750 carb good for 500hp
 

Is a 750 cfm carb big enough to support 500 hp

fixx
 

if it was set up rite it may but if it were me i would be lookin at a 830 cfm carb..

I may be wrong on this but I think its going to depend on what kind of intake your running. Dual planes typically run a bigger carb than a single plane. On my engine I'm making around 525 hp and I had Prosystems build a carb for it and it flowed 830 CFM. I'm running a dual plane. Also if your looking at holleys the number such as HP950 is not a 950 CFM carb. It will flow 850 CFM. When you order your carb make sure your getting the actual flow rate !

It's a dual plane. I have a 750 and a 800 looks like I should go with the 800 cfm

You need an 800cfm for 500hp.

2bbl engines are in getting into the mid to upper 400's now, but they are severly restricting the engines they are on.

So......yes a 750 can support 500hp, but it will be restricting it meaning a larger carb can make more hp on it.

Remember, Merc used a 800DP on the Merc 500HP.

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What Endeavour said above is true. A dual plane will need more carb than a single plane. A dual plane only lets each cylinder see air/fuel from 2 throttle bores. A single plane let's each cylinder draw air/fuel from all throttle bores.

Also, single planes usually have more plenum volume and all runners are open to each other.....meaning it has more storage area than a dual plane.

==============================

So, what would be better for us to answer your question would for you to post up your engine build and we can better help pick a carburetor for you.

Is the Edlebroc air gap a dual plane?

You need to base CFM on Cubic in and max RPM. In carb selection smaller is better. Look at CFM charts on Holleys website for best choice or call them. 750 is more than enough. You will waste more time trying to tune the carb if you go to big, than it is worth. Get it right to start with and it will work out of the box. Try BLP in Fla. 800 624 1348 ask for Rick

+1 750 is more than enough @ 500 but going a little bigger sure won't hurt. I think you'll be fine either way. The 750 should be easier to tune.

A 750 is "big enough" but an 800cfm will still make more power on the dyno at the top end.
I ran an 800cfm HP500 carb on a 425hp 454 and it was fine and not hard to tune.

A 750DP on a 330hp-400hp 5.7 with a dual plane intake (performer rpm) is easy to tune and will make max power to boot.

Just as an example...........

Missed this.

Yess, it is.

If this is used on a 500hp or higher hp BBC engine I'd strongly recommend a 1" open spacer. I'd demand the 1" open spacer if using a small (for the application) carb like the mentioned 750 on a 500hp BBC.

It's a .030 over 454 290 big oval heads with big valve bowls worked runners worked emi thunder exhaust Bob M roller cam rpm performer intake 9.2 to 1 CR

The 750 carb is square bore edelbrock
The 800 carb is spread bore Holley
Both are mech. Sec

Interesting, I tried going from a vacuum secondary 850 to a mechanical secondary on my boat this year. If you are interested in an 850 I'll cut you a pretty good deal, I bought it brand new in July for $591 off Amazon with electric choke and had it on my boat for literally 3 days. We thought initially when I began having issues this year I was having fuel problems so I rebuilt the carburator, that didn't help but it was quite corroded inside so I bought a new one to try assuming I'd use it at some point anyhow. That turned out not to be the problem so I re-installed the stock carb.

Let me know if you'd be interested, otherwise it will be sitting on my shelf for some time, or maybe I'll throw it on ebay...I'm in no hurry to get rid of it but if someone else needs it, hey what the heck.

Items Ordered Price
1 of: Holley 0-80443 850 CFM Marine Four Barrel Mechanical Secondary Automatic Electric Choke Carburetor
Condition: New
Sold by: Amazon.com LLC
$591.41


Order Placed: July 23, 2011
Order Total: $591.41

Item(s) Subtotal: $591.41
Shipping & Handling: $0.00
-----
Total Before Tax: $591.41
Sales Tax: $0.00
-----
Total for This Shipment: $591.41

Please double check your carbs.

Edelbrock carbs are vacuum secondary. Never heard of a mechanical secondary EDDY carb.

I know of the spreadbore 750 Holley carbs...never heard of a 800 spreadbore. BTW: I have not liked the automotive nor marine spreadbore Holley carbs. Don't seem to tune in as well as their squarebore carbs and require more labor.

