S-AFC tach vs Stock tach.. WHICH IS RIGHT??
10-08-02, 04:10 PM
#1
I came, I saw, I boosted.
Thread Starter
Join Date: Apr 2001
Location: Windsor, Ontario, Canada
Posts: 1,921
Likes: 0
Received 0 Likes
on
0 Posts
S-AFC tach vs Stock tach.. WHICH IS RIGHT??
OK, Most people that have installed an S-AFC in there car have noticed a discrepancy between the RPM readings on the S-AFC and on the factory tach. Usually to the tune of a few hundred rpms.
I know mine is out by maybe 100-200 rpms.
Also- I havn't checked to see if it's a ratio... eg, is it out by 100 rpms across the board, or by much more at high rpms than at low rpms? I should check....
Simple question:
Which one is right????
I know mine is out by maybe 100-200 rpms.
Also- I havn't checked to see if it's a ratio... eg, is it out by 100 rpms across the board, or by much more at high rpms than at low rpms? I should check....
Simple question:
Which one is right????
10-08-02, 06:20 PM
#4
SOLD THE RX-7!
Join Date: Mar 2001
Location: Vancouver, BC, Canada
Posts: 7,451
Likes: 0
Received 0 Likes
on
0 Posts
I'm pretty sure the afc is right.
my gap gets bigger as the rpms go up... idle is both same. off by like 200 at 2000 and like 3-400 at 4000
but it's aroud the same at redline. well when I shift using the tach the AFC max is around the same
my gap gets bigger as the rpms go up... idle is both same. off by like 200 at 2000 and like 3-400 at 4000
but it's aroud the same at redline. well when I shift using the tach the AFC max is around the same
Last edited by Scott 89t2; 10-08-02 at 06:24 PM.
10-08-02, 07:38 PM
#6
Engine, Not Motor
iTrader: (1)
Join Date: Feb 2001
Location: London, Ontario, Canada
Posts: 29,789
Likes: 0
Received 108 Likes
on
91 Posts
Actually, I'm pretty sure they're both right. The S-AFC gets it's RPM signal from the CAS. The tach get's it's signal from the trailing coil. Therefore, two different RPM sources, two different readings. The trailing coil signal is more accurate than the CAS, so take the tach as the "real" RPM.
Of course, I could be wrong. I'd check the manual (ECU wiring diagram) but I'm too lazy right now.
Of course, I could be wrong. I'd check the manual (ECU wiring diagram) but I'm too lazy right now.
10-08-02, 08:07 PM
#7
I came, I saw, I boosted.
Thread Starter
Join Date: Apr 2001
Location: Windsor, Ontario, Canada
Posts: 1,921
Likes: 0
Received 0 Likes
on
0 Posts
Aaron... I know you know your stuff... but them both being right is a physical and logical impossiblity if they are reading 400 rpms apart!!!!!!
I know what you are saying... the source is off, not the display.
I'd still like to have concrete evidence though.... anyone have a tach to hook up under the hood or something to compare??
A freind of mine works at a tool shop, and they have a snesor that detects RPM on any shaft... it just looks like a timing gun that you aim at the rotating target, and it will tell you it's rpm's!! Not sure what method it uses... radar, optical, infrared, who knows, but that sounds pretty concrete to me....
Anyone install an aftermarket tach and seen a difference with the factory one?
I know what you are saying... the source is off, not the display.
I'd still like to have concrete evidence though.... anyone have a tach to hook up under the hood or something to compare??
A freind of mine works at a tool shop, and they have a snesor that detects RPM on any shaft... it just looks like a timing gun that you aim at the rotating target, and it will tell you it's rpm's!! Not sure what method it uses... radar, optical, infrared, who knows, but that sounds pretty concrete to me....
Anyone install an aftermarket tach and seen a difference with the factory one?
Last edited by Bambam7; 10-08-02 at 08:11 PM.
Trending Topics
10-09-02, 12:01 AM
#9
I came, I saw, I boosted.
Thread Starter
Join Date: Apr 2001
Location: Windsor, Ontario, Canada
Posts: 1,921
Likes: 0
Received 0 Likes
on
0 Posts
Which reiterates the question.... which is right?????
I stumbled across a strangely dark, yet very possible theory....
Does anyone think Mazda could have exaggerated the factory tachs for bragging rights, advertizing (8000 rpm redlines..) etc????
Not exactly unthinkable!!!
I stumbled across a strangely dark, yet very possible theory....
Does anyone think Mazda could have exaggerated the factory tachs for bragging rights, advertizing (8000 rpm redlines..) etc????
Not exactly unthinkable!!!
10-09-02, 12:16 AM
#10
Damaged Little F*cker
Join Date: Mar 2001
Location: High Point, North Carolina
Posts: 840
Likes: 0
Received 0 Likes
on
0 Posts
no factory tachometer is 100% accurate. the AFC is the one that is right. ive done a little work on piston engines, using an external tach under the hood and the stock tach is always off. oh and the external tach was calibrated. some cosmic tool that the shop had, mega expensive.
10-09-02, 12:25 AM
#11
If the S-AFC gets Its signal from the Crank Angle Sensor and the Tachometer gets It's signal from the Trailing Coil Pack how are they both right? Additionally, If there Is two different RPM sources, two different readings, than which Is right? If the trailing coil signal is more accurate than the CAS, than why Is It suggested to take the tach as the "real" RPM? They both collaborate In unision. I would think something Is not displaying correctly.
10-10-02, 11:58 PM
#12
Rotary Freak
cant believe this thread died. Mabey I can bring light to someting... At 8000rpms your sopose to be going 140mph I think according to a miata calculator. You can find any speed or gear ratio using it. 23inch tires 4.1 final and 2.00 fourth gear ratio you will be doing 140 or around thier at 8000 in fourth. My tacks rpm and speed are dead on but mabey their both related? anyways at 8000 rpm my S-AFC reads 7500 rpms.
10-11-02, 01:56 AM
#15
I came, I saw, I boosted.
Thread Starter
Join Date: Apr 2001
Location: Windsor, Ontario, Canada
Posts: 1,921
Likes: 0
Received 0 Likes
on
0 Posts
Von... same for me... a negligable amount of difference in the low end, but around 500 rpms difference at redline!!
On the stock tach I don't get 140 mph untill about 8500 rpms.... next time I hit that speed I'll look at the S-AFC tach....
PS. Where is the miata calculator?
On the stock tach I don't get 140 mph untill about 8500 rpms.... next time I hit that speed I'll look at the S-AFC tach....
PS. Where is the miata calculator?
05-05-03, 12:12 PM
#16
Senior Member
Join Date: Nov 2001
Location: Spearfish, SD
Posts: 725
Likes: 0
Received 0 Likes
on
0 Posts
My aftermarket tach is slightly faster than my stock (300 or so rpms) and so is my turbo timer. I get one signal from the trailing coil, which is the same as the stock tach and one from the leading coils output. And both the aftermarket tachs are the same signal. This leads me to conclude that the stock tach is just slightly inaccurate.
Thread
Thread Starter
Forum
Replies
Last Post
streetlegal?
New Member RX-7 Technical
13
03-17-22 02:46 PM
Coolant_Leak
3rd Generation Specific (1993-2002)
2
08-30-15 11:18 AM