Green Grand Prix modding thread

[Vman455]

After 250+ posts, I think it's time to let my "3rd Gen Prius Aeromodding" thread rest. I thought I would start a catch-all thread not just for my car, but anyone else who has competed or plans to compete in the Green Grand Prix and wants a place to discuss modifications specifically for that and other fuel economy events.

The reason I'm starting a new thread for this: One thing I was not prepared for was the amount of elevation change in the Watkins Glen short course profile, something I had not researched before the GGP.



From Turn Two through the back straight, the course rises 124' at an average grade of nearly 2.5%, although it is steeper through Turns 3 and 4 than on the straight itself. Laboring the car up that grade every lap, I got to thinking--a significant aeromod (like the cargo box tail), which adds a fair amount of mass to the car, doesn't really pay for itself in an event where I have to maintain an average speed of 45mph and am speed-limited to 60mph; in other words, having more momentum or improved aerodynamic efficiency on the front straight doesn't pay off as much as it could since I can only take advantage of that up to a certain speed, for which I'm penalized anyway if I go too fast and overshoot that 45mph average. Also, while slowing down on the uphill is an option, there is a minimum 35mph speed requirement for the event. So, I can't crawl up the grade to minimize the impact of having to carry all that weight up, and I can't coast past 60mph on the front straight to recoup some of that energy expenditure by taking advantage of the increased momentum.

So, I'm re-thinking my approach for the GGP. In the next few days here, I'll be removing the tail, cargo carrier, and hitch receiver assembly (which together weigh nearly 150 lbs), and starting to gut the car to get rid of as much mass as possible. I plan on a new tail design, with light weight as a design goal; most of the aeromods on the car will stay in place (since most of them don't weigh much). Even without the tail, the Prius is sitting at Cd .21, so it's not like I'm giving up something major in that area. This is a new direction for the car; I dabbled with removing some weight a few years ago, but was never very serious about it and ended up adding a lot in the tail, sound insulation and, for a while, a big subwoofer box. I'll now be focusing more on mass reduction than new aerodynamic devices, hence this new thread, in Ecomodding Central rather than Aerodynamics.

I'm not entirely crazy, as most of my driving these days is in-town and low-speed, grocery store runs and the like. So, a drastic reduction in mass should benefit me more than it would have 4 years ago, when I was doing mostly highway miles. This is very experimental--I'm not sure what it will be like to live with a daily driver with no sound insulation, gutted interior, etc. But I'll find out! And I guess I'll find out how far I'm willing to go in the name of science, and how long before my partner refuses to ride in my car.

As of now, here's what I have taken out:
-Hatch panels: 5.2 lbs (21.6 lbs with added insulation)
-Rear door panels: 10.6 lbs (20.0 lbs with added insulation)
-Hatch door panels: 5.4 lbs (10.4 lbs with added insulation)
-Wheel covers/pizza pans: 2.5 lbs (9.4 lbs with pizza pans)
-Front swaybar and endlinks: 8.4 lbs
-Trunk mat: 5.4 lbs
-Rear speakers, miscellaneous hardware: 5.3 lbs
-External mirrors: 4.2 lbs
-Tonneau cover: 4.2 lbs
-A-pillar trim and dash speaker grills: 3.0 lbs (4.2 lbs with added insulation)
-Passenger wiper: 2.8 lbs
-Rear wiper and motor: 2.4 lbs
-Intake resonator: 2.0 lbs
-Hood insulation: 1.2 lbs
-Plastic engine cover: 1.0 lb

For a total of 102.5 lbs gone, or 63.6 lbs from OEM curb weight, and I haven't even gotten to the tail/hitch receiver or spare tire. I'll update this list as I take things out and see if I can get some pictures as I go along. I also plan on weighing the car at a truck scale later this summer (we have a CAT scale at the stop just outside town) to get an accurate weight.

Some things I've thought through already--I'll be removing the headliner and sun visors, so I've ordered a vinyl strip to go across the top of my windshield (because racecar). The pizza pan wheel covers will be replaced by light plastic or acrylic annular discs, so I have access to the lug nuts without removing them (I found this was a pain with the full covers). All safety equipment will remain in place--I won't be taking out airbags, drilling holes in bumpers, removing crash bars in the doors or anything like that. The only rule for the modified class at the GGP is that the vehicle must be street legal, so anything that violates that criterion is out.

Other than that, game on.

[freebeard]

Reciprocating or rotating weight — Swap in Titanium valve spring retainers and the wheels and tires.

I plan on a new tail design, with light weight as a design goal

What's the plan? How about a birdcage of welded welding rod shrink-wrapped with boat wrap.

