GM 4.3 automotive purchased...need help making it marine ready

[drun_trucker]

I purchased a boat with a cracked block, didn't know it but thats a story for a different day. Today however I need help with a botched purchase of a pre-vortec 4.3. Turnes out I purchased a vortec with TBI. My intent was just to use the block from the automotive engine and swap over my heads, cam and what not. As I stated my automotive purchase was of a throttle bodied vortec. I guess I have a few questions...

1) Is there a way to use the automotive intake and add a marine based TBI

2) Is there a difference in the cam in an automotive engine and marine engine

3) What is the difference in the intake from a pre vortec to a vortec
-if the bolt pattern is the same will can i just use it

Im sure I have more questions but I am having a brain fart so lets just start there. Please help.

 

[bruceb58]

You need a vortec manifold. They are completely different:
http://www.michiganmotorz.com/volvo-...nt-p-4367.html

You need to make sure the head gaskets are not steel.

Need to replace the casting(freeze) plugs with brass ones

The cam should be fine since the 4.3 is really only used in trucks.

 

[thumpar]

It will be pretty expensive to convert to TBI. You would need a VST ($1200 if you can find it) the computer and all the sensors or go cool fuel, still needing the computer. You would be better off just putting a carb on it. Also the Vortec heads match the Vortec intake so they have to be used as a set either way you go.

 

[Scott Danforth]

You will need to replace the steel core plugs with brass. I also suggest Marine head gaskets.

No, vortec and non-vortec are not interchangeable

 

[drun_trucker]

Im not sure if I worded the post wrong or not but the responses have been kinda funny. We can get away from the idea of going to T.B.I. that route will be way more expensive than I want to go.
I still am yet to figure out if the marine cam is any different than the auto cam...anybody. Either way I am quite certain that I will be swapping my came from the old engine.
After doing some research I have found that GM manufactured some engines with the Vortec name but did NOT have the Vortec head technology. Lets say these where Gen 1 motors. They included manufacturing changes such as the inclusion of the balance shaft and changes to the timing chain cover. The intake bolt pattern remained the same.

Here is what I know about the motor that I purchased.
1) The intake is a 12 bolt intake. It does NOT have vortec heads. If it did it would have an 8 bolt intake.
2) My intake from the old motor fits the newer motor but has an atomizing plate on the bottom side so it wont fit in the new motor because of the balance shaft running through the valley. (Old motor no balance shaft in the valley)

Im hoping that I can get some GM guys to chime in here and let me know what is going on. I really think I can just use the old intake and carb on the new block. What im really considering is just pulling all the stuff out of my old engine and putting it in my new block. Crank, pistons, cam, lifters, rods... The old engine only had 270 hours on it and the replacement has 120,000 miles. Not sure what that equates to in hours but Im guessing its WAY WAY WAY more than 270.

 

[drun_trucker]

Oh and I thought I should update this too...The Vortec name was placed on the V6 engines when GM introduced the balance shaft to the motor. However, the Vortec heads didnt start till 96. So a true Vortec performace motor has actual vortec heads and new 8 bolt intake with vertical bolt bosses. Engines with non vortec heads have the 12 bolt intakes. Even if it may have vortec on the valve covers doesn't make the motor a vortec motor as far as performance is concerned.

 

[Rick Stephens]

I have one of the morphodite sorta in between vortec engines as well. My block has no balance shaft, and the mechanical fuel pump cutout is there but no actuating shaft hole to connect to the cam shaft. I have Vortec top end with 8 bolt intake, of course, and an aftermarket Performa intake. So I can see where you might be wondering where and what to use. I have to be really careful what parts I buy to make sure it isn't for the wrong whatever.

What you do know: any stock GM cam is going to be the same as the Merc 'marine' cam. There is no difference between what rolled off the assembly line from GM for a pickup and what Merc calls a marine cam. Or for that matter the piston rings, or whatever else. Mercruiser bought the standard small pickup long block from GM, right off the assembly line, and what GM used as the stock cam and rings is what Merc calls 'marine'. There ain't no such thing as differences between the Mercruiser long block parts and GM long block parts for the S-10, or Safari van or whatever. Either cam you own is going to work fine as long as it is designed and used with the right type of lifters - roller or flat.

Be careful getting too morhodite on your motor. Mixing and matching years means you have to keep track of what you have. Vortec heads with roller lifters, roller cam, 8 bolt intake, and then which timing gear cover if it has balance shaft or not (15 hp cost for a little less vibration), different push rods and lifter keepers and rockers. Can get interesting.

