sheet aluminum undercarriage ?

[burldude]

I was at a tire shop and got to check out a porsche that was on a lift . The whole bottom of the car was smooth with nothing exposed . No crooks and crannies it was just awesome for airflow . My question is has anyone done this for there car ? I notice mine getting a little light at around 70 under quick aceleration and then settling back down . I hate to think of what it would feel like at 150 mph . I found aluminum to cover the whole bootom of my car which I wold rivet in place . Somone told me that at Bonneville the cars there that have been "sheeted" with aluminum have a slight downward bow in the middle to promote downforce . Any thoughts on this ? the fastest I have taken my car is 115 with uncalibrated speedo with 18 so I guess I might have been pushing 125 .Maybe a little less .

 

[once_scorned]

I was at a tire shop and got to check out a porsche that was on a lift . The whole bottom of the car was smooth with nothing exposed . No crooks and crannies it was just awesome for airflow . My question is has anyone done this for there car ? I notice mine getting a little light at around 70 under quick aceleration and then settling back down . I hate to think of what it would feel like at 150 mph . I found aluminum to cover the whole bootom of my car which I wold rivet in place . Somone told me that at Bonneville the cars there that have been "sheeted" with aluminum have a slight downward bow in the middle to promote downforce . Any thoughts on this ? the fastest I have taken my car is 115 with uncalibrated speedo with 18 so I guess I might have been pushing 125 .Maybe a little less .

Sorry to dig this one way back up. Certain bonneville classes allow for a belly pan. Competition Coupe and I believe modified sports as well as several other special construction categories. None of the stock body classes allow for it unless the car came with it from the factory.

I have done a sheet metal flat bottom before. It is really nice for cabin noise and high speed stability.

 

[thekellbeast]

I don't think you would get the best results by just bolting a flat sheet to the bottom of the car. You would need to design the shape using some actual engineering. I saw a thread on another forum (like 2 years ago) where some guys was designing an undersheet. He had a computer program where he could design the shape, then simulate airflow to see how much downforce it would generate.

That being said, this thread was ignored 2 years ago. I don't think there's that much interest for this in the DSM aftermarket. Most people who modify DSM's aren't going for all out top speed, they just want 1/4 mile times.

 

[once_scorned]

I don't think you would get the best results by just bolting a flat sheet to the bottom of the car. You would need to design the shape using some actual engineering. I saw a thread on another forum (like 2 years ago) where some guys was designing an undersheet. He had a computer program where he could design the shape, then simulate airflow to see how much downforce it would generate.

That being said, this thread was ignored 2 years ago. I don't think there's that much interest for this in the DSM aftermarket. Most people who modify DSM's aren't going for all out top speed, they just want 1/4 mile times.

The engineering is not that complex if you understand a few basic aerodynamic concepts something you could pick up from a good book. It depends on what your after, low drag, high downforce etc... so it depends on what defines your "best result" if your trying to do a wing and need certain amounts of downforce at certain speeds on certain wheels in certain corners yah it would get mega complex. But a simple decrease in drag from a flat bottom and the inherant downforce and stability that comes with it. It was well worth it in my opinion. It was most certainly not just a high speed thing when I did it on my car there were pretty substantial differences in a bunch of categories. Its a freebie mod, no compromises just good things. I love mods like that. Almost anything down there is better then what we got from the factory.

Probably advantage CFD is what he was using. I would give my left nut to get my hands on that software.

 

[Rice Over Wheat]

This isn't news. All exotics have this underneathe and its funny the OP just noticed it then. This is just a silly idea for a mod on a DSM...such things are intended for top end aerodynamics. Exotics have this because you pay for vanity. This reminds me of those people who put canards on their front end for "downforce".

But I'd still love to see someone do this so we can see what gains are realized if any. Notice the guy doing the computer sim design never updated his project .

 

[jtmcinder]

I doubt it would affect 1/4-mile times (much), but it's in the top three of important things for all other forms of racing. Even in autocrossing are there rules on bellypans, since they can be very helpful. Here's my favorite book on the subject:

http://www.ibsinger.com/product.htm?code=gaer

If you're in the mood for some serious brain pain:

http://www.ibsinger.com/product.htm?code=H692

- Jtoby

 

[Rice Over Wheat]

^^^

I agree it is effective for race cars. I just mentioned that I thought it was silly for almost any DSM application for the most part. In 16 years of DSM modding, has anyone even bothered to do this?

