I can buy a 750 carb at a good price and I want it. I currently have a near stock 302 with a 2 barrel. I will do more, just doing a 4 barrel conversion now and have access to the 750... Street Demon 750 Thanks guys Northern
Look at the venturi size differences between the various carb combo's and you will see that there are many ways to up cfm ratings. Such as simply swapping to a larger bore baseplate while running the same exact venturi diameter as a smaller cfm rated carb. There is a lot of misinformation out there about this topic and the basic rule of thumb goes like this. A dual plane manifold can allow the use and take better advantage of larger cfm carbs because they are effectively "halve" the motor in two and each cylinder firing only sees one barrel of the carbs primary side. Whereas a single plane manifold allows each cylinder firing to see 2 barrels at once. This makes a very big difference in the motors tolerance of too big a carb size. This is also why it is quite common to see dominator carbs on sub-400 inch motors running dual plane manifolds. Or take a look at a tunnel ram setup. They can be made quite streetable with larger carb's if you know how to spec complimentary parts. Another good example of what is possible with a dual plane manifold is to look closely at the engine masters competitions. Small to moderate sized motors running dom's on dual planes that see very wide operating ranges used to be very common. In the end you really just need to be honest about what future modifications may be added to the mix. No need to go overboard on carberation if you're not going to build the rest of the motor to suit the potential added airflow capability of the larger carb. Cam choice, cylinder heads, and gear ratio's are very important here too as each subsequent upping of the ante allows.. more like.. warrants.. a larger carb size to make everything work as intended.
I bought a summit carb, 600 cfm, stock 96 roller motor, and it couldn't handle anymore than that, at least to be a good driver. I would have bought a 500 cfm if summit made one that size. They're inexpensive too. Really stays in tune and runs great. But get what YOU want.
A 750 is larger than I'd run on a stock or even mild performance 302... Would be a good carb for a 390 to 460cu in engine...
regardless of size, a bolt on carb is never going to be calibrated perfectly for every driver, every engine , and every chassis combo. If you learn to tune it and calibrate it for all of those requirements.. it doesn't matter nearly as much what the cfm rating is. Vacuum secondary carbs are good for those who start out mild and eventually mod for more power since they are an "on demand" setup. The carb only flows what the engine will allow.. no more and no less. Larger carbs also give more room to grow the power curve later on without swapping carbs. The secondary spring stiffness and jet sizing spread between front to rear is what ultimately "tunes" the carb for the combo and driver preference. And the other thing to remember is that a larger primary venturi carb setup having the secondaries nearly shut off completely(stiff spring) from contributing to additional.. and as mentioned above/"uneeded peak airflow".. can be funner to drive than a smaller primary with larger secondary opening settings.
I just saw the carb on craigslist locally, and it has a good price. I'm in the market for a 4 barrel, so I am interested. Today, my car is stock, but by next summer it should be a bit better. The engine is good, so I'll just run it with simple upgrades and bolt-ons, and a set of heads until it gives up the ghost. If work goes good, obviously this all gets accelerated, or a bigger engine gets transplanted. So, the options I'm considering: buy a 750 today and run on stock+ as I build, OR buy a stock sized carb (600-ish) today and then buy another carb later when its needed. Thanks guys, Northern
Since I'm shopping, do I really need a choke on a modern carb? I live in Houston, so cold weather really isnt an issue.
Unless you're building a race 302, anything bigger than a 600 is too big. I've already been there-done that with a big carb, so I know what I'm talking about. The motor will be sluggish and burn a lot of fuel.
if you buy a...670...w/choke and vac. secondaries... today you won't build past it. that's what I had on my street 347......
so i don't want to jack this thread but I'm sure the OP is going to have a similar concern to me.... if you do buy a carb much to large for the stock 302 then what would you do to compensate for that and make it a good driver? things like: bigger or smaller jets? bigger or smaller squirters? just various carb tuning components... one question in my head is well a carb too large for an engine run too rich or too lean right out of the box compared to the proper sized carb?
At the risk of being flamed, that is way too much carb for a Windsor headed 302, perhaps if it was a true Boss 302. Even if you are thinking about reducing the jet size you can only go down so far before it will start surging, this I know from experience. The amount of CFM needed for any particular engine build is determined by a variety of factors such as bore and stroke (displacement), camshaft specs, and anything else that affects the volumetric efficiency of the cylinders. You would have to build an extremely stout 302 to need anything beyond a 600 cfm carb. You can find cfm calculators online. With a 600, as you build the engine you may have to rejet the carb, but the required cfm will probably never rise above 600. A good deal on something not needed is not much of a good deal. Let the flaming begin.
Since the 302 has a much smaller air flow you'd need to possibly increase jet size, defiantly increase squirters(and/or pump cam) and raise float to as high practical... I installed a "ready to run" 670 Avenger on my 428, was boggy & very lazy on part throttle at transition from idle to activating main metering circuit... Much better after increasing jets, and tweaking float setting, probably could still benefit from a larger set of squirters or more jet size... I put the only larger set I had in the 600 on the Comet, it still could benefit from larger jet size...
