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Ski-A-Rees
11-21-2005, 09:15 PM
While installing my new motor, the marina call me to let me know that the carb that I had (Holly 780 Double Pumper) was too big for my 454 and said it was a waste of gas! That I should down size to a 600 or a 660. We had a big carb when the boat had a blower and produced about 500 HP. What should I down size to? Discount inboard marine has a Holly 4160 on there site for a 454 but I was wondering what other people have? Keep in mind that I use the boat for show skiing and don't want just a normal carb.

Ski-A-Rees
11-22-2005, 10:32 AM
I know everyone doesn't have an EFI! Come on people!

Workin' 4 Toys
11-22-2005, 10:35 AM
I am just skeptical to answer not knowing your mods to that engine. I would think anything larger than a 750 is too large. I don't think i would hesitate to put a 750 on a 454, but again I don't know your engine, and or driving habits.
What intake are you running and what else do you have done to it?
And why did the "supplier" of the engine not tell you exactly what to use?

Ski-A-Rees
11-22-2005, 03:57 PM
I got this e-mail from a member of my ski club!

The original carb on the boat would have been a Holly 650. With automatic choke. If the engine is going back to a stock 454 than that will be plenty of carb for it. The 780 double pumber could be jetted down to work but would really be a problem. One other option is: Edelbrock builds a replacement for the Holley 650. It bolts on with no modification and is by far a more effecient carb. As far as going back to marine carb it is a waste of money and is a less user friendly carb. The most important thing is to use a marine flame arrestor breather for the carb.

M-Funf
11-22-2005, 04:41 PM
For my "other" project, I used two 600 cfm Edelbrock Marine carbs on a 390 Caddy. They work together very well, and look nice. Here's a picture of the setup, although it's not very good.

http://www.imagestation.com/picture/sraid195/p5ee29963dfb06b0540281433086c4767/f15a367f.jpg

They were under $300 each from Summit:
http://static.summitracing.com/global/images/prod/large/edl-1409.jpg

I don't know how it is where you live, but if the CGAR inspects my boat and finds a non-marine carb, I'd get cited...you might want to check into that...

Good Luck!

east tx skier
11-22-2005, 04:53 PM
Okay, I'll just say that I've had two trouble free seasons from my 4160 and leave it at that.

M-Funf
11-22-2005, 05:01 PM
Okay, I'll just say that I've had two trouble free seasons from my 4160 and leave it at that.

;) Which cfm 4160???

east tx skier
11-22-2005, 05:05 PM
600 cfm on a 351 HO (from skidim)

EricB
11-22-2005, 06:37 PM
Rees-
a 454 cu.in. will use approx. 0.98 gal of air /rev. (454cu.in = 1.96 gal, divide by 1/2 on a 4 stroke engine). At 4500 rpm, it will use 4410 galons of air, which calculates to 589 cfm. This is also at 100% volumetric efficiency (of which you do not have).

Therefore, technically speaking a 650 cfm carb is adequate.

tommcat
11-22-2005, 07:03 PM
i would strongly suggest a marine Demon carb from Barry Grant. A 650 will be sufficient but a 750 would not be too much. either will work well as long as it's jetted correctly.

http://www.barrygrant.com/demon/default.aspx?page=21

jimmer2880
11-23-2005, 07:12 AM
I got this e-mail from a member of my ski club!

....As far as going back to marine carb it is a waste of money and is a less user friendly carb. The most important thing is to use a marine flame arrestor breather for the carb.

I surely hope you're not thinking about going non-marine carb. You're messing with your life and everyone else's life on the boat on that one. There's a real good reason why marine carbs are made.

Workin' 4 Toys
11-23-2005, 08:48 AM
Rees-
a 454 cu.in. will use approx. 0.98 gal of air /rev. (454cu.in = 1.96 gal, divide by 1/2 on a 4 stroke engine). At 4500 rpm, it will use 4410 galons of air, which calculates to 589 cfm. This is also at 100% volumetric efficiency (of which you do not have).

Therefore, technically speaking a 650 cfm carb is adequate.

I am impressed....although I'd say its a bit on the economy size.

88 PS190
11-23-2005, 08:05 PM
what is the complete reason? do marine carbs offer less chance of flameup?

Do they specifically incorporate anti-corrosion features?

No flames w/ backfires?

redmike
11-23-2005, 10:20 PM
88, I heard from a carb guy that the only real difference is the "j" vent tubes at the top, so if the float sticks, gas goes down the carb, and not all over the bilge. Some of the Man. advertise special non-corrosive, but how much of it is already on a "car" model, I am not sure....I know for a fact on Holleys, you can switch the vent tubes and the carb works great....:twocents:
This is not to suggest that it is ok to run a non-marine carb, just some info I happen to have....anybody else?

Storm861triple
11-24-2005, 05:24 PM
i would strongly suggest a marine Demon carb from Barry Grant. A 650 will be sufficient but a 750 would not be too much. either will work well as long as it's jetted correctly.

http://www.barrygrant.com/demon/default.aspx?page=21
The Demon carb is by far, the way to go. It'll give you the most power and torque per cfm rating of any carb out there, while using less fuel (better metering).

I'm sorry but I can't agree w/M-funf's recomondation of the Edelbrock. I think those carbs are garbage, and I have one (not on my boat). It's a crude, poor metering, cheap, cheap CHEAP piece of equipment. I'd take any Holley, any day of the week before one of those, and the Demon is much better than that even.

A "Marine carb" has "J vent" tubes for the float vents and O-rings in the throttle shaft bores to prevent backfire flame from shooting out that area.

Workin' 4 Toys
11-24-2005, 10:34 PM
Edelbrock's carbs have no gaskets below the floats. So they claim they can't leak. I've had them and didn't have an issue. But I would probably lean towards the Holley. Or, maybe the Projection.

NSXBill
11-25-2005, 02:40 PM
http://skidim.com/prodinfo.asp?number=RA052007

or look here:

http://www.holley.com/types.asp?type=21

I always thought that the marine holleys for 454's were duel feed, vacuum secondary, 650 cfms...not what's shown here on SKIDIM but is shown on Holley site. Don't know if you had original spread-bore or Holley flange intake. Search "Holley Marine" and you'll get good info.

On the subject of marine carbs...besides the J-tubes, the Holley's also supposedly have some kind of seal aroung the throttle-plate shafts AND many models delete the external float adjustments or sight hole plugs. The last two supposedly reduce the leak chances, but reduce your ease of adjustment. SOME of the carbs on the Holley site DO have external float adjustment and site hole plugs.

Using non-marine carbs is a personnal choice (at least use J-tubes), but I would not recommend it on a forum...

darkbrown
11-26-2005, 03:10 PM
I like the Barry Grant unit myself (their tech line is great), and the volumetric calculation is a great starting point as well. Something else you might consider ths the cylinder charge. Ideally for low rpm, torque motors, small intake runners and throttle bores increase the intake velocity and result in better cylinder charging. This lessens the chance of initial "Bog" and increased power in the MC power (rpm) range.

6ballsisall
11-26-2005, 05:09 PM
You should be able to get away with that 780 with some small jets. I talked with Skidim about this on my old 86' w/ 351 and was told the 454's came with a 680cfm carb on them so you are over but if you have any mods to the motor you are probably ok. Check your oil often, if your oil starts to stink you are over carb'd