Thanks for all the info.. So what is the census here?? Keep my 750 vac sec. and try to tune it knowing it is probably over carbed or do I buy a 650 mech. sec. and start tuning from there. Obviously already having the 750 that is the cheaper option but the headaches I might have to go thru to make it right might be worth the money to just buy another carb.

Also, when it comes to vac. sec. vs. mech. sec. urban said vac. sec. shouldn't be a problem with a higher duration cam because it doesn't use manifold vacuum. So what is the more streetable carb? vac. or mech. if I would decide to go to a 650 carb.

 

Have you asked at the 335 forum yet? That is a clevelands only forum.

 

This is straight from Holley's website:

QUESTION How do I know if a vacuum or mechanical carburetor is best for me?
ANSWER For street cars the vacuum secondary carburetor works best on midweight or heavyweight cars with an automatic transmission. They are more forgiving than a Double Pumper is because they work by sensing engine load. The mechanical secondary carburetor is best on a lighter car with radical camshaft and a lower gear and manual transmission or on a car that is going to be used for racing purposes.

 

if you do alot of racing and want the most power a mech secondary is the choice, if you do a lot of street driving then a vac sec carb is the way to go. With your cam and your heads and if your running a dual plane intake a 750 is fine, especially with a stall converter a vac secondary carb can be slightly erratic but also can be tuned to run good. I would definetly run an annular booster carb though, 351c's with big heads lack low end and an annular will help big time. Call BG carbs tech line and see what they recommend, demons flow a lot more than their ratings and just about every one I have bought ran great right out of the box, I got a custom made prosystems 950hp made for my 408 to my exact combo, I spent 650.00, I was way disapointed in the way it ran, my reman 650 speed demon vac sec ran better except top end, then I called BG and they recommended a 750 mighty demon annular mech sec, I bought a reman off ebay for around 400.00 and it ran perfect right out of the box, more low end, mid and top, started better, idled better and cleaner and last MPG run netted 18.5 mpg's hwy BUT if I race around the street you can see the gas gauge drop real fast.

 

A smaller mech 2nd will always outperform a larger vac 2nd. You need to know how to tune the pump circuits though.

 

I have a friend that has both a 650 mech and a vac. so I think I will just let the results tell the tale. I am not familiar with what an annular boost carb is though. I will get back to you on what I find but the more I ask around to friends and what I read on here the vacuum secondary carb is probably the way to go. I do more showing than racing so easy starts and smooth running is more important to me.. I also want to be able to smoke these 50 series tires though...