View Full Version : Mini-Z Front Diffuser

2010.09.22, 07:34 PM
Trying out many things recently, first the "Gurney flap" and now this diffuser:


Cut from a piece of Kyosho whitebody packaging. I used the handle of an Xacto knife to curl the diffuser tray upwards. The square loop is there so I can do this:


Pretty much guarantees it stays in place. Initially I tested the diffuser by attaching it to the car with double-sided tape; I find that on the carpet drag strip (my hallway) it gives the front end a lot more stability than before, but whether that's due to weight or aero is debatable. In any case, I like what it's done to my car so I glued it on. Additionally I glued a bit more plastic onto the end of the center section to form a continuous panel all the way to the front edge of the chassis. Two more pieces were glued to that (in a stack, visible) in order to slot underneath the PN aluminum lower arm. The 911's foglamps had to be cleared so I needed to make the diffuser five-section instead of three-section like I had planned for the F430.


Classic LeMans type diffuser profile, just no strakes. The total weight added to the car is between 1.5-2g, so my car is now at 178g fully loaded. The body alone is 34.3g with the diffuser. Not terrible, but there's room for improvement. I might grind off the part of the chassis that's in the way of the diffuser right now, it's not being used and I don't forsee ever using it.


We'll see how well it works Friday, and later on a wind tunnel test. My gut feeling is that with the ground clearances that I usually run, not enough air will actually go under the body for this to produce downforce. The weight and smoothing of airflow will probably stabilize the car at high speed but not make it much faster. But on the off chance that it DOES produce downforce then I forsee myself needing to make a full Lexan wing. Let's find out Friday. :)

2010.09.22, 07:48 PM
I like the idea. Subscribed!!!

2010.09.22, 08:12 PM
Keep us posted!:)

2010.09.25, 05:17 AM
The diffuser works! :cool:

I initially kept the same setup that I had last time I went to Kenon, just with the diffuser, a 43t Mod motor and new tires (same PN X-Pattern 15 front, slick 8 rear). The first thing I noticed was traction roll, due to fresh tires. As I wore the fronts down the car started behaving more as it did last time, except significantly less twitchy: the front end looked more stable, yet had more steering at the same time. In fact, giving the car too much steering input made the car dip down, roll the rear around and either slide out or traction roll. Meanwhile the Gurney flap was slowly being chipped away by each traction roll, so my rear end got more and more nervous as time went by and I obviously could not take full advantage of the front aero. I wasn't exactly sure what to do about it so I played around with the roll center, raising the front tower bar 0.4mm above stock, switching T-plates to the PN G10 #5, and switching between PN MR02 White and Yellow springs (still using the PN aluminum front end with Reflex-style coilovers via Kyosho MR02 kingpins). Eventually I got to a point where if I didn't flog the car too hard, it would perform with good overall corner speed *provided* I picked a good line. Making corrections would agitate the rear end and all sorts of wacky stuff would happen.

We held 3 rounds of racing at Kenon tonight, and for the first two I kept that setup and swapped in a PN 70t motor. The behavior of the car did not change from before -- driveable, decently fast, but not consistent; the front end was working great but the rear was just not there. Just before the third round I cut off the remnants of my destroyed Gurney flap and had Philip fabricate me a proper Lexan scoop wing. I mounted it to the body via two damper posts (the short ones for the 94MM LCG motor mounts) in the same place as the 911 GT1's original wing. This was exactly the change that I needed. In the third and final round of racing, right off the bat I had my rear traction back (expected), but more importantly I had enough rear traction to make full use of the additional steering that the front diffuser provided. My car was so DIALED for the 5-minute duration of the race, I lapped the field twice. Turn-in was aggressive but not twitchy, mid-corner rotation was fast while staying planted, and corner exit/steady-state cornering speeds improved significantly thanks to the rear wing and diffuser keeping the car very planted at speed. My fast lap of 8.0x seems not to have gotten any faster, but the car was so consistent I was able to hit that 8.0x many times on end.

From pure subjective feeling, it seems that the front aero "kicks in" at any speeds higher than the slowest part of a hairpin turn. The second to last turn of the PN layout is the slowest hairpin, and it is there where I feel that the car develops just a tick less front bite, just a little bit less rotation. As soon as I exit that corner and turn right into the last one before the straight, the aero really seems to "kick in" and the car rotates and rockets itself out onto the straight. I can keep the throttle nailed down the back right-hand sweeper all the way to the right-left transition, where I lift off the throttle momentarily, rotate the car, then get back on the gas; at that moment the car again seems to "kick in" and drive itself out of there really fast. It feels different than your traditional wing, like it kicks in earlier but the effect does not scale with your speed as much as a wing's. Between the front and rear aero devices there seems to be enough downforce to keep everything wheels-down, I don't recall having any traction-roll problems throughout the 3rd main.