Rick

 

[bruceb58]

I have one of the morphodite sorta in between vortec engines as well. My block has no balance shaft

That's weird because balance shaft was introduced(1992) before the Vortec heads were introduced(1996). Stock block or was it modified later? How do you know it doesn't have a balance shaft?

 

[Rick Stephens]

That's weird because balance shaft was introduced(1992) before the Vortec heads were introduced(1996). Stock block or was it modified later? How do you know it doesn't have a balance shaft?

Well, I have it all the way apart right now. Besides, it has the standard timing gear cover. I bought a '93 donor boat with a nearly newly built 4.3 'Vortec'. It didn't start out a Vortec. And in fact, I don't think the block is original to the boat. The PO bought it with a new engine and never used it since the floor and transom was rotted out. I bought it since it was too big a job for that owner to do the hull repairs, and to put the engine and outdrive in something else, and then found out they had let a brand spanking newly rebuilt engine get enough rain water in it to destroy a couple cylinder walls and need reboring, again. Whoever did the rebuild did a great job. I'm just doing it again and the only parts I needed were pistons, rings and gaskets. Everything else, well, even the pistons and rings, are like new, just the pistons and rings no longer fit the oversize holes.

Point is, I have a morphodite engine. Sheet metal pan, no balance shaft, vortec top end, roller lifters and cam. Real pita when buying gaskets

 

[bruceb58]

I see...they added the Vortec heads later.

 

[Rick Stephens]

I see...they added the Vortec heads later.

Correctomundo. The heads even had S-10 written in ink stick on the ends. The block is the weird one though. Pre-vortec blocks had mechanical fuel pump. This block is only electric. I thought all the electric only blocks had balance shaft. Go figure. Again, makes it mix and match to find gaskets.

 

[bruceb58]

Pre-vortec blocks had mechanical fuel pump. This block is only electric. I thought all the electric only blocks had balance shaft. Go figure. Again, makes it mix and match to find gaskets.

Did a little browsing. 91 OMC 4.3L had mechanical fuel pumps. 92 and 93 had electric and did not have balance shafts. In 94 OMC started using the balance shaft engine.

 

[Rick Stephens]

Did a little browsing. 91 OMC 4.3L had mechanical fuel pumps. 92 and 93 had electric and did not have balance shafts. In 94 OMC started using the balance shaft engine.

Yeah, '92-'96 is when a bunch of not so obvious changes took place. I know that my '93 donor boat with a 4.3 has a non-original block. The boat/motor originally came with mechanical fuel pump and the block that was actually in it has the pump rod hole blocked off. No biggee, I am making it basically stock vortec with the right pumps and electrical switching and wiring - the wiring harness has unused the correct wiring for the oil pressure switch.

 

[harleyman1975]

Man this post is making me dizzy!

 

[DeepBlue2010]

A block with 120,000 miles on it needs at least to be mic(ed) to decide if you need to machine it or not. An out of shape cylinder will have poor compression. the same need to be done on the crank, pistons and connecting rods. If the cylinder will be bored/honed, the pistons are junk and new set is required.


In almost every build, there is no good reason to reuse cams and lifters at all. Marine cams are RV/Truck cams that generates the max power at relatively low RPM and those are cheap (relatively speaking). Not worth the headache you can get from used ones or the loss of performance due to lobe wear.


Take your new block and the rotating assembly you want to use to a good reputable machine shop and let them tell what you need to do in order to have a successful and headache free build. JMHO

 

[drun_trucker]

UPDATE

The rebuild motor has a balance shaft but does not have vortec heads. My original intake fits in place of the TBI intake. I actually swapped my original heads with the ones of the TBI block. All of my original reused componets have less than 300 hours on them. They are like new.

Engine is back together.

Used the 94' block (with 120K miles on it) and the 94' cam, crank gear, cam gear and balance shaft gear. Oh and timing chain cover.

The cracked block(90') motor utilized a mechanical fuel pump, the 94' was a casting that did NOT provision an extra lobe on the cam for mechanical fuel pump.

Had to modify the timing cover a bit to get the timing tab to fit over the harmonic balancer. (Causing a problem setting base timing, not sure my degree markers are in the right spot)

Compression is low at 150 and high at 165. So really good for a worn block. Cam lobes didn't show any aggressive or abnormal wear.

I know Im missing something but Im burned out with this thing. Im having a hell of a time get it timed and running right.

 

[bruceb58]

Make sure you wire your electric fuel pump through an oil pressure switch so that it doesn't operate when the engine isn't running.

 

[Rick Stephens]

Make sure you wire your electric fuel pump through an oil pressure switch so that it doesn't operate when the engine isn't running.

+++++++

Must do that