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Old 11-13-2006, 11:36 PM
Richomino Richomino is offline
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Manifold or ported vacuum for dizzy???

Hello all:

Got a '90 FSJ 360 swapped into the CJ.....working out final details....this is a trail only rig, so all all the air stuff was pulled, the engines got an Edelbrock performer EGR manifold, but the CTO switches are still there (Just not hooked to anything)....

Should I hook up manifold or ported vacuum to the dizzy??....I did a search and found conflicting info as to whether when stock the CTO fed ported until engine was hot, then switched to maniflod vacuum....also got three different temperatures at which the vacuum source was switched by the CTO....

Im guessing I should just hook dizzy to whatever type of vacuum was switched when the engine heated up....but....which is it???...ported or manifold when hot??

Thanks in advance!!!
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Old 11-13-2006, 11:44 PM
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letank letank is offline
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ported vacuum when warm, because the timing was designed that way

there is a good thread about the whole issue..... using manifold... but you will have to retime the timing.... change the weight around..... i did a test.... and it was running supernice on the flat... but very sluggish on the uphill.... i tried to decrease timing.... but it was still not up to power...so i went back to ported vacuum

here is the thread

http://hotrodders.com/forum/distribu...vacuum+advance
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Old 11-14-2006, 06:31 AM
GWChris GWChris is offline
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I switched my '88 to straight manifold vacuum after tweeking it so that it ran properly with the stock ported/non-linear valve setup. I did not change the timing much after that. I've found it runs the same under load, but the throttle response is better on manifold. For a trail rig I wouldn't think twice - run it on manifold. The main purpose of the ported vacuum is to retard the spark at idle to keep the combustion temperatures up - purely for emission purposes.
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Old 11-14-2006, 06:51 AM
Ristow Ristow is offline
 
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manifold will be fine.all mine run on manifold,very well.
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Old 11-14-2006, 08:38 AM
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tgreese tgreese is offline
 
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If you still have the CTO, you may as well run manifold vacuum till the engine warms up, then ported vacuum. That should help low temperature drivability (that's why your Jeep has the CTO in the first place).
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Old 11-14-2006, 09:33 AM
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710 Burner 710 Burner is offline
 
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I have studied the two CTO/Non-LNR valve setup extensively. (since mine doesn't work) The non -lnr valve feeds partial manifold vacuum to the dizzy until the engine reaches operating temperature. Then CTO No. 1 kicks in and it runs ported vacuum. Late model engines have the HDC option. If the engine starts to run too hot, the HDC CTO kicks in and feeds direct manifold vacuum to the dizzy.
I am currently running direct manifold vacuum to mine because I like the way it idles smoother and has a little more Ummph off the line. By the way, most of the modern fuel injection systems I have studied use a higher advance at idle. Your results may vary.
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Old 11-14-2006, 10:21 AM
OneLeggedJeep OneLeggedJeep is offline
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Quote:
Originally Posted by Valdez Explorer
I have studied the two CTO/Non-LNR valve setup extensively. (since mine doesn't work) The non -lnr valve feeds partial manifold vacuum to the dizzy until the engine reaches operating temperature. Then CTO No. 1 kicks in and it runs ported vacuum. Late model engines have the HDC option. If the engine starts to run too hot, the HDC CTO kicks in and feeds direct manifold vacuum to the dizzy.
I am currently running direct manifold vacuum to mine because I like the way it idles smoother and has a little more Ummph off the line. By the way, most of the modern fuel injection systems I have studied use a higher advance at idle. Your results may vary.

This is true, it will idle great, but you might have to be careful about detination problems when decelerating.

Even if you want to bypass the CTOs, I would recommend you go ported and manifold using just the non-linear valve to the distributor. It's almost the best of both worlds. It provides enough advance without spiking (problem with manifold only), and keeps some advance at idle (unlike ported only).
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Old 11-14-2006, 10:30 AM
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710 Burner 710 Burner is offline
 
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I am running 14 degree initial advance with no detonation of any kind. My Non-LNR valve is toast.
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