Most who don't understand how a carb works end up with a too big carb. Since I've run the 3x2 setup on my 331 and that 600 on the roller 5.0, I've changed my thinking too on carb sizing. The same guys who err on a carb size also err on the fuel pump for them as well as far as flow and pressure.
I have a mild built 302 (306 cu in) in my Comet. I have the Edelbrock RPM Performer intake, with a Holley Street Avenger Carb 570 CFM. I idle at 650 rpm in drive. When the torque converter kicks in, hang on! It will put you back, in the seat. I cruise the highways at 3000 rpm, 60 mph. I have 3:55 gears in the rearend. I also get awesome gas mileage (when I'm not on it). I think it's the perfect carb for my setup....Feel free to disagree...Just my 02....
A 570 SA is the one I'd like to use on my Ranger's 5.0 but these are hard to come by used. That tells you something about them, when they don't show up used very often. When I have the time, Im going to snatch a slightly used 1850 600 and a 3310 750 off ebay and build me another 600 for it. Or use a list 80783 650 if I ever run across one for a good price.
If this projects goal is a serious street/strip machine then the 650 DP is the way to go of course the fuel curve will have to be adjusted accordingly and gears, convertor, traction, compression, camshaft, etc. will have an effect. I have a 1850 Holley that I'll trade anybody who has a good DP Holley and I've never seen a Dyno win a race
That's true. You've still got to put the power to the ground. But, I don't know of one winning race team that doesn't use them.
Vacuum secondary carbs can be tuned to compensate for being a little oversized, but it's probably not the best way to do things. I ran a 3310 750cfm Holley on an otherwise stock 351w for 5 years because I knew I would be building a much better motor that could use the 750cfm later. I am now running the same carb on the 395 that I built out if that same motor, with some minor tweaks, and it works great. Even Vizard the Wizard was able to get more HP at almost all rpm ranges for a Holley Dominator on a stock 440 Chrysler than a 650, 750 and 850. When you get a carb that big to work that well, you need a dyno, a lot of time, and some custom work on the discharge nozzles and boosters, something that is well out of the reach of the average hobbyist. I have a mild 302 in my Maverick, and I use it mostly as a cruiser. For that reason I will be pulling off the 1850 600cfm Holley and replacing it with a 390cfm 8007 model. While slightly undersized, it will suit the needs for this car and I think I will get better mileage as well. I know a lot of people put a lot of faith in that mathematical formula floating around to calculate ideal cfm size based on displacement and rpm expectations. I am not an advocate of that chart for performance street or street/strip building as it does not address the rate of acceleration, and that is the whole point of performance building, I would think.
On the original post: IMO the whole idea of the swap comes down to part numbers. There are 650s that would be a good swap, and 650s that would not be so smart for your intentions. Also, what part number, how old, what condition is your 600? Same questions for the 650... They are close enough to what you need for the street. That 50 cfm won't make or break you. It has more to do with the exact part number, which indicates age and exact 'best usage' for that part. On other posts: A 650, especially a vac-secondary, can absolutely be tuned for a street 302! You can't over-carb with a vacuum carb, just under-tune. If the carb in question is a double pumper, then you have to think hard about what you are doing. Not so much for over-carbing, but just the sheer lack of economy for a 'driver'. On the antiquated CFM chart that has been idolized for decades: The recommended CFM that you come up with is a minimum recommendation. Not maximum. The chart was put together 40 years ago when most engines were lucky to achieve 80% VE on the technology of the day... Roller rockers were exotic professional race parts! Today, a good street engine can reach 110-120% VE, while true race engines go substanially higher. Just some things to consider. Edit: Forgot to mention... A mild intake tames a carb's CFM rating. A 650 on a dual plane Performer will act like a smaller carb than if it was put into service on a Victor Jr. A Performer is a very hard intake to overcarb, while the Victor is very easy to overcarb.
Here's the problem, T.L.: NOT NEARLY ENOUGH SAID. As is typical around here, someone asks for a recommendation but fails to give ALL THE APPLICABLE DATA NECESSARY FOR SUCH A RECOMMENDATION. Not that their doing so ever stops you from making your "blanket" suggestions of course. Or any of the other experts. The only technical information that Vern gave was that the car has a Performer RPM intake. Hell...this thing could be bolted to early 289 heads, ported GT-40's, or even TFS Twisted Wedge heads. Nobody knows, and yet, EVERYONE is tossing suggestions into the subject. Kinda like the exhaust pipe size arguments or the camshaft arguments that go on here. Without all the applicable technical data on this combination NOBODY can give this man a definitive answer. Yet.....most still do.
DAMMMMM sorry for asking I was at work and a guy came into the office and we started talking and he wanted to trade carbs.. So I posted it here with limited information. I did not build the motor and know very little about the motor..Let alone the carb numbers here at work. I have only had the car a little over one month and I am working on the safety issues before I get into the mechanical as it runs and drives great. The motor was built by a local drag racer who had the car for himself and wanted to make it a sleeper then sold off everything because of family issues. For all I know it is a stroked out 302 it already has alot of race parts in and on the motor I just have not had the time to rip into the motor and get spec's. As I get further educated I will post a more accurate threads SORRY I am a novice but trying to do my best with my first project car..