To the guy who gave me negative feedback for posting my opinion, thanks man. Yeah, undercarriage airflow matters for a DSM at 35mph. Riiiight. Good thing I ditched my antenna as it was causing serious drag on the highway.

 

[AndrewD5418]

I doubt it would affect 1/4-mile times (much), but it's in the top three of important things for all other forms of racing. Even in autocrossing are there rules on bellypans, since they can be very helpful. Here's my favorite book on the subject:

http://www.ibsinger.com/product.htm?code=gaer

If you're in the mood for some serious brain pain:

http://www.ibsinger.com/product.htm?code=H692

- Jtoby

Not to mention. While getting an undercarriage done, you can replace the stock plastic peices *behind the IC and crap* with fab'd aluminum.

 

[tstkl]

and it will cause the parach....er.... rear bumper to not be a huge draging force on you. Even if the underbelly was simply a flat peice of metal, it would decrease the coefficent of drag on the car, even if its a small amount. If people are willing to drill big holes into the back of their bumpers to let that air escape, It would seem that eliminating the air source for the rear bumper would be greatly more effective.

The only problem I see is that the air in the engine bay would have a hard time being recirculated, and since the exhaust (on 1ga's at least) hangs below the line of the bumper, it would have to come through a hole in the aluminum. This hole would allow for air to get in and defeat the purpose of the underbelly. Unless you could find some type of rubber with a high temperature melting point to plug up said hole, the gains would be minimal.

 

[once_scorned]

^^^

I agree it is effective for race cars. I just mentioned that I thought it was silly for almost any DSM application for the most part. In 16 years of DSM modding, has anyone even bothered to do this?

To the guy who gave me negative feedback for posting my opinion, thanks man. Yeah, undercarriage airflow matters for a DSM at 35mph. Riiiight. Good thing I ditched my antenna as it was causing serious drag on the highway.

For the record it wasnt me that left you that negative ding. With that said...

Yes I have done this:

YES it made a difference
YES at normal highway speeds
YES better handling
YES more stable at 80mph
YES quieter interior
YES decreased drag

I measured the drag decreases using a race-technology data aqusition system. two full points. .35 to .33 (and that is including rolling forces manufacturer drag tests are wind tunnel, and not counting rolling resistance)

I dont know what that means for drag times as I dont drag race, I do land speed. But I do know the 3000GT guys picked up a couple MPH in the quarter from flipping their active aero off and on.

There was also an effect on downforce you can see the suspension compressing but I prefer not to talk about those exact numbers publicly.

Removing the rear license plate on a 2g makes a difference as well, and thats good since it doesnt break the rules of my class like the flat bottom did. Thats why i had to take the belly pan off. I miss it. If you spend any time at land speed races everyone will tell you that a belly pan is a HUGE advantage for drag. Especially in factory based classes where dropping your car to 1" of clearance has associated problems.

When I did my flatbottom, well actually I had two revisions one that was just sheet metal and one that actually reinforced the chassis. I highly reccomend if you do it to design it to reinforce as well. Our cars are about as stiff as a grilled cheese sandwich. That plus the cage being tied to the chassis at 12 points and I couldnt even measure chassis flex with home equipment anymore and it used to be 1" deflection at 3000ft/lbs!

I really disagree about this being a "vanity" mod. I see it in my opinion as a no compromise mod. My $.02

 

[Rice Over Wheat]

I believe most of what you said is consistent with the original context of what I was talking about. I never refuted its effectiveness for top end aerodynamics, which is what I'm assuming you're involved in for land speed racing.

Not saying I don't believe you, but I'd like someone to post data showing the results of this mod. Preferably by means of realized gains...I dont think anyone disputes that a computer sim will measure any difference in aerodynamics but how does this work out to performance gains on the street or track? This is how we judge whether a mod is worth doing or not, no? If sheetmetal is indeed greatly effective for everyday driving and some drag use, then I'd like to do this mod.

Would love to see a how-to regarding how you shaped the underbelly and bolted it together, etc.

