Datsun Roadster: 2020 Challenge Build

Robbie said:

Imagine launching on the drag strip and having the computer rattle off 3 or 4 perfectly timed upshifts all while just leaving the throttle matted. Like I could probably make that happen for $60ish.

Fan-friggin-tastic! Only on GRM. 

In reply to Fladiver64 :

If you have a 1 inch cylinder, 80psi is greater than 60lbs of shift force. 

I don't know how much force you can apply by lifting with your left foot (I'll try to test quickly, hahaha), but I'll bet it's nowhere close to 60lbs. 

So, using that, I think any old small air container that can hold a reasonable volume at 100 psi or so would do the trick. Pump it up in pit with a bike pump. You could even get tricky and pressurize a small portion of the frame or roll cage if you're feeling lucky...

Edit, since I'm working from home, I just called my kids up to help. Had them stand on my left foot, and I lifted. Lots of effort but I was able to lift them. Then we went to the scale, one is 43 lbs and the other 40. So I think motorcycle shift effort is less than 40 lbs. Probably 15-20 lbs at most.

In reply to Robbie :

We used a paintball gun tank on the FSAE air shifter.

¯\_(ツ)_/¯ said:

In reply to Robbie :

Having tried the air shifter thing on an FSAE car, I'd recommend taking the time and money you would have spent on that and using it to practice your launches and shifting instead- you can flat shift by preloading the shifter and letting the rev limiter do the "throttle lift" for you, and with the right technique (easy to teach a human, hard-ish to teach a computer) it's fast and repeatable.  There's a lot of "just pull a little further until you feel it" or "ooh that's light under this load/engine braking/whatever" that you do pretty naturally when shifting a dogbox manually, which translates into a lot of false neutrals and crashy shifts when you try to program a computer to do it.

That's excellent feedback for when I get that far. I hadn't really considered letting the rev limiter be the throttle lift, that's smart.

In reply to Robbie :

Don't forget Calvin's $20 2-step. I feel like it might come in handy when you're trying to tweak your shift points. 

Reach out over on mcarterbrown.com forums for a cheap tank. There are ALOT of paintball equipment hoarders that can help you piece together a tank/regulator to make air shift happen.

In reply to E_NinjA :

Good idea on the paintball tank. A quick search of eBay shows plenty in the $30 range.

In today's news, I spent some time finessing this tube in here. It's close, but I still need a bit more fiddling, and I need to weld more on the existing joints before I weld this one in.

135 hours.

AWSX1686 said:

In reply to Robbie :

Don't forget Calvin's $20 2-step. I feel like it might come in handy when you're trying to tweak your shift points. 

Apparently I've already forgotten about that... Or missed it completely to begin with, how did it work? Some sort of circuit on the rpm signal that cuts coil power?

In reply to Robbie :

I did a quick search on paint ball gun tanks as well, because we might have a use for an air operated device. It looked like they are charged to 3000 psi (same as a scuba tank) and the first stage regulator said 800 psi on the few I looked at. That would mean you would need an additional secondary pressure regulator. Filling them would also require a paint gun compressor or a scuba tank to get them up to pressure. 

How about a piece of 4" pvc with end caps build into a small tank and filled from an air compressor. I think we would have space on our car for a small air tank but could be a challenge on yours.

In reply to Fladiver64 :

If you're fabricating an air tank, I bet old fire extinguishers that have lost their charge can be had for free- lop the valve assembly off, weld on the bung of your choice.

In reply to ¯\_(ツ)_/¯ :

The top screws into many of them ;)

You don't need to charge the tank to 3000 psi. Just charge it to 130 or whatever your compressor does. 

If you're looking for a really cheap air tank, put caps on both ends of a pvc pipe and slide it inside a frame rail. The PVC shouldn't take huge pressure, but that's why you're putting it inside a metal surrounding. Or just weld caps on a metal tube.

Old fire extinguisher is a fine idea too.

In reply to Robbie :

I think the problem with charging a paint ball air tank to 130 psi is that it will not hold any appreciable volume, they seem much smaller than a fire extinguisher. Guess it depends on the volume of air needed to activate the cylinder and the number of times per lap it may need to be activated. Sounds like a good excuse to do some experimentation.

