100 % eff. is noted for a naturally aspirated engine,,and I ***ume, that it is for a stock type intake,,Low rise? Tunnel Rams work on a different principle,,the idea being that they literally "ram" fuel into the cylinders by port velocity,,,at speed. Look at the engines in pro stock,,500 cubes but they require two very large carbs to make the power they do. Like the guys said,,it is all in the combination,,and what you are gonna use it for. I have a tunnel ram and two 750's on my 440,,,never had a minutes problem,,,but I did my homework before hand. They work very good when they are right,,whatever the carb you use. Tommy
I think the OP should put two 1250 Dominators on the street 327 .If two 600's are good twice that much should be even better .Its all in the tuning and has nothing to do with how big the carbs are ...
I didn't say that,,,,two 1250's would definitely be too much. However,,,,two 600's should work fine if they are tuned correctly. That being said,,,if I am not wrong Mopar put an 830 cfm carb on the 69 HP 440's,,, and I think GM also had a 800 + cfm quadrajet? I guess those old factory engines didn't need it? Tommy
A factory hp 440 Mopar with 100% eff. (which is a bit high) @ 6500 which im sure it would do with the heads /cam / comp ratio it had comes to 827 cfm,so the factory putting an 830 on it seems pretty close to me .The 2 biggest mistakes i see most people make at the track are too low of gears and (you guessed it ) too much carburation for their application .A smaller carb will give you crisper response (which eqauls more lowend and lower 60 foot times) in most cases .This is why they make chocolate and vanilla .To each his own ,but i go with the smallest carb i can get by with on every thing i have ...
Cadillac had an 800+ CFM AFB. The CFM of your carb has to do with how much air it gets not how much fuel. You can adjust how fat it is but its pretty hard to change the CFM rating. I guess with a restrictor plate. Higher compression bigger cam larger displacement engines take more air to run than their low compression whimpy cammed counterparts.
I would adjust how quickly the secondaries come in to start....Sounds like your manifold vacuum drops because the secondaries begin to open as your bringing the throttle on. As they open, the manifold vacuum drops too low, letting the fuel drop out of suspension until the vacuum is brought back up with engine RPM. On Holley's with vacuum secondaries, this can be adjusted with springs. Heavier spring keeping the secondaries closed longer allowing the rpm of the engine to come up to better match the CFM capabilities of the larger opening as the secondaries begin to move....Not sure how to adjust them on the Carters....but that's what it sounds like to me.
Been awhile since I had an AFB apart but it seems to me that they have a weighted flapper that allows the vacuum to pull the secondary open. Maybe that's a quadrajet that I'm thinking of. But if it is the case you can probably get different weights. Looks like the problem has been solved none the less.
Correct ,its all about air not fuel .Depends on how high it will /can spin as too how much air it needs combined with the cubic inches.This brings me back to what i was saying before .Two 600's can work on a 327 ,but would not be ideal on the street where it will very seldom see over 5000 rpm .To make real power at say 7000 (which is where to 600's would be helpfull ) your gunna need to have the cam and heads + compression to make it happen .Thats where the effeciency part comes into play ...
If I can run 2- 600 Autolites on a 272, You can run 2 600's on a 327. I had the same problem when I first set them up. I was over rich (to be on the safe side). I leaned the carbs out and still had the bog. I re-adjusted the timing and hooked the va***m advance up to a better source, WOW what a difference... No bog and it pulls great. Check your plug color first, so you are not too lean or too rich. Check your mechanical advance so it is working properly and set you base timing to around 6-10. (total around 32) Then hook up your vacuum advance(make sure it works) use a vacuum source from below the carbs.
Hey shocker, its in my 41' Nash coupe. Under 3k weight and pulls like a damn freight train. I just need a 4 gear now and a posi and ill be set!
