improving a softtop convertible

[serialk11r]

Originally Posted by window1

In case of reworked exhaust you may take ideas from efficient machanic

Uh, couldn't find said user, link?

Currently the car has a fat heat shield covering something (haven't looked carefully, probably the muffler) that sticks right out under the rear bumper. Talk about bad aero. What I'd like is a muffler that fits within the engine bay and exhaust that leaves through the bumper, but this will take a lot of cutting to achieve.

[serialk11r]

Well, quick little update (not really an update though).
School's FSAE team has a ton of medium? density foam sitting around that they don't want apparently, because they bought many, many tons of high density foam which is better for making moulds :O
Next time I go home, I'll be sure to swipe some of that, should be good for making temporary/experimental stuff.

Super short on time though this semester :/ Soonest forseeable time that I can work on the car is winter break, and that might not even work I do need to buy a jack and stands sometime so I can take a peek under the car. There's this floppy plastic shield sitting under the muffler for some reason, and I've been itching to get rid of it if its function isn't critical.

On the positive side, I have my Bluetooth OBDII reader coming in the mail very soon, will be able to track instantaneous and short term gas mileage soon. I've gone a bit over 100 miles on the tank and it looks to be a bit over 1/3 used up, seems like about 25mpg. Pretty bad, but half the miles were driven in hilly Berkeley infested with evil stop signs on a totally cold engine that never warmed up, much of it wasted on parking in tight spots, and half the remaining miles were driven in stop and go SF traffic. Guess I need to kill that engine more often.

Anyways back to aero, hopefully I'll have some free time some weekend to carve those foam blocks and stick them on my car. Thankfully that top isn't very tall so I'm hoping it won't be that difficult. I may want to buy a scroll saw, we'll see how the hacksaw does.

[serialk11r]

Okay, I put tufts on it today, attempted to videotape but I couldn't figure out how to hold the camera still for my life (besides it's not safe to be staring at my phone while driving) so I will enlist some help tomorrow if it's not raining.

The placement of the tufts was done in a manner that would allow me to see the ones on the side through the side mirror and the ones on the rear bumper through the rear window (but not the rearview mirror). I know there is a giant bubble of separated air on the back so there's no point in putting tufts there.

I did go for a little drive and noticed a handful of things.
First of all, I placed one yarn tuft near the top of the side scoop, and it seemed to be flapping in the wind, so perhaps the intake isn't super aerodynamically clean. Oh well, nothing I can do about that.

Second was that the tufts along the side of the car at the end were all wrapping towards the center of the car, and the tufts on the softtop were wrapping steeply upward along the surface of the top. I'm guessing there is a big vortex that's doing that.

[botsapper]

How about strapping/stretching on another fabric top. Keep the flying buttress profile, covered or uncovered rear w/ a clear PVC panel. There are MR2 rear lip spoilers that where the fabric could 'bed-corner' on. Just doodling out loud.

http://i.imgur.com/1W3rX.jpg

http://i.imgur.com/Azq6c.jpg

http://i.imgur.com/UM5PS.jpg

http://i.imgur.com/cDb0g.jpg

[serialk11r]

Originally Posted by botsapper

How about strapping/stretching on another fabric top. Keep the flying buttress profile, covered or uncovered rear w/ a clear PVC panel. There are MR2 rear lip spoilers that where the fabric could 'bed-corner' on. Just doodling out loud.

http://i.imgur.com/1W3rX.jpg

http://i.imgur.com/Azq6c.jpg

http://i.imgur.com/UM5PS.jpg

http://i.imgur.com/cDb0g.jpg

Hmmm...I thought of this but dismissed it because I thought it would involve attaching cloth to the softtop permanently, but I suppose I could stretch the cloth over the entire top :O Thanks for the photoshopped images haha. You got me curious, I need to think about this some more and examine the top to see if this would be possible. It might even get quieter in the cabin just from the extra layer of fabric!

I think the end of the engine bay cover might be a good place to secure the fabric, as that would allow the engine cover to open as usual.

I got a video of the rear today, and I think I won't post it because it's not really interesting. The tufts at the edges of the recessed area on the engine cover were flapping around, the tufts along the rear edge of the car were just "straight" (since they fall below the template line, I imagine this is the area where the air is not recirculating, but is moving slightly slower than the free stream). Good food for thought for spoiler design...

