Datsun Roadster: 2020 Challenge Build

Bigger tires/wheels could certainly give more ground clearance, but keep in mind, that will screw with the final drive. Being a motorcycle engine, I think that final drive needs to be just right. This can be made up for in gearing and such, but all of that may or may not incur unplanned costs to the budget. Also bigger wheels/wires = more rotating weight, and again, pretty sure the motorcycle engine will perform better with less. 

What is the engine out of? They generally have stainless version in other years that can be hqd for cheap and you can cut and weld back to what you need. Or: build a steel elbow that bolt between the head and header. Hat will rotate header pointing the rear.

It may be high but it will works. 

Soooo I hate to be captain obvious here, but... why don't you just move the motor back to where you had it? 

I mean, try your tipping idea first, but it seems like you actually introduced a big complexity item with the miscalculation of total clearance for the header. Unless your chain geometry got so much better it'll now clear the shift lever/rod setup?

I know this forum is the best damn bench racing forum in the entire internet, but 2.5" lower motor CG isn't a whole lot in the grand equation for ENTIRE car CG. Driver height still same, Datsun body height still same. I just feel like you inadvertently traded header clearance for intangible bench racing benefit of slighty lower total vehicle CG via motor going down 2.5"?

That make any sense? Lol

Also kidding on the 13" wheel solution, that was with with slight sarcasm.

Keep the smallest wheels you can. I'm putting way to much effort in to run 15s vs 16s. 

In reply to Stampie :

Gonna have to agree 100% Stampie. That alone is the biggest net benefit in CG, rotating mass AND budget friendly!

Also, just a heads up, I know this is a challenge build, but be wary of dbs the exhaust makes. SCCA will totally DQ you for sound with an open bike header, especially pointed skyward (as metal and gnarly as that would be). You're gonna have to test and tune the E36 M3 out of this before Florida. 

Low position: The header only interferes in one place, and that would probably be easy to fix. With engine this low, the interference is not the issue the possible slamming of engine into pothole is. I think the chain will work with no idler with this configuration, but it will be close, need to confirm.

High position: no header interference, no ground collision worry. The chain will absolutely not work without an idler setup. And due to extreme angles, even and idler might be tricky.

To be clear the high position is about 6 inches higher than the low position. And there really isn't anything in between because it makes the header interference worse AND the chain will need an idler.

Let's say that the engine is 150lbs on a 1500lb car. The 6 inch engine height change is a .6 inch change in vehicle cog. If the car's cog height is about 15 inches, that represents a 4% change. If my dreams come true and the car is 1000 lbs and the cog height is 12 inches, the 6 inch engine change is a 7.5% change in overall vehicle cog. Not saying that's big or small, just throwing the numbers out there.

You already know this, but I'll restate the obvious:. Avoid putting an idler on the tension side of the chain.

You're making good progress, keep it up

Keep in mind anytime you let off throttle the tension will be on the other side of the chain and it won't be insignificant. I would avoid idlers period.

I think the 2nd position (low) plus a timing-chain-style tensioner slider (or a piece of delrin?) running over the shifter shaft would do it. Grind away any other bumps or bosses on the engine.

In reply to Robbie :

Do you know how much your body weights?

Another vote to aim to keep the chain as simple, direct, and short as possible. 

Exhaust can be adapted one way or another. You could make one ouf ot mild steel if it came to it. Chains aren't nearly as flexible. 

Stampie said:

In reply to Robbie :

Do you know how much your body weights?

About 186.2 lbs, as of this morning. 

The datsun body is surprisingly heavy right now. But I will be cutting a lot out. I'm hoping for about 300-400 when finished. My wag is it's about 500 right now.

Frame and suspension with wheels and tires, currently 260, say 300 when roll bar added. Motor 150. Driver 200. Body @ 350 makes 1000 lbs.

maschinenbau said:

Keep in mind anytime you let off throttle the tension will be on the other side of the chain and it won't be insignificant. I would avoid idlers period.

I think the 2nd position (low) plus a timing-chain-style tensioner slider (or a piece of delrin?) running over the shifter shaft would do it. Grind away any other bumps or bosses on the engine.

I was thinking something like that. I might even have a used timing chain tensioner laying around from all my mgb stuff, I think the motorcycle motors use them too and I have a bunch of spares. That would be easy and budget friendly.

Got an hour last night before bed and another this morning. 86 total.

Snagged the rear subframe off and set it on the ground. Took some photos:

That board is exactly 1 3/4 inches. Interestingly, that is higher than the lowest point on the AMC (I can get 3 fingers under the header haha). 

And, when I get closer to final fitting, I can probably bend the header up slightly more to gain another 1/4 inch or so, if needed.

Also, while noodling on the engine height decision, I decided to start making the rear swingarm mounts better. Remember I drilled these funny? Well since I had the rear subframe off it was a good time to fix/reinforce.

The first step is to get rid of these ultra grungy rubbers 

Because I'm packrat extrordinaire, I still had the scraps of this rubber gym floor mat that I bought for the bed rails of the Saab.

This stuff is 2.39 /sqft on Menards website right now, and I used about 11% of a sqft, so let's call this 25 cents worth of material. Haha.

Setup a cutting station and cut some pieces:

So, leaning towards keeping it about there then? Seems like that'll work. Like you said, it's already more clearance than the AMC.

Back in my Formula SAE days, we would design the car expecting to touch ground once, maybe twice per lap for a autocross car.  Our frame hit first though.

Put on removable sacrificial rub strips on frame lower than the header.  Use Titanium or Magnesium for extra SPARKLE. Replace them often.

In reply to bOttOmfeeder :

That makes sense. It should be fairly easy to put a brace/shield in front of the exhaust. 

Works in Formula 1.....This could be you on the GRM cover......  find some Titanium chunks from scrap yard .....  a GRMer might know a cheap source

87 hours, got the rear swingarm mounts fixed and finished.

I had to move one misdrilled hole (facepalm), and then also I wanted something that would spread the suspension load, as well as hold the bolt to prevent it from turning. Remembering that suspension bump travel at these points is a pulling force, I grabbed a piece of scrap square tube.

Some cutting, (I did use a hacksaw, sometimes it really is the best tool for the job), and then mark the center for drilling.

And then some drilling, and you can see what I came up with. 

You can also see how much I missed the original hole location by. 

Quick lick of random old spray paint

Add the new rubbers and they don't look half bad. Also the bolts are held tight so I won't need to put a wrench on from underneath when tightening and loosening. Overall I'm really happy with this solution.

Hmmmm. Where can I find some sacrificial titanium? I do like the sparkshow.

In reply to Robbie :

How about a flange from a ruined sport bike header? 

89 hours. Made engine plate prototype number 2. Getting very close to happy with the placement of everything. Gotta take 1/2 inch off the rear of the plates and then I think we're golden.

90 hours. Took the half inch off like I said, also started doing the small jobs to prepare the engine cross braces for better mockups.

First I'm moving this adjuster to the outer position. It looks like it may have been originally here and moved in before.

Next I cut a hair off of the front slider. This is for header clearance.

91 hours. Engine placement looking very good.

I'll have to flip the rear sprocket around but there should be plenty of space.

And, of course, the ms paint engineering:

Looking good!