SDS L-Jet vacuum hose layout Options

[michaelmoo]

Ok here is the stock vacuum layout for a ’74 L-Jet. I’m going to run SDS and need help with a few of the hoses.

Since I’m going to run a Mallory Unilite (not vacuum advance), what do I do with the vacuum lines from the throttle body? Do I just leave them unplugged? Plug them?

I’m also not using a Charcoal canister. What do I do with the air cleaner and fan shroud ports? Do I leave them unplugged or connect them together?

If none of this makes sense, just look at my two diagrams below.

[Mark Henry]

Plug all open holes/ports.

Fan shroud port find a bolt about the same size and RTV it on.

You are removing the L-jet flapper box right?
Where are you mounting your TPS and MAP sensors? Map can be sensitive to where it's placed on the plenum.

I did mine by cutting down and tweeking the runners and using a 2.0 D-jet plenum/TB/aircleaner. I also used 2.0 injectors, if you kept the stock 1.8 injectors they will be fine, but if you ever hop it up you need better injectors.
The L-jet regulator didn't work good for me (worked fine on the L-jet) so I swapped it out with a D-jet reg.

(IMG:style_emoticons/default/thisthreadisworthlesswithoutpics.gif)

[ottox914]

Plug all open holes/ports.

Fan shroud port find a bolt about the same size and RTV it on.

You are removing the L-jet flapper box right?
Where are you mounting your TPS and MAP sensors? Map can be sensitive to where it's placed on the plenum.

(IMG:style_emoticons/default/thisthreadisworthlesswithoutpics.gif)

Agreed to all listed above. Plug all unused ports where ever they are. The flapper box can go away, is now a restriction. It will need to be replaced with some sort of throttle body, and on that throttle body will need to be mounted a TPS.

To clairify what I think Mark was saying about the MAP, the system does not care much where the sensor itself is located, but the port used to supply the sensor with a vac. signal is what will make a difference. I'd start out trying to mount the vac. line to the MAP sensor as close the underside the throttle plate as you can.

For example, if you were to mount the vac. signal line on the top of the plenum, over one of the runners, it would get great signal when that runner was pulling air to that cylinder, but a poor signal when the other intake valves were open. We don't want the signal line mounted above the throttle plate, ie- between the air cleaner and the throttle body, poor signal there also. Have a look at the throttle bodies in OEM cars, many have a line of vac. ports right under the throttle body. Must be a good reason for that location. The volume of the plenum will help smooth out the signal, which will result in a smoother running/easier to tune engine.

Search thru my thread on the SDS install, and you'll fine a pic or 2 that show the vac lines coming off the ITB's, right under the throttle plates. For your application, having 1 line come off the base of the throttle body will give better results than trying to duplicate my set up from the ITB's. So don't waste your time trying to figure out how to run one vac line from each runner off the plenum, and combine them at the MAP. For you that would be a step backwards, for me it was the only way to do it.