Can you fit BMW i3 19" wheels and tires?

[Vman455]

Originally Posted by freebeard

Can you fit BMW i3 19" wheels and tires?

That would be fantastic; I don't think the bolt pattern is the same, though, although otherwise I think they would fit despite being a couple inches taller.

Edit: Nope, the i3 runs 5x112 bolt circle; the Prius, 5x100.

[Vman455]

That said, let's talk about wheel weights.

I was surprised that the pizza pans weighed that much, actually--nearly 10 lbs of rotating mass. The OEM 15" Prius wheels weigh 16.3 lbs each, and the 195/65-R15 tires are 18 lbs. The lightest available wheel on Tirerack is a forged BBS 17", at 14.3 lbs, but its cost is prohibitive, more than $2000 for a set of 4, and the weight of 17" tires would more than offset the savings in the wheels. However, there are other reasonable options between 15-15.5 lbs for around $400/set in 15" diameter. Since I want to start autocrossing this car, what I might do is pick up one of those options with some 195/50-R15 Dunlop Direzzas, which weigh the same but are a couple inches shorter than the stock tires. That would give me a set of wheels for autocross a pound lighter on each corner and with the effectively shorter gearing of a smaller diameter to boot, and leave my OEM wheels and tires for daily driving, road trips, and the GGP road rally portion.

[freebeard]

Here is a discussion of VW wheels to make a point:

Centerline Classics (Wide 5)

15 x 3.5 11lbs
15 x 4 11lbs
15 x 5 12lbs
15 x 6 12lbs
15 x 7 13lbs
15 x 7.5 13lbs
15 x 8 14lbs
15 x 8.5 14lbs
15 x 10 15lbs
15 x 12 17lbs
16 x 4 10lbs

Centerline Convo Stars (Wide 5)

Same sizes and weights as Classics

Centerline Stars

Same sizes and weights as Classics

Flat 4 Reproduction BRM's (Wide 5)

15 x 5 13.5lbs
15 x 6.5 17lbs

Flat 4 Reproduction BRMs (4 lug)

15 x 5 13.5lbs

Flat 4 Reproduction Enkei Dish (Wide 5, Vanagon 5 lug, 4 lug)

15 x 5.5 17lbs

The wide 5 weights appear representative. So wheel width makes a large difference. Center Line used to advertise that they make wheels in sizes from 10 to 30", so 19x4 with 5x100 PCI is prolly available.

The low-ball approach would be used i3 rims on 5x100/112 adapter plates. That gets around hub-centric vs bolt-centric problems and introduces offset problems.

Is the Hybrid Synergy Drive sensitive to over/under on the tire circumference?

[Vman455]

Originally Posted by freebeard

The low-ball approach would be used i3 rims on 5x100/112 adapter plates. That gets around hub-centric vs bolt-centric problems and introduces offset problems.

The only problem with running adapters would be the extra width, pushing the wheels to the outside of the car. Well, that and the expense--at $300 or more per wheel, and $135 per tire, i3 wheels are an expensive modification.

Is the Hybrid Synergy Drive sensitive to over/under on the tire circumference?

I don't think so; I happened to see a Jalopnik article this morning about some guys in Washington who put a Prius on 29" tires to take it off-roading (4" larger than stock) with no problems.

Updated weight list:

Added sound insulation: 48.6 lbs
Trailer hitch receiver: 28.8 lbs
Rear right seatback: 26.4 lbs
Spare tire: 25.8 lbs
Tail: 21.8 lbs
Cargo carrier: 19.6 lbs
Hatch insulation: 16.4 lbs
Rear left seatback: 13.2 lbs
Rear seat bottom: 12.2 lbs
Rear seat belts, seat brackets, hardware: 10.7 lbs
Front speakers and baffles: 10.6 lbs
Front door insulation: 9.8 lbs
Rear door insulation: 9.4 lbs
Wheel covers with pans: 9.4 lbs (2.5 lbs wheel covers alone)
Front swaybar and endlinks: 8.4 lbs
Jack and tools: 8.2 lbs
Trunk mat: 5.4 lbs
Rear speakers, miscellaneous hardware: 5.3 lbs
Hatch door insulation: 5.0 lbs
Floor mats: 4.5 lbs
External mirrors: 4.2 lbs
Cargo cover: 4.2 lbs
Front speaker crossovers and wiring: 3.2 lbs
Passenger side wiper: 2.8 lbs
Rear wiper and motor: 2.4 lbs
Intake resonator: 2.0 lbs
Sound system wiring: 1.5 lbs
A-pillar insulation: 1.2 lbs
Hood insulation: 1.2 lbs
Engine cover: 1.0 lb

Total: 323.2 lbs/140.4 lbs from OEM

Estimated curb weight now around 2900 lbs, and I still have a full interior minus the back seat.



