Which carb for my set up...

I have a similar setup and have a 600 vac secondary which I bought the conversion kit to add a metering plate to the secondary side which basically makes it a street avenger.

I have seen the 570 street avenger be recommended alot on here.

Either carb you listed would work well, both have their ups and downs. I Think you will be happier with the 3.7x gear, than the 3.5, especially if you are running a 16 or 17 inch wheel and tire combo.

670's a bit on the big side, but the secondaries can be tuned to open with your combo at a more oportune time. A 650 DP will kill the bottomend slightly more than the 670, depending on how you use your right foot. If you want a DP carb, go with the 600. Just remember, the bigger you go on the carb, the less the throttle response will be at lower rpms, but this also moves the topend rpm peak slightly higher. You have to ask yourself, which is more important to you. You will get the maximum effectiveness out of a 570 SA by going with it.

for your application i would stay away from the double pumper carbs. like DH said they tend to hurt the bottom end performance. i would go with a 600cfm carb, i like the edelbrock carbs, but holley makes a nice 600cfm vacuum secondary carb as well.

67_Mustang said:

I talked to a tech at Holley. He suggested a 4150 - 600cfm double pumper (4776c). What do you guys think of that?

I'm debating now between the 570 street avenger and 600 double pumper. I'm hearing mixed responses as to whether I should go mechanical or vacuum secondary.

Is it really that big a deal to go with mechanical secondaries when you have a manual transmission??

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If you don't mind poor fuel mileage, go with the DP 600. The 570 will do everything the 600DP will, but the mileage will be much better. You can fine tune the 570's secondaries to open sooner (Holley usually installs a heavy spring that refuses to let the secondaries open until you hit about 5 grand ) I like em to open a second or two after I nail the go pedal. I personally don't know where or why the DP recommendation for a manual transmission came from, only that a vacuum carb can and does work better (in my opinion) when tuned properly with a manual transmission. Plus, letting the rpms come up before the secondaries open better utilizes the carb's capacity. With a mech carb, the secondary linkage is progressive, but only if you slowly accellerate the vehicle. Which is counter productive when you want to go fast, but do so, quickly. When you nail the pedal with a DP carb, all four barrels open pretty much instantly, which if the carb is too big, will over carb the motor and if it doesn't kill the engine, it will either bog it down, or make the accelleration slower than a properly tuned vacuum carb.(which is why I suggested the smallest Holley DP carb, the 600) The poor mileage of DP carbs stems from the fact that there's two accellerator pumps(which are often the larger 50 cc units) feeding gas everytime you nail (or simply work) the pedal, instead of just one 30 cc pump.

****HIJACK HIJACK HIJACK****
So, what about a mechanical secondary carb, with both pumps 30cc's? I bought a 700 Holley DP, that I plan to put a pair of Lemans bowls on. (I have a pair of "extra" primary Lemans fuel bowls).
I was thinking this would be a really cool carb for a 393 stroker, with a T5 combo'ed 69 Cougar.


****End of Hijack*****

DH hit the nail on the head.a double pumper carb is good for the race track when you need to make sure you have no issues with not getting enough fuel on initial acceleration, and when you need to get as much airflow through the carb as quickly as possible. they are not good for the street though as you tend to use far too much fuel for no good reason. tune the secondary response for proper operation and you wont be sorry. this goes for you too woodsnake.

I have a un-modified, vacuum secondary 715 as well.
I will probably build the DP, just to try it out. Plus, as I already have all the parts, it will look cool as a static display!

woodsnake said:

****HIJACK HIJACK HIJACK****
So, what about a mechanical secondary carb, with both pumps 30cc's? I bought a 700 Holley DP, that I plan to put a pair of Lemans bowls on. (I have a pair of "extra" primary Lemans fuel bowls).
I was thinking this would be a really cool carb for a 393 stroker, with a T5 combo'ed 69 Cougar.


****End of Hijack*****

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I'd leave the dual quads on

Carb selection.

Hi,

With such a combination I would recommend you a smaller carb. The 289 Hi-Po engine came with a 480cfm and it was more than sufficient.

If you go with a 600 cfm or more with a vacuum secondary, the secondary’s risk not opening at all until at least 7000 rpm's and you will only use the two first barrels and if you change the spring to make them open earlier it will just lean the engine, bog the car and slow it down. A 600 cfm DP will better provide gas with every pedal movements and cause less bog than a vaccum secondary carb with too light springs installed.

The 570 cfm street avenger seems a good choice to me or the 4776 DP if you want maximum performance but with less drivebility and worse mileage.

Good luck!