Carburator Help???

[BoatnAround]

I need to pick up a new or remanufactured carburator for my Jet boat which has a 454 BB. One person told me that the 600 cfm Edelbrock #1406 would be a good carb to put on, however I am wondering if I should get something larger? Maybe a 750 cfm? (model #1407 for the Edlbrock and i am not sure for Holley) I have a spread bore intake(at least I think it is, since the secondaries are larger than the primaries). <br /><br />It seems like the majority of the carbs are square bore (with the exception of the quadra jets, which seem to be a little more expensive) Would I loose effeciency or HP if I use one of those adapter plates? <br /><br />The carb that is on the engine now is a Holley (I do not have the model number handy) that has larger secondaries. The carb is huge, One guy said that he thinks they used to put them on buses or big trucks. It appears to have very large floats. Basically to sum things up.... I need to know if you think I would be happier with a 750 cfm since it is a 454 BB. Or should I save a little money and buy a 600 cfm if it does not make much difference.

 

[Boomyal]

Re: Carburator Help???

600 cfm seems awful small for a 454 BBC. I'll be running a 600 cfm Holley on my 331 Ford. It would not be uncommon to see them on 302's, 351's and Chev 350's. Somewhere there is a formula for calculating carb size. If I can find it I'll post it.

 

[outboardguy]

Re: Carburator Help???

http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/FMSC.html <br /><br />Take a look here.

 

[vinney]

Re: Carburator Help???

I use to play with Berkley jet drives. If the jet drive has a single blade in it. It will use up a third of the horsepower made on the pump. They are alot of fun to run but very in efficent. If you making 500 hp. you are putting 315 hp. to the water. You need to make alot of horsepower to make them go. As for the question. 600 Holley to small for a jet drive you need to make all the power you can with that big block. If you make 350 hp. with your big block your putting 220 hp. to the water. You will need all you can get from that engine. Holley 750 or 780 and jet it to the boat. We used to have custom made fuel systems to make our jet boats run fast. A jet drive will eat all the horsepower you can put to them.

 

[BoatnAround]

Re: Carburator Help???

Thanks Outboardguy and Vinney! I just learned a lot about Carbs. It looks like I should be using a 750 CFM. I will have to check my WOT. <br /><br />Vinney, Thanks...I was always wondering the type of effeciency the jet drive would have compared to a prop drive. That explains why most jet boats I see are always tricked out! Do you what kind of ratio of HP a an engine with a prop is putting to the water?

 

[BoatnAround]

Re: Carburator Help???

Boomyal, <br /><br />you were right. A 600 does seem small. I will buy a 750 for now.

 

[Walt T]

Re: Carburator Help???

600 is more than enough. The 750 will give you a decrease in performance. You cannot apply those numbers to marine use. Marine use rarely sees above 5000 rpm, and most of the power needed is at the lower rpms. Save your money. According to my figures at 80% VE you will only actually use 504 CFM at 4800 rpm with 630 cfm at 100%. And how often do you run at 4800 rpm??

 

[BRIAN03]

Re: Carburator Help???

Its a jet drive not a sterndrive. You need to turn the rpms on jet to make all the power. You need the most fuel on it the motor can handle without drowning the engine. Unless you want to cruise around slow. If you own a jet boat you shouldnt be worried about fuel burn. The jet drive is a great dyno on the water. The more power you add the faster you will go.

 

[Boomyal]

Re: Carburator Help???

DieselWalt, by that reckoning, a 600 cfm carb is too big for my upcoming 331 stroker. The calculation, without considering the VE, is only 480 cfm at max WOT rpm of 5000. <br /><br />Does this mean I need to toss out my newly purchaced 600 cfm used Holley and spring for a new 500 cfm Marine unit?(can't find them used)

 

[bluewater19]

Re: Carburator Help???

dieselwalt,<br />If that's the case why does my 4.3liter come from the factory with a webber 600cfm 4bbl?<br />Are you saying that a 7.4liter big block pumps the same amount of air through it as a v-6? <br />I know that my fathers 1969 camaro with a 454 runs much better with a holley 750 double pumper than a 600 double pumper and it never sees the north side of 4000rpm.<br />Please help me out Is my boat over carbed?

