383 with 2bl carb
 

Anyone ever thought of trying a 383 with a 2bl carb. I know you are not going to get 400 hp but maybe 325 and better fuel economy that a 350 with 4bl carb.

Chris

You are mistaken.

Having a larger air restriction will have lower volumetric effeciency because of larger pumping losses. Larger pumping losses can/will cause higher BSFC (amount of fuel used per hp)

Say if for some reason both motors have same vol eff / bsfc, then if you use the same hp, you use the same fuel.

Which brings me to a more important fuel effeciency topic with boats...

Off the engine topic......your boat's efficiency (ie: how much HP it takes to drive at X speed) and how fast you drive it (ie: X) has way more to do with fuel efficiency then the engine is responsible for.

Exyreme but real Example: Friends ski boat with stock 260hp 5.7 takes over 4 times the fuel to get to a certain place we go than I with an approx 375hp 5.7. Both are 20ft boats.

Psst: I get there faster too. Way faster. LOL.

Why is that ?

because you have full race peanut butter race ports:whistle:

From my experience the 5.7 260 h.p. was not in a very efficient state of tune. When they came out with the Magnum version they rated it at only 10 additional h.p.
I saw dyno results showing 12 h.p. alone switching from the 3" rises to the 4" risers. Then there was the high rise intake which made a huge difference plus the
less restrictive flame arrestor. I'm sure, with your skills SB, that you put together a package that is super coordinated and powerful. Ever wonder what you could do with a 427 cu. in.
smallblock and a large budget? I'm guessing 450+ on pump regular.

Creamy, not Chunky. Shhh. That's a speed secret.

On the stock 260hp Mag, a few more degrees of timing, the Highrise Bowtie intake as you mentioned, along with Felpro 1204 intake gaskets (blocks the exhaust heat crossover) and getting a dialed in prop really wakes up small single Alfalfa driven boats.

So, yes, Alfalfa can compliment peanut butter. LOL.

450hp 427 ? Serious ? A 383 can make 450hp no sweat. Medium budget. For a little more a 421cid or so SBC can go well north of 500HP on pump. Time to rethink your Alfalfa though.

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PS: Cheaper way to make your 4bbl into a 2bbl is to use less throttle. Same thing. In this instance swapping back to a 4bbl is as easy as pushing the throttle farther foward.

BTW: it's not my mad scientist tuning skills, it's because the ski/wakeboard boats plow thru the water. It doesn't ride on top of the water with little hull touching the water.

Again, my point is that what you use for horsepower to go a certain speed is what you are going to get for fuel mileage.

A little 20ft boat dancing on it's butt (ie: only say 3ft or so really on the water) will use far less than a 20ft boat with 20ft of it plowing thru the water. At 45mph his ski boat is at or near WOT - ie: 260hp. I'm at 1/4 throttle or so and a close estimate might be 100-150hp.

At 260hp I'm probably around 52-55mph. As that's what the boat did stock. So, should be a close guess.

i got a 2 bbl that out flows a hollt 600 4v..came off a old 70's school bus....hey they said stock gm carburetor in the rule book...

Ya I have seen those Fix.. So back to the question.. Has anyone ever tried or do they think a 2 bbl would work on a 383 marine. I know mopar use to do it in cars. And like fixx is referring to I have seen it on an asphalt stock car race motor. I understand the flow restriction but on a big heavy boat, trying to keep it from sucking gas with the secondaries open while just on plane is also important.

most engines with that displacement will need a 750 or bigger carb.it takes power to push a big heavy boat and power is reduced when you restrict the air flow.the sucking of gas is just going to happen if you want power.

Mike get's it.
Air pulls fuel thru the carburetor.
More power requires more air and fuel.
Reduce the power by using a smaller carburetor , you will use less fuel.
Reduce the power by not using as much throttle opening on a 4bbl and you will use less fuel.
When you use less throttle, you are effectively making the carburetor smaller.

The power requirement of the boat and the driver is what causes your fuel economy #'s.

As an FYI: A bigger engine usues more fuel at idle/very low speed than a smaller motor......frictional losses, reciprocating weight differences, etc,etc amongst other reasons.

Wrong hobby if concerned about fuel economy!

Yeah, start knitting. No gas problems there.

I am not worried about gas..I think everyone was missing the point.. I will admit Gas is the cheapest thing on my boat but it does all add up. Part of my scenario is I have a 305 with a 2bbl and an Alpha drive. So I don't want over 325 hp. Thought it might be interesting to bolt the 2 bbl onto a 375 hp or so 383 and see how it works. Later down the line when the alpha pops, I can put on a bravo and a 4bbl. Sort of a progression . If I cant make 300 hp with a 383 and a 2bbl then I will want go a different direction.

