Intake Port Question

I'm getting close to finishing my years long build - a CJ-2A on a 1970 CJ-5 Renegade chassis. When I started it, the rolling chassis had been sitting and it hadn't run for years, so anything connected to the body was missing. My question is about the ports at the rear of the Dauntless V6 odd-fire intake manifold. There are 3 ports, all the same size, and 1 is plugged. (see pic) They all appear to connect into the air intake, so I assume that larger 90 degree fitting might have been for a fuel vapor return line, and maybe the smaller was for a vacuum gauge in the dash? Thoughts? Any direction would be helpful.

 

Typically the largest manifold vacuum port is intended for power brakes. On more modern cars, there are plenty of emissions devices that are powered by the vacuum signal. You need vacuum for distributor advance, either manifold vacuum or ported vacuum, or both. Vacuum can also be used for heater control using vacuum servo motors, which I believe this year of CJ came with.

 

The one to the left is for vacuum wipers and one on the right is for heater controls.

 

I don't have a heater or power brakes, and I'm using electric rather than vacuum wipers. Looks like I'll just utilize one of these for my distributor vacuum advance, and plug the other, unless I can come up with another use. Thanks!

Big stuff is all sorted, and now I'm down to the annoying final details - you know, the stuff that takes 3x longer than it should when you're chompin' at the bit to fire it up!

 

I have no experience with the Dauntless application, but typically vacuum advance signal should come from a port on the carburetor located above the throttle plate (ported vacuum, as timgr sez above), not pure manifold vacuum.

 

X2 above. If your 225 V6 D is pretty much stock then you will want to use the carb port as above.

 

Good to know, thanks. I saw some comments about manifold vs. port vacuum for distributor advance, but haven't got to the point of dropping in the HEI distributor yet. My 225 is mostly stock except for a mild .030 bump for the cylinders, so I'll utilize the carb port. Check off one more potential problem avoided!

One additional question - I installed a Flowkooler water pump in place of the OEM pump. It has a threaded hole in the very top. I assume that is for the temp sending switch, but I actually used a larger diameter temp sending unit for a '76 K-10 Chevy six in the port on the top front right of the intake. I also purchased the original temp sender (smaller diameter) that looks like it'll fit that hole in the water pump. Is there any benefit to installing one of these over the other, i.e. will one location be more accurate for the gauge? I wouldn't think it would make much difference... but what do I know?

 

The hottest coolant is at the top of the engine. The water pump receives the coolest coolant from the bottom of the radiator. If you put identical gauges in each location you can expect to see about a 20º difference. At least that's the way it worked out on my Chevy small block.

 

Typically the heater return hose connection.

 

The temp sender needs to be of the proper resistance to match the temp gauge. Not all senders are the same.