 

[TwoBallScrewBall]

Re: Carburator Help???

There's no doubt about it, a naturally aspirated 350 4-stroke being 100% efficient could only move 506 CFM at 5000Rpm. As to why we typically use larger carbs, I don't know.

 

[Walt T]

Re: Carburator Help???

No, stay with your 600's. All I am saying is don't go to a 750 if you already have a 600. The reason the 600's are used is because they are the least expensive ones. My 350 has a 625 and the secondaries barely open at all at full throttle. It's getting all it needs through the primaries.<br />Its much cheaper to use one carb over a larger range of engines than to offer a bunch of different carbs, so thats why the V-6's have them. You may be suprised at what actually happens with vacuum secondary 4 bbls. At sea level they may actually open up a bit at full throttle, up where I am, they usually dont. Check it out sometime, set yourself up so you can see the secondary linkage and observe it move while the boat accellerates to full throttle. DONT take off the air cleaner and look down into it while its running full speed. Fuel will be spraying down and you may not even be able to see the plates. One backfire and you'll be borrowing the ol lady's eyebrow pencil.<br /><br />Now jets are sometimes run up at 6,000 and if you build an engine for it, well by all means use the 750. I've built blown gas drags that ran 8000 rpms with dual quad set ups. The blower utilizes every cfm it can get in that situation.<br />I just dont like to see folks throw away money on misinformation.

 

[vinney]

Re: Carburator Help???

How are you going to run this boat? I ran my jet boat at WOT all the time. It was a 468 inch big block with a mega blower with a 1050 holley modified by bolar fuel systems.Open headers with tip coolers and a double A blade in the jet. I buzzed the engine all the time. Ignition MSD unit with rev control with a 7000 chip and I was on(the limit)all the time. No dip stick on the engine. Pulled the engine every monday morning after a hard weekend.(It would loosen half the fastners on the engine). I never turn the engine at 5000 rpms maybe once in a no wake zone. Jet- drives love rpm's and I didn't worry about how much fuel I was buring.

 

[rodbolt]

Re: Carburator Help???

hello<br /> I run an 800 spreadbore double pumper on my .060 over 455. it works better than the 600 the 650 and the 780 did.<br /> what intake configuration are you running? and remamber the 600 secondaries are really not adjustable much. if you can find an old one they had secondary metering blocks. I like the older ones cause I can play with power valves,jets,nozzles and pump cups and such.<br /> I found that 4 corner idle circuits work well on a dual plane but really made no difference on an open phlenum.<br /> there is a lot more to it then a simple calculation on VE. there are a lot of ineffeciencies in carbs. I really dont think you will be happy with the 600. the 780 had vacum secondaries. unless you have a large cam and lots of compression I dont think you should use any mechanical secondary carbs. volvo used it on the 340 hp 7.4 for several years. merc and volvo as well as chrysler and ford used the q-jet at about 700 cfm for years and will make 340 horses with a bone smooth idle at 600 rpm.<br /> good luck and keep posting

 

[Walt T]

Re: Carburator Help???

Ya know, Rodbolt really brings up a good point here. You really never know what carbs will work best until you try them. It is very possible you put an 850 on there and it runs better. I would then submit that the previous carb was not calibrated correctly which Rodbolt alludes to. It's true these are only numbers and actual performance can be different. All I am trying to say is don't run out and spend a lot of money without knowing what you are doing. Manifolds make a big difference too. Dropping a spread bore on a stock manifold doesnt get the full performance out of a large investment. <br />The numbers don't lie however, and the engine CANNOT move more air than it is physically able to. So if you have an 800 and the engine never uses more than 600, Well I'm sorry but you paid for 200 more than you needed. If it runs better and faster, then the previous VE off the previous carb was not that good to begin with. All you may really do is increase the VE with a different carb. If you install the 750 and you're happy with it, well then you've gotten what you paid for. And that is really all that matters isnt it?<br />If you're into the weekend warrior scenes on Havasu and up on the River Bend, well then it's the guys/gals that truly understand how it all works together that own the lake and the river. They arent impressed with pretty carbs and they all laugh at the fool with the 850 double pumper on his stock 350. So start off by learning all you can and then making intelligent decisions.

