Sam (Bones) Posted April 24, 2008 Posted April 24, 2008 I would like to know your recommendation for a carb, what information would you like, this may also help others when considering a new carb for themselfs. thanks
monte70car Posted April 24, 2008 Posted April 24, 2008 Quote: RPM X CID / 3456 X VE X Manifold Correction Factor = Baseline carb CFM needed. So, for a 355 with a performance-oriented dual-plane manifold and healthy cam: 6750 X 355 = 2,396,250 2,396,250 / 3456 = 693 (where 3456 is a constant that takes into account the number of cubic inches in a cubic foot; and the fact that your engine is a 4-stoke.) 693 X .85 = 589 (where .85 is a wag at your VE) 589 X 1.3 = 766 (where 1.3 is a wag at your intake manifold's efficiency.) not sure if that will help
Archer Posted April 25, 2008 Posted April 25, 2008 I truly believe it is hard to beat a properly tuned Q-Jet on a Chevy/Pontiac. I know alot of people would disagree, but most never have been bleesed with a Q-Jet guru nearby. I stand by them untill you need 750 or better. The 750 Q-jets are very hard to find. My two cents
Mike 57 Posted April 25, 2008 Posted April 25, 2008 I think Sam is looking for a little more carb than a 750. I have no problem using a Q jet on a stock/mild configuration, but the single needle and seat really limits the flow of fuel on larger high performance engines.
kc8oye Posted April 25, 2008 Posted April 25, 2008 ARcher.. _ALL_ qjets are at least 750cfm the hard to find ones are the 800's that came on some 454 and 455's :> and you are totally right.. Qjet's own... fi you can get the fraggin things tuned right.
Sam (Bones) Posted April 25, 2008 Author Posted April 25, 2008 this is to show everthing that is considered when choosing a carb, and one carb may work on a dyno, but suck at the track, same engine in two different cars, one car may like a VS, the other a DP, so many people over carb there engines too
Guest Tech @ BG Posted April 25, 2008 Posted April 25, 2008 this is to show everthing that is considered when choosing a carb, and one carb may work on a dyno, but suck at the track, same engine in two different cars, one car may like a VS, the other a DP, so many people over carb there engines too So true, sent you a reply to your pm with what info is needed. I am in Florida right now but will try to check back in this evening and reply. We definitely see that with our carbs as mentioned since they flow more than others. Our 750's flow 920 and the 850's flow close to 1000. The formulas do not take into account the usage and a bigger carburetor will make more power on the dyno but sometimes wont act the same in the car. Typically with the double pmpers we are looking for a manual trans or a converter in the range of 3000 and up.
Sam (Bones) Posted April 25, 2008 Author Posted April 25, 2008 here's what I am looking at, approx 3900#'s w/driver 505 ci (stroked 454, .100 over) factory iron heads, ported and flowed, larger valves cam...244@.050 not sure of lift, near .600 10.0 compression t-400 trans w/ 3800-4000 stall 3.73 gear 28" tires weiand stealth dual plane intake 6500 RPM max this is mainly a drag car, engine has been dyno'd @ 650 HP
Archer Posted April 26, 2008 Posted April 26, 2008 ARcher.. _ALL_ qjets are at least 750cfm the hard to find ones are the 800's that came on some 454 and 455's :> and you are totally right.. Qjet's own... fi you can get the fraggin things tuned right. Sorry I miss spoke. You are correct. It took me forever to find my 800 QJ for my 455 RA-III. Thats what I get for speaking when i am drunk. LOL Sorry Bones I did not understand your app. I still believ the Q-jet would have a hard time hitting its limits on all but the radical to extreme engine builds. But you need to find an Old school guy that nows what they are doing with them.
