4.3l engine questions

[Oldpos]

Ok I have read a lot about the 4.3 it’s pros cons and horse power but still have a few questions.
1. Can you put vortec heads on a pre vortec block and still achieve the same compression ratio? If not is it the actual piston that is different or are the rod lengths different?
2. is there that much difference in power from a vortec 4bbl and pre vortec 4bbl. I see the mpi motors get 230hp but I am going carb and looking for the most hp I can get out of a 4bbl
3. Are the cams the same or did a certain year go roller?

I am doing a 3.0l to 4.3l swap on a 2001 24ft pontoon. At wot I get 21mph with the family and coolers and such. The motor sounds like it’s going to launch a piston to the moon at that rpm. I’m am wanting the cruise speed to be 20-24 mph and wot around 30. Yes my boat has strakes so that helps. I have two donor boats with complete engines and drives, both are 1989’s I am going to rebuild the motor anyhow so changing heads and intakes are not an issue.

if any

 

[achris]

1. Can you put vortec heads on a pre vortec block and still achieve the same compression ratio? If not is it the actual piston that is different or are the rod lengths different?

Yes. Rods, block, pistons are the same.

2. is there that much difference in power from a vortec 4bbl and pre vortec 4bbl. I see the mpi motors get 230hp but I am going carb and looking for the most hp I can get out of a 4bbl

About 20-25hp at the top end, and a better mid-range.

3. Are the cams the same or did a certain year go roller?

Change from flat to roller cam was 1987 (from serial number 0A331455).

I am doing a 3.0l to 4.3l swap on a 2001 24ft pontoon. At wot I get 21mph with the family and coolers and such. The motor sounds like it’s going to launch a piston to the moon at that rpm. I’m am wanting the cruise speed to be 20-24 mph and wot around 30. Yes my boat has strakes so that helps. I have two donor boats with complete engines and drives, both are 1989’s I am going to rebuild the motor anyhow so changing heads and intakes are not an issue.

I've run the numbers through Merc's prop calculator and I think you're going to come up short on 26knots. (Even a big block wouldn't make 26 knots.) I think more realistic will be around 22-23 knots... Pontoons aren't designed to be 'speed boats'. If you want a fast boat, buy a boat designed for speed.

Chris...

 

[nola mike]

Your mid range will be night and day vs. the 3.0. my 4.3 doesn't seem much faster than the 3.7 I replaced, but everything in between is effortless with no drama. Tops out at 48-49 still, but 40 is much easier. Still waiting to ski off the damn thing, very curious as to whether it pulls harder off the line.

 

[MichaelBC]

When I bought my new engine I have gone through many sites and all of them listed the Vortec with 4bbl at 205 hp. Only the one with the roller rocker arms was always listet with 220 hp. I guess only the rollers can not make this difference so maybe something else was changes also on the heads or camshaft. I would be insterested in details if someone knows.

 

[achris]

When I bought my new engine I have gone through many sites and all of them listed the Vortec with 4bbl at 205 hp.

Then they are all wrong. 205hp was a 4bbl non-vortec. This is a screenshot from the 1983 to 1993 V6 manual. Definitely pre-vortec era.

After this, the manuals use propshaft horsepower and there is no direct comparison. All I can do it show the difference between the 2bbl non-vortec vs vortec and extrapolate that to the 4bbl. It equates to between 20 and 25 horsepower just by fitting vortec heads.

Chris....

 

[MichaelBC]

Yes, you are right. The mixture between crankshaft horsepower and propshaft horsepower is confusing.

My original 4.3 pre Vortec with 4 bbl was listed with 200 hp in the boat papers.

 

[Rick Stephens]

Turning the balance shaft takes 15 horsepower right off the top. Having pre-balance shaft is a boost right there.

Best part of a V6 compared to the 3 liter is how quiet it is in comparison.

 

[MichaelBC]

You mean it needs 15 hp to turn the balance shaft ? That sounds a lot.

 

[Rick Stephens]

You mean it needs 15 hp to turn the balance shaft ? That sounds a lot.

Correct.

 

[Oldpos]

Then they are all wrong. 205hp was a 4bbl non-vortec. This is a screenshot from the 1983 to 1993 V6 manual. Definitely pre-vortec era.
View attachment 345550
After this, the manuals use propshaft horsepower and there is no direct comparison. All I can do it show the difference between the 2bbl non-vortec vs vortec and extrapolate that to the 4bbl. It equates to between 20 and 25 horsepower just by fitting vortec heads.

Chris....

I’m a little confused reading this. Lx ment 4bbl? So it is aging a PRE- vortec with 4bbl is 205 horse the. Your saying adding vortec heads with 4bbl adds another 20-25 horse? I’m am would like 200 or so horse and would be happy adding a 4bbl to my existing set up, changing heads will cost a pretty penny

 

[Rick Stephens]

I'm not sure horsepower is a good standard to aim for on performance. Boats really depend more on how much torque, and that does change upward with more breathing. How much theoretical horsepower we are getting is less apparent in performance.

You may be able to sell off enough of the 3.0L motor and drivetrain to pay for the entire exchange - I did. The entire cost once I was finished was a very few dollars and a whole bunch of labor on my part. If I was dropping a 4.3L in your pontoon I would surely start advertising your old parts now and upgrade to Vortec ponies and torque.

 

[Oldpos]

Turning the balance shaft takes 15 horsepower right off the top. Having pre-balance shaft is a boost right there.

Best part of a V6 compared to the 3 liter is how quiet it is in comparison.

What years had balanced vs prebalanced?

 

[Oldpos]

I'm not sure horsepower is a good standard to aim for on performance. Boats really depend more on how much torque, and that does change upward with more breathing. How much theoretical horsepower we are getting is less apparent in performance.

You may be able to sell off enough of the 3.0L motor and drivetrain to pay for the entire exchange - I did. The entire cost once I was finished was a very few dollars and a whole bunch of labor on my part. If I was dropping a 4.3L in your pontoon I would surely start advertising your old parts now and upgrade to Vortec ponies and torque.

I paid $900 for both boats with trailers, I will end up making money even before selling my current motor. I will start looking for vortec heads.

 

[achris]

I’m a little confused reading this. LX meant 4bbl?

In pre-vortec, yes. When the vortec heads were put on, they change the designation to LH or LXH

So it is aging a PRE- vortec with 4bbl is 205 horse the. Your saying adding vortec heads with 4bbl adds another 20-25 horse?

Yes, that's exactly what we are all saying.

I’m am would like 200 or so horse and would be happy adding a 4bbl to my existing set up, changing heads will cost a pretty penny

To add a 4bbl, you need to buy a new manifold anyway. So just add the heads and buy a vortec manifold instead of a non vortec. Even brand new vortec heads aren't that expensive.

In the above picture, 'Gen II' is the engine, not the drive, and means balance shaft. 'Gen+' is for balance shaft AND vortec heads.

Chris.....

 

[nola mike]

And if you feel like buying used, in my neck of the woods they are literally $15 at the pull a part.

 

[Oldpos]

In pre-vortec, yes. When the vortec heads were put on, they change the designation to LH or LXH
View attachment 345616

Yes, that's exactly what we are all saying.

To add a 4bbl, you need to buy a new manifold anyway. So just add the heads and buy a vortec manifold instead of a non vortec. Even brand new vortec heads aren't that expensive.

In the above picture, 'Gen II' is the engine, not the drive, and means balance shaft. 'Gen+' is for balance shaft AND vortec heads.

Chris.....

Thank you for the info, extremely helpful!!!