What can I cutout?

[turbogrill]

Hi,

 

Being creative with the angle grinder and curious what I can cut out and still have the car operational. I am a little hesitant to remove stuff on the drivers side for safety focusing on passenger side.

 

Is this a bad idea:

 

1. A pillar to "frame" stuff

Cut out the red circle and attach the green line to the cage. I will keep a thin skin to the outside.

Is the intention with the  area marked red to provide support for the A pillar? (In case of a roll over).

Or is it to give structure to the front engine bay "frame rails"? (Where the bumper eventually sits).

(Passenger door is a skin only. Only cutting on passenger side now.)

There seems to be 2 layers, where the outer layer has some thick stuff to keep the door in place, maybe I just cut that. Especially if I can't connect the apiller to the cage nicely.

 

 

(Images from http://www.roadster.blog/2013/05/naked-roadster.html)

 

2. Door stuff

From what I can tell the read area is just to keep the door in place. Since I don't have doors it shouldn't matter. Will need to connect the shell to the cage somehow.

(Keeping driver door functioning)

 

 

3. Strip down the A-pillar + top window frame

Not sure how heavy it is but the frame holding the window seems beefy, since I got a cage I can probably strip that down. I do run a roof so will create a little hassle with that.

 

Feel free to share you pics of these areas if you have!

 

Many thanks

 

 

[LuckyKid]

I'll add my unsupported opinion that structural sheet metal is stronger, more rigid, and lighter than the equivalent tube cage.  I regret cutting as much as we did on our chassis. 

[Hurljohn]

easy answer, yes to all.  

[Hurljohn]

2 minutes ago, LuckyKid said:

I'll add my unsupported opinion that structural sheet metal is stronger, more rigid, and lighter than the equivalent tube cage.  I regret cutting as much as we did on our chassis. 

this is also true!

[turbogrill]

25 minutes ago, LuckyKid said:

I'll add my unsupported opinion that structural sheet metal is stronger, more rigid, and lighter than the equivalent tube cage.  I regret cutting as much as we did on our chassis. 

 

Is your concern that the chassis is more sloppy and less rigid and that might affect handling? Or that in an accident the car is less durable and might need more repairs?

[LuckyKid]

4 hours ago, turbogrill said:

 

Is your concern that the chassis is more sloppy and less rigid and that might affect handling? Or that in an accident the car is less durable and might need more repairs?

Rigidity as far as handling is concerned.

[Grant]

I think cutting out the stuff below the A-pillar was about 20 lbs for both sides. Actually heavier than the windshield frame itself, which was 15.3 lbs.



Do a better job at attaching your door than what was done above. Otherwise it will fatigue and break.

I agree factory sheet metal is more effective than a cage, all other things equal. However all other things aren't equal since 1) you have to have the cage anyway, and 2) in our case the cage is much higher than any factory sheet metal, closing in the otherwise open cabin. Our philosophy was to remove everything within the cage structure. As you know we removed the T-shaped brace down the transmission tunnel.

We ran out of time and did not remove anything where the doors latch. If you do, please take pics!

[Grant]

By the way, if you look in the two big rectangular openings behind the seats you'll see solid bars going... somewhere. I think maybe they land on subframe mounting points. We didn't remove them.

Edit: Actually maybe they support the factory roll bar? I should get in there with a borescope and have a look.

Edited January 10, 2022 by Grant

[turbogrill]

3 hours ago, Grant said:

I think cutting out the stuff below the A-pillar was about 20 lbs for both sides. Actually heavier than the windshield frame itself, which was 15.3 lbs.



Do a better job at attaching your door than what was done above. Otherwise it will fatigue and break.

I agree factory sheet metal is more effective than a cage, all other things equal. However all other things aren't equal since 1) you have to have the cage anyway, and 2) in our case the cage is much higher than any factory sheet metal, closing in the otherwise open cabin. Our philosophy was to remove everything within the cage structure. As you know we removed the T-shaped brace down the transmission tunnel.

We ran out of time and did not remove anything where the doors latch. If you do, please take pics!

 

My cage follows the factory A pillars, so all that 20lbs stuff is infront of my cage. If I cut it out I really don't have any good protection from impact, we have been hit there before. I think it's the typical "vortex of danger" hit zone

I might just clean up that area.

 

Will go after the door latch area and try and make sense of those holes. I have been peaking around but can't really figure out what is going on.

 

Thanks!

 

btw, there is something strange with your pictures. They only work for a little while

 

 

 

[turbogrill]

 

@GrantI wonder if that red "floor cross member" is what you suspected.

