Installing an aftermarket tach and shift light on a 98 Cobra

[rown4au]

Last weekend and the track it became quickly apparent that the track car needs a better tach and more importantly a shift light to avoid overrevving the engine as I briefly hit 8k rpm according to the factory tach on one of the straights by mistake. This leads me to think that either the stock tach is way off or the rev limiter may be disabled in the current tune (or both) but I am checking into that as well.

Anyway while I am waiting for the tach I ordered to show up from Summit racing (http://www.summitracing.com/parts/ATM-233911/) I found the install threads below other mustang forums:

http://forums.corral.net/forums/svt-dohc/240900-tach-signal-98-98s.html


http://www.corral.net/index.php/tech/interior/86-1996-1998-cobra-tach-install

The threads all mention tapping into the wires behind the stock gauges, this might be a silly question but will this not make the new tach as inaccurate as the current stock one as it will be feeding off the same signal? Or... are the internals in the aftermarket tachs that much better so they are more accurate?

[68fastback]

Nice tach!

...and cool tech article in the making :biggrin:

[Tommy Gun]

I installed a shift light, but that was a long time ago. I don't remember at the moment where it connected. :nonono:


There is no way your car revved to 8000 rpm. :surprised:

[rown4au]

I installed a shift light, but that was a long time ago. I don't remember at the moment where it connected. :nonono:


There is no way your car revved to 8000 rpm. :surprised:

I figured as much but I looked down on the front straight at TWS and that is what it was reading, I backed off immediately. I spoke to the previous Owner and emailed the shop that did the tune after they rebuilt the engine in 2008 and they are going to check the tune they have on file but the tuner's initial response was it should not have gone higher than 7500. So either the rev limiter is not there, not working, or the factory tach is way off.

[Tommy Gun]

I figured as much but I looked down on the front straight at TWS and that is what it was reading, I backed off immediately. I spoke to the previous Owner and emailed the shop that did the tune after they rebuilt the engine in 2008 and they are going to check the tune they have on file but the tuner's initial response was it should not have gone higher than 7500. So either the rev limiter is not there, not working, or the factory tach is way off.

Can you pm me the specs on your engine? W no bottom end work I'm afraid to take my car past 6000 rpm. 7500 rpm would really get me working the track.

I hope to build something stronger after getting through this year.

[rown4au]

Can you pm me the specs on your engine? W no bottom end work I'm afraid to take my car past 6000 rpm. 7500 rpm would really get me working the track.

I hope to build something stronger after getting through this year.

Sure thing PM me your email address and I will send you the specs I have on the engine from the previous owner's rebuild. Keep in mind however that this is a 32 valve cobra so even when it was stock the heads and rest of the valve train will be different than yours and I am pretty sure that this engine revved higher from the factory than the GT's as well.

[68fastback]

fwiw, I've punched my buddy with the 2001 Cobra in the arm more than once when he's lost concentration and hit 7800 rpm :yikes: ...that's 1000 rpm over it's 6800 stock redline but on a tune that had the limiter turned off (he's since had it turned back on) ...it's bone stock for except for a JLT CAI and custom tune. The 4.6 DOHC valve train is pretty stout and can handle revs well since the NA cams don't have much lift and are rather mild overall. At 7800 there was no evidence of valve float (thank goodness).

[Tommy Gun]

Sure thing PM me your email address and I will send you the specs I have on the engine from the previous owner's rebuild. Keep in mind however that this is a 32 valve cobra so even when it was stock the heads and rest of the valve train will be different than yours and I am pretty sure that this engine revved higher from the factory than the GT's as well.


Ah, I forgot what exactly you ad. It makes sense now.


I can still take you though. :flex:


:lol:

.

[Carnut]

Tapping of the factory tach signal wire is the best place. I did it that way on my 98 Cobra, it worked fine for a shift light.

Factory tach was always accurate. You might think about just adding the shift light.

[hellfyr]

Tapping of the factory tach signal wire is the best place. I did it that way on my 98 Cobra, it worked fine for a shift light.

Factory tach was always accurate. You might think about just adding the shift light.


Was thinking exactly this. My autometer DPSS and the factory tach agree **** near dead on. The integrated shift light with the DPSS is nice though for sure. Unless like me you just ignore it and bang the 7800 limiter anyway.

[rown4au]

Was thinking exactly this. My autometer DPSS and the factory tach agree **** near dead on. The integrated shift light with the DPSS is nice though for sure. Unless like me you just ignore it and bang the 7800 limiter anyway.

Hmmm ok I spoke to the tuner and he insists that the rev limiter is set at 7,500 RPM and the previous Owner did not change the tune. If my factory tach was accurate then I am sure I would have heard it hit the limiter and it most definitely did not. He also said it is not uncommon for the factory tach to be as much as 250 RPM off at idle and much worse at higer RPM's so he was of the opinion that I am off at least 500 RPM near redline.

In any case to be safe, the tuner is sending me a revised tune with the limiter set to 7,250 that I will reload in the car when I pick it up from the shop. I figure if I set the shift light at 6,500 that should be about right and keep me from bouncing off the limiter and having something go pop.

I have to have my front fenders rolled by a local race shop this weekend so am going to have them install the autogage tach I purchased from Summit while they have the car. Realized after the fact that maybe I should have sprung for the Autometer tach instead but I am guessing it will be fine for my application.