4.3L Mercruiser TKS - Do I have the correct heads for my motor?

[TNBoatingOHL]

Just signed up and first post. I've read posts for years and the advice has helped in the past so I already owe the iBoats forum a thank you.
Boat: 2005 Tahoe Q4
Engine: 4.3L Mercruiser TKS. S/N: 0W302527 C/N: 14099090M
Outdrive: Alpha Gen 2
Problem: Last year I found my heads were cracked by the previous owner and welded instead of replaced. The boat was previously running good but my mechanic had a set of heads that he let me have. I had them professionally worked and my mechanic installed. He also gave me a Holley 4 barrel carb to boot. Writing that already feels suspicious but he is somewhat of a friend/acquaintance. After the install, the boat would idle decent but wouldn't get on plane. It wouldn't even get close to plane. I thought it was a carb issue w/ the TKS system so chased the fuel system until I gave up for the year. Getting back to the project this year, I started by taking the heads back to machine shop because I had a couple rough backfires. Sure enough they needed reworked, bent valves on adjacent intakes. The machine shop stated the heads are pre-Vortec w/ the 12 bot intake. Looking up the manual by my serial #, i noticed it has the 8 bolt intake. This is when I got worried.
Questions: I don't understand if the pre-Vortec & Vortec heads are compatible. Do pre-Vortec heads bolt up to Vortec motors? If so, will they run correctly? I'm trying to confirm if the heads I currently have will work with my motor, should I go back to the Vortec setup, ditch the 4 bbl carb, etc... Any advice on where to start would be much appreciated. The C/N #'s on the cylinder heads currently on the boat are 10238181.

 

[achris]

Hello TNBoatingOHL, and :welcome: to iboats forums...

The vortec heads are just that, heads. Both vortec and non-vortec will bolt onto the same block...

If you have a 12 bolt manifold, you have non-vortec heads. Absolutely... Giving you non-vortec heads to replace vortec and a 4 bbl Holley, that mechanic is less of a friend than you think.

You'll be down at least 20 horses just on the heads alone, I suspect the Holley is far too big for that engine and it's just not working properly, so knock off a few more horses... Starting to look like a horse graveyard in here. The only 'favour' he did you was ditching the TKS carb.

Ok, best options... Find a pair of vortec heads, slap a dual plane cast iron manifold on (or ali with brass inserts), and a Edelbrock 1409 4 bbl marine carb... Yes it's going to cost money. Welcome to boating.

Cheers,

Chris...........

 

[Scott Danforth]

those are 92-95 heads


here is some reading on 4.3's https://forums.iboats.com/forum/engi...asting-numbers

carb may be ok. for a holley on a stock V6, you would be running a 600CFM. however the brackets and throttle cables for merc tend to favor the edelbrock carb. Holleys were normally OMC and VP.

and yes, ditch the existing heads and go to a vortec head

 

[achris]

... for a holley on a stock V6, you would be running a 600CFM. ...

Odd on, it's a 750DP or some such similar.....

 

[Scott Danforth]

would need to see the numbers from the air horn. 750 double pumpers are big block carbs. the V6 and SBC's should be running vacuum secondary carbs

I ran a 650 DP on my wee little 3.8 V6 in my OPEL GT drag car, however that was an 8000 RPM motor that ran a bit rich below 2500 RPM

 

[achris]

would need to see the numbers from the air horn. 750 double pumpers are big block carbs. the V6 and SBC's should be running vacuum secondary carbs

I ran a 650 DP on my wee little 3.8 V6 in my OPEL GT drag car, however that was an 8000 RPM motor that ran a bit rich below 2500 RPM

Agreed... The one thing that struck me, and leads me to think that carb is WAY bigger than 600cfm is that it has no low end torque. Can't even get on the plane. Someone says the carb was replaced and it's no longer got low end, ya gotta think 'too much carb'....

And the 'friend' mechanic did swap out vortec heads for non-vortecs, without a word to the wise. And he had to have known, the old manifold wouldn't have fitted for a start...

Chris........

 

[Scott Danforth]

could also simply be crud in the accelerator circuit. the check valve for the accelerator diaphragm is literally on the lowest point of the bowl. it is the first circuit to plug on a holley, followed by the power valve circuit. then with a few backfires, the power valve itself ruptures (depending on year of carb) and the idle fuel mixture goes to he#

 

[Rick Stephens]

Here's the hope we get a bunch of information and feedback from the poster on what the carburetor actually is. You'll never get me to like a TKS, but swapping it for an improperly sized (or maybe even automotive) Holley is not a good move.

I run the 1409 carb and the Performa intake on my 4.3. I'm plenty happy camper.

 

[Bondo]

I had them professionally worked and my mechanic installed. He also gave me a Holley 4 barrel carb to boot. Writing that already feels suspicious but he is somewhat of a friend/acquaintance.

Ayuh,...... Welcome Aboard,........ Yer Bud, sure didn't do ya any Favors,.....

Older back-dated heads, 'n the wrong carb for a Merc,.....

The non-vortec heads cost ya 20 hp,.....
'n Merc runs the Weber AFB carb, an exact carbon copy of the Edlebrock 1409,....

 

[TNBoatingOHL]

Thanks everyone. I planned on moving back to the vortec setup but didn't realize all this would've cost me 20hp!!!! Wow.
I'll get the carb info this weekend and reply with the details.