Tach and Vacuum question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cpetersen · 12-19-2010, 11:45 AM

I got this setup for $20 on Thursday in eastern AZ. Guy didn't know what he had. The 16yr old and I refurbished it yesterday and installed it. I think the tach needs to be calibrated, its not off by much.How do I calibrate it? But the vacuum didn't work. Did you guys use steel lines for the vacuum gauge? Name: Unnamed.jpg
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Name: Unnamed.jpg
Views: 277
Size: 52.5 KB

red71cheyenne · 12-19-2010, 11:47 AM

Not sure about the vacuum guage but on mine I used a barb and vacuum hose, I don't know what it came with originally. The tach can be zero'd using the screw on the back of it. That will bring you closer to actual.

cpetersen · 12-19-2010, 11:53 AM

How much vacuum are you running normally? Scary thing was i got this out of a c-50. I looked at the SPID in the glove and it showed it had bucket seats. It was a 68 truck. The seats were gone wonder how cheap it could have got them. lol

red71cheyenne · 12-19-2010, 09:46 PM

Quote:

Originally Posted by cpetersen

How much vacuum are you running normally? Scary thing was i got this out of a c-50. I looked at the SPID in the glove and it showed it had bucket seats. It was a 68 truck. The seats were gone wonder how cheap it could have got them. lol

At idle it runs around 18-20 and drops as you get on it. There is a nice FAQ on GMC Pauls website about troubleshooting and tuning with a vacuum guage. I just like it cause it fills that hole in the dash and its fun to watch it move as I go through the gears!

oldblue1968chevy · 12-19-2010, 11:57 AM

awesome deal!

Lee H · 12-19-2010, 12:11 PM

I also run a barb and vac hose for mine. It's not real accurate but fun to watch. I think they are like the other gauges, close but no cigar. I'm interested in the adjustment for the tach. Mine reads about 400-600 to low. I do not remember the screw on the back. Does nayone have a picture of this? Later today I'll grab a flashlight and small mirror and see if I can find it.

cpetersen · 12-19-2010, 12:28 PM

Yeah, there is a screw hole on the back. You use a small screw Phillips. Tach does seam very accurate. Needless to say, i'm not going to trust that tach and run the motor at redline. lol

cpetersen · 12-19-2010, 12:32 PM

This truck didn't have a chevy motor in it. Alot of the farm truck C-50's came with tall block 427's. interesting thought wonder if you can stroke those motors?

Jacfourteen · 12-19-2010, 03:07 PM

Quote:

Originally Posted by cpetersen

This truck didn't have a chevy motor in it. Alot of the farm truck C-50's came with tall block 427's. interesting thought wonder if you can stroke those motors?

Tall deck 427's can be made into big inch motors, I know they can be stroked out to about 550 CI (not sure maybe bigger).

Jacfourteen · 12-19-2010, 05:57 PM

I don't have a stock vac gauge, I have an aftermarket one but it has a rubber vacuum line and it works fine.

cpetersen · 12-19-2010, 06:41 PM

How many pounds of vacuum does it run?

dznucks · 12-19-2010, 07:01 PM

a healthy SBC should pull 17-20" of vacuum at idle. If you have a cam, your idle vacuum will be lower. the bigger the cam, the lower the idle vacuum.

The vacuum gage is a handy tuning tool. You will be able to watch when you power valve and secondaries are coming in.

19seventeeCustom · 12-19-2010, 08:46 PM

$20, man Ill give ya 50 for it right now...lol JK

nice find.

12-19-2010, 11:45 AM	#1
cpetersen Registered User Join Date: Feb 2010 Location: mesa az Posts: 211	Tach and Vacuum question I got this setup for $20 on Thursday in eastern AZ. Guy didn't know what he had. The 16yr old and I refurbished it yesterday and installed it. I think the tach needs to be calibrated, its not off by much.How do I calibrate it? But the vacuum didn't work. Did you guys use steel lines for the vacuum gauge?

12-19-2010, 11:47 AM	#2
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Re: Tach and Vacuum question Not sure about the vacuum guage but on mine I used a barb and vacuum hose, I don't know what it came with originally. The tach can be zero'd using the screw on the back of it. That will bring you closer to actual. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty

12-19-2010, 11:53 AM	#3
cpetersen Registered User Join Date: Feb 2010 Location: mesa az Posts: 211	Re: Tach and Vacuum question How much vacuum are you running normally? Scary thing was i got this out of a c-50. I looked at the SPID in the glove and it showed it had bucket seats. It was a 68 truck. The seats were gone wonder how cheap it could have got them. lol Last edited by cpetersen; 12-19-2010 at 11:54 AM.

12-19-2010, 11:57 AM	#5
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	Re: Tach and Vacuum question awesome deal! __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4

12-19-2010, 12:11 PM	#6
Lee H Registered User Join Date: Jun 2010 Location: Upland Ca Posts: 4,147	Re: Tach and Vacuum question I also run a barb and vac hose for mine. It's not real accurate but fun to watch. I think they are like the other gauges, close but no cigar. I'm interested in the adjustment for the tach. Mine reads about 400-600 to low. I do not remember the screw on the back. Does nayone have a picture of this? Later today I'll grab a flashlight and small mirror and see if I can find it. __________________ 1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703

12-19-2010, 12:28 PM	#7
cpetersen Registered User Join Date: Feb 2010 Location: mesa az Posts: 211	Re: Tach and Vacuum question Yeah, there is a screw hole on the back. You use a small screw Phillips. Tach does seam very accurate. Needless to say, i'm not going to trust that tach and run the motor at redline. lol

12-19-2010, 12:32 PM	#8
cpetersen Registered User Join Date: Feb 2010 Location: mesa az Posts: 211	Re: Tach and Vacuum question This truck didn't have a chevy motor in it. Alot of the farm truck C-50's came with tall block 427's. interesting thought wonder if you can stroke those motors?

12-19-2010, 05:57 PM	#10
Jacfourteen Big Red - Now its a SWB! Join Date: Jun 2009 Location: Oroville, Ca Posts: 1,624	Re: Tach and Vacuum question I don't have a stock vac gauge, I have an aftermarket one but it has a rubber vacuum line and it works fine. __________________ 68 3/4 ton (Project)-350 Small Block, .030 over, 10:1 comp, 3998993 heads, C3BX edelbrock intake, comp cams XE268, Holley 670 SA, long tube headers, dual flow 40's, E-fan, Alum rad, currently under the knife getting shortened and bagged build thread 41 3/4 ton (wife's)-flatbed, fully restored to original 01 Tahoe LT 4WD (my daily driver)-Magnaflow Muffler, Rollin on 22's 02 Ford Mustang Convertable (Wife's Car)-Flowmaster 50, Clear corners, Intake, sittin on 18's

12-19-2010, 06:41 PM	#11
cpetersen Registered User Join Date: Feb 2010 Location: mesa az Posts: 211	Re: Tach and Vacuum question How many pounds of vacuum does it run?

12-19-2010, 07:01 PM	#12
dznucks Registered User Join Date: Feb 2006 Location: Smyrna, Ga Posts: 1,647	Re: Tach and Vacuum question a healthy SBC should pull 17-20" of vacuum at idle. If you have a cam, your idle vacuum will be lower. the bigger the cam, the lower the idle vacuum. The vacuum gage is a handy tuning tool. You will be able to watch when you power valve and secondaries are coming in.

12-19-2010, 08:46 PM	#13
19seventeeCustom Registered User Join Date: Mar 2010 Location: Downtown Posts: 573	Re: Tach and Vacuum question $20, man Ill give ya 50 for it right now...lol JK nice find.

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