New 818 Configurations Windtunnel Tested

[STiPWRD]

I was able to shrinkwrap the .obj surface file I got from Santiago into a solid step file using CREO but the outer surfaces still need to be smoothed out:
image.png
On a side note, I've had bad experiences with Autodesk Simulation CFD (formerly CF Design) mainly because it uses a finite element approach and converges based on element criteria instead of other CFD tools, which use finite difference or finite volume, whose convergence criteria is based on energy balance. The autodesk tool could not correlate a simple cold plate pressure drop experiment without tons of fine tuning and the customer service was poor, so I lost confidence in it. I would trust Fluent, Ansys CFX or FloEFD far more.

[nkw8181]

So those with the model would it be usable for interior redesign?

[bbjones121]

My current thinking based on what we have seen testing intercoolers seems to be pointing to different solutions based on the intended use of the car. Testing the air to water systems on the track has shown that with no recovery time they tend to gradually increase in temps over the course of the longer runs, whereas on the street the recovery time at either cruising speeds or idle allows them to stay cooler than either the top mounts or relocated air-to air units still in the engine bay. The two W2W systems we tried were different in that one used a large reservoir and a medium sized cooler and exchanger and the later system used a bigger cooler and a full sized radiator as the heat exchanger with no reservoir. The second system worked better and was overall lighter than the one using the extra tank.

For air to air I still think the top mount is viable for stock and mild builds, on both street and race cars, and that is where we concentrated our street car efforts in the tunnel trying to find the best spots to pull and from and exit air to. The plan going forward for ducting to the top mounts is to use four inlets to feed the intercooler. The two side inlets are effective if they are cut out correctly (the cutout shape made a HUGE difference which was something we missed in our first trip to the tunnel) and either the decklid vents or the roof scoop ducts for the other two depending on which model it is.

During our track testing we also tried several different very large scoops feeding the intercooler from in between the humps and this was not as successful. Even with a large top mount (Turbo XS) the temps were not as low as we would like them to be and the drag/reduced downforce was not good at all. Airflow in that area is just very turbulent and the cockpit itself is a low pressure so air will actually flow backwards into it.

As far as air exit goes the best place is the lower section of the car, the upper vents still allow air to exit but the flow is much slower and more chaotic. The rear trunklid vent is somewhat variable, with the spoiler in place you get air flowing in, but with the wing in place there is not much flow through that vent at all. I still think the vent is useful, particularly for escaping heat when the car is sitting still, but it isn't a good place to get reliable air entry or exit from. Cutting additional vents on either side of the low vent seems to make the most sense for someone needing to get additional air out of the engine bay.

The front mount in the race car is really just going to come down to testing turbo lag. This setup will only be a real possibility for R models as the tubes run through the top of the doors, but the plumbing was actually pretty straightforward and the amount of tube relative to a WRX with a front mount is not that different (maybe 50% more but not 2 or 3 times as much). We stayed with a fairly small inlet tube to try and keep the overall volume down but we still have testing to do to see if this really is the best solution for big power track only cars.

Also on the R, the windscreen makes a big difference, improves drag, downforce, and cooling and running without it does not improve flow into the rear decklid area.

Sorry to resurrect this, but how did you fit a TurboXS intercooler? I can't fit mine under the 818S lid?

[Jim Schenck]

We built a scoop connecting the tops of the humps and then cut out the area underneath the scoop which allowed for the extra size of that intercooler. I would estimate the smallest scoop we had in that location covered about the bottom third of the humps but we also tried larger ones, including all the way to the top of the roll bar. We also sealed the intercooler to the decklid in order to force all the airflow coming in to go through the cooler.

[ssssly]

We built a scoop connecting the tops of the humps and then cut out the area underneath the scoop which allowed for the extra size of that intercooler. I would estimate the smallest scoop we had in that location covered about the bottom third of the humps but we also tried larger ones, including all the way to the top of the roll bar. We also sealed the intercooler to the decklid in order to force all the airflow coming in to go through the cooler.

Was there any appreciable increase to airflow from those configurations?

[lennyspecv]

That's pretty cool to watch testing in a wind tunnel. Never seen that before.

I am optimistic that by the time I have the money for a kit, there will no longer be a need for a AWIC because of improved air flow and ducting.

[bbjones121]

We built a scoop connecting the tops of the humps and then cut out the area underneath the scoop which allowed for the extra size of that intercooler. I would estimate the smallest scoop we had in that location covered about the bottom third of the humps but we also tried larger ones, including all the way to the top of the roll bar. We also sealed the intercooler to the decklid in order to force all the airflow coming in to go through the cooler.

Thanks for the info Jim. I may try welding up my own brackets to drop the back of the turbo xs a bit.

[tmoretta]

Do the two top decklid (Intercooler) vents flow much air? I have improved the flow from these two vents by sealing them to the deck and also sealing the intercooler to the deck. I am wondering if I should add extra scoops on top of the deck vents to capture more air.

