Roy, What you found is why jets can't be safely drilled. Holley, Hilborn, Enderle, etc make jets, then flow them, then stamp a number on them. Jets of the exact same size may/will flow differently. Flowing them like you did is the best way. I changed to Holley jets in my carbs because I figured they were more precise than the older Rochester jets. Ron
Thanks for the carb information. Now, for another question; With 2 one barrels on my stock slant six, if I want to experiment with jet changes, how many sizes would you jump? The Holley one barrels have #55 jets now. I'd like to try going a bit richer. What would be a good change? My Holley jet ***ortment (for my sbc powered Crosley) begins at #64 jets. I guessing that is too big a jump. Carb gurus, is there a good rule of thumb I can follow?
Bob, When I dyno an engine I usually change 2 jet sizes. That way the change is large enough to see some results (either good or bad) but not so large as to get completely out of the ball park. If you go richer and find more power, keep going richer until the power drops off then back up to the last jet. Same procedure if your leaning the engine. I've found that I can't tell the engine what it wants, I let it tell me. I've also found that 2 different engines want as much as 10 jets sizes difference with the same carb. Listen to the engine, read the plugs and experiment. It's fun. Ron Ron
Bob you can order jets from Speedway in Nebr. for $5.98 a pair. Since you are running one barrels you only need one pair of each size. They start at number 44 and go on up. Like Ron said I would start at 58 or 59 and see how it runs. Make a full throttle run and kill the engine and tow back, look at the plugs. If you are running unleaded gas there won't be much color. But if you see any specks that look like aluminum you are way to lean. I doubt that will be the case with the jets you are running and with stock motor. Ron told you the right way to do it. I started out at 114 mph and with each jet size up I go faster. I'm up to 117.52 and we will see what the next jet size does. I am to lazy anymore to thrash in the pits between each run. so I don't do any changes till I get home. But if I slow down next week I'll thrash by changing jets between rounds. I'm glad I'm not running 6 97's anymore. Roy
I know this isn't the cl***ifieds, But it is about carbs.. does anyone have one of those br*** fittings that goes into the gas bowl of a 94.??? It's the one that is like 1/4 pipe on one end(male) and a female end for the flared steel fuel line to screw in.. I can't find one out here in California and I need one to hook up the second carb..I'm just about ready to fire it off. But not without that part...Thanks.. ****
****, I think the part your looking for can be had from your local parts store or warehouse. IIRC, Holley lists 2 sizes in their catalog. I don't think the male is a pipe thread, I think it's a straight thread. You may be able to find exactly what you need at the local hardware if they have a GOOD br*** fittings section. Then again I've slept since I had a similar problem and my memory isn't that good. Roy...6, 97's falls in the area of "self abuse". We're too old (smart)for that. Ron
Ron.. All kidding aside, I've tried NAPA, Ford parts obsolete, 3 carb shops. etc. with no luck..Our hardware stores out here are just that, Hardware. nothing else. I'll keep looking....
****, let me know if you don't find something by Tuesday. I have a bunch of old fuel line fittings for a variety of carbs and perhaps one will fit. If I don't, I'd bet Carb Carl'd either have or know where to get one.
