Mallory Hyfire 6a Installed, CDI works great...tach on the other hand |
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Mallory Hyfire 6a Installed, CDI works great...tach on the other hand |
Aaron Cox |
Aug 26 2005, 03:01 PM
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#1
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
very smooth through the RPM range.... all with a blue coil. I have an ignitor coil to go in also......
But...as we all know...tach no workie with CDI.... and...as i read here.... 914world.com writeup on how to mod a tach.... finished soldering. now for reassembly... AA |
Aaron Cox |
Aug 26 2005, 03:06 PM
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#2
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
(IMG:http://www.914world.com/bbs2/uploads/blog-1125090312.jpg)
i suck at taking pics.... but... you jumper the initial signal resistor according 'agrump' |
Aaron Cox |
Aug 26 2005, 03:28 PM
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#3
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
update again...
tach mod works!..also.... late model black center tachs require no mod...they work right out of the box (black center vs silver center gauges) |
Allan |
Aug 26 2005, 03:37 PM
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#4
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Teenerless Weenie Group: Members Posts: 8,373 Joined: 5-July 04 From: Western Mesopotamia Member No.: 2,304 Region Association: Southern California |
Aaron,
When do your classes start? |
Aaron Cox |
Aug 26 2005, 03:39 PM
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#5
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
sept 19th - why? |
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lapuwali |
Aug 26 2005, 03:41 PM
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#6
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
That really is an Andy class picture... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)
Specifically, what's going on here is the old tachs depend on the fact that the pulses coming off the coil are spikey from noise (up to 30v or so), and there's a resistor at the signal in to limit these spikes. A better way would've been to use a Zener shunting the spikes to ground, but a resistor will do. The mod is to bypass this resistor, so the clean 12v square wave from the CDI boxes will trigger the tach. You'd have to do the same if you used the tach signal from an aftermarket ECU. The later tachs don't have this problem, perhaps because they went to a shunt diode instead of just using a resistor, which will work with either the 30v spiky signal OR the 12v square wave signal. No doubt they were responding to complaints from people trying to use aftermarket CDI boxes. |
agrump |
Aug 26 2005, 06:20 PM
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#7
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Member Group: Members Posts: 141 Joined: 13-November 04 From: Atlanta, GA Member No.: 3,103 |
Glad the mod worked for you.
I had problems using a hyfire with a bosch blue coil. I know others have done it without a problem but I ended up blowing up two boxes before giving up on the coil. It would work for about a week and then it would start crapping out. The coil I had had the built in resister from aircooled.net. The coil would get hotter then hell even without the hyfire, it may have been defective. Good luck! |
Aaron Cox |
Aug 26 2005, 06:22 PM
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#8
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
that sucks..... (IMG:http://www.914world.com/bbs2/html/emoticons/unsure.gif) it worked for 6 months straight with the mallory unilite.... (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif) (which is said to be tempermental if a coil is not the correct ohmage 1.4-3.0 ohms) i have a pertronix flame throwe 45k volt 1.4ohm coil sitting here..... should i try that? |
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Aaron Cox |
Aug 26 2005, 06:24 PM
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#9
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
Dean -
also - the tach mod works great....except at idle. tach jumps around and usually sits at 2000 rpm at idle, but any throttle and it is dead on! deciding if ill keep that tach, or harvest a late model tach guts.... (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) |
agrump |
Aug 26 2005, 06:28 PM
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#10
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Member Group: Members Posts: 141 Joined: 13-November 04 From: Atlanta, GA Member No.: 3,103 |
My blue coil worked fine with my unilite as well. Jake said he runs one of his cars with a hyfire and blue coil with no problem. I talked to Mallory about it and of course they recommended one of their coils. The guy I talked to did mention that he was working with someone else having problems with a blue coil. Check out Mallory's site, they have a tech forum that may have more info.
Not sure about the tach at idle, mine worked fine. |
MattR |
Aug 26 2005, 06:55 PM
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#11
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Advanced Member Group: Members Posts: 3,279 Joined: 23-January 04 From: SF Bay Area Member No.: 1,589 Region Association: Northern California |
Awesome aaron! Im glad to see it worked out for you. That tach looks purdy in your car (IMG:http://www.914world.com/bbs2/html/emoticons/wub.gif)
Have you driven the car with the CDI? Does it sound/feel any different? |
Aaron Cox |
Aug 26 2005, 06:56 PM
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#12
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
alot smoother.... no hesitation.... gee...imagine if i just jetted it right (IMG:http://www.914world.com/bbs2/html/emoticons/owned.gif) |
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Joe Ricard |
Aug 26 2005, 07:04 PM
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#13
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CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
Nope went with a monster tach from Autometer. Best 100 bucks I ever spent. Set the shift points and it is dead nuts accurate. Using Petronics flame thrower coil.
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maf914 |
Aug 27 2005, 07:19 AM
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#14
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Not a Guru! Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None |
James, Do you mean later 914 tachs or contemporary Porsche tachs? Would my 76 tach have the shunt diode? I am such a doofus when it comes to electrical stuff! (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) |
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Aaron Cox |
Aug 27 2005, 09:07 AM
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#15
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
Joe what ohmage coil??? i have a 1,5 ohm flame thrower coil to use... |
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xitspd |
Aug 27 2005, 09:25 AM
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#16
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Technology and Tradition 3.6 and 914-6 Group: Members Posts: 1,305 Joined: 17-November 04 From: Foothills of Mt. San Jacinto, CA Member No.: 3,136 |
(IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif) Damn Aaron, you have been a busy beaver with your teener! Your BLOG is very cool! Check out my tach, crank fire = no problemo....
Attached image(s) |
Joe Ricard |
Aug 27 2005, 10:47 AM
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#17
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CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
IDONNO, Ran great with points and now runs greater with Mallory, triggered by compufire. No resistors in line anywhere. most of the writing on the coil is worn off. |
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maf914 |
Aug 29 2005, 10:58 AM
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#18
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Not a Guru! Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None |
I'm bumping this one in the hope that someone knows about early versus late tachometers. (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) |
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lapuwali |
Aug 29 2005, 11:21 AM
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#19
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
Sorry, didn't see this. "Early" 914 tachs (w/ silver center button) v. "late" 914 tachs (w/o silver button). The changeover was in '74 or '75. ('76 = '75, they were all made in '75, just leftover inventory). I'm guessing on the shunt diode, btw. It seems to match what people see, but I've never pulled one apart to verify what's inside. |
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Aaron Cox |
Aug 29 2005, 11:56 AM
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#20
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
a little update.....
car runs fantastic. BUT.... every once in a while i get an intermittant NO-Spark and the engine begins to decel, and then a second later refires with a hellacious backfire. checked all the connections. 2 people ive spoken to suggest a bad ground, or a relay that controls the ingition (skline had a no ignition relay failure also (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) ) my neg, battery terminal did not have a place to hook up the negative lead from the CDI, so i grounded it to the engine block..... could this be the issue? |
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