Whats best upgrade for power on 425??

what is the best thing you can do for more power on the 425?

 

Have your distributor re-curved. If you are going to put in a mild cam, put in stronger springs too........the increase in power is definitely worth it. I'm assuming you have a Q-jet carb, that's good for power although the dual 4's got a little more top end. Your q-jet should be fine though, just make sure the secondary lockout tang isn't holding the air valves closed. When I had a q-jet on mine, I just removed it b/c on cool days sometimes it would not let the secondaries open. That's there to prevent the motor from stumbling when cold.

Also make sure your throttle linkage switches are working properly or else your switch pitch converter will be stuck in low stall costing you performance. If you don't care about originality, you can connect it to a manually operated switch under your dash. If you do a thread search, you can find a lot of info here about that.......it's a lot to explain. :bglasses:

 

I heard on the dual 4 bl carb set up that at the lower RPM only one carb goes and then at higher performance both turn on, is that true, and also how much is your gas mialeg decreased, and one more thing.... where can you get the manifold?

 

The front carb has no idle speed or mixture adjustment and has no choke. The rear carb is almost like a regular carb, but the idle speed adjusts with an air bleed instead of a set screw. You could prolly get regular carbs to work, but I doubt if they would idle very well.......I don't know, I've never tried it.

The linkage is designed so that as the throttle is depressed, the primary of the rear carb opens first.....then the primary of the front carb........as the pedal is pushed further, then the secondaries of both carbs begin to open but they are not mechanical and the air valve will not open unless there is enough vacuum to pull them open.

As for gas mileage, mine stayed about the same as I had with my qjet, but that's as long as I keep my foot out of it. p

Your last question was where to get a manifold......Carmen has them. Sometimes he has complete setups, but be prepared for sticker shock, good complete setups are expensive....and usually the evilbay variety includes the wrong carbs and no throttle linkage or fuel lines. Also, the distributor is curved different b/c the Carter carbs use ported vacuum......with the qjet the dist uses full manifold vacuum in '66. If you go with aftermarket carbs like Edelbrock, then the throttle linkage won't fit. And the transmission switch also won't fit unless you have the correct bracket for it. That's why a complete setup is expensive, it should include the correct distributor and complete throttle linkage. The factory air cleaner (if you want it to look original) is another thing......nice ones are $$$ Also, holleys (junk IMO) won't fit b/c the carbs are too close together. Once I saw an aftermarket dual qjet Nailhead manifold on ebay though :Brow:

If you have limited funds and want to save yourself a lot of grief, stick with your quadrajet. Making anything else fit in place of stock parts just to have dual quads will prolly cause you a lot of headaches. If you want to see what Carmen has his number is (716) 693-4090. He also has camshafts and other goodies for Nailheads and can re-curve your distributor for more power. :bglasses:

 

thanks a million for all that explaining, do you know anything about the ta performance shorty headers or any other headers and if they are worth it to put on? and just out of couriosity what does re-curving your distributer intale and the price? and how much is the cam?

thanks for all your help