 

[vinney]

Re: Carburator Help???

JETs not sterndrives. Pick up any Hotboat Mag. you wont see a 600 holley on ANY boat in that mag. I guess thoses boys who go REAL FAST have it all wrong. They need to take there custom made carbs and fuel systems off and put a 600's on. A street car Rodbolt has no comparision to a boat maybe the steering wheel is the same. A jet boat is nothing like a sterndrive. I've played with jets boats and have spent my share of money making the go fast and NEVER had a 600 holley on anything we ran.

 

[rodbolt]

Re: Carburator Help???

vinney<br /> I must beg to differ.<br /> my poor street 455 has done duty in a friends jet boat with some slight mods, it also did weekend duty at green valley and ennis texas. it turns regular trips at 6500 and it has been known to shift at 7200. I am quite familiar with RPM on big blocks. the math just does not always equal what is nessasary.<br /> I am just trying to explain that the carb must be matched to the intake system which must be matched with the heads which then must be matched with the valve train which must be matched with the exhaust and all of it must be matched to his impeller size,I spent several years building and machining blocks cranks heads and rods to play NHRA and IHRA. you would not believe some of the combo's I have seen tried. the shop I worked at in texas in the 80's specalized in aftermarket and offroad modifications. the major difference in a marine verses standard grocery getter auto is that the auto rarely gets run at its rated power and the marine will spend hours at it. try to explain a lean condition at 4800 rpm to the tech at the chevy dealer and he will look at you like your a nut.or better tell him your 427 with 2 660 holleys is banging from the pipes at 6800. all me and diesel are attempting to do is point the guy in the right direction. without extensive mods a vacum secondary single carb of about 750-780 cfm will work. the 700+cfm q-jets work as well. chevy has some marine perfomance holleys in the 800 cfm range from the factory on the 7.4 and 496 as well as some 502 engines.<br /> it is rather funny that I have seen people drop thousands on the engine and never once change the impeller.<br /> anyway good luck and keep posting

 

[Walt T]

Re: Carburator Help???

Vinney, If I were running a jet with a 454 built for 6000 rpm, I would have an 850 on there. No those guys dont have it wrong. What we are saying is the guy with a stock engine who rarely goes over 5000 rpm doesnt need that. Like I said though, it's your money.

 

[vinney]

Re: Carburator Help???

I agree with you Walt. I'm trying to say that jets don't go well without alot of horsepower in front of them.

 

[rodbolt]

Re: Carburator Help???

hello<br /> boatnaround<br /> what type of BBC ya running?<br /> mostly stock ? any mods? carbs can be very confusing. I keep looking at that formula and wondering why we had a pair of 660 holleys feeding a set of lee sheppard heads with 12.5-1 closed chamber on a modified 427. it still displaced roughly 427 CID and we shifted about 6500 but I can bet 600 CFM would not make second gear. we then shifted to a 355 CID with a 1050 dominator that ran in the mid 8's as well.<br /> although we did shift that one at about 7K. my olds on a 19 ft checkmate would turn about 5700 at wot. i cant remember what size the impeller was. but my 455 is .o60 over with a luanati w-30 cheater cam some head work some neat valve springs stock covers point type ign slightly modified and an antique edlbrock torqer intake the mechanical compression ratio is about 11 to 1. you can make 450 horses with bolt ons on that BBC and still keep it below 5500 and less than 9.1 compression. you may end up with a dry type exhaust if you use very much cam. geneally if the cam cannot maintain at least 16"Hg at an idle it will suck water if a wet exhaust is used.<br /> its been years and years since I played with jet boats best I remember they were a lot of fun but twin 12 gallon moon tanks are useless . Like vinney says jets like horse power. <br /> goes back to the sign in the shop in Cleburne TX.<br /> speed costs money. how fast ya wanna go ?<br />good luck and keep posting