73-87chevytrucks.com

73-87 Chevy _ GMC Trucks => Performance => Topic started by: CMiller2709 on June 26, 2014, 06:49:18 am

Title: Which Carb to Run??
Post by: CMiller2709 on June 26, 2014, 06:49:18 am

I have a '78 C15 with a 350.  I installed an XE262 cam, headers, and weiand intake on the engine.  I have a 2004R transmission with 3.73 gears.  I have a Holley 600 cfm vac secondary carb or I could run a 650 double pumper.  Which carb would be best for me?  I would like to use the truck as a daily driver for the summer.

Title: Re: Which Carb to Run??
Post by: zieg85 on June 26, 2014, 07:04:35 am

The 600 would be the most fuel efficient, and if you have a heavy foot, disconnect the secondaries for the DD'ing and only hook them back up for special occasions...

Title: Re: Which Carb to Run??
Post by: CMiller2709 on June 26, 2014, 08:05:12 am

Is there a big difference between the vacuum secondary and a double pumper performance wise?  Also, the heads on the small block are 882's with 1.72" intake valves if that makes a difference.

Title: Re: Which Carb to Run??
Post by: Mario on June 29, 2014, 10:19:12 am

A truck is typically too heavy for a double pumper because it's likely to bog on acceleration.  The 600 will have better air velocity, which will make carburetor jetting and adjustments more effective.  You could possibly reduce the orifice size on the discharge nozzles to make it work.  I'd get in touch with one of the Holley Techs and go through some rounds of tuning on the 650.  You've made some upgrades, so the 650 could have sufficient air velocity also.  I run a 670 Avenger, and I had to reduce the pump discharge nozzle to eliminate an acceleration bog.  It was also because I'm at 5,000 feet elevation or higher.

Title: Re: Which Carb to Run??
Post by: Engineer on July 02, 2014, 09:30:12 pm

Automatic transmission?

Vacuum secondary for sure.