You might try a 600 Vacuum secondary, but you  DON'T want a double pumper for street use. Read Ted's answer and the realize Detroit hardly ever used a mechanical secondary carburetor on anything including the Big blocks.
 

Frank/Rebop

Bristol, In ( by Elkhart) 

I have never owned a double pumper carb in my life. Even my race cars had vacuum secondaries. Seems like a good idea?  I'll file that in the "bad ideas" file.  Thanks,

Funny cause i was torn between a 650 AVS2 or the 500. I went 500 but from ing this thread I am now thinking I should have gone 650 with my engine. 

With carbs, it's easy to think bigger is better.  If you look at Ted's testing you will see the difference in HP is minimal.  My Holley 465 runs great on the stock 57 iron manifold.  It never stumbles or has dead spots. My only complaint is it's not a very impressive carb to look at. For looks, it's hard to beat a multi carb setup. I have not had the best luck with these.  Over the years, I've spent countless hours tuning Y Block tri powers and playing with old carbs.  They look good.  In reality they don't work that well. I always end up selling them and running a single Holley. What I should do is hollow out an old blower and run my Holley inside of it.  

Have it refinished?

Give up on the idea of two fours?

____________________________

If I could find an Edelbrock FM 255 intake at a decent price, I would buy another Holley 465 and give it a try. I'm done with tri power. 

I'm confused Phil on your statement "it doesn't look good" . To me it looks identical to any single feed Holley. I'm guessing you want the dual feed look. On my GMC 6 racing engine I use a 650 cfm vacuum secondary that has been converted to dual feed but keeps the vacuum secondaries..A really good carb shop could easily convert your to dual feed and remove the jet plate. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

A 570 Street Avenger will get you a more performance look.  Holley sell refurbished carbs on eBay so you can get a like new carb for a better price, direct from Holley.



Lawrenceville, GA

I attend a lot of car shows.  Most of these are about eye ball.    I didn't buy my TBird to carry golf clubs.  I bought it to hot rod.   I get a lot of comments on my dog dish hub caps without the fender skirts and most people have never seen an early TBird with overdrive. The cam in my car has a noticeable idle.   What I would like is a race engine "look" with reliability and drive ability.  I had an Edelbrock FM257, but I couldn't mount Holleys straight and I didn't want to mess with old carbs.  Edelbrock carbs don't have the look I want.

An FM 255 sounds perfect if I could find one in decent shape.  I would run two Holley 465s in line like a 427 425.  I doubt the secondaries would ever open.  The manifold would clear my TBird hood and have provisions for a PVC. I believe driving around on the primaries would be spirited.  What would be really nice is if someone would make a new FM 255.  Dual quad Blue Thunder or Mummert?  Nice dream.

There’s a mold for this one sitting out there somewhere.
 

Lorena, Texas (South of Waco)