Any body that thinks they will get better mileage with a 750 carb than a 600 is an idiot by any standards You can t give proof because it is imposable to get better mileage with a bigger carb!
I'll put my popcorn down and add my 2 cents. I've owned FE's, 302 Windsors, 302 Boss's, 351 Boss's, 466 A 460 headed dual carb drag boat motors and several 351C 4V's. My personal experience has been whatever CFM carb responds the best on any particular engine is the one the I keep and refine. My Cleveland's definitely responded to larger CFM carbs more than what they should have, while my small Windsors appeared to like the smaller carbs. I am definitely of the opinion that there is NOT a specific magic formula for carb selection based on flow alone. While I agree that a 600 CFM vacuum secondary carb is a good starting point for a small displacement street driven motor, it is not the end all, especially when you add good heads, cam and a lot of gear and RPM. All of the forum members here are have expressed opinions based on their experience and I think that is healthy. When reading and digesting it, I feel it is best to say, " how is their combination similar to mine"? Carbs are relatively cheap so even if you make a mistake in choosing the wrong one, the error is not going to kill you. A 750 CFM carb, properly jetted, will run OK on a 302. It might not be the best choice, but it should not turn the engine into a gas guzzling monster that won't idle. I've run almost every carb known to man on a variety of engines over 40 years and NEVER had one that I could not make work after some experimenting. There may have been better combo's, but the point I'm making is that being wrong on the CFM should not be a disastrous decision.
lol.. now that we've finally regressed back to teenage boys with know-it-all attitudes and "how dare you injure my false pride" name calling... only an idiot thinks that cfm ratings alone affect the front boosters enough to hurt mileage. There is FFFAAAARRRRR(yeah.. that's PRETTY FAR) more to what carb size works on this or that engine and those of us who have been successful at running bigger carbs on 302's can only share what we've learned. As is typical with the male ego and pride, some guys can do something 5 times over their entire lifetimes and they're self-proclaimed "experts", while others have to do it well into the hundreds or thousands of times to get there. As I and others have said repeatedly and tried to convey(BTW, ummm.. you do realize that you're on the entirely wrong kind of forum for hardcore carb advice, right?) that we have personally run several "big carbs" on street/race/daily drivers with excellent "non-pig power AND mileage" results. It can and has been done a million times already. If you can't personally do it?.. maybe consider moving on with your lives and just letting the faster guys that can actually do it get around your "perfect little 600". No use in slowing up the entire field and potentially causing a wreck just because your UNoptimized junk is slower. So, basically, you guys who couldn't tuna fish to save your own lives are just wasting your breath between the chunks you've been blowing all over our computer screens. I triple dog dare you to send your humongous 750VS carbs into a reputable tuning shop and say... "my rules require me to run this carb on the street and track" and then test it up against that "perfectly sized 600 cfm" that you so admirably tuned for your specific application and see what happens. You'll get what you pay for and only the higher level of tuning expertise will get you the best final result. The physical differences between the 600 and 750 main body sizing will not be as large a factor as you guys are indicating they will. Thanks Larry.. glad it finally got through the ole' noggin. All tuition fees may be payable to my paypal account @ Iknowmoreaboutcarburetorsthanyoudobutit'sokbecausenobodycaresanyways.com OK.. so how bout a pop quiz to finally shiv the point home and keep it planted there? Assuming that the main body and throttle bore stays the same size..... 1. What affect does changing booster design have on the fuel curve(booster response) and how does this change affect the ACTUAL total airflow number of a carburetor? If you do not know the answer to question #1.. please skip question #2 and proceed to the second portion of this test for extra credit. No student is left behind and there's still hope for you. Scholarships are still available to open and bright minded individuals. There is also a free special class for the hard headed and/or slow learners too. This entire thread has been an introduction to that special class. 2. What affect would the change to drop down(dog leg) style boosters have on the fuel curve and this carbs peak airflow rating? If you made it this far but do not know the answer to question #2.. you still made it further than some of the others. Please proceed to the second portion of this test for extra credit. 2a. What impact would single or double stepped race boosters have on the fuel curve and peak cfm rating? And do the "I can do anything but I can't do that physically impossible task of running a HUMONGOUS 750VS on a 302" carb tuners even know what that is? If you are knowledgeable enough about carburetors to answer question 2a, please explain. If not, then at least you made it this far in the test and you may proceed to the bonus section for more extra credit. 