newbie need help on carb set up for 1976 455 olds

[wastedracing]

hey i just got my first jet boat the other day and am wanting to get it running. all it needs is a carb. it is pretty much stock except for headers. i was wondering what size of carbs i should get and do they have to be marine carbs? also will stock carbs not work that great right now? if i did get an aftermarket carb where do i find the plate to make it fit on my intake?
thanks
miles

[dirtracer1971]

what kind of intake,(any pics)you neeed to put alot more info on here!!

[wastedracing]

they are stock manifolds. here are some pictures...

[The Big Al]

I'm would worry about how much water is in the engine.

None of what I see is good!

The intake is a stock Oldsmobile Intake for a Rochester Carb.

Most all Marine Olds Engine have a Aluminum Intake to take a Holly or Carter carb.

let me do some lookup, I think there is a Edelbrock carb that will bolt to that.

Make sure you drain all the oil out, pull the plugs and turn that engine over to get the water out.

AL

[The Big Al]

<TABLE cellSpacing=0 cellPadding=0 width="100%" border=0><TBODY><TR><TD colSpan=2></TD></TR><!-- Start --><TR><TD colSpan=2>Marine Carburetors
For use in marine applications, these Edelbrock carbs comply with U.S. Coast Guard safety standards. Cast surfaces are iridited with Teflon-coated shafts and pump arm for maximum protection. Other features include modified bowl venting, specially designed throttle shafts, accelerator pump seal, 3/8" inverted flare fuel inlet fitting, tube in airhorn for fuel pump vent, 5-1/8" flame arrestor flange, universal throttle lever and revised secondaries for improved transient performance. Note: These carbs have no vacuum ports and are not for auto use. Use our Carb Stud Kits #8008 or #8024 if needed, see Installation Items.</TD></TR><TR><TD colSpan=2> </TD></TR><TR><TD background=../../images/dot1.gif colSpan=2></TD></TR><TR><TD colSpan=2> </TD></TR><TR><TD>600 cfm, Electric Choke
CALIBRATED FOR PERFORMANCE
Designed and calibrated for optimum marine performance in small-block V8 engines with a variety of manifolds that include Edelbrock Performer, Performer RPM, RPM Air-Gap, Torker II and other brands of similar design. Also ideal for Chevy 4.3L V6 engines with a Performer manifold (see Manifolds) and Calibration Kit #1485. Comes with: Metering Jets – Primary .098, Secondary .101; Metering Rods – .068 x .047; Step-Up Spring – orange (5" Hg).</TD><TD width=250></TD></TR><TR><TD colSpan=2> </TD></TR><TR><TD colSpan=2><TABLE cellSpacing=0 cellPadding=0 width="100%" border=0><TBODY><TR bgColor=#000000><TD class=tahbwh2>Description</TD><TD class=tahbwh2 align=middle width="15%" bgColor=red>Cast Finish</TD><TD class=tahbwh2 align=middle width="15%" bgColor=red>EnduraShine</TD></TR><TR bgColor=#f2f2f2><TD class=spc2>600 cfm, square-flange, electric choke, marine (non-EGR)</TD><TD class=spc2 align=middle>#1409*</TD><TD class=spc2 align=middle>N/A</TD></TR></TBODY></TABLE></TD><TR><TD colSpan=2> </TD></TR><TR><TD background=../../images/dot1.gif colSpan=2></TD></TR><TR><TD colSpan=2> </TD></TR><TR><TD>750 cfm, Electric Choke
CALIBRATED FOR PERFORMANCE
Designed and calibrated for optimum marine performance in small-block and big-block V8 engines with Performer RPM, RPM Air-Gap and Torker II manifolds and with Performer manifolds on large cubic-inch engines. Comes with: Metering Jets – Primary .113, Secondary .107; Metering Rods – .071 x .047; Step-Up Spring – orange (5" Hg).</TD><TD width=250></TD></TR><TR><TD colSpan=2> </TD></TR><TR><TD colSpan=2><TABLE cellSpacing=0 cellPadding=0 width="100%" border=0><TBODY><TR bgColor=#000000><TD class=tahbwh2>Description</TD><TD class=tahbwh2 align=middle width="15%" bgColor=red>Cast Finish</TD><TD class=tahbwh2 align=middle width="15%" bgColor=red>EnduraShine</TD></TR><TR bgColor=#f2f2f2><TD class=spc2>750 cfm, square-flange, electric choke, marine (non-EGR)</TD><TD class=spc2 align=middle>#1410*</TD><TD class=spc2 align=middle>N/A</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

[The Big Al]

You may need this. Mr. Gasket Part#1932
Or purchase a Aluminum Performance Intake

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[wastedracing]

hey thanks for all the help. o and there is no water in the engine. there is alway duck tape and a bucket over the intake holes. it was wet because it was outside just after it was raining.
thanks for all the help. so do you guys think i should get a 600, 650, or 750??

[The Big Al]

Use the part number 1410 750CFM

600cfm is way to small


Were are you located?

[wastedracing]

im located around tacoma, washington. so are you thinking i should go with the 750 cfm?
thanks
miles

[2 KNIGHT]

holly makes a marine carb spread bore 800 cfm that is what i would use

[2 KNIGHT]

and oh yea since you will be running high rpm most of the time i would run a torquer 2 intake from edelbrock/headers

[Propster]

Don't use a spreadbore on a boat. Get an adapter or new intake and run a standard type carb. The primaries on a spreadbore are ok for a car, but too small for cruise on a boat. You will always be in the secondaries right at the transition. That will increase fuel consuption and reduce performance due to poor velocity on the secondarys.

[bipolar4U]

"Don't use a spreadbore on a boat. Get an adapter or new intake and run a standard type carb. The primaries on a spreadbore are ok for a car, but too small for cruise on a boat. You will always be in the secondaries right at the transition. That will increase fuel consuption and reduce performance due to poor velocity on the secondarys."

I couldn't disagree more with these comments!

While new to the website I am not new to olds powered jet boats. Several years ago I owned a Olds powered Wriedt. I painstakenly rebuilt the engine which included an Edelbrock Performer Manifold, "low to mid range" camshaft and a Holley spreadbore carb with vacume secondaries. Maximum RPM on the engine was around 4500 and it cruised effortlessly at 4000 RPM's all day long.

Throttle response was INSTANTANEOUS and it was instantaneous because of the high velocity of the intake charge. That in turn was directly due to the small primary venturies. At around 3800 RPM's the secondaries would open and the transition was extraordianary. Gas mileage was excellent and the boat performed flawlessly.

On the contrary, depending on its intended use, spread bore carbs can be an excellent choice!. There is so much misinformation out there on carburetor "sizing" that it continues to bewilder me. There are specific formulas to apply when determining what CFM is required for a particular application and that formula is almost always ignored or overlooked. For example, a 455 Olds turning 5500 RPM's with a volumetric efficiency of 80% needs a carb that flows 580 CFM...not some "double pumper" in excess of 800 CFM!. No "dual quads"...no "tunnel rams"...and no single plane manifolds which are a DISASTER for low-end performance.

Most importantly, keep an open mind and avoid the temptation and avoid some of the cliches that never seem to go away.