500cfm Carb TOO much? Valve Question.

[Anonymous]

I am going from a 1 bbl Holley carb to a 2 bbl and I found a JEG's Remanufactured Holley 2 bbl but it's 500 cfm. I heard that 350 cfm is pretty much the max on a stock (as far as I know) 200? What would happen if the 2 bbl carb was installed?

The reason I said that "as far as I know the engine is stock" was because I took a quick measurement of the bottom of the Intake valves (while they were installed in the head) and I got 1.75 inches. The exhaust and intake valves are less than a 1/4" apart from the side of each of the valves. Could this be stock? Was measuring the valve on the bottom the right place to measure? I seriously doubt that someone put in bigger valves in this engine because 1) its a 1982 Granada Station Wagon and 2) the engine seems like it has been run straight into the ground (nobody but a inline six lover would want to fix it.). Thanks for any help you can give me.

Jamie

 

[Anonymous]

My Rule of thumb is,

Stock or slightly modified = 350 cfm Holley 2 Bbl
Modified or High Performance 500 cfm Holley 2 Bbl

78 and later heads all had 1.75" intake valves in them and they are the head of choice when looking for a replacement head.

Hope this helps!!

Doug

 

[gtm1086]

Question. On a Stock 78 head how much would you mill off? If my thinking is right 0.50 will get me down to around a 50 cc cumbustion chamber.

Gary

 

[Anonymous]

is that using a new gasket...i seem to remember something about the old gaskets compressing to about .025" and the new ones will compress to .045ish"....maybe someone can clarify this...cause that will effect the CR slightly...

 

[CobraSix]

I tend to disagree with carb flow amounts. Personally, for any NA 6 engine no matter the build up, I would think anything more then 400 CFM is overkill. I mean, I've seen some serious V-8 builds that only use a 500 CFM carb. When you go too big, you lose a lot of venturi signal. I think the only way to run 500 CFM on a 200/250 would be to go with a 4V carb, so you have better venturi signals.

Now I will qualify my statement with this fact, I have nothing to base this on other then personal opinion, and basing relative numbers from V8 builds.

Slade

 

[CZLN6]

Howdy All:

Gary- A stock OEM '78 hed will have 62 cc chambers. A mill cut of .050" will yeild aproximately 52cc chambers- BUT the only way to know for sure is to measure. All casting are not created equal.

Holley 2V carbs are rated at V8 standards. To compare CFM ratings to the one barrel standard you must divide the rated cfm by 1.4. So a 500 CFM two barrel 2300 will come out to 357 cfm.

Many modified 200s with a standard trans and 3.5:1 or lower gears can handle that amount of CFM quite well. A Holley will take some fine tuning at lower rpms and scream at higher rpms. For a daily driver with an auto and highway gearing, Dougs thumb rule makes allot of sense.

Adios, David

 

[wsa111]

This is a very good post. i lobby all us six cylinder owners to get one of the magazines to run a dyno test on things such as cylinder heads, camshafts & carburetion on these engines. with the price of gasoline rising at least us six cylinder owners can as least pass a gas station.
i will not make a positive statement on cfm for the 200 engine. i plan to use a 350 holley on my engine. i will let you know the results when finished. the head is a 80 head with fspp valves,264 fspp camshaft, flat top pistons,clifford single outlet header through a 2 1/4 inch exhaust system & 1.6 roller rocker arms. i still have a desision to make on which head gasket to use, since the head is milled .070, deck is milled .015.
respectfully william

 

[Anonymous]

The reason I was asking was because in the JEG's catalog I found the remanufactured Holley 2 bbl 500 cfm carb for about $180 and a Holley 2 bbl 350 cfm for about $300 and I thought that maybe I could get the bigger carb, save some money, and have the possbility of having a good carb for any future upgrades. For the moment other than the carburator, I am going to put a custom header on it. I live in a rural area so all I drive is in the wide open country. What would an estimate be for the gas milage for the 500 carb doing about 70MPH (thats the speed limit here instead of 65)? With the stock 1 bbl Holley 1946, it gets at least 20MPG, higher if I don't go over 65mph.