The original post of mine in question that pissed somebody off was this:

This isn't news. All exotics have this underneathe and its funny the OP just noticed it then. This is just a silly idea for a mod on a DSM...such things are intended for top end aerodynamics. Nobody is going to see it except when on a lift, and it'll hardly be functional unless you often drive at 150. Exotics have this because you pay for vanity. This reminds me of those people who put canards on their front end for "downforce".

But I'd still love to see someone do this so we can see what gains are realized if any. Notice the guy doing the computer sim design never updated his project .

So my main premise was:

1. Silly mod for DSM
2. Sheetmetal undercarriage is intended for top end aerodynamics
3. Not functional unless driving at 150.

1) I meant for most people not taking the car to top end. I think 16 years of DSM modding history and only one or two people attempting this mod bears witness to the supreme overkill for such negligible real world gains in MOST dsm applications. Read the post where a member mentions computer sim results...OF COURSE any aerodynamics improvement will net some gains in a wind tunnel or sim using computer measurement, they are so precise. How does this translate in observable real world application?

2. Further note the member who tested sheetmetal undercarriage on a dsm using computer software is involved in land speed races. That involves top end aerodynamics. How many dsm owners are involved in land speed racing? This is consistent with top end sports cars rated at 175+ mph top speed that have sheetmetal undercarriages stock. Though no one will likely reach those speeds in 99.9% of cases, they need the feature because they CAN.

3. Maybe "functional" was a poor choice of word. Yes it's functional in the sense that there is some measurable gain by any improvement in aerodynamics. But functional in the sense of everyday driving, or 1/4 mile improvement? Where is the data regarding dsm and at 35mph (since I am supposedly off by 100 mph), I will feel the difference? I think not and I beg someone to prove me wrong.

When you tell someone they are wrong the burden of proof is on both of you. Notice in my original post I said I was eager to see what real gains were had if any. If sheetmetal undercarriage will strengthen my chassis, improve my ride, and reduce drag as low as 35 mph, and thus improve my acceleration appreciably, sign me up! I'll go to home depot right now and bolt up some sheetmetal! If it only does so for land speed racing then I still think its usefulness is limited.

Edit: I am not saying it's not effective. I want to know how effective it is because if I can get appreciable gains in acceleration for street/track use, then I'd like to do this mod also. I didn't mean to sound judgemental. I know what a great suspension setup has done for me recently and actually believe suspension is more important than lsd for fwd traction. So if a mod like this is as effective as some of you say at lower speeds, I will look into doing this also.

 

[Ludachris]

^^^

I agree it is effective for race cars. I just mentioned that I thought it was silly for almost any DSM application for the most part. In 16 years of DSM modding, has anyone even bothered to do this?

To the guy who gave me negative feedback for posting my opinion, thanks man. Yeah, undercarriage airflow matters for a DSM at 35mph. Riiiight. Good thing I ditched my antenna as it was causing serious drag on the highway.

Is it a worthy mod for a DSM? Depends on who you're asking and what type of racing goals they have. It might not be worth it for 1/4 mile times but there is a decent number of people on this site who enjoy other forms of racing more than 1/4 mile. Will the majority care about this mod? Probably not. Will that have any bearing on whether those of us who could benefit from it will care to try it, no. Those of us that road race average speeds of 80+ mph around a track - will slight aero changes effect our times? Without question. Will an undercarriage make a difference? I'd bet good money it would. It all depends on your goals and what you're willing to do to achieve them. I could care less that nobody in 16 years has tried it. It doesn't prove or disprove anything, except that most people over that timespan have been into drag racing.

The majority of DSMers drag race. Let them do the things that will help them achieve their goals. My goals (and those of other road racers, autoxers, and rally racers) are different. This probably isn't a good mod for drag racers. or those who don't do road racing. It seems that point has been made. No need to keep beating it to death.

 

[Ludachris]

I believe most of what you said is consistent with the original context of what I was talking about. I never refuted its effectiveness for top end aerodynamics, which is what I'm assuming you're involved in for land speed racing.

Not saying I don't believe you, but I'd like someone to post data showing the results of this mod. Preferably by means of realized gains...I dont think anyone disputes that a computer sim will measure any difference in aerodynamics but how does this work out to performance gains on the street or track? This is how we judge whether a mod is worth doing or not, no? If sheetmetal is indeed greatly effective for everyday driving and some drag use, then I'd like to do this mod.

