FWD Aerodynamics Info

[allmotorcoupe]

Hello Everyone . .

This may not be the best place to ask this question as it pertains to a different form of motorsports, so for that I apologize . .

I just figured that aerodynamics are such a huge factor in what you guys do, that this would be the best place to ask. .

I drag race a Naturally aspirated, front wheel drive 1995 Honda Civic Coupe.
The class that I race in, is a highly competitive, "all motor" , 4cyl class. . Lately it seems to be going down the road of who ever has the biggest wallet wins the race. I am far from that man. So I am trying to think outside the box this year for ideas to compensate for less raw power. I have been racking my brain ( and limited resources)  trying to come up with some ideas to give me a competitive edge. No one has really tried anything to increase the aerodynamics of our vehicles because it is technically a "street" chassis class ( factory unibody).
We only go about 10.2-10.7 seconds at  125-135 mph in a quarter mile. Only above 100mph for 3-4seconds so I dont know how much aerodynamics will even help. But I am willing to try anything. I have access to a fabrication shop, so building or fabricating anything is possible.

I was wondering if anyone had any websites or books they would like to recommend to me in order to open my eyes to this subject as it pertains to aerodynamics of  Front wheel drive racing? A lot of the sites I have gone on , only give information about open wheel F1 cars or ways to increase downforce to the rear of the car. (not something I need with a front wheel drive car)
I have purchased Simon Mcbeath's book - Competition Car Aerodynamics and am just waiting for it to be shipped to me.

So far I have learned :

I need to seal the front of the car off. I purchased a completely sealed off fiberglass front bumper to lessen the amount of air that gets trapped into the engine bay.

I need to reduce drag on the car - So i have read to lower the car as close to 2.7inches of front ground clearance as possible. Previous ground clearance was close to 4.5 inches so I have got the front down to about 3 inches. I also have read to leave the rear of the car a little higher so that any air that does go under the car is sent out the back a little faster.

I was planning to build an underbody panel that covers the entire engine bay and ends before the firewall. This should help the air not get trapped in the engine bay as much. .

I know the most pressure build up is at the base of the windshield.  I was thinking about putting the hood up on 1 inch spacers so that the hood would be angled more . My thinking was to deflect the air higher onto the windshield in an effort to prevent it from being built up at the base. Although on the flip side of that, it might allow more air to go into the engine bay and that is not good.
I could also make something that covers the wiper cowl and comes up on an angle to about 6 inches onto the base of the window. Again, in an effort to deflect the oncoming air higher onto the windshield.

I have been debating on whether or not to build a rear diffuser of sorts. Basically to cover the rear spare tire area and have it button to the bottom of the bumper. I have read that tunnels/splitters/diffusers on that rear panel will help create venturi flow- but not sure if it is worth it on my particular application.

Same goes for a complete under body panel. I was contemplating building a complete smooth underbody panel for the car but not sure if it is worth the intense amount of work accompanied by it.

I'm sorry for bouncing all over the place in this post. Sorry if this is the wrong place to ask, but I really havent found anywhere else to ask it.
Please feel free to correct anything that I have posted. Any light that anyone can shed to help me or to point me in the right direction, I would greatly appreciate it.

Thank you for your time.

- Jake

[McRat]

You are probably right about one thing, the amount of time spent accelerating over 100 mph is pretty limited.  Money spent dropping 330' and 1/8th times will do more than aerodynamics, IMO.  We run similiar ET's and MPH in a 4x4 pickup with the aero of a barn door.  Playing with aero has had very little effect in the quarter ET, maybe 1.5-2 mph trap though.  Problem is nobody cares how many MPH, just whether you get there first.

[allmotorcoupe]

Hey I would take 1-2mph increase . . . that means something is working , right ?

My car actually has a pretty decent short track, although that probably has something to do with the lack of power haha !

Im just looking for anything that could help. Dialing the car in on the track is surely an on-going process and I am looking for some things to compliment that !

[McRat]

Lowering, filling in radiator vents, closing gaps (taping), chopping the roof, etc, can all help, but doing a little guesstimating, you are using about 140rwhp to go 135mph assuming 24sqft of frontal area and a Cd of .30, not sure about the measurements though, so I used 6' wide by 4' tall. 

In a fantasy world, you could chop that in half (not really though), so it would be like adding 70rwhp at the traps.  But wait.  Only at the traps.  The effective average HP gain for the whole quarter is going to be like 10-15rwhp.  And that is comically optimistic.

Now assuming you weigh 2500lb, spending money to drop 100lb will have a slightly greater effect and is actually a realistic goal.  Acid-dip the unibody?   

[SPARKY]

Do you have a minimum you have to weigh?

[wobblywalrus]

Jake, the streamlining you are proposing might not be a big help at the speeds you are going, for dragracing.  The solution is simple.  Go fast enough for the streamlining to help.  It is time for land speed racing.   

[allmotorcoupe]

Jake, the streamlining you are proposing might not be a big help at the speeds you are going, for dragracing.  The solution is simple.  Go fast enough for the streamlining to help.  It is time for land speed racing.   

haha great answer . . 

