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More Gauge Questions

C

Crash Bang Alpine

Donation Time
Gentlemen:

Thank you guys who posted the part numbers. The throttle stuff and air cleaner is just a toll-free call to Jegs. The shift lever from Georgia is real nice and $39.00 to your door.

Here in the frozen north, we are rural enough to not have access to big auto stores and specialized shops. Can anyone recommend a shop that can do the conversion of the speedo and tach that Jose talked about? I called one shop and they wanted around $400.00 for that conversion. The price seems a little goofy when Autometer sells a (Smith's look-a-like) Cobra tach and speedo for around $200.00. (Google E-Gauge)

Thanks for your help!

Crash Bang Alpine.
 
B

Bill Blue

Platinum Level Sponsor
Cannot find the Cobra gauges at egauges.com, but did find them at the Autometer site. The tach will operate only on 8 cylinder engines.

Bill
 
Ken Ellis

Ken Ellis

Donation Time
Bill wrote:

"The tach will operate only on 8 cylinder engines."

If it's the one that looks right, then I'm sure there's a way
around that, electronically... (unless it's a mechanical tach... in which case, I'm sure there's a way around that, too!)

They might be willing to modify one for 4 cyl, too...

Ken
 
B

Bill Blue

Platinum Level Sponsor
Ken Ellis said:
Bill wrote:

"The tach will operate only on 8 cylinder engines."

If it's the one that looks right, then I'm sure there's a way
around that, electronically... (unless it's a mechanical tach... in which case, I'm sure there's a way around that, too!)

They might be willing to modify one for 4 cyl, too...

Ken
Click to expand...

Ken, don't see how number of cylinders would impact a mechanical tach. The exact wording from the site is "Operates on 4PPR, 8 cylinder engine ignitions ONLY". (Caps are theirs, not mine). Don't know what "4PPR" is, but I do know what "8 cylinder" is. "ONLY" is pretty definitive. All in all, don't think it looks good for the Alpine crowd.

Bill
 
S

sharong

Donation Time
Nisonger can convert and repair anything you have. I have a series IV that had a positive ground tach. I converted the car to V6 and Nisonger changed my existing positive ground tach to negative ground and calibrated it for the V6. My tach was from a very early batch so they actually had to replace the guts as the model I had could not be converted to negative ground. Total cost with new insides was $163.87. It will be $30.00 less if they can use your existing parts. They polish up the finished gauge and install all new gaskets and it looks like just like new when you get it back. Took them about 3 weeks to do the job, that includes the shipping there and back. I am very happy with the work they did for me. I have a full dash set of gauges, all matched and I wanted to keep the set together so I opted for the tach conversion rather then getting new gauges for the dash.

http://www.nisonger.com/

Sharong
 
Ken Ellis

Ken Ellis

Donation Time
Bill,
As sharon noted above, if there's an outfit that specializes in repair an mods, they would be the first to turn to.

re: your comment:
"Ken, don't see how number of cylinders would impact a mechanical tach. The exact wording from the site is "Operates on 4PPR, 8 cylinder engine ignitions ONLY". (Caps are theirs, not mine). Don't know what "4PPR" is, but I do know what "8 cylinder" is. "ONLY" is pretty definitive. All in all, don't think it looks good for the Alpine crowd."

I hear you on the first one. It's more the drive interface I was thinking of, but you're right. Revs is revs, if the drive output/input ratio is 1:1.

On the electronic tach... see what I get for not actually going to the website in question?

My guess is 4PPR may indicate four pulses per revolution, so the tach might divide by 4 to display the rpm. If so, it's counting (6000 x 4) /60 = 400 counts per second at 6K rpm, which is reasonable. (The word ONLY is in all caps just to challenge me, personally.) I'll look later on tonight to see what signals the thing actually counts -- could be LV (12V) 'square waves' from the coil/points interface. Or, pulses gathered by induction from HV sparkplug wires, both with some signal conditioning applied. Or, signals from a electronic ignition system. But some knowledge about the characteristics of the signal it has to count can be used to 'fake it out' for Alpine use. If they use a commonly available IC to drive the thing, chances are good that it is a 4/6/8 device 'hardwired' for 8. Re-hardwiring it for 4 may be possible. The part number plus current databooks will reveal it. More later.

Ken
 
Ken Ellis

Ken Ellis

Donation Time
Here's some stuff from the Autometer site's FAQ:

"Typically, a "Pulse" refers to an ignition firing, so another way to think of this is sometimes as Ignition Firings per revolution, though this is not always the case. For I/O Marine applications, 4, 6, and 8 cylinder applications are normally the same as automotive. Typically 4 Cylinder engines are 2 PPR, 6 Cylinder engines are 3 PPR, and 8 cylinder engines are 4 PPR."

The above was from a discussion re: marine tachs, based on auto engines.

The site says the tach wants to see 12V square waves at the above rate.

I think the following:

Each cylinder receives a spark every other rev. 2 PPR in the above terminology. While other tachs in their line are adjustable, the Cobra is not, in the hands of the schematic-free end user. However, the number of "contact tech support for special requirements" notes sprinkled throughout their website leads me to believe that they would at least entertain the notion of generating a factory-adjusted Cobra tach, suitable for 4 cyl use. (or 6, for that matter...) It can't hurt to ask, and I'd do that before buying a new one and dissecting it. (I couldn't locate schematics on their site, or quickly on the web.)

I've been thinking how to get 4 PPR out of a stock alpine, and I can't think of a reasonable way. Sure, an electronic black box could be made, but the ignition system is a pretty harsh electrical environment, and some actual design chops would be necessary for reliability and accuracy. It's not impossible, though.

They have a couple of adaptors, one that acts as a signal preprocessor/shaper, and another that is used for magneto engine applications. 9117 and 9118, which are worth a look. They also have a Hall effect trigger, but it didn't say if it was usable with the Cobra tach. If it is,
then one of those, with appropriately distributed magnets on the right rotating object would provide your needed signals. Just make sure they don't come off at 6000 RPM. Ouch.

Anyway, it sounds like it would be worth a note or phone call to discuss the matter, even in the face of the dreaded "ONLY".

Ken
 
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