I'd get you guys a picture of the updated diffuser but I lent the GT1 to Philip for the next week or so since he wanted to try it out. I've clipped out half of the center panel to save some weight and make clipping the chassis into the body easier. All I can say is that this front diffuser, in conjunction with sufficient rear downforce, works. With a bit of tuning it could probably generate even more downforce, especially under a body that doesn't have light buckets protruding into necessary diffuser space. This is the first time with the MR-03 that I've ever found myself with a significant equipment advantage, I'm very surprised and happy it worked out. :)

Next step -- diffuser strakes?

2010.09.25, 02:36 PM

I love the diffuser idea and will be implementing this idea shortly.

Have you thought of using a thick clear tape to tape the bottom of your MR03? In keeping with the aerodynamic upgrades I think a smooth and flat floor may contribute to cleaning up the airflow under the car. i have two chassis with the exact same setup (even the same body used) and find that the MR02 chassis that i got from pinoyboy that has a clear tape as the floor to have a tiny edge over the other (non-taped)

Im very interested i following these aerodynamic changes you're trying....next you'll be submitting an article to RaceCar Engineering (my second favorite magazine ever):D

2010.09.25, 07:58 PM
Thick clear tape no, thin clear tape yes. :) Packaging tape would be great on the bottom of a Mini-Z, as long as I can avoid the static electricity. The main "troublemakers" with regards to undercar flow on the Mini-Z are the spaces between batteries and the center tunnel that suddenly gets cut off by a T-plate mount. The center tunnel probably can't be taped off (T-plate, switch, battery eject) but the side tunnels most certainly can -- in fact I just did, but that's for another thread. :)

In fact, if a flat underfloor works well enough it would be time to try fabricating larger rear diffusers and bolting them to our PN/Atomic motor mounts. I have no idea if it'll work, but that's why this is Mini-Z Science, right?

Philip promised me pictures of my GT1 on Monday, so I'll show you guys how the car looks then. ;)

2010.09.30, 02:56 PM
Philip's pics of the updated front diffuser are here.




Again, this is a *working* but probably not an *optimized* model of the diffuser. 2/3 of the heavy center panel have been ditched to make clipping the chassis into the body a bit easier. Philip decided not to take pics of the wing, which is okay I guess since I want to make a more realistic-looking V2 wing sometime, in the same vein as the original GT1 wing. Its basic specs are about a 15mm chord length, rising 6mm near the back with an arc about 5mm in radius. I'm going to copy that shape in the V2 wing but with small endplates for realism. :)

2010.10.14, 07:51 PM
Updates: Unfortunately the V2 wing didn't work out, the Autoscale Lexan is too flimsy to handle any respectable crash. I trimmed down the V1 scoop wing to reduce the excessive rear downforce, and colored it black, that's about it.

Now, the logical continuation of the front diffuser mod, I suppose:

I opened up the front air intakes again, hoping to use the front diffuser to scoop it upwards. You can see the upwards scooping shape inside the opening.

However, that air needs a way to get out, or else it's just going to create a high-pressure bubble of lift under the hood. Hence, I cut out the stock hood vents to a reasonable size.

Theoretically, the faster air flowing over the hood should be lower pressure than the slower air scooped up by the diffuser, so these holes should let air get pulled up from down below, as well as disrupt the low pressure flow on the hood, again reducing front lift. As you can see, the diffuser routes the air right up through the hood vents.

Quick road test: I slapped on the foam tires again and headed out to the linoleum hallway floor. First I tested the car with scotch tape covering the hood vents (the "stock" config) and then removed the tape to open the vents. I think it works, the car pushed a little less at speed but the effect was extremely subtle. There also might be a little more drag at speed. I will probably have to plan another trip to Kenon to test whether this mod actually works or not.


I don't feel that this mod ruins the car's lines too much.

2010.11.18, 05:06 PM
Okay, I sat down and fabbed the front diffuser for the F430. This one is much more aggressive than the 911's, extending from the bumper all the way up to the hood and with more diffuser volume. I think the angle in these pics may be too aggressive and cause flow separation, but I need to do a couple more tests before I conclusively state that (I've reduced the curvature for the time being).




In any case, the same effects were observed for this diffuser vs. the first one. More front end stability, increased steering at speed. On linoleum, rear end slides out a little bit easier but also more progressively than before. The first few runs I noticed some weird inconsistency during turns that I couldn't really explain, so I tried reducing the curvature of the very end of the diffuser (such that it ends at a 70deg-ish angle, not 90). Seems to solve everything. The car feels consistent now, and by moving the rear wing back I balanced out the leverage that the front diffuser has on the front wheels (the F430 has a long nose). Track test over Thanksgiving weekend I believe.