Yes, but it's not for airflow. It's just for bumper support.

 

I tossed mine when I got my Kuruma Z bumper, and while my car isn't slammed it is pretty low. I've noticed spiderweb cracks on the sides towards the bottom and also one or two along the top edge of the front. I wonder if not having the foam's the cause of them. Luckily my front bumper just got backed into two weeks ago and my car will [finally] be in the shop next week hopefully.

I was told my a friend who works at an auto body shop that the shop that painted it just didn't prep it properly, but now I'm starting to wonder. Should I try and find some from a junk yard or something?

 

the paint shouldn't spiderweb bad from a simple bump and go, but that stinks . Prep is everything in painting!

 

It is possible the shop used the wrong paint. Usually bumpers are painted with flexible paint and if the shop didn't use this, that might be a factor.

It is possible that without the supports under the bumper, it flexed in far enough to damage the paint, but without seeing the location of the cracks and knowing if anything tapped it there, it's hard to say.

 

i have a kuruma z bumper and just like you had tha same problem....took it to a new shop to fix it and he stated that the first shop probably didnt use enough flex agent in the paint...had it redone by the new shop and have bottomed out and hit things do to be low, no cracks

 

Yeah, I doubt the foam will prevent cracks, sounds like the prep job was not sufficient..

 

Here are some pictures:




I guess all of that makes really good sense. The shop claimed that the polyurethane wasn't of good quality. I got it from Outcast Garage so I'm assuming it was good.
Someone in my local G/Z group does auto body and said that it was likely due to poor prepping so I'm going to go through him this time since I didn't know him before. I just got my insurance money today too!

Oh yeah. Believe it or not there are actually more spider cracks now than there were in that photo. I took those photos in early September. And yeah my car is fairly low (not slammed) but I can't imagine that happening with a decent paint job.

 

Looks like poor paint prep, lack of flex paint agent/.

 

You'r problem is not because you did not install the foam piece, but because you did not bend the aluminum brackets the foam sits on. So now when you travel at freeway speed, wind pushes your bumper against those brackets and you crack your pain where bracket touches the bumper on the inside (those are the cause of your cracks in the front).
Foam would not fit with aftermarket bumper anyway.

When you take off your bumper for paint. Make sure to bend those brackets (there are two on each side of the aluminum frame piece that sits behind the bumper). Also, if you do not secure your Kuruma bumper on the bottom, it will also crack paint on the mounting points up top. Best solution for that is to get aluminum under shroud.

Reason I say all that is because I had to paint my bumper twice before I figured what was causing the cracks.

As to answer OP question. You don't need that foam piece, but if you remove it, make sure bumper is secure on the bottom. If it's a stock bumper, stock OEM plastic shroud should do. If you go with aftermarket bumper. Aluminum shroud is a must. Aftermarket bumpers usually are lower and thus have more wind resistance and at speed they bend if not properly supported

 

These are the brackets I'm talking about.
There are 4 little squares held by rivets and two large ones with holes in them. Four little ones you can just grind rivets off and take them off. Large ones as far as I recall don't hold anything, holes just go through them to gives access to mounting bolts. On those I think I just cut the welds with cut off wheel and took them off making it flat as a rear one one. No more cracks since then.

 

Your picture leads to some dumb ad... But thank you for going into detail.

 

^imposibur. You must have some redirect bug in your comp.

It's a link to a bumper support pic from infiniti parts website. It should be displayed in the post.

 

Pic doesn't work at all to me. Whatever it's linked to does't display for me

 

Now it does not work for me too.

Oh well. You got the idea. When you pull the bumper cover off, you'll see what I'm talking about.

 

I can't see your picture either. But I guess I see what you mean.

In this picture:

It does seem like those corners would be touching the bumper. I've never given that any thought. I'll look into that prior to taking it to the shop. It's COLD here.
I do have the TollboothWilley under shroud which worked fine with my OEM bumper but the Kuruma Z sits lower so the tray's currently just sort of hovering above the back/bottom of the bumper.
I also made a front splitter/lip guard that sits directly on the bottom of the bumper that goes all the way across which I guess is a bit of weight pulling down on the bumper. It was intended to protect the bottom from scraping.


Sorry for the thread jacking OP.