Guest Tech @ BG Posted April 26, 2008 Posted April 26, 2008 here's what I am looking at, approx 3900#'s w/driver 505 ci (stroked 454, .100 over) factory iron heads, ported and flowed, larger valves cam...244@.050 not sure of lift, near .600 10.0 compression t-400 trans w/ 3800-4000 stall 3.73 gear 28" tires weiand stealth dual plane intake 6500 RPM max this is mainly a drag car, engine has been dyno'd @ 650 HP We would recommend our Mighty Demon 850 with annular boosters for this. It will have plenty of air flow for the motor and the annular boosters will definitely help given the weight of the car. Actual wet flow on this car if I remember correct [am out of town right now] is in the mid 900's. The downleg version of this carb will flow over 1000 cfm but wouldbe too large for the combination.
Sam (Bones) Posted April 26, 2008 Author Posted April 26, 2008 do the mighty demons have screw-in air bleeds?
Heckeng Posted April 26, 2008 Posted April 26, 2008 They are 2 circuit carbs and have screw in air bleeds, and idle feed restrictors.
Guest cstraub Posted May 9, 2008 Posted May 9, 2008 Sam, You may also want to speak to Lance Patton at Competition Carburetors. Lance is one of the best in the biz. Remind me with an e-mail and I will get you his number.
John Burns Posted May 9, 2008 Posted May 9, 2008 our carbs as mentioned since they flow more than others. Our 750's flow 920 and the 850's flow close to 1000. Hey BG guy- help me out here- if your "750's" flow 920, then why don't you call it a "920"? If my combo only needs a 750 and I buy your 750, won't I be buying too big a carb? Also, I've seen the internet rumors- can you tell me why you don't have a relationship with Summit Racing anymore? Thanks
Andy's Auto Posted May 9, 2008 Posted May 9, 2008 Sam, I will swear by my 850 Speed Demon on my 81 Malibu. It has been on since 2001 and although initially hard to tune, absolutely rocks. I took her to the track on Weds and ran once again a consistent 1.58 short time. The motor is a 12.7:1 468. If my gifted AED 850 on the 71 faulters, I will go buy another Demon. Andy
John Burns Posted May 10, 2008 Posted May 10, 2008 I've never had a BG carb and I'm happy that others like their BGs. But I'll take a Holley any day over any of these "hot rod" carbs. A carb is a pretty simple device- even I understand what it does… a little. My bro can get any pile of garbage carb to run- his biggest secret is to keep everything surgically clean whenever it is apart. My carb story: about 10 years ago, a local hot rod shop was working with a customer tuning a 10-second strip car. The car was built to run low 10s and was barely breaking 10.9. The car owner bought one of those expensive “hot rod” carbs (spent $900- no, not a BG) and it just wouldn’t run the number. They borrowed a stock Holley from us and right away the car picked up .4 seconds. We let them use the carb for a few months and they were actually PO’d when we took it back- and it was just a box-stock carb.
Andy's Auto Posted May 10, 2008 Posted May 10, 2008 The reality is some carbs will better match your setup out of the box. But with a fundamental understanding of a carbs three basic circuits, nothing is that hard to tune for any given setup. Andy
Heckeng Posted May 10, 2008 Posted May 10, 2008 The reality is some carbs will better match your setup out of the box. But with a fundamental understanding of a carbs three basic circuits, nothing is that hard to tune for any given setup. Andy That is exactly right. I am not a big fan of any of the companies that you can call, and give them engine specs and they think that without any tuning on the car, they know exactly how to tweak the carb so that it runs the best on your engine. Like TP said above, with a fundamental understanding of the circuits, you can tune most carbs for a setup. But, every engine is a little different. Cams, flow rates through heads, around intake gaskets, all those little things may make an engine unique and will in turn make each carb tune just a little different. Also like JRB70454 had said, his buddy stuck a plain jane holley on his engine and it worked much better than the high dollar carb. All of these modular style (holley style) carbs are basically the same design as far as their circuits go, most of their parts are interchangable, so the only real difference is quality of build, and the tune. If JRB's buddy coppied the holley tune over to the other carb, it likely would have performed nearly exactly the same. Where Holley has done it right, is that their initial tunes (sizes of air bleeds, jets, and fuel restrictors) are very good combination for most engines they were designed for. Sure they can be tuned better, but they are closer than some of the other aftermarket companies who tune their carbs differently initially. I personallyhave had great luck with both holley, and Demon carbs.
