V8 cam, intake and carb swap +Random pics of 8600/1406/3731 going in...almost there!

[shiner2001]

This week away from home is killing me. I am ready to get back to the Jeep and get all this hooked up. I REALLY appreciate everyone's insight, the more I see and read about it, the more it all kind of comes together, and hopefully someone else will be able to pull this up sometime and get as much out of it as I have.

As for now...it's hurry up and wait...

[shaolinsifu]

Derek,
what kit did you buy for the throttle linkage to hook up, I had to "borrow" the ball stud from my son's project f150 to install the throttle cable,but I had to rig the return spring...

[Stumblinman]

Whoa. You have to go to Edelbrock.com and check out their tech pages.

http://edelbrock.com/automotive_new/misc/tech_center/install/1000/1406.pdf

The rear is for the vacuum for the brakes. The carb (if new) should have come with a hookup for it and a plug. Don't use the driver's side vacuum for the distributor. Use the passenger side one. It's timed. That means when you are at idle you have no vacuum advance (which is what you want) If you don't think so then try hooking it up to both and you'll see a noticable difference. You could use the manifold vacuum but it really cleans things up when you go with a central place everything is hooked up to. I cannot help with any emissions vacuum though.

[Lindel]

Both the ports that are labeled for PCV and brake go to the same place, manifold vacuum. It won't make any difference which you hook up to where. The carb won't know and neither will the PCV or brake booster.

[smearig]

Whoa. You have to go to Edelbrock.com and check out their tech pages.

http://edelbrock.com/automotive_new/misc/tech_center/install/1000/1406.pdf

The rear is for the vacuum for the brakes. The carb (if new) should have come with a hookup for it and a plug. Don't use the driver's side vacuum for the distributor. Use the passenger side one. It's timed. That means when you are at idle you have no vacuum advance (which is what you want) If you don't think so then try hooking it up to both and you'll see a noticable difference. You could use the manifold vacuum but it really cleans things up when you go with a central place everything is hooked up to. I cannot help with any emissions vacuum though.

The manual for the HEI says to use non-ported vacuum. The big port on the front is for the PCV and the rear is for power brakes. I have mine hooked up like this and it runs great.

[Stumblinman]

The manual for the HEI says to use non-ported vacuum. The big port on the front is for the PCV and the rear is for power brakes. I have mine hooked up like this and it runs great.

The small port on the left is not ported. It is timed. Meaning you have no vacuum when you are at idle. It kicks in later when you need it. If you need active vacuum advance when you are at idle then you need to relook your timing.

[Chris P.]

The small port on the left is not ported. It is timed. Meaning you have no vacuum when you are at idle

Which is also called ported vacuum.

It kicks in later when you need it. If you need active vacuum advance when you are at idle then you need to relook your timing.

Many of us here run straight manifold vac to the dizzy. Once the throttle plates are past the ported vacuum venturi, there is no difference between ported and manifold vac. Running manifold vac to the dizzy will result in better throttle response and cooler and smoother idling.

[Stumblinman]

OK sorry I don't know what I was thinking. Yes ported = timed.
I've heard a lot of different people with different theoris about ported or manifold to the distributor. As far as fact goes... The thermal CTO (the thing with the 3 prongs on it) is there to move from ported to manifold. The sole reason to change which vacuum goes to the distributor was to help cool the engine. The engineers decided that to cool a hot engine they should increase the rpm to increase coolant flow and air flow from the fan. So under normal idle there would be no vacuum advance (ported) and if the engine would heat up to whatever level the CTO is set at then it would switch to manifold vacuum which would increase RPM to try to cool the engine down. I've found these an engines from the '70s and '80s. So going by this running straight off the manifold will not give you a cooler running engine unless you keep the idle RPM at a higher rate than normal. And by setting the timing (without vacuum hooked up) and then hooking straight to the manifold and decreasing the idle RPM to a standard number it seems you would actually be counteracting the vacuum advance. The ported vacuum only kicks on when you open the throttle which increases the RPM and is the time you would actually want a timing advance. And I think if I was running a drag race I would want straight manifold vacuum because I would only run at WOT.

OK where did I go wrong with this one ?