Jamie

 

[CZLN6]

Howdy Back Jamie:

Any Carb on any engine, tuned correctly to that engine and driven at the same level of performance and load will yield about the same mileage-BUT! Don't ya just hate those "Buts"?

*Tuning a carb this big to be a daily driver will be a challenge. Tuning will involve main jets, Power valve, accelerator cams, squirters and the choke system. If you're not up to it don't start.

*Getting yourself to keep your foot out of it at the top end, where it will scream, will be a challenge.

That is a great buy on the Summit rebuilt Holley 2300s, but if it's not what will work for you keep looking.

Adios, David

 

[rbohm]

8) i agree, keep looking for a smaller carb as you will be happier. i would suggest getting an autolite 2100 from an early 289 or 302 and rebuilding that for your motor. it will deliver about the same performance as the holley, it will be more flexible than the holley, and will be closer in tune than the holley for oyur application.

 

[xctasy]

The reason I was asking was because in the JEG's catalog I found the remanufactured Holley 2 bbl 500 cfm carb for about $180 and a Holley 2 bbl 350 cfm for about $300 and I thought that maybe I could get the bigger carb, save some money, and have the possbility of having a good carb for any future upgrades. For the moment other than the carburator, I am going to put a custom header on it. I live in a rural area so all I drive is in the wide open country. What would an estimate be for the gas milage for the 500 carb doing about 70MPH (thats the speed limit here instead of 65)? With the stock 1 bbl Holley 1946, it gets at least 20MPG, higher if I don't go over 65mph.

Jamie

I can only say the advice here from these guys is world class.

Between information on little fours and big V8's, I'd say the message is clear.

The 350 cfm carb is always a better millage prospect than a 500 cfm. The bigger carb doesn't atomise the fuel as well. On a 351 to 400 Ford, a 500 may give better mileage than a 350 cfm, but certainly not on a much smaller engine.

If you are looking for economy on a 200, go 350 cfm. If you are looking for performance, then go 500 cfm. The little 350 may save you 120 bucks in fuel every 10 000 miles (with a sacrifice in peak power of course).

The 350 cfm carb is 130 to possibly 155 hp carb. The 500 is a streetable 155 to perhaps 220 hp carb.

I'd say that if your engine was able to produce perhaps 135 hp with a 500cfm 2-bbl, then the 350 Holley would loose about 5 to 10 hp, and gain at least a couple of highway mpg. That's what people found in the old days with little Pinto 2.0 liter (121 cube) engines. As the engine gets bigger, the fuel consumption loss from the bigger 500 cfm carb trails off.

In the Aussie Street Machine Magazine 'Power Games' series in the late 80's, I've seen 170 hp 350 cfm carbs on 350 Chevs make huge increases in power (up to 220 hp with a 500 cfm) with no penalty to mileage.


One other small note. In the Australian HQ Holden Racing class (GM intermediates with in line Chev-style L6's), there are single jug 202 cube sixes. They have 260 degree cams, 1.65" intakes, headers and a good amount of compression, you don't get any more than 165 hp. And the old cars are very thirsty past 65 mph, and I'd say past 70 mph, a 350 cfm carb would be better fuel wise. In Street Machines recent article, the 202 cube Holden six registered 144 rear wheel hp with a 3-speed auto and 500 cfm 2-bbl. Thats over 200 flywheel hp.

 

[MustangSix]

If economy is a prime consideration, then I would optimize performance and efficiency with a 1bbl or a staged 2bbl, but not the Holley 350 or 500.

The 200 from that year is a very low compression engine. Zero deck, mill the head, get CR back up to about 9:1 and do some work in the valve pockets to improve the flow in the intake and exhaust area. The exhaust needs a good bit of work. Add headers, single or dual, it doesn't matter, either will help. Use a 252-256 cam and a roller timing set. More power, but still very smooth.

Then reuse the stock 1bbl. The stock jetting is probably very close to what you need already. With the compression and airflow improvements, the engine should be making more power and better fuel economy.