Would love to see a how-to regarding how you shaped the underbelly and bolted it together, etc.

The original post of mine in question that pissed somebody off was this:



So my main premise was:

1. Silly mod for DSM
2. Sheetmetal undercarriage is intended for top end aerodynamics
3. Not functional unless driving at 150.

1) I meant for most people not taking the car to top end. I think 16 years of DSM modding history and only one or two people attempting this mod bears witness to the supreme overkill for such negligible real world gains in MOST dsm applications. Read the post where a member mentions computer sim results...OF COURSE any aerodynamics improvement will net some gains in a wind tunnel or sim using computer measurement, they are so precise. How does this translate in observable real world application?

2. Further note the member who tested sheetmetal undercarriage on a dsm using computer software is involved in land speed races. That involves top end aerodynamics. How many dsm owners are involved in land speed racing? This is consistent with top end sports cars rated at 175+ mph top speed that have sheetmetal undercarriages stock. Though no one will likely reach those speeds in 99.9% of cases, they need the feature because they CAN.

3. Maybe "functional" was a poor choice of word. Yes it's functional in the sense that there is some measurable gain by any improvement in aerodynamics. But functional in the sense of everyday driving, or 1/4 mile improvement? Where is the data regarding dsm and at 35mph (since I am supposedly off by 100 mph), I will feel the difference? I think not and I beg someone to prove me wrong.

When you tell someone they are wrong the burden of proof is on both of you. Notice in my original post I said I was eager to see what real gains were had if any. If sheetmetal undercarriage will strengthen my chassis, improve my ride, and reduce drag as low as 35 mph, and thus improve my acceleration appreciably, sign me up! I'll go to home depot right now and bolt up some sheetmetal! If it only does so for land speed racing then I still think its usefulness is limited.

Edit: I am not saying it's not effective. I want to know how effective it is because if I can get appreciable gains in acceleration for street/track use, then I'd like to do this mod also. I didn't mean to sound judgemental. I know what a great suspension setup has done for me recently and actually believe suspension is more important than lsd for fwd traction. So if a mod like this is as effective as some of you say at lower speeds, I will look into doing this also.

You can't make statements like "isn't functional unless driving at 150 mph" without elaborating with some specific data. Have you tested that theory? Because it sounds like you're passing it off as fact when others here have found that to be wrong from their research on the subject. The burden isn't on anyone here to prove that statement wrong. You're making a strong statement and you need to back it up with some factual data. I think that's the only problem anyone had with your statements. We don't need more hearsay floating around here. If you know it's a fact, post why.

 

[Rice Over Wheat]

^^^

Ok, I agree. I shouldn't have said it is only effective 150+ mph top end aerodynamics.

I'd like to see data regarding it's effectiveness at 35 mph though, since that's what was I was told in my rep box. If that's true I'd be interested in having this done. I think the problem here is there isn't much data out there regarding this mod on dsms. I love how sheetmetal undercarriage looks, I just wonder if it's worth doing. I don't land speed race, I don't drag at the track, but I am interested in 0-100 times.

 

[99gst_racer]

The benefits from a sheet metal under carriage would be seen progressively. As drag is seen progressively (related to speed), reducing drag would also be seen progressively.

So, the faster a car goes, the more drag it sees, the more 'helpful' a sheet metal under carriage would be. At speeds of 35 mph, the difference may not be noticeable, but neither would the amount of drag. At speeds of 135mph, drag would increase, so as would the usefulness of a sheet metal under carriage.

So, at 35mph, it it helpful? Sure. Is it very useful at 35mph? Probably not.
But there is drag at 35mph, so this would help some, just not as much as you would be looking for, but I do believe it would help greatly for 0-100mph pulls.

I imagine the benefits from this would be much more noticeable at 65+ mph, but I have to data no back that up.


But, I noticed that Shep now runs one at the front of his Talon, so they must be functional for drag racing.

 

[Morphius]

I'd be interested in data/results for a 1g from 35-65mph. I'm collecting parts for an electric varient...... this info would be useful.

More food for thought..

How do these affect the aero:
Variations of 1g/2g bumpers.
Sideskirts.
Stock wings.
Bump vs bumpless hood (ie 1G)

 

[Ludachris]

But, I noticed that Shep now runs one at the front of his Talon, so they must be functional for drag racing.

