Reply With QuoteHolleys will generally make more HP than the Edelbrock [AFB] at WOT. Another Holley that you might want to check out for your application is the list #4781 [850 D.P.] which would work good on the Stealth manifold.
coming from working on FI 5.0 mustangs, now having a carbed 460 ford is a whole new world. I got pushed into buying a pile of crap 650 edelbrock automotive carb for my medium modified 460, weiand stealth intake, decked block, slightly bigger cam,anyways, it turns 4400-4600 depending on altitude and I have not checked the mph, but its fast up top, keeps up with alot of offshore I/Os, but I want to go bigger on the carb, I heard from ***boat mag that the holley marine 830 is the best application for boats, if so, does anyone out there think it will get me anymore top end or just suck up a bunch more gas ?
Holleys will generally make more HP than the Edelbrock [AFB] at WOT. Another Holley that you might want to check out for your application is the list #4781 [850 D.P.] which would work good on the Stealth manifold.
The ***boat mag also says that Jets like b and c cut impellers. While this is true for race applications where they are spinning the shit out of the engine, I don't think the average lake/river racer would agree. I currently have an 830 DP on my 21'er and the I am very suspicious of its viability for my purposes. My mill should spin 5500 with the A-B that is in the pump right now, but it can't. I may very well be overcarbing the hell out of it. If you run the volumetric efficiency equation for your 460, it would go as follows
(460 ci)(4600 max rpm)/3456=cfm@%100 VE
So at %100 VE your 460 should require about 612.27 CFM. Want even better news, your motor doesn't even reach 100% VE, so assuming you're more in the %90 VE category giving your mill the benefit of the doubt, you would only require 551.04 cfm.
From this you could plug in your desired max RPM (providing the cam could actualy hit it) and come up with a new CFM requirement for your mill. The only problem is that there are other factors to consider when using a larger carb. For instance the mixture could be too rich in the secondary circuit causing a bog thus inhibiting you from reving as high as you would like. Of course you could jet around it, but down jetting an 830 below that of a 650 on the secondary circuit would definitely defeat the purpose of going to a bigger carb. The bottom line... unless your talking (*)(*), bigger isn't always better.
good luck,
Chris
This subject came up a couple of weeks ago on the Real Jet Boat message board.
here's the original question
At some point soon I want to change from my current 750 CFM 3310 Vacuum secondary to a double pumper. Is there any performance difference between and 800 and an 850 on a BBC that at its best may see around 5000 (currently at 4700 on an berk AA impeller). I keep seeing recs to go with an 850 but when I do the math it would seem an 800 would be plenty. What am I missing
and the answer
Best carb size is based on getting enough flow through the carb to meter and mix fuel correctly with the least amount of restriction. So sizing is based on engine displacement, rpm and volumetric efficiency.
5k on a Berk AA is 450 Hp according to their chart. So let's call that a well-built BBC engine with a volumetric efficiency of 85% Then required CFM is:
454/2 x 5000/1728 x .85 = 558 cfm.
Rounding up, your best bet is to either stick with what you have or go down to a 650 or possibly 600. This is another case of bigger is not always better. The guys at the track running big carbs are usually turning high (7000+) rpm not 5000 rpm.
If you do go with the 850 you may be over-carbed and get poor throttle response, fuel economy, and bog in the low to middle rpm range...and probably no more top speed compared to your current carb (UNLESS your current carb has problems and is not running properly...in which case a good running but oversized carb may in fact improve things)
In any case, at 850 cfm, I wouldn't recommend mechanicals as this will force the secondaries open when the engine isn't ready for more fuel.
based on what you posted, the 650 is probably your best bet. You just might need to find the right jetting and metering rods.
Cas knows his tacos on the AFB so pick his brains if you decide to stick with your current carb. Sorry Cas, couldn't resist.
Chris
O.k. Flatbroke, and Cas.. Answer this one:
502, Edelbrock alum 315 runners,ligthing headers,victor jr.manifold w/2"spacer,280 x 570 cam. ( curently a 750) oh yea turning 5200 rpm w/A impeler legend set back, droop, diverter.. Should I be running a Angular 830 or what????? THanks Carb guys.
Must agree,468... at 5200-5400 rpm.Tried a 850 DP. did nothing but use more fuel,and was flat in the midrange. Went back to my 715 vac. sec.
Lost,
If you use that formula with your motor and estimating it to have a volumetric efficiency of 90%, this is what you'd get
502/2 x 5200/1728 x .90 = 679.7 cfm
641.9 at 85% VE
717.49 at 95% VE
755 at 100% VE
that is all your engine really needs. The thing is, in order to get the optimum performance for your particular application, you will need to do quite a bit of testing. People, including myself, expect to buy something off the shelf, bolt it on and have your motor spin like a top. It's not going to happen. All carb manufacturers put together generic carbs that will run "good" on many application.
I recently contacted Edelbrock about jetting and metering for my carb with my particular motor. They gave me a set up that will be a real good starting point and said I shouldn't have to change the jets any more than one size larger or smaller.
The numbers they gave me were quite a bit different than the stock jets.
does anyone out there have that website for rebuilding Holley's? I seem to have lost my link. It has a lot of good info on it along with the above formula.
I use a holley 3310 750 vac secondary.Motor is a med modified like yours 70 429 11.5 550 lift cam.dove heads.What i did though was remove the metering block for the secondarys and put the 4150 kit on as it allows you to change the jets.(similar to double pumper but with vac secondarys)I spin an a impeller at 5000 with a pump in good cond.
reciently spent some quality time on my 715 vac sec holley put it on the boat 19' 454 bbc 330hp headers. Results were no bog 65.1 mph for the 1st time out. I'm sold this is the right carb for me even when I add more hp this winter maybe 75-100 still think 715 is good. But I'm just a jet rookie, your results will vary.
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