Well, just chewing on this for a winter project. I have built my tribute car with a proprietary spec cam that has low idle vacuum. Since it is an automatic car, the trans upshifts are late (out of wack) and the brake pedal could use a little more vacuum. At idle vacuum is 14.5-15.
Really not wanting to change away from my roller lifters, so, got to be a roller cam.
Yeah, great power when you are on it. Just a little more street manners are wanted. It idles smoothly.
What does anyone have? And where to get it.
Would Adding a Vacuum Canister help?
Quote from: tesgt350 on September 25, 2026, 02:49:23 PMWould Adding a Vacuum Canister help?
Just remember, the "canisters" don't create vacuum. :)
Is the transmission a "C6"? As if so, for the "out-of-wack" shifting of the transmission, maybe an "adjustable" vacuum modulator might help? :-\
Scott.
Good points but yes, it has the C6.
There seems to be only 1 adjustable Module for these. It has that adjustable screw inside to adjust it. Problem is, it is made for all the street cars with stock cams. So, the spring inside is set for a higher vacuum.
Those later -73 and newer cars have the Module type that locks in with a clip. The 66-73 cars have the Module that threads into the case. The later ones come in 3-4 different spring settings.
Another thing: Is there a stock 67 390 GT cam kit that comes as a roller? Seems that is what came in a 67 Shelby GT 500 428.
I have the same low vacuum issue on our roller cammed 427 Tunnelport '68 GT-500 and plan on installing a 12 volt vacuum pump. Summit has several different pumps available, and I still need to decide on which one and where to mount it.
Bob
SIIRHD88 is correct there are some great 12v vacuum pumps on the market. They are relatively small in size and work great. I have a friend with a big block Chevy with a large blower attached always had poor brakes due to lack of vacuum. He has a 440 Mopar with a purple cam that has also suffered from poor brakes and low vacuum. It also now has good brakes. His was mounted under the battery on his Mopar probably can't really do that on a Mustang. They look better than the ones that ran off the power steering.
My side oil build got a 294S cam grind. Even with the OEM vacuum canister, brakes were funky. Tapping the brake pedal would have it sucked to the floor. Sent the OEM Midland booster to Booster Dewey. That was about 20 years ago. The car has had flawless brakes since.
In another lifetime, (1981ish) I worked at the Ford Essex plant in cam mfg. Learning initial cam profiles were developed by Don Teweles of General Kinetics. In visits to Don's cam shop he shared a wealth information on SAE papers discussing cam engineering. Keep in mind, this was well before CNC cam grinding, while still being done on Landis machinery from templates. At the Essex plant there was first generation, digital, profile inspection. It was exciting to learn how lift acceleration is calculated and very rapid return is decelerated to gently set the valve upon its seat.
Fast forward. It's a minefield out there of shops making "custom" cams with no formal, OEM, engineering training or valid inspection. What I see on YouTube make me cringe.
https://vicivisionamerica.com/
Quote from: SIIIRHD88 on September 26, 2026, 02:18:09 PMI have the same low vacuum issue ...... and plan on installing a 12 volt vacuum pump.
This is the best option. No need to take the engine apart or lose any performance with a cam change. You can hide it just about anywhere and run the plumbing to where you need it. Mount it on the rubber isolators to keep the noise down.
Thanks for the low vacuum replies.
Now, how about some camshaft thoughts....
Rod,
Get the specs for the cam you are currently using and call a cam company directly and get advice from them. Summit Racing actually helped with a great tech line and answered all questions I had.
Comp Cams should also offer help. Hope it will be a simple solution.
R.R.