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Old 02-16-2003, 06:36 AM
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Post Engine Vacuum is showing 10 and no higher?

I tried timing my engine with the vacuum gauge method. But the highest vacuum I got was 10. I know the mormal operational vacuum is 12-15. I have a pretty big cam will that efffect it? It did fix my "in-gear" vacuum though. It was jumping from 1-10 but now it just stays at 10. I tried to research the sites but no one explains 10 or below. I that normal for a 355 with a (unknown) big cam and pete jackson gears?

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Old 02-16-2003, 06:45 AM
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-Vacuum Guage Interpretations-
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Old 02-16-2003, 07:06 AM
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I went to that sight and it doesn't mean diddly squat to me....
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Old 02-16-2003, 07:14 AM
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That site is for diagnosing erratic vacuum readings in a stock engine, not what you have. The bigger the cam is the more erratic your vacuum signal is going to be at idle due to excessive valve overlap.
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Old 02-16-2003, 07:20 AM
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Thanks for the explination. I guess a bigger cam means less vacuum.
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Old 02-16-2003, 07:31 AM
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[quote]Originally posted by ataririder:


I went to that sight and it doesn't mean diddly squat to me....<hr></blockquote>

Sorry I tried to help. It makes perfect sense to me.
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Old 02-16-2003, 07:32 AM
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If that site on how to read vacuum gage readings dosen't mean "didly squat" to you, then I suggest you sneek the old credit card out of your wife's purse and take the hot rod down to Pep Boys for a thurough going through! How big is the cam? How is the engine running? Do you smell fuel while its ideling? For that low of a vacuum reading, you have to have a cam in the 230s degrees of duration, give or take, area. Thats alot of cam if it's a daily driver. I had a cam like that in my auto and didn't like it so, I change to a modest grind and my vacuum jumped ut to 17". I instantly got better milage, a much nicer idle and even got noticably better low end torque. Unless you're running a big carb and big tube headers and low rear end gears, I'd stay away from a cam that gives you that low of vacuum but thats only my .02 cents worth! Good luck
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Old 02-16-2003, 09:27 AM
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Ok, so where on that list of guage interpretations does it account for a hairy cam with excessive valve overlap?? Which example, cause I didn't see it anywhere. Dallam you contradict yourself, you say you switched to a smaller profile cam and it increased your engines idle vacuum but yet you say that a set of gauge interpretations set up for interpreting stock engines with no variables for cam variations should have been able to explain to ataririder why his engines vacuum signal was low (the first thing ataririder said was he had a pretty big cam). Now we don't know exactly what his cam specs are but I do know that if he's got any radical cam in that engine his vacuum readings are not going to be the same as a stock engine. Why do you think they invented vacuum reservoir cans for hairy engines? Could it be because they don't sustain vacuum at idle like stock engines do. And if you think taking any car, let alone with a high performance engine, to Pep Boys is a good idea you're the one that needs to open up your boyfriends purse so you can go back to school for a real education.

And back to the original question asked, will an engine with a big cam have lower vacuum readings than a stock engine, yes as I already stated. The bigger the cam the more erratic the vacuum signal will be at idle.

[ February 16, 2003: Message edited by: dmorris1200 ]</p>
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Old 02-16-2003, 12:29 PM
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dallam1,
Thank you for the advice. Well you're exaclty right about that cam. Its going to be changed right away, because it idles erraticly and gas is bein sucked like you don't believe. I got it to idle smoother with advancing it 8 degrees. Can you recommend a cam that suits me car for a daily driver. I have a 355 with headers, 4bbr carb, 3:73s and a Turbo 350. TIA
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Old 02-16-2003, 12:41 PM
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Don,

Please tell me you aren't going to start throwing around PHD's and factory certifications again are you? Why is it that you can't have a friendly disagreement once in a while?

The gauge demonstration shows why the cam is producing little manifold vacuum. Maybe you missed that class on FORDSTAR?

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Old 02-16-2003, 12:56 PM
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[quote]The gauge demonstration shows why the cam is producing little manifold vacuum. <hr></blockquote>

Maybe I missed something, could you please specify where? The only low vacuum gauge reading I saw in those examples was for an engine vacuum leak, no mention in cam overlap as causes for low vacuum at idle. And I didn't see any PHD's flying around you anal, paranoid, old man that you are. By the way, good to see you fighting with woodz428 in this thread too <a href="http://www.hotrodders.com/cgibin/ubb/15/004564" target="_blank">Cobra Jet</a>. Does the term 'doesn't play well with others' ring a bell???

Back to your question ataririder about cam choice. I'm running a dual-pattern cam from Summit Racing with a .471 lift, 218/228 duration @ .050" and I think the advertised duration is around 286*. In my opinion a dual-pattern cam around these specs is a great street cam. Still idles well and produces good power.

[ February 16, 2003: Message edited by: dmorris1200 ]</p>
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Old 02-16-2003, 02:36 PM
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[quote]And I didn't see any PHD's flying around you anal, paranoid, old man that you are. By the way, good to see you fighting with woodz428 in this thread too Cobra Jet. Does the term 'doesn't play well with others' ring a bell???<hr></blockquote>

I was wondering how long it would take you to go this far...now we know.

BTW...A common cam grind does not an engine series make.

Have a nice day...
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Old 02-16-2003, 03:24 PM
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Boy KULTULZ, you have an amazing habit of waiting till you see that I've logged out to respond to my posts. At least I don't run and hide. By the way I'm still waiting for you to answer my question. Where on those gauge interpretations does it show low vacuum readings due to valve overlap???? Come on, just answer the question. By the way I never said I agreed with either of you two on the Cobra thread, just found the whole arguement funny. Now how about my question?? The guy asked 'is it normal for a big cam to produce lower vacuum at idle', where is that info in the link you provided?
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Old 02-16-2003, 06:31 PM
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[quote]Originally posted by dmorris1200:


Boy KULTULZ, you have an amazing habit of waiting till you see that I've logged out to respond to my posts. At least I don't run and hide.<hr></blockquote>

...huh?

Gee, guess I had better check the board posting rules...I didn't know I had to wait here with bated breath to await your reply.

[quote]By the way I'm still waiting for you to answer my question.<hr></blockquote>

Really? And why is it you feel I should answer you? With your demonstrated wealth of knowledge...you should know. I mean, you are certified aren't you?

[quote]By the way I never said I agreed with either of you two on the Cobra thread, just found the whole arguement funny.<hr></blockquote>

Thank goodness for that. Had you agreed with me I would most likely have been wrong...

Oh...BTW...The guy obviously had more wrong than cam event timing...

Again...Have a nice evening...
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Old 02-16-2003, 06:58 PM
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I KNEW IT!

Don didn't stay on long enough to read my reply...

Well...TWO can play that game....

...stomp...stomp...SLAM!
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