4.3 DD Help Please!

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Mo0se
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4.3 DD Help Please!

Post by Mo0se »

Howdy! I'm new to airboats so I'll get that out there first. I'm new, not stupid lol.

I bought a used 12ft fiberglass hull seller said its a cottonmouth with a 4.3 DD on it. I'm having several issues and all I would like to do is correct what's wrong with it. It's got an aluminum intake, headers, An Edelbrock 600 cfm which I've heard is too much for the 4.3 engine. I bought a new Whirlwind 68" Carbon Max for it, I installed that a couple days ago. Any prop I've used I have to run with very little pitch to get the rpms up around 3000. I suspect I need a smaller cfm carb and I'm about to buy one.

Here are the problems I need help with,


1. This boat refuses to go on plane in deep water. In shallow water its fine.
2. I feel like the thrust angle might no be right
3. When on plane I'm getting spray from the near the front of the boat rather than directly under the engine/operator
4. The rear of the boat pushes down in acceleration from a stop in deep water and the front plows water.

I've put the boat level on its trailer, put a level on the stinger, and one on the valve cover and it I thought I had it level? Is that the proper way to check and set thrust angle? Should those two angles be the same? Or should I check it with the bottom of the boat? I'm new and
I've searched thrust angle on this site and come up with little on the subject. What are the ideal setup measurements? I don't have any interest in putting a reduction on it, I don't need to run dry. I just want to optimize what I have and at least be able to get on plane in deep water. I appreciate the help!
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Slidin Gator
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Re: 4.3 DD Help Please!

Post by Slidin Gator »

600 CFM is definitely too much carb for a 263 in^3 direct drive, 300 CFM is what you need. You can try disabling the secondaries on the carb. You describe a boat riding hard on the nose, setting the engine level to hull as you describe is a good starting point, but not necessarily the conclusion. Does the hull have jacks in it now, if so it may have too much jack and you should back off on them a bit. Use a string or long flat material to confirm there is no lip in the stern. Next is some engine trim adjustment, try angling rear of engine up a little (1/8") at a time.

Some good info in this recent thread:

viewtopic.php?f=48&t=73124
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.
Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

Thanks for the reply!

I raised the back of the engine up some with some washers today. I tried to match the level in the floor (and stringers) best I could. ( I set the boat level with a bubblestick and then used another bubblestick on the prop adapter and the face of the hub. I put at least an 1/8th In washer in there and it seemed to help some. There are no jacks in the hull. I took it out after the adjustment and it seemed to be marginally better. Also those bushings under the rigging at the back of the motor, anyone know a source for those? Mine are cracked and need replaced. I've got that WW Carbon max 68" pitched to get to 2950 rpms and still no planing in deep water from a stop. (I mean over 3ft) I'm gonna buy a replacement carb for the engine asap. I have a feeling that beat up old hull may be waterlogged, it has poly in decent shape. It runs about 35 mph wot and crusies nice at around 2200. Thanks for the link I'll dig in and see what I can use.

Jeff
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John Fenner
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Re: 4.3 DD Help Please!

Post by John Fenner »

Ok, I set up a 4.3 DD, built an adapter for the TBI intake with aluminum tubes down into the plenum to raise velocity, also only ran a Rochester monojet, it spun the same prop to 3100 and very aggressively, the engine came out of a truck so it was cammed for torque already, the owner was impressed.
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Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

John,

I bought this as it sat. Edelbrock aluminum intake and the wrong carb. I'm slowly making progress, I'm searching for a 300 to 350 cfm that will mate up to that aluminum intake. I think its just a square bore standard size. I could buy an adapter and run a two barrel of some sort. Thats not out of the question. It's definitely drowning with a 600 cfm. Throttle response is laggy at best. This is pre vortec engine according to the cast number. a run of the mill 262 at best. Even though it has vortec heads on it. I appreciate the reply and any help would be appreciated.
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Re: 4.3 DD Help Please!

Post by Mo0se »

Anyone know where I can replacement bushings for rear of the engine rigging?
SWAMPHUNTER45
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Re: 4.3 DD Help Please!

Post by SWAMPHUNTER45 »

Are they a conical bushing? Round or egg shaped on botton and flat on top with a hole in the center?

If they are there are 3 colors (white, blue, black) The white are very hard, blue medium and black softer

Most shops stock one or more of the colors.