I've got some thoughts on this after going thru a few years of tuning large CFM multi carb Qjets for street and race use. Might help with these, so I'll share. I have learned from my dual Qjet 1500cfm setup is that fuel delivery to the carbs and the needle/seat size is VERY important with a dual setup. These get looked at last and are overshadowed with accel pump issues or secondary transition issues as the problem for bogging, poor responsiveness... AFB/Carter/Holley have much more reserve fuel capacity so it's not as big of a deal, but still important to think about and tune. I've seen track evidence of routing fuel lines parallel vs series feeding off the regulator to the carbs making a .1 to .2 difference in the runs when using Qjets. (back to back testing with both series and parallel fuel line setups, interchanged within 30min trackside and retested) Yes, the total fuel area is the same from the carbs perspective, but the delivery is different....could of made the single -6 into a single -8 to help too, but it's not what I wanted to try. The other important thing with responsiveness (has been mentioned some) is the fuel level and pressure vs. the needle/ seat size. While under transition, hard accel etc. the internal p***ages are affected by the fuel level, thus throwing you off in thinking that it's an accel pump issue, or poor timing of the 2nd main circuit transition. In my case, with the dual Qjets on the tunnel, I found that changing to SMALLER seats & adding more fuel pressure corrected some of my tuning inconsistencies, and the car picked up .2 with less transition issues. I'm seeing some small fuel pressure drops thru the Holley regulator still under full load, and I am currently going to a byp*** style regulator from RobbMc with return line to help balance and stabilize the fuel pressure...dual carbs have to be handled differently from a single carb setup for sure! Still learning, so I'll fill y'all in when I'm done Good luck with it!
Dual Q-Jets....I've ALWAYS wanted to try that. I'll bet it's a steep learning curve, for sure. You would have to be super-patient because a Q-Jet is a very complex carburetor. They flat kick *** when they're tuned correctly, though. So, how does it sound when you crack the secondarys on both carbs at the same time? That's gotta be cool.
Forgot to mention that I run them 1:1, not progressive...against all advice from the "carb pros" Any carb setup takes time, most people don't want to spend the time it takes to get them crisp and "right"...the good Carb shops know how to run single applications, not duals. Lots of speculation and bad advice for dual setups like "reduce this because you have two of them"...NOT the case. Dynaflash_8: you mentioned your plugs.... Do you find that the plugs get fouled up under lots of part throttle cruising? I had some "false" tuning bugs in the beginning that ended up being cured with fresh plugs...magically started running good again. Musta gone thru 3-4 sets of plugs in a few months time due to learning what the engine wanted, getting it set up right. On a funny note, the first time I had these on the car, it was humid and cool...got the car back to the house and nearly ****ped myself when it appeared like there was fuel all over the top of the intake... condensation was all over the top of it! (carbs sticking outta the hood) BTW, got any pics of your tunnelram linkage? Always like seeing what people do... -QQ
I met you and saw your Quad Madness Olds at the Yellow Belly deal last year and i was very impressed with it .You have obviously done some homework on Qjets to make that thing run that well .Very different indeed ...
I ran a T-Ram on my 302 powered Falcon for a year or so (till i sold it) ,but i ran a single carb top .I must say the topend from 5-7 grand was incredible vrs. the low single plane it had on it before.My Falcon weighed 2600 lbs and i was running a 4spd. with 4.57 gears .Lots of fun indeed ,but i was mainly after the look .I drove the car daily year round and it was doable .I have nothing against T-Rams on the street its just over carburation that i have seen cause lots of problems for people and they blaim it on the T-Ram.Mine had a dead spot off idle at first with the T-Ram ,but i tuned most of it out with the carb work and timing .BTW i like those early Nash's ...
Shocker: Car actually ran like **** back then, was sorting out these duals for the first time, took forever...looking forward to the THAW in March though Single carb top? We had one, but sold it, thought it would cause a distribution issue on the furthest cylinders away from it...so dove into the duals, cause we like a "challenge" ;P
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