Engine replacement help…

[Scott06]

So I found an older 350 probly 4 bolt main it’s in a boat now which is nice cause il need the manifolds an stuff, but distributor looks like an hei for a truck doesn’t look like it has any of the mercury harness. Don’t really wanna use any non marine parts. I understand why they did, hei is as easy as It gets to make run. The way the engine tucks in tho I’d have to pull the engine out to change the distributor later. Where’s a good place to find parts ? Id wanna redo all the gaskets.

If you have a Thunderbolt distributor on your original engine i Am confident the distributor body is the same for V6 and V8. You just need a new cap rotor and trigger wheel, plus a V8 ignition module To use it. Merc ingtion modules are pricey , otherwise use a delco est set up.

 

[Lou C]

If looking at older engines remember if yours is a one piece rear seal then you have to stick with the same design. The flywheel changes with the design of the rear seal & then your coupler might not fit. 1985 & older is 2 piece 1986 & newer is one piece.

 

[nola mike]

If you have a Thunderbolt distributor on your original engine i Am confident the distributor body is the same for V6 and V8. You just need a new cap rotor and trigger wheel, plus a V8 ignition module To use it. Merc ingtion modules are pricey , otherwise use a delco est set up.

Wasn't someone on here using a v6 in a V8 or vice versa? Though I'd think at a minimum the timing map would be off

 

[Scott06]

Wasn't someone on here using a v6 in a V8 or vice versa? Though I'd think at a minimum the timing map would be off

that’s why you need to swap out the ignition module To match the engine. I test ran my 5.0 with a 4.3 module. On a stand it ran fine. It certainly would not have the correct total advance and not sure if it would think the rpms are higher and kick in the rev limiter. i thought I saw something some where where the go fast crowd will use a v6 module on a blown v8 beacuse total advance is less But could be a wives tale

 

[Lou C]

Well I don’t know about Merc electronic units but for sure on the old points/centrifugal advance distributors (Prestolite) used by both OMC & Merc the V6 had much less advance than the V8s. I have the graphs in my OMC factory shop manual. Not sure if the V6 was more prone to detonation than the V8 & why this would be the case. Mine has a sticker on the flame arrestor to use 89 octane fuel or higher.
IIRC on the V6 you have 6* of base timing at idle & only 12* of advance by 3200 rpm for a total of only 18*. The V8 has more like 24 total but I have to look it up to get the exact #.
My gas dock sells only 93 octane gas & diesel.

 

[nola mike]

that’s why you need to swap out the ignition module To match the engine. I test ran my 5.0 with a 4.3 module. On a stand it ran fine. It certainly would not have the correct total advance and not sure if it would think the rpms are higher and kick in the rev limiter. i thought I saw something some where where the go fast crowd will use a v6 module on a blown v8 beacuse total advance is less But could be a wives tale

No, I meant using the module as well. Trying to think about why it wouldn't work. Biggest issue I'd think is that it would get the rpms wrong. It would depend on the advance curve (dunno what the total is on both engines), would advance too soon on the V8 and also screw with idle (though maybe not on a tbiv). No Rev limiter on the IV. It would probably work at least to some extent

 

[Scott06]

No, I meant using the module as well. Trying to think about why it wouldn't work. Biggest issue I'd think is that it would get the rpms wrong. It would depend on the advance curve (dunno what the total is on both engines), would advance too soon on the V8 and also screw with idle (though maybe not on a tbiv). No Rev limiter on the IV. It would probably work at least to some extent

The V6 definitely has less total advance than the V8 modules. Also think the 5.0 has less advance than the 5.7. The 5.7 modules usually also have the knock control piggy backed with it. I have yet to see Kock control on a carbed 4.3 or 5.0

They give less info about the TBV than the older tb4 modules that had the advance on it. I had kept my V6 module until I found a 5.0 for a spare, sold the v6 module on ebay for what I paid for my spare V8 module.

it is a shame the TB modules are either NLA or not affordable , it is an excellent system. Hottest spark I have seen on any of cars

 

[Ogbign]

I think this engine was wore out

 

[Ogbign]

Can I just buy a new v8 module, ? I don’t wanna do a buncha crap to make this engine work then have it run like a v6 still.. I don’t have room to remove distributor after it’s in the boat, I can probly get it up to turn a tooth but that’s it,

 

[nola mike]

Can I just buy a new v8 module, ? I don’t wanna do a buncha crap to make this engine work then have it run like a v6 still.. I don’t have room to remove distributor after it’s in the boat, I can probly get it up to turn a tooth but that’s it,

No, they're NLA. Can find one ebay.

 

[dubs283]

I don’t wanna do a buncha crap to make this engine work then have it run like a v6 still..

In that case you should not reinstall a V6 engine

 

[nola mike]

In that case you should not reinstall a V6 engine

He said if he installs a V8

 

[dubs283]

He said if he installs a V8

Where was that?

1978 IMP APACHE. With a 1990 4.3 v6 merc.

I think I’m gonna stick with the v6 for now

Every picture posted by OP is of a 4.3L V6

I don’t wanna do a buncha crap to make this engine work then have it run like a v6 still..

AFAIK and have been told the 4.3L is the ONLY engine OP has in hand

 

[Ogbign]

If you have a Thunderbolt distributor on your original engine i Am confident the distributor body is the same for V6 and V8. You just need a new cap rotor and trigger wheel, plus a V8 ignition module To use it. Merc ingtion modules are pricey , otherwise use a delco est set up.

 

[Ogbign]

My v6 is not fixable blocks cracked, I only pulled it apart to see if they wer telling the truth, I do not have a second engine , I had a 5.0 mercruiser I was gonna get but it sold fast , my outdrive gears are 1.47 also. I have a few sets but not for the 4.3

 

[flashback]

See post #2

 

[nola mike]

Where was that?

Posts 129, 119,89, 90,61,79... Probably more if you keep going back

 

[dubs283]

See post #2

Cheers

B answered both questions OP posted

This thread reads like a "choose your own adventure" book. A lot of wondering and speculation

 

[dubs283]

Posts 129, 119,89, 90,61,79... Probably more if you keep going back

These posts reference engines OP does not own

I don’t wanna do a buncha crap to make this engine work then have it run like a v6 still..

OP owns a 4.3L V6

telling the truth, I do not have a second engine

OP does not own an engine currently available for install

Context aside, information posted throughout this thread has been tracking towards possible repairs. Speculation is fun, even rewarding when the option comes to fruition but so far, all we have is a broken 4.3L and talking/encouragement about purchasing, fabricating and installing a V8 that OP currently does not possess.

When OP mentioned "this" engine it seemed to me given prior information they were referring to the engine they currently own and have been dismantling.

 

[flashback]

Yep, some times folks have fun but not necessarily is it help, although most of the time the information given will be useful but maybe not for the present question.