BrownWater Airboats, Floral City Airboats, Neds Fabrication, AlumiTec Airboats, GTO Airboats will all have them in stock.

I tend to run the blue ones fyi the white will not compress as much but you pick up more vibration in your rigging.
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Re: 4.3 DD Help Please!

Post by Gary S »

classic airboat has them and will ship.
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John Fenner
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Re: 4.3 DD Help Please!

Post by John Fenner »

I would recommend this carb adapted to a TBI intake, the edelbrock will have less velocity for direct drive application.
https://www.ebay.com/itm/133017215939?_ ... E6EALw_wcB
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Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

These aren't the standard ones I've seen online. They are more like isolaters. Ill get a pic and post it.
Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

SWAMPHUNTER45 wrote:
Tue Apr 20, 2021 5:21 am
Are they a conical bushing? Round or egg shaped on botton and flat on top with a hole in the center?

If they are there are 3 colors (white, blue, black) The white are very hard, blue medium and black softer

Most shops stock one or more of the colors.

BrownWater Airboats, Floral City Airboats, Neds Fabrication, AlumiTec Airboats, GTO Airboats will all have them in stock.

I tend to run the blue ones fyi the white will not compress as much but you pick up more vibration in your rigging.
Thanks for the insight, what I have on there is nothing like those but knowing the blue is a good choice helps if I do go that route.
Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

John Fenner wrote:
Tue Apr 20, 2021 10:56 am
I would recommend this carb adapted to a TBI intake, the edelbrock will have less velocity for direct drive application.
https://www.ebay.com/itm/133017215939?_ ... E6EALw_wcB
Thanks for the link! By velocity are you meaning responsiveness or rpm? I don't currently have a tbi intake but if its worth it I can get one.
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John Fenner
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Re: 4.3 DD Help Please!

Post by John Fenner »

Any boneyard will have one, yes, the velocity will bring the torque in at a lower RPM.
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Re: 4.3 DD Help Please!

Post by Slidin Gator »

John Fenner wrote:
Wed Apr 21, 2021 9:03 am
Any boneyard will have one, yes, the velocity will bring the torque in at a lower RPM.
If you would have driven by my house a couple of years ago, you could have gotten one before a scrapper snagged it. :lol: :lol: :lol:

Those factory iron intakes are some heavy some b*!@hes. I'm not so sure the added torque/power is gonna compensate for the swap back from aluminum to cast iron, given the rest of your complaint I might be thinking aluminum heads too.

Edelbrock makes an aluminum TBI intake for the non-vortec heads, I don't immediately find one for Vortec heads. You could stack a bunch of adapters up on your existing 4 bbl intake, the added height will help with low end and then you are not constrained on carb selection, a custom adapter is not that difficult either. A few years back we made an adapter with a 8" long piece of pipe welded to home made flanges to marry an old Varijet to the TBI intake on my buddies buggy. This put the carb and filter up and away from the water, but it also made torque.

You need to think long and small about all this, seriously, long and small :scratch: Small carb, small long intake passages (shove some pipes into the intake runners to neck them down??), small long exhaust tubes. It goes against every thing you think of when hot rodding something, but you need torque down low. You might think about advancing your cam timing, check for valve to piston clearance.

https://www.compcams.com/cam-timing-lob ... tion-angle

Finally, probably the single most effective upgrade you could make is to add 2 more cylinders, but that is off topic. :thumbleft:
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.
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Re: 4.3 DD Help Please!

Post by Slidin Gator »

I think this post on a Ford board just about sums it up.
Contrary to most parking lot stories, you never really lose torque, it simply moves in the power band of the engine.

Want the MOST torque possible out of the combination, build the biggest displacement you can afford. Now, air flow is what will determine when the power (torque and HP) peaks occur. A smaller cross section induction package will have a very high velocity and will result in most efficient cylinder filling lower in the RPM window. A high flow combination, large cross section etc.... will have poorer cylinder filling capability low in the RPM window, but will come on strong mid range and support a higher RPM capability.

As for exhaust, stock manifolds wont do anything to improve a situation. Problems, or should I say dissapointments come into play when someone takes an engine that has a cam designed around a restrictive exhaust and then adds headers. The long duration, early opening exhaust valve timming is no longer needed and power production in the engine is sacraficed when it shouldn't be.


