Fiat x1/9 + bike engine challenge build

Post 101!

In honor of this post, let's make some goals:

1. 1500lbs with driver

2. 150 WHP (or 10/1 lbs/hp)

3. In attendance at the 2018 challenge

These are lofty goals but I think achievable. Let's start on the first goal - the weight. Doing some quick math-

• driver ~ 200
• engine/trans ~ 200
• all 4 corners of suspension ~ 220
• chassis ~ 510
• roll bar + fiberglass ~ 100
• wheels/tires ~ 200

That's 1330 so far, so that leaves 170 + whatever can come out of the chassis for things like seat, steering, fluids, reinforcement, pedals, gauges, windscreen, electrical, etc. I'll grab some of the known weights so we can get even closer, but I think for now saying I need to get 30 lbs out of the chassis is a good goal so we can have an even 200 for this stuff.

coexist said:

More bike parts for high performance

 

That thing is hilarious, but smoking crack for $3500. I did save the pic though as we are essentially doing the opposite... haha.

In reply to gumby :

Sent you a pm, let me know if you didn't get it.

Robbie said:

Post 101!

In honor of this post, let's make some goals:

1. 1500lbs with driver

2. 150 WHP (or 10/1 lbs/hp)

3. In attendance at the 2018 challenge

These are lofty goals but I think achievable. Let's start on the first goal - the weight. Doing some quick math-

• driver ~ 200
• engine/trans ~ 200
• all 4 corners of suspension ~ 220
• chassis ~ 510
• roll bar + fiberglass ~ 100
• wheels/tires ~ 200

That's 1330 so far, so that leaves 170 + whatever can come out of the chassis for things like seat, steering, fluids, reinforcement, pedals, gauges, windscreen, electrical, etc. I'll grab some of the known weights so we can get even closer, but I think for now saying I need to get 30 lbs out of the chassis is a good goal so we can have an even 200 for this stuff.

On the Q45 we dropped ~10 lbs a corner going with a smaller diameter coil spring and using aluminum spacers to set ride height .

In reply to Stampie :

That's a great idea! I will look into that. I would love to setup a single brake disk on the diff (or even use the sprocket as a brake disk) for the rear so I could dump the rear brake calipers and rotors for a large weight saving, but that isn't priority one two or three.

Some more accurate weights of things to go back on the car. No particular order.

1. Wheels are a little tire dependent but the wheels I plan to use with junk tires are about 40lbs per corner.

2. Steering gear (wheel, column, shaft, rack and pinion, inner and outer tie rods) was 35-40. That is part of my 170 "extras" bucket (or it's the 35-40 I just got by bringing wheels and tires from 200 to 160).

3. Roll bar is currently 35lbs, I will add a bit to that, but with 40 lbs of fiberglass I think 100 total for those two will be right on.

4. Engine was 120 in current state. Still needs basically everything bolted to it, so 200 total once I add in the mounts I will have to fabricate and the diff and sprockets I think is about right.

Robbie said:

In reply to Stampie :

That's a great idea! I will look into that. I would love to setup a single brake disk on the diff (or even use the sprocket as a brake disk) for the rear so I could dump the rear brake calipers and rotors for a large weight saving, but that isn't priority one two or three.

 

That is an interesting idea, I would just be concerned of the effects that would have on the engine. Like when you put a lightweight flywheel on, the engine can rev faster and is more responsive, but you lose torque. You may be thinking of some way of hooking it up that it might not have this effect, but how I am picturing what you are saying would almost be like adding a heavyweight flywheel, so it might not want to rev as easy. 

In reply to AWSX1686 :

Well, yes, any weight in the drivetrain is like increasing the flywheel weight. But adding a brake to the diff means you get to remove 2 from the wheels (one for each rear wheel). So it's a giant net reduction in drivetrain weight!

Just got caught up, this is going to be awesome!  Thanks to FSAE I have a little bike engine car experience- your chain is going to have a very limited lifespan being that short, which is fine, but plan for it.  You can extend its' life by running it in an oil bath, although that increases complexity a bit.  We ran 520 chain on a car which was sub-500lbs with driver and rarely (if ever) had failures as long as we replaced the chain at reasonable intervals, so you may be OK with 530 chain but again... it's very short, the beefier the better. 

Careful with the brake on the diff- make sure it's a pretty tight LSD or a spool if you want to go that route, since things get very weird if you have a torsen/open diff and lose enough grip for one wheel to lock.  It will also beat up the CV axles a bit more, but you're right about the big drop in unsprung weight.  If you want to run a sprotor, make sure it's beefy- interesting things happen when you get a sprocket hot enough to begin warping and then snap the chain tight with whatever the full torque of your engine is!

