Tach says 5400, Holley 950 says 4350...

Reply Subscribe

Thread Tools

Search this Thread

Oct 14, 2002 | 12:09 AM

Spifz

Thread Starter

Member

Joined: Jan 2002

Posts: 203

Likes: 13

From: Phoenix, AZ

Car: 1986 Z28 / 2012 CLS550

Engine: F-1R -> Aluminum block 540

Transmission: T56 Magnum + GForce gears

Axle/Gears: Ford 9" 3.00's + Eaton Truetrac

Tach says 5400, Holley 950 says 4350...

How likely is it that the Tach is wrong? Could it be the Holley Commander 950 that is wrong?

Oct 14, 2002 | 01:09 AM

funstick

Supreme Member

Joined: Jun 2002

Posts: 1,787

Likes: 0

From: great lakes

tachs are inccoerct quite a bit. the ecm is probobaly quiet accurate by comparison

Oct 20, 2002 | 05:30 AM

Ward

Supreme Member

iTrader: (1)

Joined: Aug 1999

Posts: 2,842

Likes: 6

From: Rowlett, TX

Car: 1988 GTA

Engine: 5.0 TPI

Transmission: T5

Axle/Gears: 9 Bolt, 3.45

Stock, the tachometer is the most inaccurate gauge. Not sure why, thats just what I have heard.

Oct 29, 2002 | 07:25 AM

GofasterFirebird

Supreme Member

iTrader: (3)

Joined: Mar 2000

Posts: 1,287

Likes: 0

From: Warsaw, Indiana

Car: 1991 Firebird

Engine: 427 LSX

Transmission: Turbo 400

If anything the tach is slow. And the tach would say 4350 and the ECM 5400. Is there a 6 cylinder setting for the tach or something?

Oct 29, 2002 | 01:23 PM

Spifz

Thread Starter

Member

Joined: Jan 2002

Posts: 203

Likes: 13

From: Phoenix, AZ

Car: 1986 Z28 / 2012 CLS550

Engine: F-1R -> Aluminum block 540

Transmission: T56 Magnum + GForce gears

Axle/Gears: Ford 9" 3.00's + Eaton Truetrac

Nope, appears to be the other way around, the ECM definately reads higher, and the rpm logged by the ECM is consistent with the trap speed encountered at that rpm, and much closer to being mathematically correct than the calculated speed based on the factory tach.