carb question

[jungledave]

Need to get a new carb for my 454 build. Engine is 10.6:1, cam is 242 @ 50 and .567 lift on exhaust. 049 heads with 2.19s Performer RPM airgap intake. I have the original 730 cfm vacume that came on the indmar engine but it is sitting on top of my olds sleek. Should go with an 850 or 750 and will a vacume secondary still work with the cam???.

[SmokinLowriderSS]

750 cfm 4150 style mech secc. carb for max performance. A vac secc. should still work fine in that combo but will yeild SLIGHTLY less top performance.
What RPM do you expect to see?
If you expect to get close to 6-grand, step my size rec. up to 800 CFM, no larger.

[jungledave]

750 cfm 4150 style mech secc. carb for max performance. A vac secc. should still work fine in that combo but will yeild SLIGHTLY less top performance.
What RPM do you expect to see?
If you expect to get close to 6-grand, step my size rec. up to 800 CFM, no larger.The engine is built for 6000 rpm but I don't what it will turn my A impeller. I am guessing around 5 to 5500. I need most of the performance at lower rpms so it sounds like the vacume will work. I was worried about how the engine vacume would work with the carb, but I figured a vacume would yeild a little more economy.

[cfm]

My quick guess is an 800-850 vac or mechanical sec. Driver has more control over mech secondary and also may give a little more top speed depending on tuners abilities.
Dual plane with divider can effectively use more carb than same engine with single plane. Rough guideline for carb cfm to shoot for on a single plane is 110-130% of what engine will demand and 120-150% for a dual pane with divider.
Remember, carb cfm is supposed to be rated at 1.5"Hg intake vacuum. For the performance enthusiast looking for more power actual 1.5"Hg intake vacuum at WOT shows a restriction. Most shoot for just under 1.0"Hg while hardcore racers will shoot for even less intake vacuum. IE: less restriction IE: larger carb air flow.

[ck7684]

Sounds very similiar to mine. I went with a Holley 750 with vacuum secondaries. Doing the math I came up with a requirement of about 750 cfm and it's recommended to go slightly smaller rather than slightly larger on carb size. This engine is still in progress and I havent had it on the water yet, so I cant say how well it works...

[Blown 472]

750 cfm 4150 style mech secc. carb for max performance. A vac secc. should still work fine in that combo but will yeild SLIGHTLY less top performance.
What RPM do you expect to see?
If you expect to get close to 6-grand, step my size rec. up to 800 CFM, no larger.
Grind this out on your desk top dyno?? you are the man.:rolleyes:
Why would it "yeild" slightly less top performance?????

[jungledave]

I was hoping for a 750 vac cause I can buy one cheap. If it will get me by and still run good I should be happy. I won't be spending much time above 5000 rpm but quite a bit in the 3000 to 4000 area. I gotta get this thing running and tuned so I can drag it to table rock next month. Any one have a place diverter and control laying around?

[SmokinLowriderSS]

Where's your helpful genious advice clown472?
Oh yea, you still don't have any. :idea: Duly noted.
The 750 will be good, especially if you are able to get 5500 RPM out of it.
You'll need 500HP to get 5400 RPM out of a Berk A. That's what it takes me.
You won't have that much HP unless you've got headers on it.
My 454 has less compression, very similar cam ( 10* less duration), same heads but still stock, same intake, and her orriginal 700 CFM 4150. Makes 400 HP even, with Lightning thru-transom jacketed headers under the hood. Same only made 350 before the headers.
500 on the fun-gas, 5,400 RPM there.
You MAY have another 100+HP in the heads and the compression, if the valve size increase included a decent stage 1 porting job, if you aren't making it wheeze thu log manifolds.

[jungledave]

Where's your helpful genious advice clown472?
Oh yea, you still don't have any. :idea: Duly noted.
The 750 will be good, especially if you are able to get 5500 RPM out of it.
You'll need 500HP to get 5400 RPM out of a Berk A. That's what it takes me.
You won't have that much HP unless you've got headers on it.
My 454 has less compression, very similar cam ( 10* less duration), same heads but still stock, same intake, and her orriginal 700 CFM 4150. Makes 400 HP even, with Lightning thru-transom jacketed headers under the hood. Same only made 350 before the headers.
500 on the fun-gas, 5,400 RPM there.
You MAY have another 100+HP in the heads and the compression, if the valve size increase included a decent stage 1 porting job, if you aren't making it wheeze thu log manifolds.I have done quite a bit of work on the heads, port matched way down into the heads and quite a bit of bowl work after the machine shop porter went through them, I think you have to be an artist to port heads. I left the guide area mostly alone since they weren't flowedI only cleaned up the exhaust ports after the bowl work cause unfortunatly I am running logs for now so my 500 hp engine won't be in my boat. I figure I will be happy getting 5000 out of it. So It sounds like the 750 will work this year till I get headers right?

[hotbo]

i have a 750 proform carb love it had it for 5 years.:D i have tried 850 with my boat i have ot headers 294 comp cam 9.1 with large valve 781 heads air gap an all msd igniton.the 850 absolultely done nothing but drin more fuel period i my application:devil: the 750 out perfroms it all around.now thats just my boat yours may not like it as well but im sold on the 750 for mild motors.:idea:

[Blown 472]

Where's your helpful genious advice clown472?
Oh yea, you still don't have any. :idea: Duly noted.
The 750 will be good, especially if you are able to get 5500 RPM out of it.
You'll need 500HP to get 5400 RPM out of a Berk A. That's what it takes me.
You won't have that much HP unless you've got headers on it.
My 454 has less compression, very similar cam ( 10* less duration), same heads but still stock, same intake, and her orriginal 700 CFM 4150. Makes 400 HP even, with Lightning thru-transom jacketed headers under the hood. Same only made 350 before the headers.
500 on the fun-gas, 5,400 RPM there.
You MAY have another 100+HP in the heads and the compression, if the valve size increase included a decent stage 1 porting job, if you aren't making it wheeze thu log manifolds.
Spoken like a true desk top dyno dickhead, I pieced together one moter that my wife let me and I am expert on carbs, give it a rest dipshit and go back to licking boots as that is all you know.

[cfm]

So It sounds like the 750 will work this year till I get headers right?
Yes, it should work fine for you in the meantime.
Most 750 'universal calibrated for general performance' are very forgiving and can be used on may applications with just some simple jet changes and such. Decent small blocks up to decent big blocks. That's why the 3310 series Holley's have been praised on street cars for many decades.
The problem most people have is buying a specific application carb and putting it on another application. There is a reason why Holley has ton's of part #'s !
hotbo - the Proform carb fits into this category too. So far my use of them has shown to be one that works well on many different 'typical performance' type engines.
No matter how matched the airflow rating, if the fuel metering (we are not talking jets here) is incorrect for an engine the power / driveability / effeciency will not be there. Not the carbs fault but the fault who ever bought the damn thing without finding out it's intent of application.