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· Cole SS
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124 Posts
Discussion Starter · #1 ·
I would like to replace my carburetor on my stock 454. It is in a 20' cole jet. I think the original carb is a holley 715 vac. secondaries. I do plan on doing some performance up grades, down the road. What do most owners use for a replacement? I have always used holley. Not sure about edelbrock. Would a 750 be to big for my stocker? Would you use mechanical or vaccuum secondaries? Thanks for your help. I know others have had the same problem.
 

· E-7 Sheepdog (ret)
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6,625 Posts
For a heavy 20' boat, unless you intend some massive performance upgrades, you have plenty of CFM untill you get to arround 5500RPM, if you desire 6-grand, go to looking in 830/850 CFM land.
For absolute max performance a double pumper is where you'll get it, but, on a heavy big boat, doubt the difference is anything worth noting.
 

· Sit N' Spin
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1,345 Posts
I would go with the Holley simply for the ease of tuning and ease of rebuildability.

On a jet boat you can run either vac or mech secondary and I doubt you'd notice a difference between the two on a stock motor. They both flow the same air (a vac secondary 750 will flow the same as a mech secondary 750) and as long as you have the right spring in the vacuum diaphragm, the secondaries will open all the way at WOT just like they will on a mech secondary. However, the one benefit you will have with the mechanical secondary is that the secondaries won't open unless your foot tells them to, whereas with a vacuum secondary they open when the motor and the diaphragm spring allow them to.

As far as the fuel economy between the two, if you had a vac secondary 750 and a mech secondary 750 and they were both jetted the same, I doubt you'd notice a difference between the two. The only reason it may seem that a mech secondary at WOT would give you less fuel economy than a vac secondary would be due to the fact that a mech secondary has two accelerator pumps (i.e. "double pumper") whereas a vac secondary does not have a secondary accelerator pump.
 

· Registered
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1,592 Posts
I would like to replace my carburetor on my stock 454. It is in a 20' cole jet. I think the original carb is a holley 715 vac. secondaries. I do plan on doing some performance up grades, down the road. What do most owners use for a replacement? I have always used holley. Not sure about edelbrock. Would a 750 be to big for my stocker? Would you use mechanical or vaccuum secondaries? Thanks for your help. I know others have had the same problem.
Holleys are great. I've also had the Edlebrock 750 on some potent 454's and they work great and are easy to tune. I think they also make a marine version.

I'd wait until you have a design on the other mods before you pick anything bigger so you can match the need. It's real easy to over carb.
 

· Half a bubble off
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2,433 Posts
Holleys are great. I've also had the Edlebrock 750 on some potent 454's and they work great and are easy to tune. I think they also make a marine version.

I'd wait until you have a design on the other mods before you pick anything bigger so you can match the need. It's real easy to over carb.
X2... I've currently got Holleys but the Edelbrocks I"ve had the the past on milder motors were easy to tune, worked out of the box all the time and were pretty much turn key. As others pointed out, the Holleys provide MUCH more tuning opportunity.

Good luck

PS.... we need to bring you into the fold of NW boaters. You'd be surprised how many of us there are and not far from you.........plenty of help and assitance nearby....john
 

· mo balls than $cents$
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11,635 Posts
Holley is the way to go, but for the price of them...I would have Patrick @ Prosystems build you a nice carburetor for just a pinch more. It will be well worth it and have better parts/flow #'s. They will come perfectly tuned and ready to go out of the box as well.

http://www.prosystemsracing.com/proseries4150.html
holleyyyyy:)devil gets my vote as well. i've only had 1 edel carb that i thought was worth a damn
 

· Registered
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587 Posts
Rochester huh, just down the rode from me. I vote holley as well, I'm with Impatiant on this maybe one ran right out of the box the rest I had to by their calibration kit and redo to get the hesitation out of them. If you ever need any help give me a call,pm for phone number. I own a auto repair shop here in Olympia.
 

· Cole SS
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124 Posts
Discussion Starter · #9 ·
Would the 750 be to big for my 454 with peanut heads? I do have some 049 that I will swap out later. I can only seem to pull 4,400 rpm. I am not sure If carb. is working properly. 49 mph is my top speed, so far
 

· Registered
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187 Posts
CFM for 454 turning 5500 RPM AT 83% VE = 599.68 CFM
CFM for 454 turning 5500 RPM AT 100% VE =722.512 CFM

This is based upon a basic engine without performance mods
!00% VE is accomplished by Blower or NOS etc.
 

· E-7 Sheepdog (ret)
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6,625 Posts
Would the 750 be to big for my 454 with peanut heads? I do have some 049 that I will swap out later. I can only seem to pull 4,400 rpm. I am not sure If carb. is working properly. 49 mph is my top speed, so far
IMO it will be a LITTLE big, for it's current condition, BUT, not to bad as to cause driveability problems, and should be just right untill you mod it a good deal and start turning significantly over 5-grand with it.

