someone told me you can get better gas mileage depending on how you drive a 4bbl because you can drive on the 2 smaller ones on the carb? what do you guys think?
definitely... the 2 barrel are more cfm than an appropriate Vac secondary carb For an automatic. as long as you get a progreesive 4 barrel that runs on 2 then 4 as you hit the gas. I like Holley carbs. Doesnt apply to 4 bbl double pumpers..
double pumpers are progressive. you can get just as good gas milage with a double pumper as you can with a vac. secondary carb. as long as you dont go past 1/2 throttle. a double pumper properly sized for the motor will give you the best throttle responce when you floor it.
The 4 bbl carb CAN give better mileage, but the reality of most situations is that people tend to become addicted to the full throttle acceleration. mileage depends more on the way you drive the car than the way it is carburated or what accesories are hung on it. Truthfully, you can get the same mileage with a two barrel as you can with a four barrel carb. each carburetor will mix a quantity of fuel with the air to make it burn in the cylinder - if the same amount of air is allowed in, by the driver, then the same amount of fuel will be added to it. Believe it or not!
The 4 bbl carb CAN give better mileage, but the reality of most situations is that people tend to become addicted to the full throttle acceleration. Ha! Hey Paul I knew somebody would come back with that... True..an air pump is an air pump. In theory. I have a customers boat with two identical 350 GM engines different carbs, and two separate tanks. Both engines are run together at the same rpm's always. One engine was using way more gas than the other. One of the carbs was just not capable of being tuned right...by me or my engine guru go to guy when I cant get er done. too rich I guess secondaries opening up too soon...who knows. and guuuuzzling gas. it wan't obvious that it was a problem..after rebuilding it twice the owner said just get a new one so we put a marinized edelbrock on it and problem solved. I had a 2 bbl on my 383 Mopar that was sucking gas too...I really battled with that carb...it kicked my ass good. My holley 4 bbl I put on get really great milage... so its carb expertise tuning, and not lead footing of course..
the 4bbl will give you a bit more power. you can only make as much power as the most restrictive point in the motor. on these 302s the heads and exhast are really restrictive. if you want a big power gain replace the heads with beter heads and put headears on. you can get a set of heads from a 87 to 95 mustang. they are refered to as e7 heads. you can get them for really cheap. they will need the valve springs changed to match your cam. the next popular inexpensive head is the gt40. it came on 93-95 cobra mustangs and on v8 explorers untill 97.
To swap to a 4 barrel you have to install a different manifold. Usually its an aftermarket one they give you a nice boost in power.
It all depends on what size carb (not all two bbl carbs are the same cfm rated, just as not all 4 bbl carbs are the same) you have now versus what intake and carb you replace it with. I've yet to see someone do a 4 bbl swap and get better mileage, due to the tendency of the right foot of the driver to "mash the gas" every chance he gets after the swap. If you're concerned about fuel economy, learn better driving techniques and pocket what you'd spend in doing a swap. There are other, more cost effective ways to improve fuel economy than doing a 2 to 4 bbl swap.
i've seen an adaptor from 2 to 4, and if you turn it around it works from 4 to 2, it goes between the carb and the manifold. i asked about it on another thread but got no response, does anybody know something about it?
A less restrictive intake and exhaust along with a good tune-up will probably gain you the most improvement, along with of course driving technique. I had a 75 plymoth fury in 1976 with a 318, 2bl. It was getting lousy milage, so I stripped off all of the smog junk and had a set of dual exhaust installed and a good tune up and increased the milage by 5 plus mpg. You increase milage by increasing efficiency.
It's a band-aid approach to swapping carbs. In a 4 bbl on a 2 bbl intake, it's a complete waste of time, if you're expecting improved performance. 2 bbl on a 4 bbl intake ? It'll do if all you have is a 2 bbl carb to work with and no access to a 4 bbl carb.(or vice-versa)
yes, but the combustion chambers on the E7's are a full 10cc's larger than most 289 heads. Look for about a point and a half drop in compression.
Carbs don't make power but they can restrict it. Swapping on a four barrel intake and carb on an otherwise stock engine will make you feel like you have more power but the actual power won't increase much unless you add headers and a cam - then you might need to add more compression to match the cam. The engine is a group of components that work together to pump air and heat. All the parts have to match to get the power out of any single component. Using an adapter does not increase the airflow through the engine - don't waste your time and money.
