Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

[Michael W.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

3. "convert to full time Vacuum Advance", God I wish I knew what you meant by that. Can you explain a little bit on exactly how to do that?

Many cars of the era were plumbed so that no vacuum signal was given to the distributor when the engine was at hot idle setting; an effort to reduce emissions by increasing combustion and engine temperatures through retarded timing. This worked, but at the expense of driveability and with the possibility of overheating.

The recommendation is to replumb the vacuum canister so that it receives a signal at all times. This is achieved by selecting a different source on the carb base plate.

[Duke W.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

On a Q-jet you can tee into the choke vacuum break hose.

There are many threads in the archives about how to convert from ported to full time vacuum advance using either a simple method as above or modifying the internal passages of various carburetor designs so the modification is not visually detectable.

Duke

[Mike F.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

I believe that your original 1970 quadrajets vacuum port provides manifold vacuum (or signal) to the TCS solenoid all of the time. It's the TCS solenoid that actually blocks the vacuum from going to the distributor in 1st & 2nd gear.

You have two options for "all the time" manifold vacuum.
1. A rubber hose going from the carbs vacuum port connected directly to the distributors vacuum can, or
2. If you have a functioning TCS System installed, all you have to do is disconnect the plug from the transmission which will default the solenoid in the open position providiing full time vacuum to the distributor in all gears.

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Thanks for the reply.

OK, Here are some pics (with arrows) of the ports available. You can see on this correct Q-Jet there is an "upper" port on the front right side. This is where I have the Vacuum Advance hose connected on my personal car (not the car in question). I don't have TCS nor does the car in question.

I don't know about the "choke vacuum break hose". but there is a large port on the base of the carb that is connected to a hose which goes to the driver side valve cover. Is that what you are talking about?

Also, so what you are saying is that the stock location for vacuum advance is not "full time"???? Or maybe the way i have hooked up IS full time?

[Mike F.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Thanks for the reply.

OK, Here are some pics (with arrows) of the ports available. You can see on this correct Q-Jet there is an "upper" port on the front right side. This is where I have the Vacuum Advance hose connected on my personal car (not the car in question). I don't have TCS nor does the car in question.

I don't know about the "choke vacuum break hose". but there is a large port on the base of the carb that is connected to a hose which goes to the driver side valve cover. Is that what you are talking about?

Also, so what you are saying is that the stock location for vacuum advance is not "full time"???? Or maybe the way i have hooked up IS full time?

The port pictured with the arrow is the correct port for the distributor and should provide "all the time" vacuum to the distributor with a simple hose connecting the two. (This is the same port that would go to the TCS solenoid had it been installed.)
The smaller vacuum port (on a 45* angle) just underneath the one mentioned above goes to the choke pull-off.
The larger vacuum port on the base of the carb goes to the PCV valve located on the driver side valve cover.

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Thanks so much.

Will post again gain as we get things together.