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11-04-2007, 08:09 PM | #1 |
Wishin' I had more money!
Join Date: Feb 2007
Location: Eugene, OR
Posts: 1,242
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Question about my Tach
I just put a new tach in the truck, and I'm not completely sure if it's accurate or not...
I did a WOT run in the truck, and according to the tach, it shifted first to second at 4000 RPM. Shifted from second to third at 4200 RPM. Here's the engine I have... http://www.jegs.com/webapp/wcs/store...55609_-1_10763 Now either the tach is inaccurate, or it's shifting too early, because the specs on that engine show 290hp at 5200 RPM, and I'm about 1000 below that according to the tach. I've got it hooked to a main power source in the fuse box, and I've got the actual RPM wire hooked to the "tach" terminal on the dist. cap. It also shows it's idling at about 500rpm in gear, which I think is a little lower than it actually is. I could be wrong though.. |
11-04-2007, 10:56 PM | #2 |
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Join Date: Jun 2007
Location: Springfield Mo.
Posts: 1,086
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Re: Question about my Tach
Is this an aftermarket tach or a factory one? If it's an aftermarket, it should have a switch on the back of it for a 6 cylinder or 8 cylinder. It may be on the 6 cylinder setting and just need to be changed. I used to have a Sun tach in my 82 years ago and that's how that tach was.
If it's a factory tach, it's very likely that it came out of a 6 cylinder truck, and that's why it's reading off as the 6 cylinder and V8 tachs are different. ...Joe
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11-05-2007, 12:44 AM | #3 |
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Join Date: Nov 2000
Location: Ft. Mill, SC USA
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Re: Question about my Tach
If you put in a factory tach, do this. Turn your ignition switch to on, don't start it; your tach should read 0. If it dosen't, your tach is off/bad. I have one good tach in my truck, but have three more that are off/bad David
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PROJECT TRUCK: 1985 SWB C10 Silverado Black/Charcoal, 1990 V2500 Suburban, 2018 Suburban, 2005 GMC 2500HD CCSB, 2014 Toyota Camry SE, HAD.....1968 Camaro RS/SS Family owned since new; 350 3 speed SOLD |
11-05-2007, 10:34 AM | #4 |
Wishin' I had more money!
Join Date: Feb 2007
Location: Eugene, OR
Posts: 1,242
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Re: Question about my Tach
It's an aftermarket sun pro tach, and I already made sure it's on the 8 cylinder setting, but I guess it wouldn't hurt to double check that
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11-05-2007, 12:04 PM | #5 |
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Join Date: Nov 2003
Location: Brookings, SD
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Re: Question about my Tach
I think I am missing something. Why would the specs on the engine determine when your tranny will shift? Wouldn't the tranny control the shift points? How does a tranny decide when it will shift?
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11-05-2007, 12:59 PM | #6 |
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Join Date: Feb 2007
Location: Austin, TX
Posts: 3,930
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Re: Question about my Tach
The transmission doesn't care what your engines power band is. Wide open throttle shifts are going to happen whenever they are set to in the transmission.
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11-05-2007, 02:46 PM | #7 | |
Wishin' I had more money!
Join Date: Feb 2007
Location: Eugene, OR
Posts: 1,242
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Re: Question about my Tach
Quote:
What I'm getting at is that if the tranny is set to shift at 4200rpm, well then, the engine is capable of much more than that. |
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