[Jim Schenck]

The center decklid scoop did not flow as much air as we were hoping in any of the configurations we tested (determined from post intercooler air temps) and that was even with the windscreen removed completely on an R. The decklid vents are functional and maintain a positive airflow through the intercooler as measured using the wind tunnel flow meter. Our attempt to make these vents flow more air with an extra scoop on top (a scoop from the type 65) did not help the flow although some more tests in that area could likely see some design that shows a benefit. We also have prototype ducts made now for the side scoops which should take advantage of the cutout shape we found worked best in the tunnel.

[bbjones121]

The center decklid scoop did not flow as much air as we were hoping in any of the configurations we tested (determined from post intercooler air temps) and that was even with the windscreen removed completely on an R. The decklid vents are functional and maintain a positive airflow through the intercooler as measured using the wind tunnel flow meter. Our attempt to make these vents flow more air with an extra scoop on top (a scoop from the type 65) did not help the flow although some more tests in that area could likely see some design that shows a benefit. We also have prototype ducts made now for the side scoops which should take advantage of the cutout shape we found worked best in the tunnel.

Sweet! When can we see these prototypes? Carbon fiber option hopefully

[Jim Schenck]

This is what we have so far, subject to change after testing of course. The flange on these is set up for 4 inch ducting.
sidevent3.gif
sidevent2.gif

[bbjones121]

This is what we have so far, subject to change after testing of course. The flange on these is set up for 4 inch ducting.
sidevent3.gif
sidevent2.gif

Nice. For some reason I was thinking they were extensions out, but this is perfect. I was trying to figure out a way I could do something like this as I trying to keep the air to air. Please let me know when they are available.

[Flamshackle]

This is what we have so far, subject to change after testing of course.sidevent3.gif
sidevent2.gif

Have you got a testing date for these coming up?

[Jim Schenck]

We are installing these on the coupe we are currently building.

[Lumpyguy]

These bigger vents are what I have been doing. I added 1" to the depth and raised the top line horizontal which opened it up as well. I was looking at putting ducting and tubes up to a shroud on the top of the coolerl. Has any one confirmed just how much air goes thru that side vent?

[Sgt.Gator]

Jim, any updates on all this? I'm especially interested in the side vent solution and the FMIC solution. Any details on the FMIC you can share?

Also, if possible could you post up some of the vehicle weights for the various FF 818 cars here: http://thefactoryfiveforum.com/showt...t-Your-Weights
Thanks!

[Jim Schenck]

The coupe we built with those side vent scoops was the one with the Ford 2.3 Ecoboost. We figured out as we were building it that the way the intake was routed down low it wasn't practical to use them as a source for the intercooler due to its location on that specific engine. We originally had a mustang intake that had a higher throttle body but was much tougher to package, instead we now have an AWIC mounted under the front of the engine which fit very nicely and helps a little with the higher center of gravity that the inline four has. Our older coupe still has the Top mount so we will retrofit the side vents to it in order to test them, but that will have to be once the spring comes and the roads get clear again.

The race car with the front mount is out at the tuner right now as we are working through an issue with the EFI that held us up during our final test last season. That was the only test we had the front mount installed as the rest of the year we were switching between several AWICs and different configurations of top/remote mount air to air we were wanting to test. Once the engine issue is sorted we will be doing some testing on the dyno with the front mount and then bringing that car down south to do some early season track testing. That will likely be either late March or early April.

[Hindsight]

Thanks for the update Jim. Please let us know where you are going to be racing so we can come watch. Would love to see the 818 at Road Atlanta.

[Mitch Wright]

Thanks for the up date Jim.

[bbjones121]

Thanks Jim

[Sgt.Gator]

Many thanks Jim.

[Sgt.Gator]

Jim,
Any Cd numbers to compare the R with the S? I'm asking because I'm considering an R with an S windshield and full halo cage. It would look similar to a Mazda MX5 Pro Cup car. But I don't want to go down that road if the drag is significantly worse on a S than an R.
Have you tried testing a rear wing on a S ?
Thanks

[tgf05354]

That's pretty cool to watch testing in a wind tunnel. Never seen that before.

I am optimistic that by the time I have the money for a kit, there will no longer be a need for a AWIC because of improved air flow and ducting.

I too am planning to buy an 818s in a few months. Were can I find more information on ducting for an air to air IC. I'm planning a stock street setup and would like to avoid the complexity and cost of an air to water unit.

[Jim Schenck]

Haven't tried a rear wing on an S, just a couple different heights of spoilers. The drag on an S with a windshield and no spoiler is almost identical to the R with no windshield but with the big wing on the back. On the R the wing adds about 18% more drag, so even though we didn't test that exact combo (an R with a full windshield) and the R cage might have slightly more drag I still think that is a good approximation of the difference. Also though, the windshield will for sure take away some drag and downforce from the wing as well unless the height is raised considerably, so while I think that the windshield adds around 18% drag and the wing adds similar, the two of them together would not likely add up to that total combined.

[bbjones121]

Any updates on the side vent ducts?