Chris

You'll make 300hp with a 2bbl no sweat.

Makes no sense to me, but if you want to do it, do it. Your $$$ and displeasure. LOL.

Put a throttle stop on your 4bbl. Cheaper. Just a small bracket and a bolt. Done.

You stated secondaries being the source of low fuel economy.

What size / weight / type boat do you have ?

What size is the 2 barrell? Some 2 barrels are pretty good size. Try putting it on, just be careful on the jetting. Like has been stated before horsepower is fuel and air (put very simply). A 383 at 5000 rpm would use 500cfm or so. If the carb is around 500 cfm(and the intake is decent) I would think 300-325 would be realistic for a 383 that would make 375 with a proper 4 barrell if jetted correctly. Even if you lose some horsepower up top, you will still make a lot more torque down low than the 305.

FYI: A 500cfm 2bbl is not like a 500cfm 4bbl.

The 4bbl is rated at 1.5"HG depression, the 2bbl is rated at 3.0"HG depression. "HG is how we measure vacuum. If the 2bbl was rated at same 1.5"HG, it's flow rating would be substantially smaller.

i agree this would be the smartest,cheapest way to do it,the 4 bbl carb is a 2bbl carb if you dont open the secondary,s.

Just stay out of the secondary's. my experience ;18 GPH part throttle cruise, 60 GPH WOT with twins

I will have to admit, I never even thought about a throttle stop. As cheap as that is, its not as cheap as trying the 2 bbl. I did find this chart that showed the jetting for a 2 bbl on a 305 and 350. http://www.cfm-tech.com/2bblmercarb.htm
Interesting that it shows 170-185 mains for the 305 and 165 mains for the 350. If the same would hold true for the 383, i would not be too lean by just slapping the 2 bbl on. Someone asked what boat this is. It is not my go fast. It is a 25 ft cabin style boat that weighs about 5500 lbs loaded down. It does 34 right now. It will never be fast but it is getting time for a new engine and I want something that will hopefully keep the boat on plane at 20 and max out at 40. Right now it is hard to plane with over 4 people and will fall off plane at 25. I figure 300 HP or so with a 4 blade will be right on the money.

Chris

Well, that's interesting. That's my website/company. LOL.

remember the old chevy caprice with the 400 sb with a rodchester 2v?..if this is a cruiser style boat its a fact that a 2v carberator has more torqur on the bottom end then a 4v carb..i just built a 383 for a friend of mine for his late modle stock car..he had C&S specialties build him a carb that flowed 650 cfm..you might want to give them a call and see what they can bucks on a carberator..do for you..but your going to spend 750.00 on that carb but well worth it..

http://www.candsspecialties.com/

Excuse the French, but what the hell is the fascination with a 2bbl ?

Only time we run them in a performance application is when rules dictate it !

It has absolutely no benefit for freakin fuel mileage other than reducing the performance of the engine !

If you want to reduce the performance of a new engine build, why spend extra money on that engine for performance parts ?

I must say now - WTF guys ?

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I have a quazzillion of hrs on the dyno and track with performance 2bbl motors. Why ? 2bbl carbs reduce engine power to a huge extent and it takes time/$$$/knowledge/and stupidity to make some power back.

Why again ? Rules ! if it weren't for performance decreasing rules forcing the use of 2bbls, we/I wouldn't have gone thru all of this.

This thread is getting frustrating and comical at the same time. Okay, not getting, as it started out this way, but why is it still going on ?

If you count 2500rpm-3000rpm as low end torque (I do as this is where most I/O boats plane) I will totally kick your 2bbl motors azz with a 4bbl. 100% ! I've shown this to many people live - especially those that think the 2nd barrels don't open up this low...even on a stock Merc engine with quadrajet.

The difference is massive !

I have the boat and the resources.

Bring it on !

I'd love for this thread and subject to end.

LOL.

BTW: i'm not pisses, if it sounds that way, just frustrated you guys are still carrying on about this insane subject.

BTW: The 650 cfm 2bbl carb was bought/used because of rules saying that you have to have a 2bbl carb.

If you didn't have this rule, what power/fuel effeciency benefit would you have over a 4bbl carb from same company that flowed the same ? None ! In fact, the 4bbl will have smaller throttle bores / venturi's then a comparable cfm 2bbl. Plus, you can tune opening rate of the secondaries.....and because of this probably get a better fuel curve out of the 4bbl.