The 049 heads are the good-guy ones to run, BUT, IMO, get a little port/bowl work done to thema nd, also, if possible, put the large factory size valves in them if they are not already (unlikely).
2.19" x 1.88".

Most 049's I've seen and heard of came with 2.06's and 1.72's, mine did.

Light cleanup bowl work and full-size valves makes a BIG difference.
Just don't go get them hogged out "full-race" style.:)st
 

· Registered
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3,879 Posts
Rochester huh, just down the rode from me. I vote holley as well, I'm with Impatiant on this maybe one ran right out of the box the rest I had to by their calibration kit and redo to get the hesitation out of them. If you ever need any help give me a call,pm for phone number. I own a auto repair shop here in Olympia.
Holley, the EDELBROKE IS THE OLD CARTER AFB SERIES. Vic bought the rights to the design and just made it pretty, but still the same carb. for you're app I would hunt down a list 4780 holley and be happy! Jetting is easy and anyone can rebuild them. I have played with both and for ease of tuning for your'e app the holly is the way to go! IMLAO M
 

· Registered
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1,592 Posts
Holley, the EDELBROKE IS THE OLD CARTER AFB SERIES. Vic bought the rights to the design and just made it pretty, but still the same carb. for you're app I would hunt down a list 4780 holley and be happy! Jetting is easy and anyone can rebuild them. I have played with both and for ease of tuning for your'e app the holly is the way to go! IMLAO M
Not that it really matters, but I beg to differ! Unlike me, there is nothing old or obsolete about this carb. The Edlebrock version is improved, and extremely simple to tune. If I can do it, it HAS to be simple. It's a proven carb, and they have great support and well thought out combinations of tuning parts.

Yes, Holleys are highly tuneable, but not simple to tune for the novice. Certainly not as simple as the Edlebrock. Rant over...
 

· steelcomp was here
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11,830 Posts
Not that it really matters, but I beg to differ! Unlike me, there is nothing old or obsolete about this carb. The Edlebrock version is improved, and extremely simple to tune. If I can do it, it HAS to be simple. It's a proven carb, and they have great support and well thought out combinations of tuning parts.

Yes, Holleys are highly tuneable, but not simple to tune for the novice. Certainly not as simple as the Edlebrock. Rant over...
If you want to go with a Holley, the 750DP (4779) is about the cleanest, easiest to tune of all the DP's. The 800 and 850's are calibrated for a much wider range of applications and tend to be "rich" running carbs. I call them "dirty" carbs. That's just my experience, anyway. However, If you want clean idling, smooth cruising and nice crisp throttle response, the Edelbrock is going to give you better results and for ease of maintenance, tunability and drivability the Edelbrock is a much more user friendly carb but because of the venturi design, as a rule, they will give up a little power on top vs. the Holley. On a peanut ported 454, I doubt you'd see any performance difference.
 

· steelcomp was here
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11,830 Posts
CFM for 454 turning 5500 RPM AT 83% VE = 599.68 CFM
CFM for 454 turning 5500 RPM AT 100% VE =722.512 CFM

This is based upon a basic engine without performance mods
!00% VE is accomplished by Blower or NOS etc.
Those are minimum cfm requirements for carb sizing, but not anything near a performance or marine guideline (as you stated...basic engine, no mods). It's also not difficult to reach or even exceed 100% ve on today's NA engines.
 

· resident gearhead
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20 Posts
I have had tons of holleys. all worked good after the tuning process. i have had a few eldelbrocks and they tended to work a little better out of the box. but here lately i have found a interest in predator carbs. just redid two for my cousins boat on a tunnel ram. i think that my next new carb will be a predator. after i use the holley hp750 i have on the shelf.
 

· AKA Blownjet 468
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1,193 Posts
Predators? don't you mean "screaming chicken box"? ran one on a car app.
years ago! work well with high manifold vacuum, wide lobe sep. camshafts, BUT if you try to run a large cam with a lot of overlap, and too narrow lobe sep (low man.vac) beware!! all those are is a big 930cfm vac. controled 1 barrel! better have the one with the " optional " idle circut as
well!! didn't think they even made them any more!! good luck with that!!
 

· Sit N' Spin
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1,345 Posts
Best way to tell if you have the correct carb size for your motor is to measure manifold vacuum @ wide open throttle. Most 4 barrel carbs spec their cfm rating at 1.5" hg of vacuum. So if you have 1.5" hg of vacuum @ WOT, you have the correct carb. Higher than that, you're undercarbed and lower than that you're overcarbed.

On a 10:1 motor with Edelbrock Performer RPM heads, Performer RPM Air Gap intake, a cam with 234/244 duration @ 0.050, 112 LSA, 0.332"/0.334" lobe lift, 12* overlap @ 0.050, and a Holley 750dp carb, my engine at WOT measured right around 1.5" hg of vacuum. This tells me that the carb is maxing out at exactly 750cfm of airflow and does not pose a restriction to the motor. If the engine were trying to pull more air than the carb can flow, I would've seen a higher vacuum reading.
 
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