I put a new Edelbrock marine 750 on my new 468bbc. It was running lean on the dyno with the stock jets, we had to put in the biggest jets Edelbrock makes to get it to run safe and my engine only made 407hp. Go with a Holley carb much better tune ability.

Holley 800 part# R84017-1

Edelbrock Design
 

I believe the Edelbrock secondaries are not the same as the Holley vacuum secondaries. The Edelbrock secondaries work off an Air Valve with a counter weight just above the secondary throttle plates. IMO the Edelbrock Air Valve secondaries should work better than a Holley with vacuum secondaries. Holley Mech Secs are more for the marine application

Both the Edelbrock 1409 600cfm and the 1410 750cfm are square bore carbs.

Guys -if you have a blower does that impact the CFM of the carb or is the flow a restriction in the venturi?

sorry to jump into this thread..

My Application
 

I currently have a 355 sb mild build 350 hp approx flywheel.

Replaced my stock Weber with a 1409 Edelbrock 1409. Direct bolt in replacement. Bought the calibration kit but did not need it. Ran better from starting to WOT. Did not have my GPS but with full tank of fuel and three on board, I can say it woke the motor up big time. I will post next time I am out on the water for comparison to stock carb. Did notice that the primary butterflies on the Edel were smaller than on the stock Weber Merc and the secondary blades were the same size.

IMO the larger 1410 750cfm would be adequate for 454 but anything larger in cubic inches would require a larger cfm. Edelbrock does not go higher than 750 for the marine segment. The Holley or BG would be the best option for larger displacement motors. IMO

That's one of those 4011 model carb's.....the one piece main body deal where the top comes off ......body is polished...etc,etc ???

I did not have good experiences with those models in the automobile end, therefore have never tried the marine versions. I do believe Holley stopped making those not too long after there debut. Never caught on.

I also have not had good experience with the 4175's (spreadbore) in either marine nor automobile either.

I like the conventional 4150's and 4160's that have metering blocks on both Primary and Secondary sides. Work much better and are much more flexible.

Yes SB that's the one. Guess I should just brake down and buy one. Next question 750 or 800 ? Or I was just looking at a 830 holley 9381 how would that work ?
And do you really nead marine carb what's the difference?
I have 454 .030 over
Gm 290 heads had big valves installed intake an exhaust Bowls worked and runners worked
Bob m little over 600 lift cam hydraulic roller
9.2 to 1 CR
And going with performer rpm intake
EMI Thunder exhaust
If I left any thing out just ask I'll post it up

Make sure it's a marine carb...the answer is yes, there is a big difference. The marine carbs are designed to have any excess gas in the fuel bowls and vents, vented into the engine and not outside as in automotive carbs. It's a safety issue to prevent fires and explosions. ALWAYS marine, not automotive in a boat, especially if you want your insurance to cover anything in the unfortunate event of a fire...

EDIT: Oh and you said you were going with Performer RPM intake (maybe you already have it, not sure) -- check out Amazon -- they had the best prices by far when I was looking a few weeks back. Plus no tax in certain states and free shipping.

You don't actually need the curved vent tubes, that was just something that Holley came up with. The carburetor tests for USCG compliance were written sometime in the early seventies and are easily passed by almost any modern carburetor. We do a lot of mechanical inspections and testing for local insurance companies and have never seen an issue with an aftermarket carb, or braided or push lock fuel hose which also aren't recognized as CG compliant..

Haxby,
The insurance adjuster has never mentioned anything about braided SS hoses on the fuel system? I always wondered about that since they are not CG approved. I ran into it a few times with building engines for boat builders. They all specified to NOT use SS braided hose on the fuel system. This was when I was selling and shipping an engine directly to the boat manufacturer. I don't use SS hose anyway, so no problem on my end. I just figured it was an issue since I have had several of them specifically mention it to me in the past. Thanks
Eddie

My Insurance company had me do a self-checklist, and if I answered NO to any of those questions they are not liable, it's BoatUS by the way, don't know offhand what company they went through and don't have the paperwork with me. No Coast Guard sticker no coverage, I had this conversation with them after I filled it out.

I'm not arguing on the safety of other systems and I agree some of the requirements are ancient, braided lines, blah blah blah etc. I just don't know why you'd risk it if you don't have too. I do know, you don't want gas in your bilge...to many of have seen what that leads to...

Either way good luck on this project Artate78, let me know if you are interested in that carb.

+1 Use a Marine Carb CG approved for a boat.

