The car: 68 Cutlass

The build: 1970 455 30 over, stock crank / rods, forged flat tops, took 18 thousandths off the deck (yes it was warped that bad) bareback Orange chicken Procomp heads (used brand name hardware and had heads looked at closely) 4150 Posiflow intake, and long tubes.

The cam: 520/542 lift, Dur 234/244 @5O Hyd flat.

M20 Trans

3.08 Type O Posi

Now I talked to Holly over the phone and recommend a 770 Ultra Street Avenger vacuum job or a Quick Fuel ss 780 also another vacuum carb. The guy pointed out that even though its a stickshift car, it still only has 308s. On the other hand everybody else i talk to goes double pumper double pumper!!! Iv never owned or driven one before, everything at my house has a Qjet lol.

What are some Pros & Cons of a double pumper. Also the reason it has a 3.08 is the car sees a lot of 85-90 MPH highway driving, and at highway speeds is where I really want the power. If the car sees a drag strip once in its life it will be lucky.

 

The double pump is mechanical ( instant secondary open) rather than vacuum.
I have run about the same 1/4 times cam with both carbs.
Double pump gave me slightly better 60' time of a couple tenths.
Highway you are running on the jet size not on carb response time.

Happy pickens

 

With a manual trans I prefer the double pump, automatic I like vac secondaries.

 

Ive been told that before.
Not true

 

I said it was my preference...

 

As said, a double pumper has mechanically operated secondaries. If you are on the highway and going fast enough, the secondaries may be open even when you are cruising. With a vacuum secondary carb, the secondaries won't open until there is engine demand. I think this could translate to reduced fuel economy with the mechanical secondary carb, so which one you use depends upon what is more important to you - power and acceleration, or highway mileage. I think with the correct carb you can have the best of both.

 

I found this article. For a bit, I thought you were talking the vacuum air horns but mechanical secondary like a quadrajet, but these actually are vacuum secondaries.

https://www.hotrod.com/articles/vacu...ry-carburetor/

 

I like Oldcutlass, prefer my double pump

I do have an 870 Holley Avenger (like new in box) I would make you a deal on if that is your direction.

 

Having dealt with Holley carbs all my life and having rebuilt and tuned dozens and dozens of them, on your car (even with the manual transmission) with the 3.08 I would probably lean towards the vacuum secondary carb, if it had 3.91 gears it may be a different story. The double pumper can be made to work well, but it takes someone that knows what they are doing to get it working correctly. The vacuum secondary carb is very forgiving, and much easier to tune. I would not doubt that you put a vacuum secondary carb on your engine and it just works, it may not be optimal, and with some tunning you can get some additional performance, but it will work. A double pumper carb may have issues with bogging and falling flat on its face at low RPM and sudden acceleration, and sometimes even at higher RPM's. If you have a single plane intake with a big pleneum it will be even worse with a double pumper, without a lot of tunning. Again, a double pumper can be made to work, but it will probably take a lot more time, patience and knowledge to get it working right. Vacuum carb will probably drop in and just work, with little tunning.

 

The quadrajet actually is a double pumper. It uses vacuum on the secondary side some call it POE hole (pull over enrichment). The qjet can be tailored to run with the best Holley's. Qjets are running 9sec. quarter mile times in NHRA stock and superstock classes. I hope you have good results whatever carb you select.