Ive seen before on several cars as far back as 2 years ago. So far ive only seen it done on hatches, and as far as i could tell they were pretty raced out, usually no interior, small light weight wheels, basically function over form. I wanted to know whether or not holes in the rear bumper actually improve ET's. I wouldnt mind doing it to my hatch, but I dont want to ugly up my car if I know that it wont help in the 1/4 mile. If it helps atleast .3 seconds then Id definitely do it. So does anyone know? Or ever tracktimed the difference? Im not into road racing, just drag.

 

i have them on my car. its called a diffuser. I dont know how much it helped on my car because everythng on it is a new set up. but off hand on my friends Ek, i think we dropped 3/10's off his times and gets an extra 60 miles he said to the tank.

 

DAHM!!!! 60 miles?!??!?!? Thats crazy. looks like theres alot of air geting trapped back there. If you look at the rear bumper, thats all it does, just scoop and hold air like a parachute. The car I saw yesterday had this metal insert around the holes, it looked cleaner then juist holes by themselves. I was thinking why not do it body kit style, like the Wings West Ef kit. It has two rectangular holes in the back with a thin seperator and a grill. It would maybe look better to cut 2 rectangles in the buvmper with a spacer in between. I dunno, ive got an unwanted 4 door bumper in the garage, Ima try out the rectangle cut and see how it looks, Ill post pics too.

 

I did mine with a holesaw. the EK we did with the STR style cutouts, only in carbon fiber.

 

where ya get the carbon fiber one?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by itr206 &raquo;</TD></TR><TR><TD CLASS="quote">I did mine with a holesaw. the EK we did with the STR style cutouts, only in carbon fiber. </TD></TR></TABLE>

I jus cut holes in my back bumper with a jig saw.. I borrowed my friends STR defuser and traced the holes, then cut them out.. Still looks good i think...

 

I gained .4 on my quater mile times when I did mine.

 

Carbon Fiber

http://www.macqc.com/raceplates/diffuser.htm

 

i like the way those CF ones look too...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Group Tenacity &raquo;</TD></TR><TR><TD CLASS="quote">

I jus cut holes in my back bumper with a jig saw.. I borrowed my friends STR defuser and traced the holes, then cut them out.. Still looks good i think...

</TD></TR></TABLE>
looks real nice! alot better then just cutting round holes! im gonna be making carbon fiber ones pretty soon,ill post em as soon as they are done!

 

what is the advantage of a 'diffuser' over just cutting holes?
kinda seems like a waste of cash....unless there is something i am missing.


is it just for looks?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sir Poopalot &raquo;</TD></TR><TR><TD CLASS="quote">Ive seen before on several cars as far back as 2 years ago. So far ive only seen it done on hatches, and as far as i could tell they were pretty raced out, usually no interior, small light weight wheels, basically function over form. I wanted to know whether or not holes in the rear bumper actually improve ET's. I wouldnt mind doing it to my hatch, but I dont want to ugly up my car if I know that it wont help in the 1/4 mile. If it helps atleast .3 seconds then Id definitely do it. So does anyone know? Or ever tracktimed the difference? Im not into road racing, just drag.</TD></TR></TABLE>

i did it 4 years ago... i also used a hole saw, the only thing i noticed was about 2 more mph in the 1/4

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SadisticRacing &raquo;</TD></TR><TR><TD CLASS="quote">I gained .4 on my quater mile times when I did mine. </TD></TR></TABLE>


did you take your gas tank off your car? or by just making holes you gained .4?
is it street leagle?

i'm not sure but i think taking gas tank and putting fuel cell in trunk might help a bit more or its the same thing

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Group Tenacity &raquo;</TD></TR><TR><TD CLASS="quote">

I jus cut holes in my back bumper with a jig saw.. I borrowed my friends STR defuser and traced the holes, then cut them out.. Still looks good i think...

</TD></TR></TABLE>

Sorry to all for the OT but... Do you have a trunk mounted battery? Also, what sanction and class are you racing? I know when I read thorugh the rules for NHRA that you only need the battery cut off if you have a trunk mounted battery... just wondering; trying to get my ducks in a row

BTW nice diy diffusion going on there

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by h22 civic &raquo;</TD></TR><TR><TD CLASS="quote">where ya get the carbon fiber one?</TD></TR></TABLE>


My friend has a CF shop and makes them , He has like 2 sets in stock right now. i think he said $150 or so for thme with all the hardware

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by h22avid &raquo;</TD></TR><TR><TD CLASS="quote">

Sorry to all for the OT but... Do you have a trunk mounted battery? Also, what sanction and class are you racing? I know when I read thorugh the rules for NHRA that you only need the battery cut off if you have a trunk mounted battery... just wondering; trying to get my ducks in a row

BTW nice diy diffusion going on there </TD></TR></TABLE>

you also need the cut off if you go over 135? or 9.99

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b0jan &raquo;</TD></TR><TR><TD CLASS="quote">did you take your gas tank off your car? or by just making holes you gained .4?
is it street leagle?

i'm not sure but i think taking gas tank and putting fuel cell in trunk might help a bit more or its the same thing</TD></TR></TABLE>

No I'm still using the stock gas tank. I went from running 13.8's all day to at the last race running 13.41 and two other 13.4's with two 13.5's so you can see .3-.4 of a difference. As far as street legal I don't see why not.

 

Yea, my battery is in the trunk, thats y i have the kill switch. I run Sport FWD / Pro Am FWD class, but my car has yet to hit the track since last year.. still getting the bugs out..

 

be sure any cutting or drilling you do is legal for the class you intend to race if you run with a sanctioning body. I know according to Nopi Rules its Illegal

"No cutting or drilling of body or chassis or removal of other components"

 

So your saying diffusers are illegal?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by itr206 &raquo;</TD></TR><TR><TD CLASS="quote">So your saying diffusers are illegal?</TD></TR></TABLE>

im not saying anything. if you have questions ask ndra tech. but i interpret cutting or drilling to be illegal. if you had to cut or drill out a body component to install it. well i think that is self explanatory.

 

i doubt they would make it illegal, but ill check now.

 

I used a 6" whole saw on a drill to cut mine.... Cut out six of them...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by itr206 &raquo;</TD></TR><TR><TD CLASS="quote">i doubt they would make it illegal, but ill check now. </TD></TR></TABLE>

I am interested in this also...

 

Offical words from NDRA

itr206 (4:10 PM 5/25/2004): Hey Glenn . are rear diffusers illegal in the street classes. I am curious since its considered cutting the body?
sold9secteg (4:25 PM 5/25/2004): They are legal, since it concidered a cosmetic/appearance modification. Basically, it will help the race cars, but all the show guys are doing it.