Engine Vacuum Problem 340 6-pack • The Dodge Challenger Message Board

by **TAGibb** » 24 Mar 2010 16:45

I recently had my 340 6-pack engine completely rebuilt. The cam is near stock, but I am only getting about 11 inches of vacuum.

Any ideas where to loom for a problem?

by **dave-r** » 24 Mar 2010 20:30

When you say near stock what do you mean exactly?

For example a 440 with a MP 284 advertised duration cam will only have about that much vacuum.

Also was the cam degreed or just fitted with the dots lined up?

Was it an aftermarket timing set or original?

by **TAGibb** » 24 Mar 2010 21:54

Hi Dave R,

The cam is a Comp Extreme Energy CK 602 (.262 lift, etc.) The timing set is most likely after market, and I assume it was not degreed, but just lined-up (I will need to check with the machine shop).

Dave

by **dave-r** » 25 Mar 2010 8:54

I hope it has more than .262 lift. :shock:

I would need to see the actual cam spec to give an opinion. But how much vacuum you have at idle is down to the valve timing events, initial spark timing, and carb tuning.

For the cam I need;
Duration @ 50thou
Valve lift and rocker ratio.
Valve opening and closing points.

For the ignition I need;
Amount of initial timing and how and if the vacuum advance is hooked up.

For the carb I need;
What methods have you used to tune the idle mixture and speed.

by **TAGibb** » 26 Mar 2010 17:42

My mistake on the lift, it is .462. I have attached a cam card FYI, although we now have the vacuum up to about 15 inches, and the power brakes are working (that was the biggest problem). There was a carb problem causing the low vacuum. I am taking the car to the shop that re-built the carbs, and they are going to set them up and optomize the timing for me, so hopefully we will be good to go! Thanks!

by **Eddie** » 02 Apr 2010 11:40

Just make sure you have plenty of initial timing, 18-22 degrees should be fine. That cam is a nice one for street and Hi-Perf. the idle should be as smooth as the factory 340 6bbl. :thumbsup:

Oh and listen to Dave's tuning advice! :thumbsup:

I had to send my Six-Packs to the shop as well, they required extensive machining and other mods to run right. But once it's right it's pretty awesome. I also had to send my distributor to Don at FBO for a complete re-work,,lots of initial advance,(mine was 20 with 14 mechanical and 12 degrees of vacum advance). Once these 2 things were accomplished it's never ran this nice before! :s003: