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The benefits of a Vacuum Gauge!!!
I answered a question about vacuum and what it was good for a couple years ago on this board, and in the past 24 hours, I have seen several posts that would benefit from it, so I dug through the archives and found it. Here it is, and I hope it helps someone.
posted 09-29-1999** **** ** ------------------------------------------------------------------------ Chipdog-Five did a good job of covering the basics. Take note. The vacuum that is created in a normaly aspirated engine (one that is not blown or turboed) also gives you a great tool for diagnosing engine problems. Just about any internal engine problem can be identified with a vacuum gauge !!! I'll teach you some of the basics: 1) A steady reading of between 17" and 22" is considered normal for a stock motor. 2) A low but steady reading between 10" and 15" would be caused by retarded ignition or valve timing, or low compression. 3) A very low reading between 4" and 9" means you have a vacuum leak. 4) If the needle fluctuates as you increase the engine speed, you have either an ignition miss, a blown head gasket, a leaking valve or a weak valve spring. 5) A gradual drop in reading at idle means you have excessive back pressure or partial blockage in the exhaust system. 6) An intermittent fluctuation at idle means you have either an ignition miss or a sticking valve. 7) A reading where the gauge needle drifts anywhere between 12" and 22" indicates that your idle mixture is unstable. This is more common on carbureted motors. 8) A high and steady reading indicates that the ignition timing is too far advanced. 9) If, when you quickly close the throttle after running at 2000 rpm for ten seconds or more, the gauge needle DOES NOT jump two or more inches above what it is at idle, your piston rings are shot. 10) If the reading at idle is lower than normal, but the gauge needle fluctuates three inches on both sides of normal, your valve guides are excessively worn. These are but only a few of the things you can learn about the condition of your engine with a vacuum gauge. Keep in mind that a blower or a turbo will create a false reading because the boost they create offsets the vacuum reading. posted 09-30-1999 **** ** ------------------------------------------------------------------------ I love using a vacuum gauge. Here are a couple more "old timer" tricks that you can use on a non computer controlled, carbureted engine: 1) To adjust the ignition timing to the best spot without a timing light, just hook up a vacuum gauge to manifold vacuum and advance the timing, slowly, until the needle on the gauge stops going up, then retard the timing until the needle drops 1/2" on the gauge. 2) To set the idle mixture on a carbureted motor, basicly do the same thing, except with the mixture screws. Richen the mixture until you get the highest vacuum reading you can, then lean it out until the needle drops about 1/2". Enjoy. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!! |
Another good use of a vacuum gauge would be to determine of your air filter, mass air body, throttle body and plenum inlet are flowing enough to supply the engine. If you are at full throttle, max rpm and do not read zero vacuum then you have a restriction supplying air to the engine.
------------------ 88 347, Twisted wedge heads,Comp Cams 224/230 cam, 1/4=10.718 @ 123.02 mph dyno= http://www.fbody.com/members/LarryS/mustdyno.jpg |
It's also good to check backpressure in your exhaust. I found a plugged cat that way on a supercharged engine. I drilled and tapped a gauge in the header collector, it had boost in the collector!!
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Wow, Chris! Where ya been, man? I haven't seen you around here in a while!
------------------ Joe! 1988 GT, 167,000 miles!!! 13.58@105mph Check out my listing! Click here! Or my website:www.joe4speed.com 99 Ninja ZX-6R:10.32@135mph! 1993 Olds Eighty Eight LSS 16.40@88.8mph http://www.duhspot.com/users/smiley/.../outtahere.gif |
Hey, nice to see your posting here again chris. Hope to see you around here more! I think I'm gonna hook up a vacume guage and see what it shows now.
Skyler ------------------ -1989 Saleen Mustang #406- TFS TW Heads, E-303, Edelbrock intake, 70mm TB, 73mm MAF, 24lb injectors, 1 5/8 shorties, Off Road H, 3 Chamber flows, Jaz Race seats, Back seat removed, sub-frames, Roll Cage, and a 80 shot of N20. 12.55@107 Motor |
Hey,Welcome back
Haven't seen you post here in a Looooong time,nice to see you back http://www.mustangworks.com/msgboard/biggrin.gif Another member that i've been wondering a awful lot aboutwhere he is,is 88Workcar,where the heck is he ?????????????? ------------------ Paxton Blown 87GT ICQ:91504337 |
He gets out next month. Just kidding, I don't know when he gets out.
Yeah, life got extremely busy for me about a year or so ago, and I just couldn't find the time. I'm busy these days too, but I'm on a much better Sprint car team this year, and it's very smooth sailing. In fact, we're leading in the points in our division! I recently made my first attempt at a website, and it has alot of pictures and info about the team. It's not an interactive website, so if you like it or dislike it, you're either going to have to email me or tell me here, but I am interested in feedback. I add to it every other day or so. There is a link in my signature. Anyway, it's nice to be back! Thanks. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!! |
Holy Cow Sky!!!!!
You've got almost 3k posts!!! I remember when I had twice as many as you (but who's counting). Wow. ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!! |
OK Chris, you sound like the guy I need to talk to. What would cause this vacuum problem...
At idle I have 5" of vacuum. When you rev it to about 2000rpm it goes up to about 10". I have an F303 cam and have buddies with the same cam and they make 15" at idle. There are no leaks anywhere because we plugged every line but one and checked it on the upper intake and still only got 5". Any ideas? ------------------ Gunning for 12's! My Stang Page Buy your parts here ICQ# 42269241 |
What's your ignition timing set at? Who installed your cam? Sounds like the cam is off. Check the compression too. Let me know.
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This is AWESOME!
Thank you, i just bought a vacuum gauge a few weeks ago and only had a very basic idea of how to use it. Excellent! Thank you PKRWUD and welcome back! ------------------ '84 Mustang 5.0 LX My car |
Yeah, I put in my regular couple a day, and I don't post anywhere else. So I'm gettin up there. http://www.mustangworks.com/msgboard/smile.gif Unit is right behind me.
Skyler ------------------ -1989 Saleen Mustang #406- TFS TW Heads, E-303, Edelbrock intake, 70mm TB, 73mm MAF, 24lb injectors, 1 5/8 shorties, Off Road H, 3 Chamber flows, Jaz Race seats, Back seat removed, sub-frames, Roll Cage, and a 80 shot of N20. 12.55@107 Motor |
How hard is it to hook up a vacume gauge? I was thinking of getting one for my 92GT.
Scott ------------------ 1992 GT 5.0L Convertible BBK Shorties, Flowmasters, Super Chip, Mass Air, Under Drive Pullies, Hurst Shifter, Duck Tape AIM: SmokeyDP |
Smokey-
It's the easiest of all gauges to install. All you need to do is locate a source of manifold vacuum. I don't know where it is off the top of my head for your car, but all you have to do is follow the vacuum line that goes to your fuel pressure regulator until you find where it plugs into. If at that point, usually a "vacuum tree", there is an extra nipple that has a cap on it and is not being used, you can hook up your vacuum hose there. If they are all being used, you can safely cut the existing vacuum line and insert a "T", and then attach your vacuum hose to the third nipple on the T. If you are mounting the gauge inside the car, just run the vacuum hose through the firewall and hook it to the gauge. If this is just for occasional use with a gauge that won't be mounted in the car, do the same thing with the T, but have a cap for it for when it's not in use. Pretty easy! Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!! |
Smokey-
I just noticed where you are from. I used to live in Bound Brook! What a small world! |
Cool, yeah thats the town over. Ever hear of the Pirone's or Buono's, thats my family? Oh well at any rate, good thing you moved when you did...Bound Brook flooded when Floyd came along...pretty bad too, 40 feet of water in places.
------ all you have to do is follow the vacuum line that goes to your fuel pressure regulator until you find where it plugs into. If at that point, usually a "vacuum tree", there is an extra nipple that has a cap on it and is not being used, you can hook up your vacuum hose there. ------ Yeah, I need more help finding my nipple http://www.mustangworks.com/msgboard/biggrin.gif, I dont have a fuel pressure regulator, my engine is stock. ------------------ 1992 GT 5.0L Convertible BBK Shorties, Flowmasters, Super Chip, Mass Air, Under Drive Pullies, Hurst Shifter, Duck Tape AIM: SmokeyDP |
Smokey, if you're engine is fuel injected, you have a fuel pressure regulator. it's that little round can on the fuel rail, you know, the one with a vacuum hose going to it! All fuel injection systems have a regulator, high performance systems have an adjustable regulator. Now go find it!
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