Carb Selection Advice

[HealeyRick]

I had an engine fire in my '63 Austin-Healey 3000 with a 306 ci SBF Explorer motor. TFS 1 cam, Air Gap intake, block-hugger headers, Dynoed at 345 hp at the crank. Presently has a 570 CFM Holley Street Avenger, vacuum secondaries and mechanical choke. Car has Tremec Z 5 speed and 3.55 rear. Car weighs 2300 lbs. I'm wondering if I should just stick with the 570 SA which runs good without any bog or hesitation. I'm wondering if I'm leaving any horsepower on the table and should I think about looking at a carb with mechanical secondaries, double-pumper, etc. or whether there are any newer carbs that would be an improvement over the SA? It's only street driven with an occasional autocross. My Cobra buddies have always been helpful and since the motor and car weight are close to FFR territory, I came here for help with my Fauxbra!
https://i.vgy.me/OICWZc.jpg

[Jim1855]

I think a 600cfm mechanical, double pumper would be about right. I've played with vac carbs, once you try a DP you'll be amazed at the snap. They are not any harder to tune. I wouldn't use a choke either unless you are driving in cold weather. You will need to feather it a bit, keeping the RPMS up until you get a little heat in the engine, this is when you do your pre-drive check.
Sounds like a fun car. I always liked the 3000s.
FYI, I started with a 670 SA on my 427, ran well, great bottom end. Switched to a 770 SA, ran better. Then went to a 780 DP, no choke or horn, runs the best yet but it needs a few RPM to be happy. A friend used my 780 in place of his 750 vac. He was amazed at the throttle response.
Jim

[ggunter]

Kudo's to your Healy 3000 with a small block in it. Back in the early 70's I had a 66" 3000 with a 327 small block Chevy in it and boy was it a hoot to drive, but I could never keep it cool enough. Couldn't get a radiator to fit the opening with enough cores in it. I ran a Holley 650 double pumper and it had much better acceleration with the mechanical secondaries. The vacuum secondaries are ok if you spend the time to change out the diaphragms till you get them opening when you want.

[RoadRacer]

I love my brawler 650 double pumper. Worked flawlessly out of the box. I removed the choke motor and wired the choke flap open, I don't need it even in (texas) winter.

https://www.holley.com/products/fuel_systems/carburetors/street/parts/BR-67212

[cv2065]

x2 on the Quickfuel Brawler. And don't forget the mechanical secondaries!

[CraigS]

Yes absolutely go to a double pumper. On my 351 I had 2 vac secondary carbs. Worked like crazy to get the secondary to open as quickly as possible . Then I finally went to a QF SS650AN. Not so much at full throttle but in all your normal 1/3 to 2/3 throttle acceleration it felt like I picked up 40hp. I was VERY happy to learn that all the recommendations that 'a DP carb in a light car is the way to fly' were 100% correct.

[MB750]

I went Edelbrock AVS2, 500cfm for my 306. Based on my build I estimate it in the upper 300's for HP, and this carb can do over 400hp with great street manners. I like how it atomizes the fuel much better than other carbs.

[ggunter]

I like the Brawler carburetor. I run a 750 double pumper on my Cobra and find the only difference between the Holley and it are price. Plus
I like the cool anodized red base plate and metering blocks.

[BradCraig]

Someone on here had previously said to stay away from vacuum secondaries on the lighter cars, do mechanical. I'm sure there is some science behind that....

Anything is that 600 range should be more than adequate. I had an AVS2 on my Camaro prior to the Sniper...good carb.

[ggunter]

I agree with the vacuum secondaries on a light car. I had a Holley 750 with vacuum secondaries and when the car would accelerate you could feel the secondaries open, but it wasn't till almost 5000 rpm and then it was time to shift. I did change the diaphragm and spring to a lighter one and it helped but still they came in later than I wanted them to. Double pumper with mechanical secondaries fixes all that nonsense.

[skidd]

I ran a summit vac secondary 600 for a few years on mine. It ran like a scalded ape!! Plenty of response, and no obvious secondary transition. The trick is fine tuning the transition point. And, not having too much carb. The 600 was plenty on my mild 302.

I've since put my vac secondary on a friends 67 mustang, and put a new double pumper 600 on mine. Honestly, the difference is not substantial. It's there, sure, but not night and day.

Don't fear vac secondary carbs.

[Stangarang]

I have built engines since 1986. I have built carbureted all the way to the new LS and Coyote's. That said I would recommend a 600cfm mechanical for up to 350hp, a 650cfm mechanical up to 400hp, and a 750cfm mechanical for anything up to 500hp. I have had excellent results with Quick-Fuel carbs. Hope this helps.
Michael