Well there you go - even drag racers can benefit from it.

 

[2gGSX]

Well there you go - even drag racers can benefit from it.

I think it's safe to assume that it has a much more pronounced effect at his trap speed than the other 99.9% of peoples'

 

[AndrewD5418]

For the record it wasnt me that left you that negative ding. With that said...

Yes I have done this:

YES it made a difference
YES at normal highway speeds
YES better handling
YES more stable at 80mph
YES quieter interior
YES decreased drag

I measured the drag decreases using a race-technology data aqusition system. two full points. .35 to .33 (and that is including rolling forces manufacturer drag tests are wind tunnel, and not counting rolling resistance)

I dont know what that means for drag times as I dont drag race, I do land speed. But I do know the 3000GT guys picked up a couple MPH in the quarter from flipping their active aero off and on.

There was also an effect on downforce you can see the suspension compressing but I prefer not to talk about those exact numbers publicly.

Removing the rear license plate on a 2g makes a difference as well, and thats good since it doesnt break the rules of my class like the flat bottom did. Thats why i had to take the belly pan off. I miss it. If you spend any time at land speed races everyone will tell you that a belly pan is a HUGE advantage for drag. Especially in factory based classes where dropping your car to 1" of clearance has associated problems.

When I did my flatbottom, well actually I had two revisions one that was just sheet metal and one that actually reinforced the chassis. I highly reccomend if you do it to design it to reinforce as well. Our cars are about as stiff as a grilled cheese sandwich. That plus the cage being tied to the chassis at 12 points and I couldnt even measure chassis flex with home equipment anymore and it used to be 1" deflection at 3000ft/lbs!

I really disagree about this being a "vanity" mod. I see it in my opinion as a no compromise mod. My $.02

You know, you really could make some $ if you fab em up and sell em . How bout 1g? Undercarriage is also not ment JUST for aerodynamics. It's also for protection. Doesn't the EVO have one covering their center diff?

 

[tstkl]

As to drag racing cars, if you had read my previous post, you would see where I said it would DEFIANTLY decrease drag. Just look under your car and how many protruding objects there are. They ALL add surface area to the "cross sectional area of the car."

Now some might say, but hey, tstkl, that area is already accounted for in the front of the car. Well, thats what the drag coefficient does, it accounts for numerous stacks of dragging items (somewhat). A flat piece of metal held perpendicular to the direction of the wind will create less drag than multiple layers of metal with the same cross sectional area. Its because they all contribute a drag and slow the car down. You may not account for the cross sectional area when calculating the force needed to be overcome by the car when you do Cd X Ca, but that is because the Cd increases due to most of these things (since most of them are at 90 degree angles, unlike the hood, the windshield, and the majority of the body of the car) and you can never really get the cross sectional area down anyways, so its always a close guess.

Putting a smooth piece of metal under your car will make the air underneath the car less impeded, and flow easier, so you can cut through the air with less force at higher speeds.

 

[Rice Over Wheat]

Damn shep's engine bay looks clean as hell.

This is the undercarriage of a C6:

You must be logged in to view this image or video.

Doesn't seem like that tough of a project. Certainly low tech. What is everyone's thoughts regarding the use of fiberglass panels instead of sheetmetal?

 

[somdturbo]

Sheetmetal is easier to keep clean from oil and other substances. It is also more durable in the long run as its not prone to cracking compared to fiberglass.

 

[Rice Over Wheat]

I guess I would prefer a lighter material that is easier to cut. True about the fiberglass cracking. How about a durable plastic? Plastic panels weigh about the same as cf of the same thickness. Since the paneling would be done in sections, if there were damage just unbolt the panel and replace.

 

[somdturbo]

Only downfall of plastic would be heat damage. With the engine and exhaust being so close to it, its hard to find a plastic that wouldnt deform over time.

 

[Morphius]

Damn shep's engine bay looks clean as hell.

This is the undercarriage of a C6:

You must be logged in to view this image or video.

Doesn't seem like that tough of a project. Certainly low tech. What is everyone's thoughts regarding the use of fiberglass panels instead of sheetmetal?

The underside of a DSM in that similar area of the vehicle, is really that clean. Unless you have mongo sized exhaust hanging down. The areas that would be dirty are, the suspension and crossmember areas.