Wow SB.. Too much red bull or something.. This is my thread and its a discussion of what is possible not what is better. Why a 2bbl.. Because I already have one.. If I really wanted to start spending big bucks, I would go Fuel Injection and **** can the carbs.. But thats a different subject. I am sure there are tons of people out there with a 305 -350 small block and 2 bbl carb that would love to see what power it makes if they slapped it on a 383. SB I might even buy one of your spacers off your web site if you kiss and make up...lol...

Chris

sb is giving you good advice,listen to him but forget about kissing him.lol.

I was thinking about putting a single barrel rochester off a 1966 Chevelle Malibu straight 6 250ci onto a 540ci marine engine, mostly for fuel economy. I would be looking for lots of low end torque and I hear a single barrel is where its at. Thoughts SB?

Just kidding guys, continue on

i like that idea,i think i will dump the 2 1050 on my 588 whippel engines and get a pair of carbs from a 1979 chevy caprice 307 2 bbl carbs,bet the torque will be tremendous!but the most important thing will be the gas mileage because that,s why i have these engines,gas mileage and low end torque.

So this is what offshore only has come to. Cruiser owners arguing 2 barrel vs 4 barrel. Did I just go 88.8 mph and end up in 1955?

2 barrel carbs.......they should come with a coupon for 50 cents off a box of tampons and a Ford pinto wall poster.

Can I run a two barrel on this ? I like turtles .

http://i1243.photobucket.com/albums/...DS/blower1.jpg

Yes ! Keep the 1bbl / 2bbl on big motors coming !

You are onto something !

from my pavement experience... 2 bbl to "6" bbl, I at one time had a 66 gto with a 389 tripower (3 two barrels with a mechanical linkage opening the extr 2 carbs ) It was a beast. Anyways, when it rained in southern ca. trying to drive it was a beech. either it would light the back tires or lug and stall trying to leave a traffic light. The easy solution was to open the hood and pop the linkage when it rained so it only ran on the single 2bbl. So from the assdyno point of view, your going to drop a lot more than75 hp going to a 2bbl unless you go with a 2bbl with venturies the size of 5 gallon buckets.

An NA motor works on vacume. It takes X amount of fuel and air to make a certain amount of hp per displacement and compression.

It takes Y amount of hp to plane your cruiser. X and Y are going to find equilibrium whether you have a 2 barrel or a 4 barrel. the difference will be with the 4 bbl you give it partial throttle, with the 2 barrel you stuff it to the dash.

Wow. People claim the fountain cig or v cat arguements are ruining oso. I believe this is the thread that is the downfall!! Hahaha. 2 barrel carbs should only be mentioned here if they are are going I'm the garbage for a 4!! This thread is hilarious and right ups here with Korean boats and coked out pandas stealing iPads. Hahaha

I may be on Red Bull. But your eating too many mushrooms and hallucinating.

I'll take your bet, and raise you.

I have a few Stromberg carbs at work I could give to you for no $$$$. That's cheap. Should be fantastic on gas on 383's.

No f'n reason to to spend $$$ on a bigger engine and put a 2bbl on it.

I make my spacers for performance. Not fuel efficiency.

Again, your money and that's fine....but trying to make it look to others like it's a viable thing to do ? Nope, nah, nada, zilch....

I think the 1bbl on big cubic inches mentioned above may be a good idea.

4 Split Dominators On A Sheet Metal Tunnel Ram will get me excited talking about 2bbls !

http://i249.photobucket.com/albums/g...2020220314.jpg

Yeah. That's sweet. So I was mistaken. Op is gonna put 4 2 barrels on his 383. Ok. I'm back on board. Haha

sb,those 2bbl,s will really help the gas mileage,lol.wonder what would happen if you put some red bull in the tank.

i was thinking the same thing..

I would bet it depended on which red bull was used I heard the 0carb 0 sugar gives more power.:whistle:

In my limited experience I have found that the more cubic inches you have, the easier it is to make torque. You don't have to rev the chit out of a big motor like you would a smaller one to achieve the same speed if they are propped correctly. I get better gas mileage and more power towing my boat with a BBC in my truck than when it had a SBC. Had to run the small block wide open all the time but only have to run part throttle with big block power. If you have a big heavy boat, I would run a mild big block. Still get good mileage and lots of torque with a bigger prop. Or you can rev the chit out of your small block.:eekdrop:

This is the engine I am planning on putting the 2 bbl on. I am going to have them put a smaller cam in it for smoother idle and I really don't need all that power. So its not like I am putting a 10k motor in the boat and slapping on the 2 bbl. This is just a budget build using take off parts from my 305.

http://pmcmachine.com/index.php?main...arine&x=58&y=1

Chris