However, no sound system, and the headunit is the next thing to go.

Of course, it can't be a race car without some decoration, so I added pinstripes to the wheels.



And a windshield banner.



And a plug for the forum.

[California98Civic]

This is great. Subscribed.

[freebeard]

My friends have a Prius that's missing one wheel cover. I tell them it would look better if they took the other three off, but they say they like the sliver cover better. Just not enough to replace the missing one.

I was looking for a place to post that:


https://jalopnik.com/this-lifted-prius-trolls-jeeps-1825777000

Ha! Regen joke.

[Vman455]

A few more little things today. First, updated weight loss:

Added sound insulation: 48.6 lbs
Trailer hitch receiver: 28.8 lbs
Rear right seatback: 26.4 lbs
Spare tire: 25.8 lbs
Tail: 21.8 lbs
Cargo carrier: 19.6 lbs
Hatch insulation: 16.4 lbs
Rear left seatback: 13.2 lbs
Rear seat bottom: 12.2 lbs
Rear seat belts, seat brackets, hardware: 10.7 lbs
Front speakers and baffles: 10.6 lbs
Front door insulation: 9.8 lbs
Rear door insulation: 9.4 lbs
Wheel covers with pans: 9.4 lbs (2.5 lbs wheel covers alone)
Front swaybar and endlinks: 8.4 lbs
Jack and tools: 8.2 lbs
Trunk mat: 5.4 lbs
Hatch door panels: 5.4 lbs
Rear speakers, miscellaneous hardware: 5.3 lbs
Headunit: 5.2 lbs
Hatch door insulation: 5.0 lbs
Floor mats: 4.5 lbs
External mirrors: 4.2 lbs
Cargo cover: 4.2 lbs
Front speaker crossovers and wiring: 3.2 lbs
Passenger side wiper: 2.8 lbs
Rear wiper and motor: 2.4 lbs
Intake resonator: 2.0 lbs
Sound system wiring: 1.5 lbs
Vehicle Proximity Notification System: 1.5 lbs
A-pillar insulation: 1.2 lbs
Hood insulation: 1.2 lbs
Engine cover: 1.0 lb
Horns: 0.5 lb


Total: 335.8 lbs/163.6 lbs from OEM
OEM curb weight: 3042 lbs
New estimated curb weight: 2878 lbs

Second, after driving around without any speakers for a couple weeks, I removed the headunit. This took some doing, since the wiring for the steering wheel switches (that control the tripmeter and MFD display screens) runs through the receiver. After grounding the proper wire, everything works without the unit. I've got a clear acrylic panel where the radio used to be (not pictured); I like that you can see into the dash where it's missing.



Third, after reading this patent, first brought to my attention by a thread here a few years ago, I thought I would experiment with conductive tape on the resin body panels. After some Google searching to make sure the tape I had on hand actually had conductive adhesive, I applied some to the car. In the patent application, one of the illustrated vehicles, in Figs. 12, 15 and 16, is actually a 3rd-gen Prius, so some of my tape is placed where those figures indicate.



I also added it where a CFD pressure map shows low pressure, indicating possible flow detachment, and where the initial Japanese press on a Toyota 86 outfitted by Toyota suggested.





Up next, I've ordered a Magnahelic pressure gauge, which I'll use to draw a pressure map of the top side and underside of the hood before adding hood vents to evacuate high pressure and hot air from the engine bay. I'm hopeful this will improve radiator efficiency as well as improve Cd, as Hucho seems to suggest in 2.1.1 of Aerodynamics of Road Vehicles. I'm becoming more concerned with cooling efficiency with all the recent press on heat-related inverter failures in Priuses, even those that had the E0E software reflash performed (like mine). Currently, one California dealer is suing Toyota over it. So, for the time being I'm removing my grill block just in case--if Toyota ends up recalling and replacing the inverter, great; if it fails under the extended warranty, I don't want Toyota to be able to point to a grill block as a possible cause and deny coverage.

Also on my mind, I'm thinking about ways to lighten the exhaust, but still conducting research on that as the last thing I want is a loud car.

[California98Civic]

The conductive tape is a new twist. Interesting. Did you see any testing data? Online, I found copper and carbon (black) conductive tape too. But all those are more expensive than aluminium, unspurprisingly.
https://www.tedpella.com/SEMmisc_html/SEMadhes.htm