 

Edit. NVM those solid bars seems to go from subframe and up. 

Edited January 11, 2022 by turbogrill

[wvumtnbkr]

Weird, semi related question...

 

How much laptime is 50 lbs worth?

 

For example, on a track like NCM, is 50 lbs worth .1 seconds a lap when you are going after the last bit of weight?  

 

Or, to put it another way, is 2% of the overall vehicle weight going to make a noticeable impact?

 

I have generally left the sheet metal inside the car alone.  I have taken a pretty good shot before and didn't like how much the car folded WITH the stock metal.  Not sure what it would have done if I had taken structure out (especially at the door "junctions").

[turbogrill]

1 hour ago, wvumtnbkr said:

 

I have generally left the sheet metal inside the car alone.  I have taken a pretty good shot before and didn't like how much the car folded WITH the stock metal.  Not sure what it would have done if I had taken structure out (especially at the door "junctions").

 

Good point.

I think I will focus on some of the "inside the cage" and other stuff first and maybe come back to this later. We are still >1s between drivers. Ideally I would need a different cage design and I don't want to mess with that.

 

[TiredBirds]

We gutted the hood, doors, deck lid, roof, cut out some of the material on the b pillar. we shaved a ton of weight off the car. (88 Firebird) The door bars alone weigh 30lbs. We also removed most of the wiring harness, that thing weighed a ton. I was shocked how heavy it was. 

[Grant]

18 hours ago, wvumtnbkr said:

Weird, semi related question...

 

How much laptime is 50 lbs worth?

 

For example, on a track like NCM, is 50 lbs worth .1 seconds a lap when you are going after the last bit of weight?  

 

Or, to put it another way, is 2% of the overall vehicle weight going to make a noticeable impact?

Back when Bosch LapSim had a free version I ran some simulations with weight. Where it is makes a huge difference. Removing weight from the rear axle of a powerful RWD car often results in no benefit at all. Removing weight from the front axle of a powerful RWD car has about twice the benefit of removing it from the CG. I mention powerful cars because they're in the same boat as Champcars when it starts to rain. You want a lot more rear weight, or better yet downforce, when surface friction drops.

 

This is echoed in my own personal testing. In a powerful RWD car I usually don't see lap times drop as fuel level drops. My NC however gets noticeably faster - or maybe I should say more noticeably slower when it goes from an empty tank to a full one.

 

Weight off the driver's side is also worth more. LHD cars pull more gs turning left than right - measurable even with my old 10 Hz PerformanceBox.

NCM is a long track. In my car 50 lbs is 2.2%. That's 2.2% less acceleration everywhere, and maybe 0.004 g less grip. It's hard to measure magnitudes this small, especially as temperature and wind vary, but if this weight is at the CG I bet it's worth 6 tenths or so.

Edited January 12, 2022 by Grant

[wvumtnbkr]

47 minutes ago, Grant said:

Back when Bosch LapSim had a free version I ran some simulations with weight. Where it is makes a huge difference. Removing weight from the rear axle of a powerful RWD car often results in no benefit at all. Removing weight from the front axle of a powerful RWD car has about twice the benefit of removing it from the CG. I mention powerful cars because they're in the same boat as Champcars when it starts to rain. You want a lot more rear weight, or better yet downforce, when surface friction drops.

 

This is echoed in my own personal testing. In a powerful RWD car I usually don't see lap times drop as fuel level drops. My NC however gets noticeably faster - or maybe I should say more noticeably slower when it goes from an empty tank to a full one.

 

Weight off the driver's side is also worth more. LHD cars pull more gs turning left than right - measurable even with my old 10 Hz PerformanceBox.

NCM is a long track. In my car 50 lbs is 2.2%. That's 2.2% less acceleration everywhere, and maybe 0.02 g less grip. It's hard to measure magnitudes this small, especially as temperature and wind vary, but if this weight is at the CG I bet it's worth 6 tenths or so.

Wow!  I wouldn't have expected that!  Hmmm...  maybe time to actually go after some of the more difficult weight to remove....

[mcoppola]

7 hours ago, Grant said:

In my car 50 lbs is 2.2%. That's 2.2% less acceleration everywhere, and maybe 0.02 g less grip. It's hard to measure magnitudes this small, especially as temperature and wind vary, but if this weight is at the CG I bet it's worth 6 tenths or so.

Interesting that this seems in line with Troy's comments a few years back that weight reduction is worth 1 second per lap per 100 lbs on (most) tracks.

