That'll take up Most of your 8 Grand,.........
'course,......
Then you'll also Need a new or regeared Outdrive to go with it........

 

[MikDee]

Re: 21' w/ blown 4.3l engine... swap options?

Maybe I'm wrong, but unlike the smaller 4cyl I/O's, I thought the gear ratio on the 4.3 was the same as the V8's? Approx 1:5X1 reduction, if that be the case, you can put your mind at ease about that. Then get onto putting that small block V8 in there.

Superpop had some good idea's for you, just make sure all parts are marine specific, for safety (spark, & fuel vapor proof), and durability (corrosion proof), that's why he suggested using the electrical, & fuel delivery, parts off your old 4.3, by the way, car engines don't have brass freeze out plugs, or stainless head gaskets either, like marine engines.

 

[riverjet502]

Re: 21' w/ blown 4.3l engine... swap options?

OK here we go... It sounds like you really want to get rid of the lawn mower engine and have a bigger engine. That being said. I would look for a 350 block with a one piece rear main seal. Mid 80's on up. This could come from a junk car or truck. Trucks generally have 4 bolt mains. Nice option to have but not real critical since we won't be building a 8,000 rpm sprint boat engine here. Once you have the donor motor, if you are capible stripe it down to the bare block. Or take it to a reliable machine shop and let them do it. Once the block passes inspection it will need some machining to square everything back up to begin the build up. From what I have found is that a marine engine will have a bit looser tolerences then a car motor. (Bearing & piston clearances) This is due to the engine block not heating up evenly like a car motor does. "The expansion rate can be different then a car motor due to the cooling system." Jet boats are notorious for this. You would want to use a GOOD rotating assembly preferly all forged (pistons, rods, crankshaft) You will want this for the nitrous you want to run. You want to keep your Cr 9.6 - 10 tops for use with pump gas on the river. Contact Crane cams and talk honestly about your intended use and desired hp level. A nice hydraulic roller cam should be in your future based off a 112 degree lob.. Take their advice. I would forget the vortec heads. Go aluminum !! I run Edelbrock aluminum performer RPM and do a little port cleaning on them. Then port match them to a Edelbrock Air Gap dual plane intake. This will save you some serious weight plus help disapate heat better then the cast iron heads. Assemble the engine with Fel-Pro gaskets and a MSD distributor. A nice 750 holley double pumer on top. The shop you choose to do your work should have a dyno on site to tune your new motor on. Then give you a print out of the power curves. This will help in your prop selecton. Just make sure to use the proper marine hardware were dictated as you already know. You should be in the honest 400 hp range when done...very reilable. Next you will need to ditch the stock exhaust in favor of a more free flowing exhaust to help your motor breath more easily... Just some things to think about....

Crate motors.. Yep they work. The jet sprint boats run ZZ4 350's right out of the box. Period. But keep in mind that some also run dry exhaust too. Check some of those sites out they are plain crazy there !! ZZ 502/502 works too. Take your time and due your homework.

 

[slia67]

Re: 21' w/ blown 4.3l engine... swap options?

Maybe I'm wrong, but unlike the smaller 4cyl I/O's, I thought the gear ratio on the 4.3 was the same as the V8's? Approx 1:5X1 reduction, if that be the case, you can put your mind at ease about that. Then get onto putting that small block V8 in there.

Superpop had some good idea's for you, just make sure all parts are marine specific, for safety (spark, & fuel vapor proof), and durability (corrosion proof), that's why he suggested using the electrical, & fuel delivery, parts off your old 4.3, by the way, car engines don't have brass freeze out plugs, or stainless head gaskets either, like marine engines.

Cams are different, fuel delivery (mounting) may be different, etc. Not worth the trouble. Do it right the first time. I believe MikDee is right about the gear ratios, 4.3s and small V-8s had the same gear ratio, but double check then triple check before you spend the money.

If they are the same, check out http://www.michiganmotorz.com/Marine+Engines/Complete+drop-in+engines or http://bpi.ebasicpower.com/c/ENG/Engines+%28Inboard%2C+Sterndrive%29 they have "drop-in" engines and should have everything you need to get you back on the water quick. http://www.dougrussell.com/Products/index.cfm?fuseaction=Products&Category=6 also has "drop-in" packages, but they also have engine/sterndrive packages. They have a 5.7L/Bravo3 package for less than $11k, talk about an upgrade in power!!!

Hope this helps. For what its worth, I would go with new and not rebuilt or remanufactured.


Doug