500cfm or 650cfm carb for stock 302 with headers?

[Jeff B]

Okay guys, need a little help here on getting the right carb. I've got a 74 EB with stock 302 and think an Edelbrock 1406 650cfm carb is going to be overkill. I wish Holley would make a 500cfm Truck Avenger but they don't so I'm probably stuck with getting an Edelbrock 1403 500cfm.

What do you guys suggest? Would like to get a little more power without dumping a lot of $$$. Will be pairing the carb up to an Edelbrock Performa Intake.

TIA.

 

[KJHill]

I know Holley makes a smaller TA carb now. You might want to check that out. I think it's a 470 cfm.

 

[66BroncoWA]

Holly actually makes a 390 CFM 4 barrell carb which works very well on a fairly stock small block ford. I have one on my 73 Bronco and it works very well.

Russ

 

[Flash69]

I have Headers and I had a 670 on mine and it was too much. I went down to a 570 and it does a lot better.

 

[BUCKETOBOLTS]

I would forget about the Edelbrock and buy a Holley. I run a #4776 600cfm DP. The engine is stock with manifolds, a cast iron 289 intake, and rv cam. I love my carb! It is crisp, responsive, and gives you a great seat of the pants feel on the street. Not to mention it works flawlessly offroad. Holleys are easy to tune, easy to find parts for, and very reliable.

 

[superfly53]

I am running a 500 cfm holley 2bbl on a slightly modified 302. I have stock intake, stock heads, a mild cam and shorty headers. I originally bought it as an interim fix for the stock 350 cfm motorcraft when I could not find jets for it.

I have not had any problems with it, and it runs great. It seems that for wheeling a 4bbl carb does not make a lot of sense because you are mostly running very slow. I am no expert but I don't think 4bbl secondaries will even open until you have your foot in it (like maybe 75% throttle).

Again, just my two cents. It was a very quick, easy, and cheap install, and I definaltely noticed a difference when I first put it on.(before the headers).

 

[DownhillManiac99]

I have the Holley 500 cfm 2 barrel on my stock 302 and I love it. Best carb for the application in my opinion.

 

[Krawln68]

I third that!

 

[broncnaz]

I've run a Holley P/N 1850 600 CFM which is the universal carb for years never had a problem with it. I recently bought a Road Demon jr. carb 525 CFM which is basically a better made Holley but I havent put it on yet but I expect it will be just fine. Got it from summit racing it was on clearance $202 but I did have to buy a choke kit for it as it came with out one $34 I believe it still came out cheaper than the base Holley

 

[Skuzzlebutt]

I know Holley makes a smaller TA carb now. You might want to check that out. I think it's a 470 cfm.

They are working on the smaller (470?) TA. One of the members here was to have Holley use his Bronco as a test vehicle for this carb, but the deal fell thru. This was very recent so I don't think the carb will be on the market any time soon. Maybe by the end of summer.

 

[mtkawboy]

Ive had the 390 Holley on mine for 2 months and the mileage is way up over the worn out 4160 600 CFM that I had on it. The only annoying thing is the electric choke fast idle deal every time you shut it off for 5 minutes. Ive adjusted the speed down as low as it will go and leaned the index mark down some which helped. It seems to have a lot more bottom end now. If you do the math a near stock 302 can only use about 415 CFM anyway. You can put any size you want on but your just slowing down the air speed and signal to the carb and it cant use it all because of the vacuum secondaries

 

[vbro]

I have a Holley Economaster 450cfm. It still gives me the power I need but it's only a street carb. I found a site just yesterday for the TA 470. I don't remember the site but they had it listed for $420 and shipping. I'm going to call my local shop and see if they'll order one and for how much.

 

[NYLES]

Isnt there a calculator to help figure this out?

 

[broncnaz]

I believe there is a calulator on the Holley site. If not this is the formula

Carb CFM =

engine CID x Max RPM divided by 3456

basically for a 302 turning 6000 rpm operating at 100% efficiency would need a 525 CFM carb most engines stock operate at around 70% therefore CFM requirements are lower by about 200 CFM, High performance engines run at about 85% efficiency still lowering the CFM by avout 120 CFM from that 525 CFM starting point.

