Datsun Roadster Forum-311s.org

Can a rev limiter me added to a U20 with the stock distributor? If not what’s the best option?

By far the easiest answer is a 123. Another great built in feature. In addition to true rev limiting, you can simply back off on the timing curve as you
rev too high, that way the engine pulls less strong as you get out of line and it begs you to shift.

Someone on FB asked about theft prevention too, also built into the 123. j

Jim, I have thought about the 123 distributor but I have no issue running with the stock ignition and the 123 is pretty expensive, though not as expensive as a blown motor. That being said, I have not ruled it out, however I see your website shows them to be out of stock. Do you know when they will be available and can one be purchased outright without a core?

I just need to order some more units and set them up. Typically just takes a few days since we normally keep them on hand anyway. I'm sure we can find a core unit for you if needed. My guess is though, once you tinker with and play with the 123system, you probably won't ever want to bother with weights and springs again..

It's kinda like comparing a slide rule to a programmable digital calculator. Sure they both work, but beyond that, there isn't really much comparison.

If cost is the main concern, I think I have an MSD box around here somewhere that I'll never use, some of those provide basic rev limiting and can be triggered with points. Much bigger pain to install though, and you are still relying on a points distributor with mechanical advance. Of course the 123 is a complete, brand NEW programmable distributor unit too, not just a rev limiter, so that accounts for the price difference.

Just as an aside, a rev limiter will not prevent over revving the engine if you downshift too many gears in one change.
If, for example, you are going from 5 to 4 and inadvertently select 2, the car will overdrive the engine regardless of any ignition cut and cause the same sort of damage.

Nissanman wrote: ↑Tue Mar 07, 2023 1:16 am Just as an aside, a rev limiter will not prevent over revving the engine if you downshift too many gears in one change.
If, for example, you are going from 5 to 4 and inadvertently select 2, the car will overdrive the engine regardless of any ignition cut and cause the same sort of damage.

2000 Toyota Celica GTS (Yamaha designed head, 8000rpm redline, VVT switched to high lift cams at 6000 and it reacted like a freakin scalded cat)... got on a long freeway on-ramp and wrapped that puppy to 8000... 1st! 2nd! 3rd! 4th...? uh oh... WHAM! Noooo! Missed the shift and went 3rd back to 2nd at 8000rpm. She's not happy now... limped it home with all 8 exhaust valves bent. Fortunately I had a good head repair shop; new valves and good as new (head gasket etc etc of course). Not sure you'd be as lucky with a U20. The Celica 6 speed was known to have close gates... yep. Good syncros too, slotted right in! As stated above, electronics won't save you from yourself...
That was a cool engine though...

Nope, you can’t insure every scenario, but you can lessen the odds. In my case on some of the longer straighter slalom sections I think my car with the short gears is nearing red line. Of course it’s right at the point that you need to concentrate on that last cone and there’s not enough time to focus on the tiny tach. You can hear some of the modern cars going braap, braap, braap as they hit their rev limiter. I’m afraid I’ll just hear BAM, CLANG, CLUNK!!

For sure Mike! As mentioned, it may be easier to add a spark box with a rev limiter. The most powerful/best output system I had before going crank-fired was an EI dizzy with a Jacobs Pro-Street ignition box with their Ultra coil. That thing gave multiple sparks at low rpm as well as sensing a "flame out" where it would re-strike the plug if needed. It really impressed me after I foolishly used some Autolite plugs that (two) literally lost their center electrode from the plug... the "gap" was huge, yet it ran just fine around town and would only misfire at higher rpm. I still have the broken plugs in my tool box just for fun. Unfortunately the company died with Dr. Jacobs, so MSD may be the best option. The Jacobs was nice because once installed you could simply reroute the coil wire back to a stock coil and run the car without the box if it failed (never did, traded it to a friend).