I like the fie extinguisher idea as I might even have a couple around. 

Robbie said:

AWSX1686 said:

In reply to Robbie :

Don't forget Calvin's $20 2-step. I feel like it might come in handy when you're trying to tweak your shift points. 

Apparently I've already forgotten about that... Or missed it completely to begin with, how did it work? Some sort of circuit on the rpm signal that cuts coil power?

My quick explanation probably won't do it justice, but I'll try.

Cheap aftermarket tach w/ shift light. Use shift light power to trigger solid state relays to quickly be able to cut coil power.

In reply to AWSX1686 :

Oh that's berking genius. Luckily for me, the gsxr stock cluster comes with a programmable shift light built in. So maybe I can intercept the signal.

In reply to Robbie :

Calvin is a genius!

Might need a transistor or some kind of "step up", but the output that should light up a light could drive the positive side of a relay coil. Ground negative side.  The tach should be a great starting point for this.

Can we get a diagram or link to the right parts? 

In reply to AWSX1686 :

Thanks! Wasn't familiar; was gonna ask, but you got done. Thanks to Calvin, also. Cool thought.

Dusterbd13-michael (Forum Supporter) said:

Can we get a diagram or link to the right parts? 

I'm going to guess at some reverse engineering here, but I think you could get something like this $18 shift light:

https://www.amazon.com/RICO-Instrument-Adjustable-0-10000-housing/dp/B07BQQL2NY/ref=sr_1_2?dchild=1&fst=as%3Aoff&qid=1585836241&refinements=p_85%3A2470955011%2Cp_36%3A1253493011&rnid=386419011&rps=1&s=automotive&sr=1-2&th=1

and also this $7 (well, 14 for two) DC to DC solid state relay:

https://www.amazon.com/TinaWood-SSR-25DD-Solid-State-5-200V/dp/B07F3WGRP4/ref=sr_1_18?dchild=1&keywords=dc%2Bto%2Bdc%2Bdc%2Bsolid%2Bstate%2Brelay&qid=1585837084&s=industrial&sr=1-18&th=1

And basically intercept the light output to be the input to the relay. Use the relay output to shut off the coil.

What's annoying is that it doesn't seem like normally closed solid state relays are cheap or common, but normally open ones are. So you might have to do some trickery to flip its operation. Probably best is to 'invert' the control signal so that when the light comes on, the control voltage on the relay disappears, and then the relay shuts opens the power or ground line to the coil. I'd think that any old regular relay would work instead of a SSR (and you could use the NC contacts), but may not last that long with all the switching that would be needed. I'll draw up a circuit here in a sec.

I drew two circuits, one for normally open relay and one for normally closed. You can see I even screwed up the normally open option initially.

Now, what this would do is limit the engine rpm to whatever the shift light is set to come on at. So you would also need a system to shut the two step off when you actually want to go (and leave the coil on, haha). I think in both cases you could just put a switch in between 12v and the shift light. Switch closed means 2 step is active switch open means 2 step is off and coil is still powered.

Or do like the off roaders and make your tubular frame (or part of it) the air tank.

Is this it?

That looks right. In that video Calvin is essentially doing exactly what I drew up, except he is doing it 8 times (one for each coil). It does look like Calvin is using the SSRs to cut signal to the coil and I was thinking of cutting power to the coil. That said, I think it is probably a lot easier on the coil to just interrupt the signal. Not to mention a lot less potential for voltage spikes back through your electronics caused by turning a coil on and off repeatedly.

Thank you guys for bringing this up. I 100% will use this on the datsun or some future car.

Don't build your own pressure tank.  In some areas it's illegal to do that.  (Like all 50 States I believe). The exception would be using commercially available pressure rated components in their approved layout.  So PVC pipe with unmodified endcaps and maintained Bellow the rating.  ASME code section VIII covers pressure vessel fabrication and it's one of those codes that isn't because we wanted standards it was developed to keep people from dying.  There are entirely to many off the shelf high pressure certified vessels for you to mess around with building one.  A Fire extinguisher is a decent option.  Also C02 cartridges for soda machines may work.  Small oxygen or nitrogen bottles (like the size of MAP gas) from welding rigs are available from Most home stores and would also be a good source as would paintball guns.