4.3 Vortec valvetrain.

CHARGER2

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This spring I will be upgrading my entirely stock 4.3 Merc. Seems like everyone and their mother who has a 4.3 has done this specific upgrade, but I can't find anything that answers this specifically.

What I currently have:

1990 Mercruiser 4.3L
2 BBL Mercarb
Non-balance shaft
Non-vortec
Open cooling
Fresh water use

What I am upgrading:

Edelbrock 1409 4 BBL Performer 600 CFM carb
Edelbrock 1485 carb calibration kit
Edelbrock 2114 Performer intake
Used/Rebuilt 8 bolt Vortec heads from Ebay

My question:

Is my current valve train sufficient/safe for the Vortec swap? Specifically, will I be OK with my current pushrods and rocker arms? Will the Vortec valves/springs/combustion chamber cause any issues? I assume my current rockers are stock Mercruiser PN 35329. I am unsure of the ratio.

Anything in general I may be forgetting?

Thanks for any help
 

Bondo

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Ayuh,... I might be wrong, but I believe the rockers, 'n push-rods are different with the Vortec heads,....
 

Scott Danforth

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have the heads modified from the junk push-in rocker studs to ARP rocker studs.

FYI - you dont need EBAY, any pull-a-part salvage yard such as LKQ will have heads cheep....dirt cheap.

new heads are about $500 a pair.
 

CHARGER2

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Thanks Scott. Looks like I can get a set at my local junk yard for under $100. Heads for any 4.3 with an 8 bolt intake should work right? Should be something like 1996 onward. Why ARP studs? Stock studs aren't even listed on GMpartsdirect for this motor.

I'd like to pull the pushrods and cam from whatever junker I pull the heads from, but I don't think a balance shaft cam will go in a non balance shaft motor.

Guess I will have to pull my heads early and measure what I have to see how it matches up with the vortec I end up with.
 

Scott Danforth

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Stock studs are press in junk that will pull out if you run a heavier spring.

Why ARP.... Because they make aftermarket screw in studs and your machine shop probably has them in stock
 

Scott06

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Look up @ Rick Stephens for carb tuning . I think his results on vortex heads were the 1485 calibration kit was lean
 

jimmbo

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I think your wasting your money on a 4bbl carb, that engine is not going to flow more than 300 CFM @ 5000 rpm with 80% VE. Even the small Holley 2bbl flows 350 Cfm
 

CHARGER2

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Wow. Thanks for that Rick Stephens reference: http://forums.iboats.com/forum/engi...ves/10154544-stumbling-edelbrock-1409-4-3l-v6

Looks like that might save me $30 and a few days of tuning.

Jimmbo, as far as I can tell the 4bbl 600 cfm carbs perform significantly better on the 4.3L than the stock 2bbl. I am not sure why. Your math and logic makes sense: with 100% VE @4800RPM this engine only requires a 365cfm carb. But all posts say they have a noticeable increase in the top end. Even Merc rates them 10-20 HP higher from the factory.

Again, any insight on the valvetrain is much appreciated. I'm running a stock 1990 cam and rods. I'd like it to plug and play with the springs/valves/rockers from a late 90's Chevy.
 

jimmbo

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The stock 2bbl Mercarb(Rochester) must really be a low CFM carb then. I'll bet the engine will never need the secondaries of a squarebore 600 cfm carb

These would be my two choices for a 4.3
https://www.holley.com/products/mari...arts/0-80320-1


A spreadbore, very versatile on a range of engine sizes
https://www.holley.com/products/mari.../parts/0-80552. I have this one, I installed it on my 5.7 and it increased my rpms and speed by 10% higher than the stock 2bbl https://www.holley.com/products/mari...arts/0-80402-1

Valve train. A roller cam and lifters would be a good idea. Todays oils just don't have the Extreme Pressure additives flat tappet cams and lifters need to survive
 
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Scott Danforth

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the throttle response and mid-rpm response with a 4-barrel is better than a single large two barrel.
 

jimmbo

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the throttle response and mid-rpm response with a 4-barrel is better than a single large two barrel.

If the calibration is correct, and the secondaries aren't opening too soon, I will concur. When I put the 650 on my boat, I had to increase the pitch to keep the rpms back in the WOT range. The smaller primaries did help keep my holeshot close to what it was with the lower pitch prop used with the 2bbl
 

Scott Danforth

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Fyi, VP uses the throttle body from a 7.4 liter on the 4.3 for throttle response. Both Merc and VP used a 600 cfm vac secondary carb on the 4.3
 

Lou C

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On the subject of the valve train, I bet that 1990 has a roller cam. My 1988 definitely does. It also came with the Rochester Q-Jet and while I never tried a 4.3 with a 2bbl it always performed well with the Q-Jet.
 

CHARGER2

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No Title

I ended up getting a pair of remaned heads on ebay for $260 shipped:

http://www.ebay.com/itm/361909408395?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

It was faster and more convenient than heading to a junkyard and getting heads machined, at not much of a premium.

They won't arrive untill next week, but I will start tearing into the engine this weekend.

I have a couple questions about rockers and valve lift. See attached picture for clarification:

Question 1:

The vortec has about .020" more lift than the pre-vortec. Can/should I get rockers that will give me a little more lift with my stock cam? I'm not too familiar with the nuances of lift and rockers and such. I do not want to re-cam this engine. What would be the expected results of sticking with current rockers versus going for a bigger ratio?

Question 2:

The lift math doesn't exactly work out in the service manual. (Lobe lift) * (Rocker ratio) = (Valve lift)

On the pre-vortec intake valve, this should be .269 * 1.5 = .4035, but the listed intake valve lift is .394. Same applies to the vortec valves even at max tolerances. What gives? How is Merc measuring/calculating total lift?
 

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Lou C

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I thought of doing this as well but due to the unknowns involved I decided to stick with my pre-vortec. I got a set of re manned heads setvup for marine use from a local speed shop for 275 each. Same casting #s as the old ones so I know that everything should go back together. I'm re using my old intake and the QJet...
 

CHARGER2

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Well I cracked open the old heads only to find standing water in 5 cylinders. Went on to find the oil was milky and was two quarts over full, so whatever the problem is, it went on long enough to ingest a half gallon of water into the crank case without notice or effect on performance. I guess this is why the Adults Only section says to do your oil change in the fall :facepalm:.

I'll open a new thread in the engine repair section if I can't find enough info through research. Hopefully I can find a cause and get away with a quick cylinder hone. I don't think its quite toast because I was able to turn it by hand, but that water was in there for a solid 9 months....

Thanks for the help of everyone in this thread. Hopefully I can come back some time with a completed project and let you all know how the vortec swap went!
 

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CHARGER2

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I resumed this project last weekend. I think I solved the water intrusion, but that's a different thread (http://forums.iboats.com/forum/engi...1-4-3-milky-oil-and-water-in-5-of-6-cylinders).


I got hung up on the rocker arms. The pre vortec heads have press-in 7/16" studs without a shoulder. The new heads have 3/8" screw in studs with shoulders.

These are the pre vortec studs for adjustable rockers: http://www.mercruiserparts.com/34522-stud
These are the vortec studs for non adjustable rockers: http://www.mercruiserparts.com/8018821-stud

Can I use my current rocker arms with new nuts and new balls? I don't know if the rocker geometry the same between the two, just with different nuts and balls.

Can I get a set of these and be OK? Or do I need to get a set of new rocker arms?

https://www.summitracing.com/parts/...olet/engine-family/gm-v6/engine-size/4-3l-262

Thanks
 
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