Hi everyone
When I replaced the engine for the FIRST time, I did not install the plastic belly pan. After breaking in the replacement engine, I did a high-speed run on the interstate.

Around 110 mph the front end felt light and needed more steering input then what I had originally.

I put the "engine under cover" back on and the light feeling front end ceased, it was back to normal, rock steady!

Now as I get ready to install the next replacement engine I came across this:




It is an aluminum bottom pan, only used on JDM cars.

I am hoping for even better hi-speed handling.

So, two belly pans are better than one?

 

That one's in great shape. They were on a few models but the infini had em too in Japan. I haven't put mine on since it isn't compatible while also using the under support bar (whatever you call it). Cool find.

 

The plastic belly pan is very important for proper airflow into the radiator from the bumper opening as well as proper aero passing under the car. Additionally that aero plate under the oil pan helps decrease drag coefficient slightly as well. There is an aftermarket version that I use from LRB products. The fit and finish is very good.

-M

 

I think that silver pan came on my car when I got it 2nd hand, didn’t think it’s jdm specific. My car is a 88 gtu. Thought I heard it’s part of the aero package or something.

but yes, it’s been well documented the plastic under tray (or equivalent) is required for proper cooling. Just went through the same thing with my sti.

 

Lrb speed makes pieces for each, if cant source originals. The smaller one was part of a aero package.

 

They came on 10th Anniv cars (maybe others) from what I know, have one on mine.

Greg O.

 

My 10th Anniversary RX-7 has an aluminum belly pan. What funny is that i had an early Porsche 944 and it had an aluminum belly pan. My late 85 Porsche 944 has a plastic belly pan. I much prefer the aluminum pans and was excited to see it on my 10AE!

 

If you have either or both of these pans, install them. As part of the Aereo package on certain models they do make a large difference at high speed.

In certain competitions they are banned due to the unfair advantage they give.

I watched an Utube video of a run with a very hi-performance rotary, the cockpit video camera captured the bucking up and down at top speed. The first thing that occurred to me was that he didn't have any belly pans and all that fast air was getting into the engine compartment and causing the lifting of the front end!

What do you think?

 

Yes I could imagine not having the main plastic under tray creates front end lift, and the aluminum one helps reduce front end lift even more.

I was also impressed by the effects of an aftermarket front lip, but that’s getting off topic.

I have a 06 Subaru sti which I got 2nd hand and it never had the front undertray. Was seeing some weird temps ~40-60mph so I finally got one and it drove way differently, could tell less front lift, more stable at highway speeds and fixed my temp issue.

 

I know an factory upgrade to the front stock lip was available. Does it have a noticeable effect on high-speed handling?

If so, I will have to try to find one and install it!

 

Sorry, didn’t mean to go on a tangent. I never tried the stock front lip, but I did have a corksport odura front lip for s5 which is more aggressive.

Drove 2 hours on the highway to a rx7 meet & uninstalled & sold the lip there. Then drove 2 hours home and I was surprised how much more floaty the front end felt. So I’m a believer in effective aero upgrades.

 

Mentioning about the front lip segways in perfectly with the belly pans.

How about the effects of adding that mini spoiler to the top of the hatch? Or is it just for looks?
At 140 mph everything matters!
I need to install hood hold downs, my friends Duster had his hood fold up on the windshield at top speed!
Sliding along the guardrail saved his bacon.

Oh, officer, I was just blowing the carbon out of my engine, I don't think my car can go that fast! It's just a little 1.3 liter!

 

Definitely recommend hood pins, I’ve had my sti hood pop from locked position getting onto the freeway. I run locking aerocatch pins on my fc & sti, plus I can see if they are open from the driver seat.

I’ll defer to others on the effect of the stock duckbill wing, but in theory it should reduce drag by reducing the vortices shed off the top of the car. The s4 aero package also had little black plastic pieces which mounted on the side skirts in front of the rear wheels. I believe s5 t2 had clip-on side skirts & a stock front lip.

I’ve ran the re amemiya type iv wing (This one) but it was more of a wing than a spoiler, definitely felt the rear held down. On certain freeways with harmonic bumps without the wing the rear would porpoise. With it, the rear stayed planted over those bumps. Just found that an interesting observation.

so again, I’m a believer in aero mods. It’s a balance of getting them to work together to balance out the feel of the car. My sti has all stock aero pieces (sti wing, sti flat floor pieces, roof vane spoiler, side skirts, stock diffuser) , but now I’m interested in little enhancements (subtle aftermarket lip & diffuser, vortex generators).

One thing I’ve noticed is to watch the newer electric cars vs traditional daily driver sedans in the rain, and you can see how much more pronounced the spray of the rain off the rear top & bottom are from the ev’s aero (flat floors, rear diffusers, spoilers). Gotta nerd out every once in a while.

If the stock aero parts aren’t ridiculously priced, I’d say try them out, especially if you’re going for that subtle oem+ look. Or could get into the aftermarket for more aggressive aero effects. The more you f around, the more you find out.