| |
Click on image for the lowdown. 
====
| | | Forums66 Topics128,108 Posts1,056,230 Members48,436 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | 
#62601 07/05/2006 9:49 PM | Joined: Nov 2000 Posts: 582 Shop Shark | | Shop Shark Joined: Nov 2000 Posts: 582 | Doing the final H/W plumbing on my 261 with the Offy intake and dual carbs bought from Tom Langdon. He states that you can try coming off one carb vacuum tip to the distributor vac advance or you can try coming from the full Offy intake port. Since I'm doing this in stainless steel, I really only want to do it once. What have my fellow SB's found to work the best? Off one carb base or off the Offy? Thanks! | | |
#62602 07/05/2006 10:22 PM | Joined: Sep 2003 Posts: 324 Shop Shark | | Shop Shark Joined: Sep 2003 Posts: 324 | I ran the plumbing up to the carbs and Teed it and went to both carb vacuum ports and it works fine.
Tom | | |
#62603 07/05/2006 10:51 PM | Joined: Dec 2003 Posts: 2,733 Shop Shark | | Shop Shark Joined: Dec 2003 Posts: 2,733 | I took the lazy mans approach and went directly to the manifold which also works great. Since either is acceptable it really doesn't matter. | | |
#62604 07/06/2006 8:31 PM | Joined: Aug 2005 Posts: 99 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2005 Posts: 99 | A dual carb intake creates less vacuum under load at each carb than a single carb intake but hooking directly to the intake manifold will subject the vacuum advance to approximately 22lbs of vacuum at idle instead of 0lbs if hooked to the carb. Hooked to the carb vacuum increases under load from 0lbs and then decreases as it reaches WOT. Hooked to the intake manifold 22lbs decreases under load as it reaches WOT. This basically defeats the gas mileage benefits of a vacuum advance.
I would recommend putting a T in the line and going to both carbs. | | |
#62605 07/06/2006 10:45 PM | Joined: Dec 2003 Posts: 2,733 Shop Shark | | Shop Shark Joined: Dec 2003 Posts: 2,733 | I understand this theory as well as anyone. BUT, (there's always a but) my engine runs very strong throughout the power band and does not suffer from being advanced too far at idle. It will turn 4K rpm without a hitch and will do it under a load too. So go figure. It desktop dyno's at 170 HP and acts like it too. | | |
#62606 07/07/2006 8:19 PM | Joined: Dec 2005 Posts: 324 Member | | Member Joined: Dec 2005 Posts: 324 |
"It ain't a truck if you can't hose out the cab."
| | |
#62607 07/07/2006 8:57 PM | Joined: Aug 2005 Posts: 99 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2005 Posts: 99 | Sorry 22" of Hg... Never was that good at physics because I didn't care how the unit of measure was identified just that there was one. | | |
#62608 07/08/2006 12:54 PM | Joined: Nov 2000 Posts: 582 Shop Shark | | Shop Shark Joined: Nov 2000 Posts: 582 | Will try it at the carbs first and use the manifold vac opening for my dual action pump for the wipers. Thanks! | | |
#62609 07/10/2006 5:19 PM | Joined: Mar 2006 Posts: 76 Wrench Fetcher | | Wrench Fetcher Joined: Mar 2006 Posts: 76 | For what it's worth, I have twin H/W's on my Cadillac 261 with a little cam in a '50 3100 and I ran the vacuum to the dist from the front carb and it seems to work fine. The engine pulls hard from idle to 5K. It gets driven every day (mostly) and raced on weekends. Down the road it gets 20-22mpg with 4.11 gears and a 5 speed. | | |
#62610 07/10/2006 10:00 PM | Joined: Nov 2000 Posts: 582 Shop Shark | | Shop Shark Joined: Nov 2000 Posts: 582 | That't the way I've plumbed it. Just to the front carb and will plug the rear one for now. Thanks. | | |
|
|
| |
