I have a holly 600 currently on my 302 with performer rpm intake. I have been offered a 650 holly in exchange for my 600.. would this be a good swap or should I just stick with my 600???? My car is being built as a street/strip car not a daily driver just a toy to run around in.
The differences are; are you able to tune the 650? It would tend to be higher power at the very top rpm, over the 600, but not by much. You have no auto contol over the secondaries except by throttle. This means you can't open that much 'area' off the line without without possibility of getting into stumble. Why is your frend willing to swap? May be to get out of some of the above things?
If your carb is the 4160's 600 cfm and your friend's carb is the 4150 650 dual feed carb then jump on it. But if there are both 4160 single feed, I would rather see you get a 4150 dual feed 650 when you can. You can do alot with the carb you have. Could you give us more info on set-up?
There are no "single feed" 650's, if there are, they're extremely rare. The are 2 styles of Holley "dual feed" 4 bbls. One is the mech secondary "double pumper" and then there are vacuum secondary "dual feed" Holleys. You're being vague here in this suggestion. The two most common 600's are the list 1850 & 80457 single feed 4 bbl and the most common 650 is the list 4777 650 double pumper mech. secondary 4 bbl. These are likely the 2 carbs he's refering to here.
I agree with 'baddad' unless someone is trying to trade you a 'Single Feed' 'Spread Bore' model 4175. If the 650 has a list #4777 (which is stamped on the 'Choke Horn') I would go for it, get us some numbers
I'm not making any recommendation here as to which is better. If he's got a stock to mild 302, the 650 DP is too much. The 600 is a better choice when tuned to the motor.
You cannot rejet the total cfm capacity. Rejetting only changes the fuel to air ratio. I've had a 650 DP on a roller 5.0, the equivalent to an Explorer 5.0 and it was too much at WOT. The truck ran better with a tuned list 1850 600 cfm carb. With the 650 on there, it actually lost acceleration when at WOT. With the 600, you could feel the accelleration when secondaries kicked in.
Bigger? I have a friend Mike who owns a machine shop and dyno. He tells me that most folks overcarb rather than undercarb. And, as David Vizard once said, "I don't have an opinion, I have a dyno." When my friend Mike talks, I listen. We just put together a brand X 406 for my son's Nova. It's a basic street engine. Hyper pistons, 5.7 rods, Dart Iron Eagles, roller cam, 1.5" headers, RPM, and 600cfm Edelbrock carb. It idles at 650rpm in Drive, powers the brakes, and dyno'ed at 397hp and 455 tq at the FW. Right now we are working on traction since it fries the tires. It cruises the interstate at 75mph and 180 degrees. In a nutshell, a perfect street engine to enjoy the Nova. I argued for a 750 carb all along, but I was wrong. There's an article on AFR's site describing a roller 306 build with AFR 185s and Comp XE282H cam. The engine made 450 hp! This with a 650 cfm Demon. It made no more power with a 750 cfm Demon. I believe that the vast majority of street machines would be best served with a 600cfm carb. On a mild 302, the 500cfm Edelbrock is a good choice. A vacuum secondary carb will dampen the effects of too big a carb, but why go too big to start with? Feel free to disagree. Jim
