Tinkering on the 4.3l this winter...

[Pmt133]

If that is an engine out of a Car/Truck, it is not going to be much use in a boat, until some Changes are made to it.

Marine grind cam, ~9:1 compression on a 115 lsa and peaks around 5000 rpm... it was supposed to go in a boat and ended up in the vette. Does 300+ lb-ft from 1900 rpm onward. Only thing I don't remember about it is if I left the marine headgasket in it or not which I'd be checking/changing anyway. Core plugs and the peripheral parts are all set up for marine application and good to go.... long story.

I also came from a 3.0 powered boat its a nice upgrade.

I think most people get tired of the trough hulls pretty quick. Captains Call is probably the better bet.

Yeah. I'd probably have decent mufflers on it too. I'm not that guy. But the choice is nice.

Looking back, it impresses me how well the 3.0l did push this thing around.

 

[Scott06]

Marine grind cam, ~9:1 compression on a 115 lsa and peaks around 5000 rpm... it was supposed to go in a boat and ended up in the vette. Does 300+ lb-ft from 1900 rpm onward. Only thing I don't remember about it is if I left the marine headgasket in it or not which I'd be checking/changing anyway. Core plugs and the peripheral parts are all set up for marine application and good to go.... long story.


Yeah. I'd probably have decent mufflers on it too. I'm not that guy. But the choice is nice.

Looking back, it impresses me how well the 3.0l did push this thing around.

I enjoyed my 3.0 powered boat as well. With the right prop could do ok skiing and was cheap to operate and maintain. Now that the family is bigger the boat is as well.

What year vette? My other ride is a 65 GTO, just waiting for the builder to finish a new engine for it.

 

[Pmt133]

I enjoyed my 3.0 powered boat as well. With the right prop could do ok skiing and was cheap to operate and maintain. Now that the family is bigger the boat is as well.

What year vette? My other ride is a 65 GTO, just waiting for the builder to finish a new engine for it.

84. Nothing special. My uncle built a 67 firebird. We had to have the 400 redone a few years ago after he passed Sadly. Beautiful car those GTOs.

 

[Scott06]

84. Nothing special. My uncle built a 67 firebird. We had to have the 400 redone a few years ago after he passed Sadly. Beautiful car those GTOs.

its a 41 yr old car... hopefully in good shape.

 

[Pmt133]

its a 41 yr old car... hopefully in good shape.

It's a driver. Paint was resprayed in the early 90s. Interior is in good shape, just went through the suspension etc. It's just a go cart lol

 

[Pmt133]

So I figured I will bring this one back. I got to the initial testing with the 4 barrel and intake swap last year. I still need to hone in the jetting some but it was at a serviceable place. The testing was done on similar weather days, about 80F light chop. I abandoned all other modifications. If I am going to do any of that, I am starting with a non balance shaft block.

I have months of data on the 2 barrel and 42 MPH gps was about all it would ever do. This was with my old mirage an running ~4700 RPM. I then traded one of my other props for a 21p Mirage. (Why the mirage? it seems to run the best on this hull based on the dozens of props I've tested) with the 2 barrel it pulled RPM down to 43-4400, bottom of the range and speed at (drumroll) about 42 MPH.

Swapped the 4 barrel on and jetted it up and am consistently getting 4700 RPM with the same prop and base timing for the thunderbolt V. I confirmed timing before testing the 21 on the 2 barrel too so it was a fair a/b. At 4700 I see 46 MPH GPS. so a gain of 4 mph with nothing more than a carb swap. I feel that is a worth while investment and the 4 barrel runs and drives way better than the 2 ever did. Smoother idle, response is better... I am happy. I think with pulling a little jet out up top (it is very rich right now) another mph may be possible while staying safe.

Just guesstimating, it would seem like 25 horsepower gain isn't an unreasonable estimate based on mph gains. I will hopefully get out on it in the coming weeks and get the numbers finalized. I suspect my summer speeds with humidity will drop slightly too.

 

[Scott06]

So I figured I will bring this one back. I got to the initial testing with the 4 barrel and intake swap last year. I still need to hone in the jetting some but it was at a serviceable place. The testing was done on similar weather days, about 80F light chop. I abandoned all other modifications. If I am going to do any of that, I am starting with a non balance shaft block.

I have months of data on the 2 barrel and 42 MPH gps was about all it would ever do. This was with my old mirage an running ~4700 RPM. I then traded one of my other props for a 21p Mirage. (Why the mirage? it seems to run the best on this hull based on the dozens of props I've tested) with the 2 barrel it pulled RPM down to 43-4400, bottom of the range and speed at (drumroll) about 42 MPH.

Swapped the 4 barrel on and jetted it up and am consistently getting 4700 RPM with the same prop and base timing for the thunderbolt V. I confirmed timing before testing the 21 on the 2 barrel too so it was a fair a/b. At 4700 I see 46 MPH GPS. so a gain of 4 mph with nothing more than a carb swap. I feel that is a worth while investment and the 4 barrel runs and drives way better than the 2 ever did. Smoother idle, response is better... I am happy. I think with pulling a little jet out up top (it is very rich right now) another mph may be possible while staying safe.

Just guesstimating, it would seem like 25 horsepower gain isn't an unreasonable estimate based on mph gains. I will hopefully get out on it in the coming weeks and get the numbers finalized. I suspect my summer speeds with humidity will drop slightly too.

25 would make sense as the 4.3 2 bbl is rated at 190 hp, the reman 4.3 with 4 bbl webber eddy is rated 225. I had heard somewhere on here that it takes 10 hp per 1 mph but can only assume the hull has something to say about it.

I found the midrange throttle response on the 4 bbl to be way better than the 2 bbl. Not sure if it is due to 4 smaller throttle bores vs 2 larger ones.

I also found a similar top speed wall with my boat (47-48 mph) change props moved the rpms one way or another but speed was the same.

Id say it worked out well in your case to do the upgrade.

 

[Pmt133]

25 would make sense as the 4.3 2 bbl is rated at 190 hp, the reman 4.3 with 4 bbl webber eddy is rated 225. I had heard somewhere on here that it takes 10 hp per 1 mph but can only assume the hull has something to say about it.

I found the midrange throttle response on the 4 bbl to be way better than the 2 bbl. Not sure if it is due to 4 smaller throttle bores vs 2 larger ones.

I also found a similar top speed wall with my boat (47-48 mph) change props moved the rpms one way or another but speed was the same.

Id say it worked out well in your case to do the upgrade.

The horsepower per mph also changes the faster you go... figure drag.

Oddly, the alpha 4v was rated 225. Per service manual 18 mine would actually be 210 HP with the 4bbl. Using one of those online calculations I cone up that 215 hp is about right. Obviously some wiggle room on those but I've bench raced cars against those calculations too and they're typically spot on if you have good performance data to start with.

Either way, 3-4 mph for ~$400 is an incredible ROI.