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Old 03-02-2010, 05:47 PM
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Vacuum for hei

Is it better to run hei on full manifold vacuum or the ported on carb?

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Old 03-02-2010, 05:54 PM
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Manifold vacuum works well for me.
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Old 03-02-2010, 05:57 PM
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Real men run on manifold vacuum.
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Old 03-02-2010, 05:58 PM
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Well depending on engine and its purpose and what size of cam you have etc there are many pros and cons of full manifold and timed port vacuum. I hook mine up to my timed port location and it works just fine that way for me. But like I said you can do some research on the subject and you will get many opinions and why it works better for some ways and not for others.

Eric
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Old 03-02-2010, 06:15 PM
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Quote:
Originally Posted by eric32
Well depending on engine and its purpose and what size of cam you have etc there are many pros and cons of full manifold and timed port vacuum. I hook mine up to my timed port location and it works just fine that way for me. But like I said you can do some research on the subject and you will get many opinions and why it works better for some ways and not for others.

Eric
If you are running timed vacuum you are doing it wrong regardless of the engine. If it runs better with timed vacuum then you don't know how to tune an engine. The only reason timed vacuum even exists is for government mandated emissions compliance in the 1970's. It was a crutch that the auto manufacturers came up with to meet the emissions requirements in the dark days of the 1970's. It has absolutely NO place on any engine you expect performance from.

Sorry to step on peoples feelings, but this is a known, proven fact.
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Old 03-02-2010, 06:27 PM
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Well I am only learning on some things here but I do know how to tune an engine here. I have done two cam swaps several carb rebuilds and some other things with my two trucks I have. Am I an expert? No but I do know some things on how to tune. I just got done doing away with a computer controlled 87 chevy caprice 305 and I just got done installing a brand new HEI and just rebuilt a holley 600 carburetor from top to bottom.

Yes to some that does not seem like much but for me who knew nothing about cars or engines for that matter to be able to do what I can do now I am proud of what I can do. Not trying to start anything here but there are different methods to tuning an engine here. I don't tune my engines to get every last horsepower. I get mine as close as possible with out a dyno type tune.

Perhaps I will dig into some more info on full manifold vacuum here but people can at least be respectful here. Everyone here had to learn everything they know now. But not taking it personal everyone has there ways on tuning. If everyone did it the same way there would not be a variety of different engine combos to make.
cheers
Eric
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Old 03-02-2010, 06:47 PM
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Well doing some more reading on ported vs full manifold it seems the full is better. I will have to try and hook mine up that way and see how it works. Thanks Ericnova 72 for the heads up appreciate it and to others who can teach new beginners like me. It seems it gives better overall results and better fuel mileage and better response.

Eric
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Old 03-02-2010, 08:28 PM
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Eric32, I didn't mean to look like I was hammering you personally, and I'm sorry if it came acrossed thar way. I sometimes come acrossed a little too direct. I just have a problem whenever I see improper information spread around and try to stamp it out when I see it. It's a pet peeve I guess.

It's hard enough to find the correct information, I feel as informed gearheads we should all be trying to eliminate the bad info (mostly shade tree) that is incorrect so that it will disappear and not trip up other poeple.
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Old 03-02-2010, 09:40 PM
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If you do a search on here, you will find the paper by the ex-GM engineer that, to me, is the ultimate answer on the subject. After reading that paper, I don't understand why anybody would NOT run full manifold vacuum to the distributor.
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Old 03-03-2010, 05:06 AM
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Well I swapped my vacuum hose over to full vacuum and wow. Seemed to smooth it out on idle. It still stalls and farts because of the cam but it seemed like it had a flat spot when you would barely throttle it , but now thats gone. Thanks fella's. I put a little red vacuum cap on the timed port.
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Old 03-04-2010, 06:01 PM
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Thanks ericnova72 no problem's here. Also glad to see that hooking up full manifold vacuum helped out the the gentlemen who made this post here. I wish I could hook mine up to full manifold vacuum but all my ports are taken up.

I have one port on the front of carb for my transmission and the back port for the breaks. I can't use the one off of the intake cause my carb hits it. So I am only able to use the timed port on the metering plate. I have read its not good to tie into the brake and vacuum modulator on the transmission. Take care guys appreciate all the info here.
Eric
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Old 03-04-2010, 08:02 PM
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Quote:
Originally Posted by eric32
I have read its not good to tie into the brake and vacuum modulator on the transmission.
Eric, "T"-ing off the manifold vacuum port to supply the modulator valve and the vacuum advance won't hurt the performance of either the tranny or the vacuum advance.

I've run T's like this before- works fine. Actually, my DD '80 Malibu wagon is set up this way as we type. The amount of volume in the line back to the modulator doesn't delay the vacuum advance when viewing the timing marks w/a light.

Best thing is to give it a try and see. I assure you, nothing will be harmed by doing so. You may need to lower the idle some, and it wouldn't hurt to see if the idle mixture screws will take an adjustment w/the engine fully warmed up.
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