 

[mtkawboy]

For the guy running the 500 CFM 2 barrel carb, you have to multiply 2 barrel CFM by .707 because 2 barrels are tested at 1.5 inches.vacuum and 4 barrels at 3 inches of vacuum. Not trying to be a smartass, just thought Id let you know. Your 500 is actually a 353 CFM carb. Still an excellent carb

 

[broncnaz]

For the guy running the 500 CFM 2 barrel carb, you have to multiply 2 barrel CFM by .707 because 2 barrels are tested at 1.5 inches.vacuum and 4 barrels at 3 inches of vacuum. Not trying to be a smartass, just thought Id let you know. Your 500 is actually a 353 CFM carb. Still an excellent carb

Its not that the 500 CFM carbs are 353 CFM's its the fact that the engine will only pull 1.5 HG of vaccum at WOT and at WOT with 1.5 HG of vaccum the engine will only pull 353 CFM through the carb either way its still a 500 CFM carb it just wont flow that much under WOT conditions

 

[mtkawboy]

The cubic free per minute, CFM, rating for 2 BBL and 4 BBL carburetors can not be directly compared. 2 BBL carburetors (and 1 BBLs) are tested with a 3 inch vacuum while 4 BBLS are tested with a 1.5 inch vacuum. In other words the CFM tests for 1 and 2 BBL carburetors are done with the testing equipment sucking twice as hard. If you want to compare the CFM rating of a 2 BBL to that of a 4 BBL multiply the 2 BBL rating by 0.707.

 

[68ford]

I would forget about the Edelbrock and buy a Holley. I run a #4776 600cfm DP. The engine is stock with manifolds, a cast iron 289 intake, and rv cam. I love my carb! It is crisp, responsive, and gives you a great seat of the pants feel on the street. Not to mention it works flawlessly offroad. Holleys are easy to tune, easy to find parts for, and very reliable.

i agree with you 100% about hollys being easy to work on and tune, i used to run the basic 600cfm vac secondaries also, great carb, worked good offroad too, i now run a road demon 625 vac secondaries. thats probably too much for a stock motor but mines not and it still get great gas mileage and works great offroad just like the holly. it is nice that everything is cnc and not that potmetal stuff like a holly and comes with reusable rubber type gaskets. but they cost more to though. i like demond to because they have idle air on all four barrels not just two, can really dial in the idle pretty easily. i definately wouldnt waste money on a truck avenger, just make your own little tube to go from vent to vent, my friend did that to a holly and now it never stutters at all and we're racing and jumping alot. check out the road demon jr. at summit. cant say enough about demon carbs.

 

[broncnaz]

Well either way you look at it the carb manufacturers rating what ever it may be are close to what they advertise but they test the CFM on carbs differently I believe (water flow tests) I may be wrong. and yes with these formulas we posted are based more on actual engine parameters But you still need a 500 CFM carb to pull the 353 cfm the engine will pull through it so yes in reality the carb is probably only a 353 cfm carb. But depending on engine displacement and efficiency you can pull more or less air through the same 500 CFM carb.
Thats why the engine CID x Max RPM divided by 3456 = Carb CFM size needed is a better way to determine what you need.

 

[bmc69]

i now run a road demon 625 vac secondaries. thats probably too much for a stock motor but mines not and it still get great gas mileage and works great offroad just like the holly.

I just spent most of the weekend building a custom Holley to repalce the 625 Demon I ran in three events last year. I had the floats set so low it had to be running on fumes but it still wouldn't handle extreme angles for beans without flooding out.

I took a stock 4180 600cfm off an 84 5.8HO (which, BTW, also has 4-corner idle adjustment like the Demon) and reworked it to match up with the 408 that is in my '69. I had decided to try a Demon last year and was not a happy camper..even ignoring the various quality control defects that it had right out of the box. I'm not a big Holley fan either..but after 20 years of fiddling with them, I can get them to do want I want them too..even at extreme angles. the nice thing about the 4180 Holley is that it has open external bowl vents so you simply run a hose between the ones in the air horn..as the last post said. The 4180 also has the canted main jets and raised bleed ports...