Datsun Roadster: 2020 Challenge Build

TurnerX19 said:

I am surprised to see the steering wheel behind the cowl. All the other photos made it appear to be 6" or more forward of that. This negates my previous post!

Well, the reality is it's right in between. Basically directly under the rear edge of the cowl.

It's something I'd been concerned about since the beginning of the build, since the roadster places the drivers back like right on the axle and with an engine behind the driver the driver has to move forward significantly (chain drive doesn't help either). I'm happy that it's not worse.

I will still probably bump that section of the cowl up a bit however, as 1-3 more inches for hand room would be good.

This is so freakin' cool.

Is the cowl vent area wide enough to gain clearance around the steering and shifter by simply removing some more metal and laying the corners back? Possibly add some structure back to the original firewall area above the chassis? Then place your NHRA air deflector further forward on the cowl to blend everything in.

I wouldn't even try to clean up that paint. wash it, clear it, full send.

as someone who's tried, and failed, to bring a BEC to the challenge, I've been so happy to see this thing come to life. rock the berkeley on.

Glad you have an upright fmod, mine would have me looking out the grill (not joking).

Gotta second on the patina preservation, add weathered race graffiti, clear and send.

Looking forward to a with body weight.

A few more hours yesterday and one this morning, and we have rear mounts!

Did some tricky cutting and folding to give the square tube mucho strength against crushing, and as a bonus it makes bolting a lot easier.

Next I welded it into the car and gave it triangulation.

Then, as we often have to do with cars, as soon as you've made one, you get the bonus of having to do the other side.

Good bonus because you get more practice fabricating, bad bonus because you're not making something novel anymore. 

Either way, it made me harken back to my roots on this build of cutting a tube from the old chassis, grinding it down to bare metal, and then fiting and welding it into place. These triangulation bars are the original front roll hoop supports, reimagined.

But now, drum roll please, the body is sitting entirely on the frame.

And that, my friends, is one way to mount a datsun roadster body to a formula car frame in one week. Took almost exactly 20 hours. I'm at 411 total right now.

But wait! Before I pay myself on the back, I notice a potential problem.

Even though these rear tires have a perfect tuck, since there is hardly any suspension travel I'm worried I won't be able to get the wheel off without lifting the body...

Ok, let me try to answer some questions. 

1. Yes, I can probably just cut the cowl area back and angle the corners. It's adding probably close to zero stiffness currently so I don't think I'd have to brace anything back. But I will still need a wind deflector for NHRA as you note. 
2. Patina. There is absolutely no time for body work or paint right now. So I'm glad you guys like it the way it is!! If it fits, it ships. 
3. Upright or layback. I'm not sure which kind this originally was. It had been modified away from F440 rules long before I got it, and then I lengthened the chassis another 9-10 inches, moved the pedals and wheel back significantly, increased the height of the roll bar, and so forth. But I should get a photo with a regular person for scale. The top of the doors are approximately halfway up between your knee and your hip. It's low. 
4. Weight. You and me both want to see the final weight. But simply guessing based on hoisting this body around I think the body is about 200 lbs, with much of it nearer to the front. We will see. 

Put the rear body mounts on pip pins if you need to raise it for wheel access.

Looks really awesome!  Nice work!

I think the car is just needs some vintage appropriate stickers, scuffed to the proper patina, and you are good to go.

Congratulations, watching this come together has been very enlightening.  Yes and educational too.

Thought you showed an easy body tilt setup where the rear end lifts up from a hinge in the front.  Seems like you already dealt with rear wheel access?

Cool cool cool project.

Would the wheels come off if they were aired-down?

RACEC4R said:

Just caught up.  48 hours in already!  Damn dude, don't do this to yourself!  I prefer not to know how big of a waste of time my car lyfe is (lol).

Over/under on total time invested?  Do you think you'll hit that magic 1000 hour mark?!

I'll place first bet.  I'm betting the following:

• Motor/ancillaries (exhaust, intake, etc) final fitted and mock mounted @ 70 hours
• Frame measured and stretched @ 130 hours (this includes roll hoop changes)
• Body fitted, trimmed, and mounted to tube chassis @ 200 hours
• Debugged/running/driving under own power @ 280 hours
• Finished product making first autocross debut @ 380 hours
• Final development making challenge debut @ 450 hours

You can beat those times like a drum, get it!

Also, please stop going to NY.  Killing the flow.