[FFRSpec72]

Haven't tried a rear wing on an S, just a couple different heights of spoilers. The drag on an S with a windshield and no spoiler is almost identical to the R with no windshield but with the big wing on the back. On the R the wing adds about 18% more drag, so even though we didn't test that exact combo (an R with a full windshield) and the R cage might have slightly more drag I still think that is a good approximation of the difference. Also though, the windshield will for sure take away some drag and downforce from the wing as well unless the height is raised considerably, so while I think that the windshield adds around 18% drag and the wing adds similar, the two of them together would not likely add up to that total combined.

The windshield on my challenge car takes away about 8MPH at WOT over the windscreen

[Jim Schenck]

Any updates on the side vent ducts?

All the cars are still packed away for the winter except the 818R is out at the dyno. The FMIC in that car is up to be tested next and then we may either test the side ducts on the street car or swap the race car back to a top mount and try them there.

[longislandwrx]

I vote for the latter, I would love my top mount to work effectively on my R.

[Mitch Wright]

I am also running a top mount and will be 100% track ready the end of April early May, I will let you all know if the duct work I am doing is successful.

[nucleus]

Interesting discussion on aerodynamics - it it so counter-intuitive!

High speed is low pressure, low speed air high pressure.

When I built my RV-6A I used a custom cowling and ended up building a plenum for cooling as well.

I actually think that a plenum for the intercooler makes a lot of sense. For best flow keep in mind that you want gentle bell mouth type curves for the high speed air, then increased area for the air to slow down, and once the air is slowed down, it can change direction easier due to reduced momentum.


Then I look at this image, the transition into the oval section looks too abrupt, but with the strange magic of moving air, perhaps that abruptness is what makes it work.


Here are some examples of ducts that slow the air down and increase pressure.

Not great, but better than most


Here is a simple way to test your airflow mods, you hot glue some sponge onto tubing


and use a water manometer to measure static pressure from the changes you make.

So-called NACA ducts were designed for high speed aircraft to feed turbojets that were already sucking air. They are not appropriate for anything but a APU turbine on a big jet.

[Frank818]

So-called NACA ducts were designed for high speed aircraft to feed turbojets that were already sucking air. They are not appropriate for anything but a APU turbine on a big jet.

Why are they used on race cars?
What would you suggest as a replacement to flow air in with minimal drag if NACAs are crap for cars?

[bigAl]

"So-called NACA ducts were designed for high speed aircraft to feed turbojets that were already sucking air. They are not appropriate for anything but a APU turbine on a big jet."
I would respectfully disagree. They have been successfully used on many non-jet airplanes and certainly on many automobiles.

[Sgt.Gator]

That must be why the crappy Ferrari aero engineers use them.

[Mechie3]

It's actually quite the opposite. They were intended for feeding jets, but did a poor job at that and are better where lower flows are needed.

From a few different sources:

Designed in 1945 by the National Advisory Committee for Aeronautics (precursor to NASA), the NACA duct was intended as an air inlet for jets. Only it was a failure. The design wasn’t any good for bringing fast, “clean” air into the fussy, rotating impeller blades of a jet engine, so the engineers who invented it lost interest. Luckily for today’s racers—and many generations of Italian sports cars—the qualities of the NACA duct that made it unfit for jets make it ideal for most other kinds of engines, and its low profile, simplicity, and small size earn it love from designers for aesthetic reasons.

And:

The original goal of the NACA duct was not applications requiring maximum pressure recovery (ram pressure), unlike the prominent ram-type intakes seen behind the driver's head in Formula One cars. The application was intended for applications where is desired to minimize the parasite drag added to the aircraft or car. This works well for air vents and such as the drag remains low whether the vent is opened or closed. It is not very useful for engine air intakes, bur is useful for cooling air supply. They are low-drag intake channels used mostly for a variety of cooling requirements such as brakes, engine, and for driver cooling intake. Distinctive geometry includes a widening mouth at the inlet, with the duct floor slightly opening up the flow area.

[Frank818]

I'm going to use one on the top side of the hump to feed my air intake filter, but it's an addition to using the side scoop as well for the air intake, I'll use both air sources and only the top, right from the hump, will have a tiny NACA duct in order to open up more the duct floor and bring more air. I think it'll work, although we haven't seen much of wind tunnel results on these 2 818 top side scoops.

[mindinclouds]

That must be why the crappy Ferrari aero engineers use them.

They do work well if sized, shaped and located properly...

Note the sharp corners along the longitudinal edges of the inlet. These are very important in developing a vortex off of the edge and rolling towards teh inside. I see NACA vents all the time (even on cars built by high tech racing teams) that have the corners nicely radiused (I guess it seems logical that they would be better if shaped that way, but if you read the old NACA documents it explains just the opposite).

[mindinclouds]

I think it'll work

Keep in mind that a NACA duct will not work very well at any location with an air pressure below ambient.

A common example is any surface that is more than a rather large outside radius when the surface is diverging inward.

[UnhipPopano]

Out of curiosity, if FF has been "Testing" the side and rear vents, did they try changing the shape of the openings to the NACA duct shape, and if so did it reduce the drag?

[tmoretta]

Do you have a pic. of the side inlets "correctly cut out"?

[bbjones121]

I would love to know whatever happened to the Factory five ducts that were being developed.