This should not even be debated??

If you're using a low quality hose that has permeability issues then it could be a problem. Any good quality SS hose or pushlock will exceed the requirements. Insurance adjusters can deny initial coverage if they feel like it and most insurance companies don't like to pay at the best of times. However, if they try to deny a claim based on a component not being CG approved then they would have to prove that it is what caused the damage and that it is inferior to the CG approved part. I'm not advocating using cheapo automotive parts and you need to use common sense when selecting your components but you're certainly not limited to Holley's "marine" line. I could understand why an oem wouldn't want to cause a problem with an end user getting insurance though.

That's cool that you've built engines for several of the boat manufacturers. Did someone order a new boat and specify your power, or was the builder just trying something different?
What kinda boats did they end up in? I always see Teague engines being tested in new boats but rarely see stuff from smaller independent builders. I think it would be cool to see more new boats tested with custom engines.

I have done it both ways where a customer ordered a boat and specified my power and where the builder offered and recommended my power. For a while I was doing engines for Nortech. This was a few years ago when Merc didn't really have anything in between the 525 and the 1075. Potter was working for Nortech building the carb engines. If a customer wanted efi, Nortech would sell them my engines. I built quite a few for them. Once Merc added the 600,700, 850 etc., it made more sense for them to go that route on a daily basis. I had trouble keeping up, and certainly couldn't supply all of the engines to them that Merc does. I only build about 25 a year since they are all assembled by me and only me.
I've also done a few for Hustler and a couple others. I'm currently building them another pair for Hustler that's going in a 39 Rockit to be one of their Premiere boats in the Miami show. Should be a really cool boat with around 1150 hp a side.
I really enjoy working with the boat builders. I get to see the boats from start to finish. It pretty cool to see how different companies go about the same task in totally different ways. The end result is the same but they took 2 totally different paths to get there. All in all, a pretty neat deal.
Like I said, they were all adamant about not using SS braided hose. I've always used push-loc anyway. I have had them even mention that they would not get CG certification if I used SS braided hose on the fuel system. I'm not sure if that's true, that's why I was asking. I don't have much dealing with insurance companies and that's how I would like to keep it.:drink:
Eddie

You can easily replace the straight vent tubes with J tubes. This is an easy way to make a non CG carb "complient" without having to buy a new carb, assuming you already have one. The tubes are just pressed in and are fairly easy to replace. Just a thought that I wanted to throw out.
Eddie

850 carb
 

What king of price do you have on the carb?
Thanks eric

Are you 100% sure?
 

Can you guarantee 100% that the Insurance company will accept the modified carb (Non CG approved)?

Why take that risk??? I wouldn't!!

I will research, but don't marine carbs have additional differences built into them?

No I am not 100% sure. I just wanted to point out that the vent tubes can be replaced. I should have been more specific. The addition of J tubes will make that aspect of a carb complient, but I do not know if there are other differences in the 2 carbs. Maybe someone smarter than me knows the answer to the question of if there are any other differences between a CG approved and Non-CG approved carb besides the J tubes.
Eddie

I thought marine carbs also had the butter fly shafts grooved so that any gas would be directed into the motor, vs past the base plate shaft bores and to the outside????

But then, I've never seen those grooved shafts myself.

J tubes are not part of the Coast guard requirement. As I said earlier they were something Holley created. One of the CG tests is to crank your engine for 30seconds with the ignition off and the throttle at 50%. If less then 5cc (I think) leaks out of any external part of the carb it passes. So, I would guess that Holley put those tubes on back in the day when they had chitty needle and seats so that if the floats overflowed it would just dump in the carb and still pass the test. Like Eddie said (and was not recommending) you could throw those Jtubes in there and no one would notice the difference.

It's time for OSO to take it's skirt off.. If you're biggest concern is following your insurance adjusters instructions to the letter then IMO you're missing the point. Do you run your bilge blower for 2 minutes every time before starting too?

It's got nothing to do with following insurance adjusters. It's about abiding by the rules governed by the CG which in turn will be checked by insurance in the unfortunate chance of a claim.

You professionals should know this better than the average .
boater.

Bye the way, what is meant by the strange comment "It's time for OSO to take it's skirt off". You are missing the point.

Yes I do run the bilge blower before starting my engine.

Sold. And I got $375 if that helps...it was a DEAL for them...

??? Honestly???