The majority of people tell me to use the full port for better throttle response and cooler engine. So why is there a timed port in the first place?

How many people are using the timed port? Speak up!;)

i love the way the car idles with the timed port and a 106LSA cam. But "sound" alone is a stupid reason to use it I guess.

Timed port for emissions purposes. Retarding timing reduces HC if I recall correctly, not to mention putting hot gas down the exhaust to keep the converter warm at idle.

I use full.

Most normal performance setups will like manifold vacuum better due to the need for more advance at idle.
However if you have a large enough cam that you have erratic varying vacuum at idle, it won't work as well as ported.

Each combo is different.

shawn, we have read lots of info about full or timed vac.
I have decided to use full vac as well:
More Info:http://www.nastyz28.com/forum/showthread.php?t=44867

The problem with that thread is that half of the posts support one side, and half the other. GM's literature for their ZZ4 says "ported" but full vacuum makes more sense.

Mine works best with no vac advance

Because you are all wide open throttle...all the time...;)

Seriously though, can you explain why that would be... I did for a summer. No adv. and it worked just fine, but could it have been better... ?

Mine works best with no vac advance

Sounds like a big big CAM,,, I like the way your ride idleZ;)

It works OK without any vac advance, but on any reasonable street engine, you end up leaving fuel mileage on the table. It's usually a couple of MPG.

Now if you're running 12:1 on an iron head pump gas motor, you have no need for such things.;)

I have to run mine on ported b/c of the reason Jake mentioned above. When I first crank up cold, I'm lucky to have 8" vac and that's not enough to open my Crane adjustable VAX advance at the lowest setting. My mechanical advance is 22* so I run 17* initial for a total of 35*. It might not be the best, but it works.

CorkyE, wouldn't that be 39 total?

Oh!! I only have 9" at idle in gear. My cam 228/235. I wonder if I won't have enough to pull in this vac adv? I wonder if I should port it or not use it at all..

If i can't use manifol vacuum then should I use the timed port, or none at all?

MWilson, yea you have a huge cam, so I see why you don't use vacuum.

The engine doesn't care where the advance comes from. If you use a ported source, dial up a couple extra degrees of initial advance. I time and set idle with a vacuum gauge anyway. Timing lights are kinda useless on a modified motor. I use ported vac. I get a better idle and see no loss of MPG. I get vac anytime the throttles are opened, just no vac it idle. It tapers off again at WOT. Run a vac gauge into pass compartment, drive around. I think you'll be surprised at what the gauge does and when.

Really? I get a much rougher idle (that I actually prefer) on ported. You know, my car is a "cruise-in" "car show" car anyway. So it only goes back and forth to the shows. If my idle is lumpier at idle with the ported, and *IF* I can still run at a cool temp, and *IF* I don't car about fuel savings, and because a timed or full vac source doesn't matter when you do smokey full throttle burn outs anyway, then ported doesn't seem like a bad idea. Is this a stupid way to look at this?Now, if i was running a daily driver, performance car around the city, I would choose full manifold vac, if the idle vac was enough for the canister..


I still want to hear from more people about whether I should use ported or disconnect than can if my idle vac. is too low for the can to work.

I did run extra initial at one point 22-25 and kept the total at 36 with no vac and that worked well. I played with vac advance but kept getting detonation even turned down to 10* so I said the heck with it and locked my timing at 34 all the time. I dont think locking it is good for most street cars though and I have noticed my starter sounds different (not good for the starter) But it really liked more initial when I had no vac advance.

CorkyE, wouldn't that be 39 total?

.

:screwup: I knew that 3rd grade education would come in handy sometimes. I run 35* total so yes, my initial is a bit lower....