Recipe for lots of grunt, big displacement, efficient but "smaller" cross section induction package, a cam designed to maximise efficency and a free flowing exhaust. (Never need a cork to make something work better, just a cam designed around what you do have.)
Much more to read here.
https://www.460ford.com/threads/what-bu ... ue.101486/
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.
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Re: 4.3 DD Help Please!

Post by John Fenner »

The later model vortec has aluminum intakes.
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Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

dyno_2111_3.jpg
Thanks for the info! this is the intake I have..I also have headers already on the engine. Looks like the best I could hope for is around 150hp at 3000 rpm. Theres a boost in torque from the manifold over stock. For simplicity sake I'll probably put a holley 390 on it and swap out the jets. That way I don't have to change manifolds, I do have an adapter to run a 2bbl but finding a decent 300 cfm carb ain't easy these days.
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Re: 4.3 DD Help Please!

Post by hdsadey »

Speaking from experience about intake manifold velocity in a direct drive application, my 408 Windsor picked up 300 rpms when I swapped out the 4 barrel FiTech that flows 1000 cfm to a 2 barrel FiTech with 500 cfm without a prop adjustment. It's extremely important to speed up the fuel charge at low rpms to produce power. A 4.3 liter engine at 3000 rpms only requires a max of 190 cfms in a street application per Summit's cfm calculator. 390 barrel will work but if your tryin to get the max performance right now an old 2G Rochester would be perfect!

https://www.ebay.com/itm/REMAN-Rocheste ... 890.l49286
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Deano
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Re: 4.3 DD Help Please!

Post by Deano »

hdsadey wrote:
Fri Apr 23, 2021 10:38 am
Speaking from experience about intake manifold velocity in a direct drive application . . . It's extremely important to speed up the fuel charge at low rpms to produce power. . . .
There is no way you can underestimate the truth in that premise.
I had a friend that ran a 351 and we put a old 2100 2 barrel on it (don't remember if was a Motorcraft or an Autolite).
In any case, after removing the 500 Holley that was on it, it was one of the best running SB DDs I've been around.

Chinese knock offs are very afforable, you just need be aware that they came in different sizes which is determined by the venturi size.
The 1.08 venturi flows at 287 CFM, which would be the one I would use if I were doing it, based on hdsadey's previous post.
The 1.02 venturi flows at 245 CFM and the next larger at 1.14 flows at 300 CFM, which I would expect to be fat.
Mo0se wrote:
Thu Apr 22, 2021 10:04 pm
I do have an adapter to run a 2bbl but finding a decent 300 cfm carb ain't easy these days.
Given that be the case, this one IS the 1.08 version and should give you another viable option to consider.
https://www.ebay.com/itm/133458985974

I was a little surprised that hdsadey being the Ford guy he appears to be, didn't mention on of these rather than the Rochester. :D
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but it is not the path to knowledge; it has no place in the endeavor of science."
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Re: 4.3 DD Help Please!

Post by hdsadey »

Lol truly didn't even think about it. I had a 1965 Pontiac tripower setup a few years back for a 64 GTO that never got finished so my familiarity is with the 2G. Also had a 70s era C60 Chevrolet welding truck with a 400 sbc and a 2G that we used to move a stacker race trailer around the yard, damn thing would pull a house down. That being said the 2100 would be a righteous choice as well! Really any that would produce a Shop Vac type of suction just off idle :bounce:
02 Predator 12' 0320 Lycoming
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Slidin Gator
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Re: 4.3 DD Help Please!

Post by Slidin Gator »

https://quadrajetparts.com

They support all kinds of carbs, mostly rebuilt OEM.
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.
Mo0se
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Re: 4.3 DD Help Please!

Post by Mo0se »

I bought the rochester 2G I hope it helps give the engine a little pep! I wasn't sure if the mounting holes for the Ford model would work with my adapter, so I went the safe route. Thanks for the help y'all!

This one!

https://www.ebay.com/itm/REMAN-Rocheste ... 890.l49286
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Re: 4.3 DD Help Please!

Post by John Fenner »

That is perfect, find a piece of 3/8" aluminum plate, lay out the bolt pattern of the holley base, then lay out the bolt pattern of the Rochester dualjet as well as the throttle bore pattern, grab a hole saw the size of the throttle bores make your own adapter.
I never finish anyth,,,.
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