680HPStroker Posted May 13, 2008 Posted May 13, 2008 Sam, call AED Carbs in Richmond VA before you do anything. Talk to the carb shop. They matched me up perfectly. Even if you plan on some street driving you like me need a dominator no matter what other people say. A properly built 1050 can be tuned to be just at home on the street as it is on e the track. That is where my Pro Street Dominator shines.
Cali Z28 Posted May 13, 2008 Posted May 13, 2008 Big fan of Pro Systems - they nailed it right on the money (and not much more $$ then a box stock Holley HP
Guest Tech @ BG Posted July 8, 2008 Posted July 8, 2008 Originally Posted By: Tech @ BG our carbs as mentioned since they flow more than others. Our 750's flow 920 and the 850's flow close to 1000. Hey BG guy- help me out here- if your "750's" flow 920, then why don't you call it a "920"? If my combo only needs a 750 and I buy your 750, won't I be buying too big a carb? Also, I've seen the internet rumors- can you tell me why you don't have a relationship with Summit Racing anymore? Thanks I was looking through some old threads and found this and saw we did not answer it. My auto notification must not be turned on or something but will answer it now. [1] Our 750 dl will flow a little over 900cfm due to its patented air entry we use. This air entry is much like when we used to hand port the other carbs . It is called a 750 because it still uses a 1.400 venturi and a 1 11/16 butterfly just like the 750. In all of our technical information we always advise to call us for a carb recommendation to get the proper size carb . In regards to Summit.... Barry chose to close their account several years ago after their returns exceeded 10 times the average of all of our other 400+ distributors including other large mail order warehouses. We were finding carburetors being returned with nothing wrong with them and at the time even bolted one on to Barry's wife car and drove it around. Hope this helps and sorry it is a little late in coming.
Guest Tech @ BG Posted July 8, 2008 Posted July 8, 2008 Originally Posted By: TurtlePimp The reality is some carbs will better match your setup out of the box. But with a fundamental understanding of a carbs three basic circuits, nothing is that hard to tune for any given setup. Andy That is exactly right. I am not a big fan of any of the companies that you can call, and give them engine specs and they think that without any tuning on the car, they know exactly how to tweak the carb so that it runs the best on your engine. Like TP said above, with a fundamental understanding of the circuits, you can tune most carbs for a setup. But, every engine is a little different. Cams, flow rates through heads, around intake gaskets, all those little things may make an engine unique and will in turn make each carb tune just a little different. Also like JRB70454 had said, his buddy stuck a plain jane holley on his engine and it worked much better than the high dollar carb. All of these modular style (holley style) carbs are basically the same design as far as their circuits go, most of their parts are interchangable, so the only real difference is quality of build, and the tune. If JRB's buddy coppied the holley tune over to the other carb, it likely would have performed nearly exactly the same. Where Holley has done it right, is that their initial tunes (sizes of air bleeds, jets, and fuel restrictors) are very good combination for most engines they were designed for. Sure they can be tuned better, but they are closer than some of the other aftermarket companies who tune their carbs differently initially. I personallyhave had great luck with both holley, and Demon carbs. We agree in that our carburetors are designed or a little closer tailored to a range of cam durations and engine combinations but like any other carburetor they will require the normal tuning. Guys will call us and ask if they give us their engine combo can we tell them what jetting to use.... My answer is always lets start with the baseline and go from there because unless someone has your engine there on the dyno there is no way they can tell you exactly what it needs where it is just a bolt on and never touch it. Do they get lucky sometimes? sure they do but we have had plenty of customers do the same. Bottom line is that in most cases the carburetor will need to be tuned for the individual application.
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