Rev Limiting Rotor, /4 motors |
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Rev Limiting Rotor, /4 motors |
914werke |
Oct 4 2018, 05:51 PM
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#1
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"I got blisters on me fingers" Group: Members Posts: 10,542 Joined: 22-March 03 From: USofA Member No.: 453 Region Association: Pacific Northwest |
how many still run the OE (& expensive!) rev limiting rotor? (IMG:style_emoticons/default/idea.gif)
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JeffBowlsby |
Oct 4 2018, 06:32 PM
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#2
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914 Wiring Harnesses Group: Members Posts: 8,663 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None |
Rich, I recall that the service and training manual lists the rev limiting rotor as only for the 1975-76 2.0L 49-state cars.
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Martin Baker |
Oct 4 2018, 07:03 PM
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#3
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I just heard I sold my cars! Group: Members Posts: 1,140 Joined: 11-February 03 Member No.: 290 Region Association: Northern California |
I have a 6500 in my 2.0, the engine has JE forged pistons and lighter pins. Works great!! Tested several times, OH WHAT FUN!!! I have several different RPM limits in cars I have parted out over the years...7300 in my 914/6 2.4 S Spec engine...it functions correctly as well! I thought they all came with a 5800 in the 4 cylinder types. I have a pile of the 5800 ones.
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914Sixer |
Oct 4 2018, 08:01 PM
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#4
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914 Guru Group: Members Posts: 8,988 Joined: 17-January 05 From: San Angelo Texas Member No.: 3,457 Region Association: Southwest Region |
Personally, I like them. It saved an engine for me one time. I had a throttle cable get hung open when the return spring got bent. Kept the engine and me from going to fast.
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Krieger |
Oct 4 2018, 08:27 PM
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#5
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Advanced Member Group: Members Posts: 4,754 Joined: 24-May 04 From: Santa Rosa CA Member No.: 2,104 Region Association: None |
I have for the last 16 years of autocrossing my four cylinder. I just drive the snot out of it and never look at the tach.
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ThePaintedMan |
Oct 5 2018, 02:23 PM
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#6
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Advanced Member Group: Members Posts: 3,886 Joined: 6-September 11 From: St. Petersburg, FL Member No.: 13,527 Region Association: South East States |
Got one in my track car after I got tired of trying to figure out how to get the MSD to work. Have used it several times and it kicked in perfectly. Though, the motor pretty much falls flat on it's face after 5000 anyways, lol.
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Dave_Darling |
Oct 5 2018, 05:46 PM
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#7
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914 Idiot Group: Members Posts: 15,048 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
I'm using it. If I didn't, my wife would zing the motor any time she autoXed the car. She hates the gear shift, so she just leaves it in 2nd and rides the limiter....
--DD |
Mark Henry |
Oct 6 2018, 07:14 AM
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#8
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Using the rev limiter as a shift light is bad practice. Loading and unloading the engine this way is very hard on the rod bearings.
Really the rev limiter is the lesser of two evils and is just a safety device that should be used sparingly. Most T4 engines the redline is about 400-500 rpm past the peak HP output. |
Dave_Darling |
Oct 6 2018, 10:35 AM
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#9
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914 Idiot Group: Members Posts: 15,048 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Yes, I know all of that. It's also hard on the exhaust because fuel loads up in there and lights off!! But I can't get her to shift the damned thing, so that's what happens. Fortunately she doesn't autoX it often, and doesn't usually run out of 2nd gear when she does, so it's not exactly frequent.
--DD |
Jamie |
Oct 6 2018, 01:02 PM
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#10
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Senior Member Group: Members Posts: 1,056 Joined: 13-October 04 From: Georgetown,KY Member No.: 2,939 Region Association: South East States |
Point of information here! I didn't know there was such a rotor, and I assume the original on my 73 has one? How does a rotor limit RPM at a certain redline? (IMG:style_emoticons/default/WTF.gif) |
Krieger |
Oct 6 2018, 01:44 PM
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#11
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Advanced Member Group: Members Posts: 4,754 Joined: 24-May 04 From: Santa Rosa CA Member No.: 2,104 Region Association: None |
A spring in the rotor stretches and grounds out the spark from the rotor at the appropriate rpm
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saigon71 |
Oct 6 2018, 01:59 PM
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#12
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Advanced Member Group: Members Posts: 2,006 Joined: 1-June 09 From: Dillsburg, PA Member No.: 10,428 Region Association: MidAtlantic Region |
I still use one.