Sorry guys I should have mentioned this part before, the class is a street chassis so it is limited to things like factory body, Glass windows - so things like chop tops and different angle for front window would be out of the question.

The minimum weight for the class is 2150lbs . . The chassis with me in it weighs 2071 so I have the other 80lbs placed mostly over the front end for traction but in spots to even the distribution at all for corners.

I was thinking that at the speeds I am going, It may not have a great affect at all. . . The thing that got me was that in all my research- I came across more Gas saving studies then anything else. These were more or less based around decreasing the CD of the vehicle at highway speeds (55-65mph). . . A lot of the same things they suggested were the same ideas present in some of the studies about racing aerodynamics. I realize that the cars in these tests were at highway speeds for an extended period of time and in drag racing , there really isnt an extended period of time for these things to come into play.

I am perfectly fine with you guys telling me I am crazy haha. I will probably still do back to back tests on the ideas I do have this year just for my own curiosity.
I wasnt really expecting to be given the silver bullet and to hear - here is how to drop a second off your time lol . .
Last year I lost a race by 2thousandths of a second . . It hurt haha. . I think it is feasible that some of these thngs may help (or hurt) for me to gain a thousand here or there. And to me, that would be a win in my book.

[McRat]

Well, if you're at min weight, and power is capped, little is left but traction, rolling resistance, rotating mass, and aero.

There's some pretty smart aero guys who post here (obvious not me, I race pickups) and a low-cost windtunnel operator posts here as well.

You probably aren't having traction issues at the big end, so aero downforce isn't needed.  And you probably realize that the thrust from exhaust is free HP, and it can be significant in some engines (ours is most likely over 100lb thrust).

A belly pan can be a lot of help and can be made cheaply (might double as diaper if necessary?),  wheelwells are very dirty (can you make them tighter against wheels?).

Run side windows flush against skin if allowed.  If trim trips the air, make it flush.  No body gaps.

[Glen]

Is it legal to make aero additions in the street class you run. Hate to see protests.

[willieworld]

more oats for them ponies                                   willie buchta

[dw230]

If you are running in a true street class many of the mods you mention may not be allowed. We do not allow belly pans, covered front ends, etc. in our Production, read 'street', classes.

DW

[robfrey]

I think you are on the right track especially if they will be fairly inexpensive.
All these little things add up. If you are the only one doing them, you will have that little advantage.
I would say that keeping the air out from under the car would be one of the easiest thing to do.

Welcome to the forum.

[allmotorcoupe]

Thank you for everyone's willingness to offer any bit of help. . . It is all very much appreciated. .

Traction up top is not an issue so downforce there is not needed. In fact Really the only traction issue is in 1st gear and I shift into 2nd at about 44-46mph. . That is also roughly 1.65-1.9 seconds into the run.

McRat- you actually touched on a subject I was curious about. Wheel Wells . . Right now, I do not have any. The car from the factory has plastic oem liners and being that the car is 15 years old, they were trashed and I got rid of them long ago. . Being that I have a closed off front end and was planning to build at least a pan for under the engine bay (you were correct- also doubling as a diaper), I would assume that the point of building wheel wells would be to direct the oncoming air out of the engine bay and to the side of the vehicle. I wont be naive enough to think that I wont have any air coming into the engine bay, even with a sealed front, but would constructing wheel wells be even worth it ? Right now i have none. They basically are just open.

My question about a belly pan would be - Does anyone have any design tips ? We run an open header so the header ends a little after the firewall . . I dont know if I could build a complete one piece belly pan for that reason . . Without running  a full exhaust (which would hurt hp) the exhaust gases wouldnt really have anywhere to go . .

The good thing about the events that I race in , is that the tech is pretty laid back . . While something crazy like chopping the top would be caught and not allowed, I believe what I have proposed to do will be legal . . After all, anyone can really do it. No one has really attempted to do any of these things on a non pro-level car , ie: tube chassis, one piece front end, etc. . I suspect that I might get protested on a few things and I am perfectly fine with that. Although, me not being a top dog and running as quick as some of the other guys should help me because no one will really care. .

Not every event has the exact same rules as others in our style of racing . . So i may be able to get away with more at some events in comparison to others . I am fine with that as well haha. .

I'd be more than happy to post pictures of anything if someone needed to see them in order to make a suggestion

[McRat]

Ideally, you'd have none of the tire or wheel exposed to the airstream, and no "pocket" either.  The closer you get to that goal, the less power it take.

I'd make the belly pan in multiple pieces using Dzuz fasteners.  To stop wind vibration, you will need to either form ribs in the sheets, or rivet braces.  A thin unsupported sheet will vibrate enough to crack.  Carbon fiber probably wouldn't have that problem?  

[allmotorcoupe]

My thoughts were to make it in a few sections, and attach it to the under body with Dzus fasteners . . I never thought about wind vibration on a single sheet of metal . . Thats a very good point . .

I would also think a thicker piece of carbon fiber would not flex. . .Definitely Food for thought . . Thanks for that input sir !