[Ristow]

OK sorry I don't know what I was thinking. Yes ported = timed.
I've heard a lot of different people with different theoris about ported or manifold to the distributor. As far as fact goes... The thermal CTO (the thing with the 3 prongs on it) is there to move from ported to manifold. The sole reason to change which vacuum goes to the distributor was to help cool the engine. The engineers decided that to cool a hot engine they should increase the rpm to increase coolant flow and air flow from the fan. So under normal idle there would be no vacuum advance (ported) and if the engine would heat up to whatever level the CTO is set at then it would switch to manifold vacuum which would increase RPM to try to cool the engine down. I've found these an engines from the '70s and '80s. So going by this running straight off the manifold will not give you a cooler running engine unless you keep the idle RPM at a higher rate than normal. And by setting the timing (without vacuum hooked up) and then hooking straight to the manifold and decreasing the idle RPM to a standard number it seems you would actually be counteracting the vacuum advance. The ported vacuum only kicks on when you open the throttle which increases the RPM and is the time you would actually want a timing advance. And I think if I was running a drag race I would want straight manifold vacuum because I would only run at WOT.

OK where did I go wrong with this one ?

ported vacuum to the distributor is an emissions move. it works by RAISING combustion temps at idle by RETARDING ignition at idle.

switching to manifold vacuum will noticably raise your idle speed with no other adjustments-because the engine is idling more efficiently. it will also idle COOLER-due to LOWER combustion temps.

that is why the engine will cool down when switched from ported to manifold by the cto.

lean charges take longer to burn than rich charges. idle/cruising charges are lean. acceleration/heavy throttle are rich. the vacuum advance adjusts for that. running the vacuum advance on manifold vacuum gives the engine the needed advance at idle it needs.it will be noticably more responsive on the throttle.

if i were running a race engine i wouldn't use a vacuum advance at all.

[tgreening]

One thing I had to do on my waggy when I used that carb was to use a really thick carb spacer, about an inch thick I think. Without it I had been getting pretty bad stumbling issues from the carb getting too hot and fuel boiling out. I can't pull the proper description out of my brain right now but I know someone out there will have it at the ready. Other than that it ran great and believe it or not I was pulling about 14.5 mpg on the highway on a 360 turning 33s with 3.31 gears.

[shiner2001]

All great info about the ported and manifold vacs. I have been away from my computer for several days, so it's nice to catch up.

Tgreening, were you using the 3731 intake manifold as well? Anyone else have that fuel boiling problem?

[Stumblinman]

Ok here I go again.
I've seen the problem on them and even a high rise Offenhauser intake. It has been remedied by a simple square bore riser. (the one with 4 holes)

[Lindel]

Blocking the exhaust riser will help too. A set of real intake gaskets (Mr. Gasket makes them) will cover the offending holes in the heads and block off a LOT of heat going in the vicinity of the carb.

That, and an insulating (phenolic) carb spacer will go a long way to solving vapor lock, even back home...

[tgreening]

All great info about the ported and manifold vacs. I have been away from my computer for several days, so it's nice to catch up.

Tgreening, were you using the 3731 intake manifold as well? Anyone else have that fuel boiling problem?

Not sure about the manifold part number but it was a edlebrock performer. Pretty run of the mill. The spacer was a phenolic spacer I picked up at summit racing and it solved the problem. The first spacer I tried was about 1/4-3/8" thick and it didnt do the trick at all. The second one was about 1" and the problem went away. I ended up changing that carb out because of its off-road reputation (or lack thereof I guess) and put on a holley truck avenger because of its good off-road rep. Of course I ended up yanking THAT after my fuel mileage dropped about 3.5mpg and put on howell efi. I figure I might have been able to tune away that fuel loss, or at least some of it, but then I remembered that was what I was trying to get away from, fiddling with carbs.

I always get there in the end but I never claimed to do it the smart way.

[shiner2001]

Derek,
what kit did you buy for the throttle linkage to hook up, I had to "borrow" the ball stud from my son's project f150 to install the throttle cable,but I had to rig the return spring...

I was going back through and rereading this thread and realized that I missed this post when it was put up. I didn't buy anything additional for the linkage (yet). The new carb came with what I needed to hook it up. The only thing I may end up having to do is either get the Lokar trans kickdown or just fab something to work.

Sorry about missing the question shaolinsifu...my bad!