Robbie said:

In reply to AWSX1686 :

Well, yes, any weight in the drivetrain is like increasing the flywheel weight. But adding a brake to the diff means you get to remove 2 from the wheels (one for each rear wheel). So it's a giant net reduction in drivetrain weight!

True... And I was thinking of that as I was typing up my earlier post, but here's my counter thought: (And please, I'm just throwing thoughts out there, not trying to argue. I do like you idea.)

If you put the brake on the diff, (I'm picturing a brake rotor beside the drive gear or something along those lines) then that weight will have to spin 4.11 times more than rotor weight at the wheels. So it would give you an overall weight savings (depending on the bracketry required to make it work, but most likely) and would be a driveline weight savings, but I am pretty sure where the weight is in the drivetrain is going to make a difference. 

Think, upgrades (larger) brake rotors on your car are more unsprung weight, effects handling, isn't too noticeable in engine response. But if you take weight out at the flywheel, it is usually very quickly noticeable. Technically given the bike engine has a built in trans, your diff brake idea would be more like a heavyweight driveshaft, than a heavyweight flywheel, but still would have some effect I think. 

My main concern would be the bike engine in a car in the first place is asking it to pull more weight than it was intended to (Not that I think it's a bad idea, I love that too.), so I just wouldn't want to stress it or make it work any hard than it has to. 

Hopefully that makes sense...

In reply to AWSX1686 :

I think he's talking about putting the brake on the diff, not the coutershaft.  Think of it as being on the ring gear in a normal differential- so it rotates with the wheels.

¯\_(ツ)_/¯ said:

In reply to AWSX1686 :

I think he's talking about putting the brake on the diff, not the coutershaft.  Think of it as being on the ring gear in a normal differential- so it rotates with the wheels

Hmmm. Interesting idea. 

In reply to ¯\_(ツ)_/¯ :

Like in a mud truck?

Specifically like in this sort of FSAE diff:  

Or this:

or a Kart:

In reply to RevRico :

That one spins at driveshaft speed and would have the issue awsx mentions because the driveshaft usually spins faster than the axles.

I'm thinking more like a go cart.

In reply to Robbie :

But with sprotor!  

In reply to ¯\_(ツ)_/¯ :

Yes, that would be the dream. But I don't think we are going to have the space. It's gonna be tight already.

Maybe I will do inboard brakes on the diff output flanges. Could still use motorcycle rotors and calipers for weight savings.

In reply to Robbie :

That could work, although motorcycle rotors can be surprisingly expensive.  If you get a complete set of forks off a sportbike with dual front discs you might be able to get everything you need, then zero it by selling the forks, triple tree, and wheel.

Robbie said:

In reply to RevRico :

That one spins at driveshaft speed and would have the issue awsx mentions because the driveshaft usually spins faster than the axles.

I'm thinking more like a go cart.

Ahhh, ok. I was picturing in my head that the sprocket would be on the input shaft of the diff for some reason. Sounds like with your setup I don't think it would be too much of a concern then, besides any open vs LSD possible quirks as mentioned by ¯\_(ツ)_/¯ 

I hate to be the nay-sayer, but I predict a lot of time, money, headaches and issues for no measurable improvement other than cool points.  

you have such a massive undertaking, i would save unnecessary changes for after you are reliably on the road.  

jfryjfry said:

I hate to be the nay-sayer, but I predict a lot of time, money, headaches and issues for no measurable improvement other than cool points.  

you have such a massive undertaking, i would save unnecessary changes for after you are reliably on the road.  

I fully agree with you, and I am not currently treating the single rear rotor with any priority. Just something I would love to do eventually. 

Whacha doin for reverse?

coexist said:

Whacha doin for reverse?

Get out and push. Maybe I'll get an oar and put a little notch on the side of the car so the driver can row backwards.

I've considered building something with a parking brake handle that essentially does the oar thing from under the car, but again, that is WAAAY down the priority list.

What about using these for shocks? $80 for a pair. I have read about these for UJM bikes and if you properly charge them, they work pretty well. 

 https://www.ebay.com/itm/2PCS-Rear-Shock-Air-Absorbers-13-5-340mm-For-BMW-Suzuki-Universal-Motorcycle/252221649541?epid=3011029643&hash=item3ab994f285:g:6MUAAOSw9gRaApvd&vxp=mtr