 

[Anonymous]

two things to remember
1) Gas prices
2) Gas prices

 

[CZLN6]

Howdy Again Jamie:

Wow! Jack hit the nail on the head. If you're truley interested in a major improvement in your engines performance, put the $170 plus shipping into a quality valve job that would include a mill cut of .070", a three angle valve job, back cut on the intake valves and buy and install an exhaust port divider. If you did the disassemble and assemble yourself you could get the whole thing done for about for about that amount.

The extra CR and flow will do more for performance and economy than the Holley. Fine tune your stock carb and ignition and enjoy.

Adios, David

 

[Anonymous]

I am beginning to lean more to the 500 because it is cheaper but with all the extra fuel that is getting pushed in there, will it constantly flood or make it even worse to start or more prone to stalling? I want to go for max performance but I need the car running now so I won't be able to do all the upgrades I want to do. My 242ci inline 6 Jeep Wagoneer's tranny is start to die on me.

The stock carb on the 200 has a piece broken off so I can't reuse it. Well I could but with that carb and the vaccum leaks, driving the car became a bitch. It stalled every time I touched the brakes. I need this car to haul some ass! A lot of these mechanics around here would probably charge me extra to to work on a Ford. Everyone one of them are like "if it isn't Chevy or a Hemi, take it to the junk yard". So the saying "If you want it done right, Do it yourself" became a part of my life.

Do any of you know where to buy some good 2 bbl carbs that are 350cfm at a fairly reasonable price? If so, I would gladly get a 350. I am not too worried about economy since I will only need it for a part of the summer until I get my Jeep fixed then its back to working on the Ford 200 and then I can get the performance upgrades done. My job is 15 miles away so its not that far. Thanks for all your help.

Jamie

 

[MustangSix]

Carbs are simply mixing devices. They only flow fuel in proportion to the amount of air flowing thru them. At any given speed, a 200 will suck the same amount of air thru a 350 as a 500. Only the velocity of the airflow and the pressure drop under the throttle blade will change. The carb responds to that pressure drop and delivers fuel accordingly.

A 500 will not flow excess fuel unless you jet it to do so, but most Holley's are jetted rich out-of-the-box. That's to help prevent damage. Very few engines need the fuel a stock Holley delivers, so a bit of tuning is in order.

For a near stock 200 a better choice for less money would be a 2bbl Holley/Weber from Stovebolt.

 

[Anonymous]

Does the Holly/weber carb have an electric choke? I also seen a Carter Weber carb, would that be good for this engine too? Are they both 350cfm?

Thanks. All of you guys have been a great help!

Jamie

 

[CZLN6]

Howdy Jamie and All:

The Carter/webers are very similar to the Holley/Webers. Yes, they have an electric choke. I have not seen factory CFM ratings on them, but am guessing they will be in the 240 - 270 CFM range. That's just about right for a nice performance increase for your 200. Since they are progressive tey should be economical too. Linkage and air cleaner will have to be adapted.

I don't believe that Tom Langdon at StoveBolt has any more of the rebuilt Holley/Webers he was selling. that's why we bought the Carter/Webers.

Adios, David

 

[66Sprint6]

Jamie,
I bought the 500 Holley from Summitracing.com. I drove around with Dan's (importkillers) 350 holley for a while before swapping to the 500cfm carb (he needed his back, ) and I like the 500 just the same. See, my car stalled when I tried to launch hard with Dans, now it does fine. Only set back is that his had a better response when your cruisin and decide to punch it, now it kinda bogs a bit. The 500 is amazing on the interstate tho, itll flat out haul!!!!!! Im looking to run some boost in the next couple months so I bought the 500 to try and gain as much as I could. I drive it every single day, gas mileage isnt bad, and on the interstate, its really not bad either. Thats just lookin at the gauge, I dont know the exact gas mileage tho.
Matt

 

[Anonymous]

Would enlarging the intake hole for a bigger carb help with the engine performance? Make it easier for the engine to handle the extra fuel and air.

Jamie