[serialk11r]

Hmmm I examined the top today to try and figure out how cloth could possibly work. The only places I can attach the cloth are to the metal brackets as the top's own fabric is not attached at many locations and will be pulled out of place. The only attachment point on the body that I can see working (must be fully reversible for resale value) is the trunk lid (engine cover). Probably something like loosen up one of the bolts, slip a bracket under it, and then attach the fabric to that.

My main concern is the location where the fabric attaches to the soft top brackets. The only location I can see working would have the fabric wrapping around the weather seal, and I feel like this could cause some problems. At the very least it should be taped to reduce wear via abrasion, but I wonder if being squeezed by the fabric would cause the rubber to deteriorate quicker...

By the way, what fabric should I use, and would a tailor have it in stock?

[serialk11r]

Well, I went to OSH and checked out their selection of double sided tape and...well, Scotch's "5 pound" (they have a 20 pound) double side tape is apparently strong enough to resist prying with a flathead screwdriver, except it is also essentially non-removable. I don't think I want to mess with the fabric anymore. I thought about attaching something to the rear window, but there's no way I can fit something big enough and have the top still fold.

I guess I'll just give it a spoiler, then modify the rear belly pan (and do wheel fairings if I still have time) and then not bother with it anymore. Somewhere down the road if I see an exceptionally good deal on lowering springs I might grab some, most kits lower the rear less than the front, so that should help with the softtop's sucky shape by giving the car some "rake".

It will sure be hard to get over the ugly 27 degree angle on the top though

[serialk11r]

Started working on the bottom today by taking off the stock rear engine diaper. After I took it off I realized why they did what they did; The main cat hangs VERY low!

The attachment points on the rear bumper for the diaper are much too high, the flow there would be separated even if I covered it with something smooth.

I think I will grab some coroplast, protect it from the cat's heat with aluminum foil, and then use some long bolts and nuts to let it sit lower than the stock piece. I might consider reinforcing it with some Bondo Hair. The idea is air from the engine compartment can escape from above the coroplast, and air from under the car can escape underneath without separation.

(excuse this gentleman's ridiculous bodykit and fake diffuser, my exhaust also happens to be on the other side in the same location). I will check with sign shops and TAP plastics to see if they have some suitable scrap material tomorrow.

I'm starting to give up on finding sandable polystyrene foam in a small piece, what do you guys think about using wood+spray foam for the spoiler? It'll be harder to work than foam and might have issues with expansion with humidity changes. Foam would also be much easier to work with for rear wheel fairings.

[serialk11r]

Okay it's been 9 months and I haven't really touched my car, but I just bought someone's intake camshaft to do a regrind on (Atkinson!), and I'm giving aero serious consideration again. Among the other planned mods are new muffler primarily for a more satisfying sound, and slight ride height reduction with taller rear tire to gear the car down a bit and give it some rake.

Last month I did go grab some stainless steel screws and finally made a permanent mount for my front license plate, that conveniently blocks 1/3 of the grill. I'll show you guys pictures after I figure out what to block off another 1/3 with, this car barely ever gets warm.

Last winter I took off the engine diaper (that the previous owner paid 500 dollars to replace -_-), and the cat has just been hanging out there. I think I'm just going to grab a piece of sheet aluminum for 30 bucks or what not and toss it under there. Still need to figure out what to do with the wheel fairings though, I think the conveyor belt material someone suggested is out of the question as there isn't really a place to put it. Maybe I'll extend the diffuser with some "U" channels, but I don't know how effective that'll be.

I also was checking out spoilers since I decided it wasn't a good use of time to make one from scratch, there is this nice Honda S2000 ABS spoiler for 60 bucks that I should be able to cut 2 inches off (too wide) and then sand a little to produce a nice little spoiler that almost hits the template that at the same time looks fantastic (it's got that nice curve to it). Gonna order it when I stop being lazy.

Long term I'd like to do a lot more to this car but those mods and maybe some chassis bracing should do nicely.

[kach22i]

Originally Posted by serialk11r

I also was checking out spoilers since I decided it wasn't a good use of time to make one from scratch, there is this nice Honda S2000 ABS spoiler for 60 bucks that I should be able to cut 2 inches off (too wide) and then sand a little to produce a nice little spoiler that almost hits the template that at the same time looks fantastic (it's got that nice curve to it).

Will you be taking the 2-inches out of the middle to retain the end arc?