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Martin Baker |
Oct 6 2018, 04:14 PM
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#13
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I just heard I sold my cars! Group: Members Posts: 1,140 Joined: 11-February 03 Member No.: 290 Region Association: Northern California |
To answer the question; yes they are marked. Each one of them that I've ever seen has the RPM limit stamped into the rotor itself. It's not hard to find or hard to read. It's very obvious.
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Dave_Darling |
Oct 6 2018, 06:03 PM
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#14
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914 Idiot Group: Members Posts: 15,048 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
How does a rotor limit RPM at a certain redline? Here's a photo of one: (IMG:http://www.914world.com/bbs2/uploads_offsite/cdn2.pelicanparts.com-121-1538870633.1.jpg) There is a weight mounted to a horizontal slider. A spring holds the weight in toward the center of the rotor, and centrifugal force pulls it out toward the outside. When the slide moves far enough, the metal contact on it touches the path that the spark would take, and instead shorts it to ground. (To the distributor drive shaft, actually.) This means the spark does not get sent out to a plug wire. Different weights or different springs will give you different RPMs that the spark gets shorted out. --DD |
914werke |
Oct 7 2018, 11:40 AM
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#15
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"I got blisters on me fingers" Group: Members Posts: 10,542 Joined: 22-March 03 From: USofA Member No.: 453 Region Association: Pacific Northwest |
Martin I assume you are referring to a /6 application as I was unaware there was more than one "limit" for /4 cars.
Is it possible to McGyver a /4 rotor with diff springs/weights, any BTDT? Like many I often use an aftermarket non-rev rotor, but recently tried to apply OE Rev limit rotor when installing a Pertronix unit (IMG:style_emoticons/default/headbang.gif) For the application you often have to "trim" the bottom of non-OE rotors to get everything to fit just right but that's not possible on the the rev-limit version due to its construction. (IMG:style_emoticons/default/sad.gif) |
Martin Baker |
Oct 7 2018, 04:23 PM
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#16
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I just heard I sold my cars! Group: Members Posts: 1,140 Joined: 11-February 03 Member No.: 290 Region Association: Northern California |
Here it it, it is a 911, 914/6 rotor but it works in the DJet distributor. I was told by a well known 914/4 road racer, who is also the builder of my engine, 6500 RPM was fine, as long as it was not sustained. The man is an expert. I trust him emphatically.
I am not sure how many different RPM limit rotors there are. But I can assure you there is nothing MacGyver about this rotor. Like I mentioned in my earlier post I have a box full of different ones. You can clearly see the RPM stamp of 6500 on this one. MB Attached thumbnail(s) |
Dave_Darling |
Oct 7 2018, 08:51 PM
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#17
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914 Idiot Group: Members Posts: 15,048 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
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914werke |
Oct 8 2018, 09:18 AM
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#18
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"I got blisters on me fingers" Group: Members Posts: 10,542 Joined: 22-March 03 From: USofA Member No.: 453 Region Association: Pacific Northwest |
You wouldnt, it didn't occur to me that 911's might use the same (or similar) part & have multiple vers.
Good tip, thanks Martin |
Martin Baker |
Oct 8 2018, 09:26 AM
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#19
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I just heard I sold my cars! Group: Members Posts: 1,140 Joined: 11-February 03 Member No.: 290 Region Association: Northern California |
You wouldnt, it didn't occur to me that 911's might use the same (or similar) part & have multiple vers. Good tip, thanks Martin You are very Welcome! I will dig out my box if you like to see what I have. I KNOW I have a few of them. I just took for granted they would work and threw it in there, you know VW/PORSCHE interchangeability is good very often! MB |
IronHillRestorations |
Oct 8 2018, 09:47 AM
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#20
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I. I. R. C. Group: Members Posts: 6,759 Joined: 18-March 03 From: West TN Member No.: 439 Region Association: None |
FWIW, both of my '74 1.8's, one purchased in '78 and the other in '79 had this kind of rotor. At 4 and 5 years old (when I got them), I know it doesn't mean they were delivered with them.
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