Yep I have boxes full of them ........here in New Zealand, no use to you in California though. The thread form is 1/2" 20 TPI both male and female ends, with 11/16 nut size. Smaller than the regular Holley size (9/16) . .......... I buy them from Walker Products in Garden Grove ......... part number 90-3 or 90-80. They may send you to a retail supplier , but at least they will be able to tell you who stocks them near you. Walker Products, Inc. 14291 Commerce Drive Garden Grove, CA 92843 USA Phone: 714-554-5151 Fax: 714-554-5125
Thanks 97.. Much appreciated.. GG is just a stones throw from us so that will work great. In fact, I think I'll buy 2 new ones.. Thanks again..****
Hey 97, Ron, or anybody else who may know. I am looking for the cfm rating of the Ball&Ball one barrels. The only number I ever had for those was the large 1.750" ****erfly and ??? venturi size @ 175cfm. I'd like to know the full rundown of the different sizes if anyone has that? On jet flow. I have no way to test that. I am in love with my A/F meter however. On tuning the AFB for my driver, I was noticing a difference between the front and rear header O2 meter in the main cirucit. One slightly rich, one slightly lean. Out of luck, I swapped metering rods from one side to the other - and hit the same A/F number dead on the nose in the number I was wanting. Moral of the story - neither the jets nor rods are perfect, but can be matched up right. I love this carb thread - some dang good info coming out of the woodwork! Hud
The problem, or one of the problems with discussing air flow is that 4bbl carbs are rated at a pressure drop of 1.5" Hg ( 1.5 inches of Mercury) whereas 1bbl and 2bbl are rated at 3" Hg. Therefore the rating is not directly transferable. The formula for comparing ratings is Flow (in CFM) @ 3.0" Hg = 1.414 x Flow (in CFM) @ 1.5" Hg BBS is rated ... 200 CFM @ 3" Hg. BBD ... 285 CFM @ 3" Hg). Holley 1920 140 to 220 " 1945 170 " 2300 220-625 " 7448 350 " 4412 500 " 2280 and 2210 250-350 " 2245 300-320 " 2305 350 & 500 " 5200 230 Weber DGAV is practically the same carb as a 5200. Australian made Bendix Strombergs were fitted to Holdens Ford Falcons and Valiant/Dodge 225 slopers. I have the flow charts for them somewhere but cannot lay my hands on them at the moment. Here is something I plagarised from somebody else's website ( can't remember where) I give it to customers when they question airflow on racecars and want the same for street cars. Carburetor Air Flow Ratings: What Do They Really Mean? AIRFLOW (CFM) RATINGS ARE CONSTANTLY QUOTED AND COMPARED, BUT ARE ACTUALLY ONE OF THE LEAST UNDERSTOOD AND MOST CONFUSING AREAS OF CARBURETTOR DESIGN. The basis for most cubic feet per minute (C.F.M.) air flow ratings such as those used by Holley and other carburetor manufacturers was established long ago by the Society of Automotive Engineers (S.A.E.). Standard test vacuum was 1-1/2 inches of mercury for 4 barrel carburetors and 3 inches of mercury Vacuum for 1 barrel and 2 barrel carburetors. This was reasonable as it was about what a p***enger car would develop. Of course, for the numbers to mean anything, tests have to be run at a certain temperature and barometric pressure. Or be corrected to standard temperature and pressure. If not otherwise stated, ratings in cubic feet per minute are at standard temperature and pressure. This system is confusing for racing applications for several reasons. Some racing engines actually develop much more or less vacuum than these ratings, so are difficult to compare. For example, a Nascar 390, 4 barrel equipped car might have 3 times the 1-1/2 inches of mercury standard or a very large 2 barrel equipped car might have only 1-1/2 inches of mercury vacuum. Even more confusing is the fact that most flow benches measure dry air at low pressure drops, commonly 10 inches of water column (W.C.), one bore or venturi at a time. This result is multiplied by a factor to arrive at what that bore would flow at a higher vacuum (i.e. 1-1/2 or 3 inches of mercury), then that figure is multiplied (by four, in the case of a 4 barrel carburetor) to get the C.F.M. rating. This rating is usually much higher than it actually flows. Besides previously mentioned airflow calculations, multiplying, reading and measuring errors, four bores will not flow four times what one bore will flow when they are close together, as in a 4 barrel carburetor. The bores are actually fighting for the same air. Another factor is no provision is made for fuel flow. The actual air flow will be 8% to 16% less wet than dry flow rating. Two reasons for this are, fuel takes up space so it uses up space for air. The second reason is fuel has more m*** than air so Hollow Cone of vaporized fuel slows down flow velocity. This can be easily observed on large wet flow benches which will flow wet or dry. Alcohol carbs will lose more air flow than gas simply because there is more fuel to handle. In order to properly specify or compare carburetors much more must be known than simply a number. (Not to mention the dishonest practice of inflating ratings to increase sales.) Another common pitfall for racing is using widely published carburetor size selector charts that use parameters such as engine size, lowest RPM at wide open throttle etc. Drawing a line across the selector indicates maximum recommended carburetor size. These calculations are for Street Cars and they work reasonably well in that application. If used for racing, the engine would be expected to develop 1-1/2 inches of mercury vacuum at wide open throttle (W.O.T.) unless prohibited by rules, using a larger carburetor will result in much improved racing performance. Engines that need a broad RPM range work best generating about .8 to 1 inch of mercury. Heavy drag cars will work at .6 to 1 inch depending on weight to horsepower ratio. Lighter drag cars can use carburetors so large they generate only .1 to .2 inches of mercury vacuum and work very well at the high RPM narrow RPM range needed for these cars.
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