I want to replace my vac secondary carb with a small double pumper. I see there are square bores and spread bores. Can someone school me on the different small Holley DP's. SBB, tow cam, dual plane, 2400 stall, shift @ 5000. launch on a 2-step Cheers!
Go with a 800 CFM Q jet, there is nothing better for a mild 350. A 750 Holley is OK too if you take the time to change the jetting and pump shot. You will give up a ton of hp with the 650 carb.
That is old school. With the new tuning features available you could probably go with an 850. I dropped my 950 on my sisters 302 Mustang and it actually drove pretty good. It was too big but that is in the way out there catagory.
We have gone through this a million times. The Buick 350 loves a larger carb than most 350s. Both track and dyno testing has proven this time and time again. Even a stock 350 likes 800 CFM carb. Here are the reasons the 350 likes a large carb: - Tall narrow ports with high velocity - Restricted intake and head flow requires a larger carb - It is best for a carb to not be maxed out, they work best at about 85-90% capacity if you go with a 650 Holley you will give up about 10-20 HP.
You ever see a 800 double pumper on a 350? I leave with the pedal on the floor, i imagine it would fall over at launch? I don't care if it slows down, i just want it consistent.
Well if you do not care how fast it is then sure use the little carb. I never had any bog with the 800 DP on a stock 350 however I had to spend a lot of time with the jetting to get the correct air fuel ratio at all RPM and throttle positions. The same goes for the 650 it will need mods to run it's best. I would be willing to bet a stock spec 350 Q jet would be more consistent anyways but that is just my opinion.
I run a 750DP, my engine does not seem to mind. Does not bog and I have had 1.70 60 ft times, does that sound like a bog? I never had a consistency problem with this carb, easy to work on and very easy to calibrate. Way easier to work on than the Q-Jet. But to each his own. You have to have a car to put it on before...
square bore has the primary throttle plates same size as the secondary plates. Spread bore is like the Qjet, small primary, and large secondary. Some intakes will require an adapter plate depending on what type of carb the intake was designed for. The Buick 350/4bbl had a 750cfm quadrajet from the factory. Like Sean said, Buick engines perform better with higher cfm carbs because of the engine design. And yes, I like the Qjets also, and how they deliver the power when set up correctly. Best low speed and top end. If you go with a holley DP, you can play around with the power valves and squirters to get it right for your ride. Good luck and have fun!
I had a similar 350 Buick bracket car for years. The 650 worked far better for me than the 750. The 60' times were better and the MPH was just as good. I say you should definitely choose the the Holley model 4777 650 Mechanical secondary. I bet it will be near perfect right out of the box.
Speedtigger I bet you are dead nuts correct. The smaller carb will probably leave the line quicker and will be more consistant. The car will probably be slower overall, but it is bracket racing who cares what the speed or time is. The importamt part is can it run that number again. The smaller carb may just do that. But I would hate to buy a new 650 carb only to find out the 750 made you go faster without any more trouble than the 650 and would be more cfm correct. The trick to the Holley ddbl pump is to get that pump shot and the shooters matched up. Once I have the engine up on the tq convertor there is no bog in the secondaries on take off. I would get the 750 carb. Get the one with 4 corner idle system and you will have more tuning ability. Replace the pump diaphrams every spring startup and you will be good to go. 20 minute operation if that taking your time and drinking a beer.
My set up was a 64 Buick Special with a bone stock 73 Buick 350, TH400 with a 2500 stall and 390 gears. I ran a 650 4777. It ran 14.70s @ 89-90 (9.40s @ 72 1/8th)on the motor and 13.20s @ 101-102 on a 125 shot. I bracket raced this exact set up for 2 years. It was deadly consistent and took me to the Dixie Division 2 NHRA championships in 1989. I started out with a 750 4779 and traded it to a friend for the 650 4777. The car was quicker, cleaner and more consistent with the 650. The carb never came of the car for anything for the entire 2 years. The OPs car has a little more power than mine did, but not much.
There you have it, A good idea to use if you go bracket racing a lot. I have been thinking about running just a 50-75 shot of nitrous to see if that will help the car be more consistant since the nitrous does have a cooling effect on the intake. I ran a 75 shot and ran in the low 12's, Being in the 12 second range will put you in the same place as a lot of other cars racing. I would hope to be in the middle of the pack with this set up. Racing slow or fast cars are hard to judge at the big end when you going 100 or so. I did run a 650 spread bore dbl pump on the old stock motor and it did ok but I was not as versed then as I am now on the Holley carb. I had to use this carb for the stock intake. It does have some huge rear throttle plates. Put a 1 inch spacer on this and I bet it would just about be as fast as the larger carb. If you have access to one it would not hurt to try it and see how it works.