 

 

 

 

Edited January 12, 2022 by mcoppola

[Grant]

10 hours ago, wvumtnbkr said:

Wow!  I wouldn't have expected that!  Hmmm...  maybe time to actually go after some of the more difficult weight to remove....

Derp I had the magnitude off in my g guestimate... I think it's more like 0.004 g less grip. Roughly 1.5% per 10% weight. Impossible to measure with 50 lbs added, but I have experimented with passengers in street cars. I've seen 1-2% less grip per 10% weight added, but the 1% figures are typically passengers adding weight to the inside, so the real figure might be 1.5-2%. Or more if that weight is on the outside of a corner.

 

Of course the key to my NC is that it's light enough that I can run softer tires, which has a bigger impact on grip than weight reduction alone IMO.

 

The straight-line effect is easier to see. Whenever I start out with a full tank of gas, the real-time delta-T readout in my dash always ticks up (it reads hundredths) in the straights. Doesn't matter how well I exit a corner, I still end up losing time.

Edited January 12, 2022 by Grant

[Hillar K]

On 1/10/2022 at 5:52 PM, Grant said:

I think cutting out the stuff below the A-pillar was about 20 lbs for both sides. Actually heavier than the windshield frame itself, which was 15.3 lbs.



Do a better job at attaching your door than what was done above. Otherwise it will fatigue and break.

I agree factory sheet metal is more effective than a cage, all other things equal. However all other things aren't equal since 1) you have to have the cage anyway, and 2) in our case the cage is much higher than any factory sheet metal, closing in the otherwise open cabin. Our philosophy was to remove everything within the cage structure. As you know we removed the T-shaped brace down the transmission tunnel.

We ran out of time and did not remove anything where the doors latch. If you do, please take pics!

Would like to see the picture. Any chance of uploading it again.

[MMiskoe]

23 hours ago, mcoppola said:

Interesting that this seems in line with Troy's comments a few years back that weight reduction is worth 1 second per lap per 100 lbs on (most) tracks.

 

 

 

 

Well........  Not entirely.

 

It is hugely dependent on the type of track.  If you have to pick between 100# or 10 HP, at Daytona I'd take the the 10hp.  At Thompson, I'll take the 100#.

 

 

[mender]

And adding 30 lbs of aero might be worth 100 lbs of weight reduction.

 

This series is interesting:

https://yousuckatracing.com/2021/11/08/rwd-vs-fwd-part-1/

Edited January 13, 2022 by mender

[Grant]

14 hours ago, mender said:

And adding 30 lbs of aero might be worth 100 lbs of weight reduction.

 

This series is interesting:

https://yousuckatracing.com/2021/11/08/rwd-vs-fwd-part-1/

As grip drops, static weight and/or downforce on the driven wheels becomes more important. So it's weird he'd start with a stock 90s Miata on 90s tires... No one who cares about lap times would drive something like that.
 

On 1/12/2022 at 12:42 PM, KGRacing said:

Would like to see the picture. Any chance of uploading it again.

Try this link?

[Ray Franck]

   And before someone else hacks off a major portion of ther car using the rule that says 60% of the body must remain, it DOES NOT say you can remove the frame.  And for those that say well mine is a unibody just roll over to your parts counter and you will find that the things that support front and rear are called frame rails.  We rely on these frame rails as crush zones that were designed to absorb impacts If they are not there to do that in a crash the energy is transferred directly to the driver's body. 

   Some have done this in the past but that day is gone and we will not allow such practices as we move foreward. 

[Bill Strong]

On mid-engine and rear engine cars, sometimes those reinforcements behind the passenger and driver's seats are put in place to keep the engine from pushing forward in the case of a rear impact. They are designed to push components like the engine and transmission/transaxle down under the car. Or to rotate the assembly away from the people inside.
Basically, the reinforcements can delay the bending of metal long enough for the component to find an easier path to move forward, which could be down.

 

Think about where those components go if your rental driver is racing backward towards a solid object like a cement wall at 100+ mph (161 kph for you Porsche peeps). Does the floor buckle? Thus causing the floor-attached seat to move forward towards the steering wheel?
Most of you don't run a floor-mounted roll cage tube between the main hoops.

[mender]

9 hours ago, Grant said:

As grip drops, static weight and/or downforce on the driven wheels becomes more important. So it's weird he'd start with a stock 90s Miata on 90s tires... No one who cares about lap times would drive something like that.

It's a sim exercise for comparison of weight distribution so the lap time isn't the priority.

 

[enginerd]

1 minute ago, mender said:

It's a sim exercise for comparison of weight distribution so the lap time isn't the priority.

GIGO ?