 

I remembered this post and I wanted to go back and look at it to see how you did. 

Now I'm a little creeped out to see how close the last two were... first autox debut was about 390 hours, and since I'm in the 4teens now the challenge number will be darn close too.

Witch! RACEC4R is a witch!

Sooo, this thing is gonna kill it at autocross.  Does it have enough speed to be competitive in drags?  Do you need bigger rear wheels for that portion?

Edit:  you could just change gears too.

My satisfaction in knowing how well I estimated time of project development milestones is palpable.

You'd almost think I was a professional or some such...

However, can confirm.  Am witch.

In reply to wvumtnbkr :

I don't have the spreadsheet for gearing, but I think it tops out around 110-120mph.  So it should go 12's with ease.  It's absurdly fast (about 8.5 to 10lbs per hp? Need to dyno it, lol), sequential no-lift-to-shift.  Just plant your right foot, get to 12-13k and bang gears till you're done.

Just don't make any sudden movements Robbie...I don't know if I have the cajones to pilot such a machine to those speeds.

Is this trans actually capable of doing no-lift upshifts?  I know it's back about 20 pages; the engine & trans is from a Honda CBR600 of some sort like an F3 or F4.  It will be interesting to see what the final weight will be.

pres589 (djronnebaum) said:

Is this trans actually capable of doing no-lift upshifts?  I know it's back about 20 pages; the engine & trans is from a Honda CBR600 of some sort like an F3 or F4.  It will be interesting to see what the final weight will be.

Usually the barrier to that (for a bike trans) is an ignition cut , not necessarily something with the trans itself. A very short power cut to unload the gears is all it needs. 

And this build included that?  I never no-clutch shift my motorcycles and I can't imagine the axle in this thing, let alone other parts, are going to like this sort of treatment.

In reply to pres589 (djronnebaum) :

Yep!  Robbie outdid himself and this feature is included with the build.

It is ignition cut to unload driveline via shift cable load sensor (I imagine pieziocrystal, but I can't comment on exact type).

I can 100% attest that it works, and works well.  Back straight of slalom I had it pinned and grabbed 3rd every run (launch in 2nd).  Feels like F1 car with RPM's singing and gears banging.

pres589 (djronnebaum) said:

And this build included that?  I never no-clutch shift my motorcycles and I can't imagine the axle in this thing, let alone other parts, are going to like this sort of treatment.

I mean, I guess it could be hard on the woodriff keyway? But it really wont be that much worse than drag launching it. I managed to explode a sprocket carrier (see below) on my Fmod and I would advise having a spare at hand, as well as keystock and files for dressing the keyway, but my failure was certainly an old aluminum part that had been lightened too much. As far as the axle itself, its gonna be plenty strong, the key will go first and for me, even a stronger sprocket carrier is a good failure fuse. 

When I say old part, this was on the car when I got it and went through several autocrosses with me and a decent roadrace history with the PO. It let go after I regeared it (from 150mph top speed to 89mph) and went from a belt drive with a solid rear sprocket to a chain split sprocket and on the 3rd or 4th launch. There was some fretting indicating that the part had been cracked prior and I didnt inspect/catch it in time. It now has a place of honor hanging on my wall and I intend to make a plaque for the wall with "offerings to the gods of speed"

Impressive.  

I think the thing to remember here is that it really isn't a "no lift shift".

The driver is doing that, but the engine computer is sensing the attempted shift and is lifting for you.

I'm using woolitch racing software (which is like hptuners for bikes) to reprogram the factory honda ecu. This allows you to setup a table of rpm and throttle position, with each grid space an amount of time in milliseconds that the engine kills the ignition during a shift. And you can do a different table for each gear change!

You do need the strain gauge that racec4r mentions to be the sensor to tell the engine when the driver is attempting a shift, but then the computer works the magic from there. It is slick and quite smooth.

Also, re drag race gearing, we might actually hit the top end. But honestly hitting the top end a few yards before the finish wouldn't theoretically really hurt your times that much. 

a 12 high drag pass (according to Wallace racing calculators) has an ideal MPH of 100-105. 

The stock 2009 CBR600rr seems to magazine test in the 10.9 second 1/4 range. and with a dry weight of 410 lbs, I guessed about 600 total with rider and fluids, etc. Adjusting that weight up to about 1000 lbs slows the 1/4 mile time to about 12.9 seconds. So I think 12s are possible, but we will need to drive it well.