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Old 01-25-2006, 03:22 PM   #1
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Need some ideas for my front undertray

Told MetroMPG I would get these a while ago, so here they are. This is the front of the CRX. What do you think about a front undertray? Planning on using some linoleum flooring that's about 2 foot wide and screwing it right up to the front. Does that sound good? Any input appreciated. What about some blockage on the front holes? Plexiglass?






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Old 01-25-2006, 07:44 PM   #2
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know what? that's a pretty

know what? that's a pretty decent stock undertray already. i remember how my accord was like that.

compared to your car, my firefly is an aero disaster under there - it's basically a gaping hole from the edge of the bumper back to the firewall, with the oil pan, control arms and stabilizer bar hanging down fully in the airflow. i'll do pics of it in the spring.

one area you might improve is around the "tow hooks". in the top pic, i would try to fabricate something to match the smoother transition you have under the center of the car. that means covering up the hooks. but what good are they aside from bashing on parking berms?

aside from that, are you planning to fully enclose the engine compartment right to the firewall? that will help some, though obviously you have to find melt & fire-proof material for near the exhaust, and large enough openings around the steering gear & axles for heat to exit.

and as for the holes in the bumper, block off all airflow through the front of the car that isn't needed for cooling. it's up to you to figure out how much - monitor the temp gauge (and listen for the fan frequency). start with half and go from there. my car has about 1.5 sqare feet of openings in the bumper. i blocked it completely this winter. above freezing, i've opened about 15 square inches, and the engine temps have been stable. (then again my 993 cc's don't generate as much heat as your motor.)

for me, the grille block alone increased efficiency by about 3% - a combination of a warmer drive train plus reduced airflow thru the engine compartment.

judging from the pics, i wouldn't hold your breath for a 10% gain, but it's still worth improving. if the *top* of your car was shaped like the existing front undetrays are, would you just leave it as-is? me neither.
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Old 01-25-2006, 07:57 PM   #3
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Quote:one area you might

Quote:
one area you might improve is around the "tow hooks". in the top pic, i would try to fabricate something to match the smoother transition you have under the center of the car. that means covering up the hooks. but what good are they aside from bashing on parking berms?
And smashing a curb I skidded into once.

I've already been out cutting material. It's nice, but it can be better, still gonna do the tray, if only to even the stuff out and direct the air a bit better. The tow hooks will be covered.

Specifically on the front I meant about the black dips where it sinks into the mold but does not go into the engine.
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Old 01-25-2006, 08:07 PM   #4
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oh, the "indents" where the

oh, the "indents" where the optional fog/driving lights might go. gotcha.

similar question came up on the yahoo max-mpg group a while back - whether the front of the bumper should be made as "flush" as possible (specifically, whether it matters if you block grille openings from behind - leaving an "indent" like your fog light areas - or in front).

phil knox (the toyota pickup / knowledgeable aero expert) said on that topic that on the front face of the car, it won't matter terribly much. the pockets "fill in" with high pressure, making it appear to the approaching air flow as if it's already physically flush.

that said, none of the record top-speed or top mileage concept cars have indents on their front bumpers, do they...
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Old 01-25-2006, 11:01 PM   #5
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Step One

Step #1: Clean off the Jersey salt -- will reduce drag by 68.47%.

RH77
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Old 01-26-2006, 08:36 AM   #6
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You're sarcasm is not

You're sarcasm is not appreciated. Any water I throw on it will freeze to it,, but I am going to wax the thing.
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Old 01-26-2006, 10:04 AM   #7
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Re: Step One

Quote:
Originally Posted by rh77
Step #1: Clean off the Jersey salt -- will reduce drag by 68.47%.

RH77
Haha, man I take that for granted.
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Old 01-26-2006, 10:21 AM   #8
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Dude Relax

Quote:
Originally Posted by SVOboy
You're sarcasm is not appreciated. Any water I throw on it will freeze to it,, but I am going to wax the thing.
I didn't have anything constructive to add, so I thought I'd make a "funny" to keep things light -- a little humor.

If I had a dollar for the number of times I got a sarcastic response from you on my posts, I could retire.

Since I've apparently offended you, first I apologize. Secondly, I feel obligated to offer an idea. Since the lips applied to the area in front of the wheels on the Insight reduce drag, could a similar lip be constructed across the entire front underside so the air is directed away from the underside of the vehicle - this way, trays wouldn't be entirely necessary. Last, for the air to exit the vehicle effectly, perhaps a diffuser on the rear would offer clean flow.

Also, thanks to Dax for understanding that my comment was for FUN.

RH77

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Old 01-26-2006, 10:33 AM   #9
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Re: Dude Relax

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Originally Posted by rh77
could a similar lip be constructed across the entire front underside so the air is directed away from the underside of the vehicle - this way, trays wouldn't be entirely necessary
good idea - but instead of either/or, i'd do both: a smoother front undertray PLUS deflectors ahead of the front tires.
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Old 01-26-2006, 11:26 AM   #10
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Re: Step One

Quote:
Originally Posted by DaX
Quote:
Originally Posted by rh77
Step #1: Clean off the Jersey salt -- will reduce drag by 68.47%.

RH77
Haha, man I take that for granted.
Crap. I need to wash my car. After a fresh paint job I already have rust this year. Looks like I'll be doing rust removal AGAIN in a month or so.

You just can't win with ths salt.
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