 Tachometer Conversion, ...from 4 cylinder to 6 or 8 |
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| nick mironov |
 Feb 1 2006, 12:35 PM
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#1
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nickm  Group: Members Posts: 204 Joined: 12-June 05 From: San Francisco, CA Member No.: 4,264  |
How does one convert the standard 4 cylinder tachometer for use with an engine with a greater number of cylinders? I have a V8 conversion. I have read the various postings and it is not clear on how to do it for a 75 914. I assume those who have 6 and V8 conversions have made the necessary tachometer modifications. Also, the tachometer bounces around. I understand that there is also a fix for this condition, and again, I am not clear on what is involved. Anyone know how to make the conversion and fix the bounce? |
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| ClayPerrine |
Feb 1 2006, 12:39 PM
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Life's been good to me so far..... Group: Admin Posts: 15,459 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille 
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Normally, for a six conversion, a 911 tach is substituted for the factory 4 cylinder tach. It has the correct redline for the six.
As for the V-8, either build a divider circuit to half the number of ignition pulses, or just send the tach to North Hollywood or Palo Alto speedo for repair and recalibration. They can fix your bouncing problem too. |
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| lapuwali |
Feb 1 2006, 12:47 PM
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743  |
The conversion is usually performed at a shop like PA Speedo or NH Speedo.
The bouncing is usually external to the tach. Check the wires at the coil and the back of the tach very carefully. A dirty or even slightly loose connector will cause this. It may LOOK fine, but can still be loose. Take the tach wire at the coil and check for any breaks in the insulation. If you're feeling brave, bend the wire and see if the insulation breaks. They often do from 30 years of engine heat. The fix is to replace the entire engine harness (see Jeff Bowlsby for this), as all of the insulation will be in the same state. |
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| 914efi |
Feb 1 2006, 12:48 PM
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#4
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Member Group: Members Posts: 140 Joined: 14-June 04 From: Westport,MA Member No.: 2,204 Region Association: None |
Buy a cheap pep boys/JC Whitney tach and transplant the movement to the Porsche case. Just make sure it has the correct sweep. Did my 914-6 crankfire and my A-H 3000 V8 this way.
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| WRX914 |
Feb 1 2006, 12:50 PM
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#5
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2.5 WRX STI hybrid powered beast Group: Members Posts: 782 Joined: 16-September 04 From: Las Vegas, NV Member No.: 2,771 Region Association: Southwest Region |
North Hollywood Sppedometer does excellent work. They rebuilt my tach for the Subaru engine. Works perfectly and looks outstanding. The only gripe I have is now I have to have my other gauges refinished to match the brand new looking tach!
(IMG:http://www.914world.com/bbs2/html/emoticons/mueba.gif) |
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| markb |
Feb 1 2006, 01:03 PM
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#6
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914less :( Group: Members Posts: 5,449 Joined: 22-January 03 From: Nipomo, CA Member No.: 180 Region Association: Central California
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(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif) |
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