Tinkering on the 4.3l this winter...

[Pmt133]

So I've said it in the past just don't think I have it documented here. I have some go fast parts for the 4.3l I'll probably throw on this winter then in the spring document any improvements.... The parts I think will show the most improvement based on threads here are the 4 barrel carb and Edelbrock 2519 intake. The intake is the proper marine one with the lined water passages. This was given to me so the cost was $0. The carb is actually a Mercruiser unit off a 96 marine engine. I did the electric choke conversion and rejetted it based on what most people with the vortec headed v6s jet to as a starting point. (pretty near what the service manual calls for) The carb was a trade and cost me ~$20 for the core. The rest of the peripherals and rebuild set me back another $80. So for about $100 I have the conversion plus gaskets and time.

I will be curious to see how much an improvement it is and how close the tune up ends up being. I plan to document in this thread any improvements in hole shot and top end. I suspect I will have to reprop as I am kissing the limiter with a lighter load as it is so any more power will probably have me run right into it.

The other thing I have a question on and this is again a "cheap" upgrade.... I have a set of 1.6 ratio self aligning rockers laying around. My heads have the non adjustable valve train but not the trunnion style rocker arms so it has studs. The studs on there are screw in however. For ~$50 I can snag a set of conversion studs and utilize those rockers. My question is, is it even worth doing or should I just put that towards the extra fuel I am going to burn. I figured it's cheap enough and I am right there anyway, but given these engines are supposed to be near the edge of reversion as it is, maybe I shouldn't tempt fate lol.

I plan on selling the 2bbl intake and carb and would most likely recoup any money I put out anyway but still figured that it is something to keep me busy one weekend. If anyone else wants to convince me to either spend more money or not, please be my guest lol.

 

[alldodge]

I have a set of 1.6 ratio self aligning rockers laying around. My heads have the non adjustable valve train but not the trunnion style rocker arms so it has studs. The studs on there are screw in however. For ~$50 I can snag a set of conversion studs and utilize those rockers. My question is, is it even worth doing or should I just put that towards the extra fuel I am going to burn. I figured it's cheap enough and I am right there anyway, but given these engines are supposed to be near the edge of reversion as it is, maybe I shouldn't tempt fate lol.

Other then the Merc racing motors, no factory motor is even close to reversion

@Scott Danforth should help with the rockers

 

[Scott Danforth]

the 4.3 is on the verge of reversion due to the exhaust pulses.

@Tail_Gunner did a hot 4.3 about 15 years ago on Hot Rodders. will check his old threads as he hasnt been on iBoats in about 6 months. https://www.hotrodders.com/threads/4-3-marine-upgrade.155256/

4.3 Vortec build up and traps

2000 4.3 tbi setup http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=576&sb=0 I know that cam is a bit hot for a boat but will reversion be a big issue here??? Revised to: http://store.summitracing.com/partdetail.asp?part=CCA%2D08%2D417%2D8&autoview=sku Milder duration with less...

forums.iboats.com

1.6 should be OK. However need to check total valve lift and interference with the keeper and seal

 

[Lou C]

I think for both Merc and OMC when you went from the 4.3 2bbl to the 4.3 4bbl you went from 175 hp to 205 hp so it's not a big jump but I guess comparable to what you get with the Vortec heads. My pre-Vortec came with the 4bbl Quadrajet and you can feel a definite surge in power when the secondaries open up, when you run on the small primaries it is surprisingly economical. If I could do it for the price you're getting lol I would for sure do it!
As far as being on the edge of reversion, what I have read is that this became more of an issue with the Vortec engines due to the more aggressive cam, but I guess that depends on what cam the marinizers actually used.
Not sure about what Merc did but OMC/Volvo actually changed the exhaust system twice with the Vortec V6 engines, first they changed the shape of the 90* aluminum down pipe that connects the elbows to the Y pipe, they made the angle of the down turn sharper to keep water from climbing up the down pipe due to vacuum in the exhaust pulses. Then they added one way check valves in the elbows to break the vacuum in the exhaust by letting air to enter via the one way valve. So if they bothered to spend the money to do that, I'd assume there was some kind of concern.
When I converted mine from the batwings I used the updated down pipes, thinking if I ever repowered with a Vortec it would be less likely to have a problem, I didn't add the check valves because with my current pre-Vortec it's not needed IMHO. I never had reversion problems either with the batwings or the current 2 piece later exhaust style.
I think you'll be happy with the Edelbrock intake and a 4bbl. It will wake up that 4.3 above 4000 rpm.

 

[Pmt133]

the 4.3 is on the verge of reversion due to the exhaust pulses.

@Tail_Gunner did a hot 4.3 about 15 years ago on Hot Rodders. will check his old threads as he hasnt been on iBoats in about 6 months. https://www.hotrodders.com/threads/4-3-marine-upgrade.155256/

4.3 Vortec build up and traps

2000 4.3 tbi setup http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=576&sb=0 I know that cam is a bit hot for a boat but will reversion be a big issue here??? Revised to: http://store.summitracing.com/partdetail.asp?part=CCA%2D08%2D417%2D8&autoview=sku Milder duration with less...

forums.iboats.com

1.6 should be OK. However need to check total valve lift and interference with the keeper and seal

I actually thumbed through tailgunners threads not long before posting this. The hotrodders one seemed to go off on tangent but the iboats one was pretty good though had some gaps.

I think somewhere I have a box of the offset keepers for a vortec as well if that does become an issue. But I seem vaguely to recall my shop machining down the guides when rebuilt anyway... but obviously I'd measure lift while apart and do the calculations.

I think for both Merc and OMC when you went from the 4.3 2bbl to the 4.3 4bbl you went from 175 hp to 205 hp so it's not a big jump but I guess comparable to what you get with the Vortec heads. My pre-Vortec came with the 4bbl Quadrajet and you can feel a definite surge in power when the secondaries open up, when you run on the small primaries it is surprisingly economical. If I could do it for the price you're getting lol I would for sure do it!
As far as being on the edge of reversion, what I have read is that this became more of an issue with the Vortec engines due to the more aggressive cam, but I guess that depends on what cam the marinizers actually used.
Not sure about what Merc did but OMC/Volvo actually changed the exhaust system twice with the Vortec V6 engines, first they changed the shape of the 90* aluminum down pipe that connects the elbows to the Y pipe, they made the angle of the down turn sharper to keep water from climbing up the down pipe due to vacuum in the exhaust pulses. Then they added one way check valves in the elbows to break the vacuum in the exhaust by letting air to enter via the one way valve. So if they bothered to spend the money to do that, I'd assume there was some kind of concern.
When I converted mine from the batwings I used the updated down pipes, thinking if I ever repowered with a Vortec it would be less likely to have a problem, I didn't add the check valves because with my current pre-Vortec it's not needed IMHO. I never had reversion problems either with the batwings or the current 2 piece later exhaust style.
I think you'll be happy with the Edelbrock intake and a 4bbl. It will wake up that 4.3 above 4000 rpm.

Kind of why I'm doing it lol. Merc calls the 4bbl crate 4.3l around 225 hp. I'd say the edelbrock intake may be a little better than mercs production manifold but I haven't seen the aluminum one they're using lately. Figure 230hp with intake plus rockers lol.

 

[Scott Danforth]

Not sure on Merc, however both Volvo and Edelbrock marine come out of the same mold at Barr

 

[Pmt133]

One other thing noted I'd have to check... the 4.3 pushrod slots look like they could get pretty tight if I increase the ratio.... Might need to clearance them a tad if I end up using the 1.6 rockers....