2b. What impact would annular discharge style boosters have on the fuel curve and how do they affect the carbs peak cfm rating? DING.. DING.. DING... advanced bonus questions for those of you who may have failed any or all of the first sections of this quiz. Experts may take the bonus section test just to prove how much of a carb badass they really are. 3. How does an engines rotating mass affect(including EVERYTHING attached to the crankshaft.. ie: flywheel/flexplate/clutch/converter/balancer, even an underdrive AL crank pulley has an impact here) affect the optimization of a carburetors sizing? Double bonus question worth 1,000,000,000 points for those of you who have bombed all portions of this test so far. Passing this bonus question will give you a D+ final grade. 4. How does gear multiplication and vehicle weight affect how an engine tolerates and reacts to any given venturi size and booster design? Double bonus question worth 1,000,000,000,000,000 points for those of you who have bombed all previous portions of this test so far. Passing this final question will give you a C+ final grade. 5. How does cylinder head flow, compression ratio, and camshaft lift/duration affect how an engine tolerates and reacts to any given venturi size and booster design? Can a well optimized engine combo "come up on the carb booster and cam" differently than one which is not as well optimized? For those of you who are open minded enough to have actually learned something from all this "tennis match like" thread?.. put the popcorn down, toss your graduation cap up in the air as high as you can fling it, and pat yourself on the back. More throttle response, wiiiddder power-bands, and greater peak power are in your future should you decide to accept this mission. For those of you who are about as rigid as a brick-wall and set in your ways for life because all the magazines have you brainwashed into thinking that you've surely got it all figured out.. and everything related to carb sizing is set in stone based on engine size alone?.. you can just eat my rubber dust on the street and track, go to the back of the line, do not pass go. And absolutely do not collect that $200 dollars. my work here is done.. professor airflow, out
I love my linkert carb the most 53 years old mech choke the float goes down it fills up with gas it sprays into motor the motor burns it the float goes down it fills up with gas it sprays into motor the motor burns it however every twenty years I have to change the throttle shaft bushings they wear out way too fast
as an aside.. my LAST AND FINAL above response in this thread(petty flamers and last worders, come one.. come all, can get your final digs in now) was only intended to be a tongue in cheek type smart ass rhetorical kinda deal. Not much more I can say that hasn't been said or eluded to already. You either learned something or you didn't from this thread and there's no skin off my back either way. Anyone interested in carb tuning help or further comments regarding this thread may PM me, but I will not continue responding here simply because some undies are starting to get all bundled up. If you're really that serious about carb tuning and have the level of knowledge to seriously answer such questions already.. yet you're still hanging around this thread anyways?.. you're likely either very passionate in helping others(whether they have a willingness to learn or not) who do not fully understand the physics involved here.. or simply trying to pad your pride or ego by arguing against the physics and logic involved with making a "too big carb work on a little engine". Either way.. teaching, learning, building ego and pride, and horsepower discussions can be fun for all. It's simply a discussion.. not an attempt to end world hunger or cure cancer. Lighten up and enjoy the ride.
The Street Demon mentioned by the OP in post #1 would have run fine on his 302. Small primaries and triple boosters. Then everyone started going off on a tangent about Holley modular carbs. They're two different animals.
You must be a millionaire since you know more than any carb designer/manufacturer on the planet. The fact of the matter is, what you are talking about is not "tuning". It is essentially a complete redesign of a carburetor which is out of the realm of the average motorhead. As for "ego and pride", you should take a good look in the mirror. You come across as a "know-it-all" and talk down to others with snide remarks such as "you don't know how to tune a carb" and the like. I've encountered lots of your type with the "bigger is better" mentality. No matter what information from automotive engineers has been published, you'll contradict it with some sort of righteous indignation. This is just an observation on my part and I don't hate you or anything like that. I'm just calling B.S. on your carb advice to the average enthusiast. It's of little to no help, and then you call it "tuning".
So what size carb should I be running on my 306 cid c4 trans edelbrock performer rpm long tube headers e303 cam
For automatic trans cars I prefer to stick with a vacuum or air valve operated secondary. What heads and rear gears?
