MR2 SpyderChat banner

21 - 36 of 36 Posts

·
Registered
Joined
·
48 Posts
Good examples of how to factor drag into the performance equation. A point of reference: A typical large car only needs about 10-12 HP delivered to the driving axle to maintain highway speeds on a level road with no wind.
What is highway speed?
 

·
Registered
Joined
·
48 Posts
So what is everyone doing for battery setups for "Just a couple of HP" worth of weight reduction? I've been looking into options for that and haven't really come up with anything yet.
 

·
Registered
Joined
·
161 Posts
Somehow whenever these discussions come up, no one talks about the driver weight reduction mod
 
  • Like
Reactions: markthegrea

·
Registered
Joined
·
1,027 Posts
So what is everyone doing for battery setups for "Just a couple of HP" worth of weight reduction? I've been looking into options for that and haven't really come up with anything yet.
My Li-ion battery weighs 3 lbs.; large motorcycle size. perfect for anything except winter cold-starts. Mine is on a custom aluminum bracket in front of the pass-side brake/turn light.

Dave
 

·
Registered
Joined
·
5,174 Posts
So what is everyone doing for battery setups for "Just a couple of HP" worth of weight reduction? I've been looking into options for that and haven't really come up with anything yet.
There is a thread about lithium batteries here. I have been using A123 or LifePO4 batteries daily for about 7 years now. I have never put an external charger on them. I use two batteries as I drive year round. One is behind the pass seat the other in the OEM location with a custom aluminum mount. My total battery weight is about six pounds, the 51R lead acid weighted about 26 pounds.

Driver weight is one of the cheapest ways to reduce total car weight as well as driving with a less than full tank of gas. I run without a spare but carry a pump and flat fix. I have also removed some interior trim that is unneeded. Overall my spyder is about 100 pounds lighter and I have lost a bit of weight also :)
 

·
Registered
Joined
·
161 Posts
I remember a number of years ago, one of these overweight professional racers was complaining that Danica Patrick had an unfair advantage.
Haha, I always think that when I see the bigger guys doing everything to shave an ounce off the car....then you got a jockey sized driver in the other car. No matter what it costs, it ain't as 'expensive' as the commitment to dropping some weight
 

·
Registered
Joined
·
1,558 Posts
LOL nice throwback, the "damn fine rat's nest of rope and wiring terminals" refers to my old car that I crashed. When your battery weighs close to nothing, it kind of doesn't matter how it's secured; the rope did fine. For a little more effort you can modify the stock battery clamp (buy a thread tap, tap the rod down further, then cut a lower hole into the post). Another nice solution is a 3d printed or sheet metal holder to position the base of the battery.

Speaking of aero, the bigger ducktail spoiler should reduce the drag by a measurable amount, if you can tolerate how it looks. Lowering the car also helps since the underbody is far from smooth. I wouldn't be surprised if those two cut 10% off the drag, which comes out to around 4hp @100mph I think. The Spyder needs 15hp to do 65mph like dblotii said.
 

·
Registered
Joined
·
3,046 Posts
So what is everyone doing for battery setups for "Just a couple of HP" worth of weight reduction? I've been looking into options for that and haven't really come up with anything yet.
I made a battery bracket that mounts on the rear crossmember . I used a 2010 honda fit battery , it's a little shorter than the spyder battery , I'm sticking with good old lead acid . I'm making a couple extra when I get some extra time .



 

·
Registered
Joined
·
48 Posts
The fit battery is a good idea especially if colder temps are an issue. That is a crazy long thread on batteries with a ton of info, I stumbled on it a while ago but it's hard to sift through everything. I was always considering the Lithium route but ideally I'd like one that just drops in to the factory spot. I was always worried about the elevated engine bay temps of a turbo setup.
 

·
Registered
Joined
·
48 Posts
Speaking of aero, the bigger ducktail spoiler should reduce the drag by a measurable amount, if you can tolerate how it looks. Lowering the car also helps since the underbody is far from smooth. I wouldn't be surprised if those two cut 10% off the drag, which comes out to around 4hp @100mph I think. The Spyder needs 15hp to do 65mph like dblotii said.
I'm pretty sure downforce and drag go hand in hand for the most part, isn't that the trade-off? Does that mean the ducktail style spoiler doesn't make down force? I don't have a lot of experience with street car aero so I might be wrong but on more purpose build racecar applications anything that makes downforce also makes drag according to CFD sims.

Also, I appreciate the consensus that an MR2 spyder at 65mph is only robbed of 15 or so hp but how is everyone coming up with that number? To me the best way to do it would be drive the car at 65mph, note the spot on the VE table where the car is spending most of it's time, take it to a dyno, and see what power it makes there. Has anyone done that kind of testing before throwing numbers around? I haven't, so I'm not going to speculate. I do know a tight 1zz MR2 spyder is an absolute turd from 60-90 especially when compared to more powerful cars with worse or near identical power to weight ratios.
 

·
Registered
Joined
·
1,601 Posts
I'm pretty sure downforce and drag go hand in hand for the most part, isn't that the trade-off? Does that mean the ducktail style spoiler doesn't make down force?
True. A spoiler is intended to reduce drag by modifying the airflow behind the vehicle. By disrupting the laminar flow over the vehicle, it causes the air to drop in quicker and thus reduce the vacuum and turbulence behind the vehicle which causes drag. Spoilers are often confused with wings, which produce downforce with a drag penalty.

Spoilers can work on any vehicle, but they work best on wagons, vans, SUVs and trucks, where you see them often. Wings only really work on high power rear drive cars, when they are well up in the airstream. Such vehicles may need them for stability at high speed. I am not familiar with the device under discussion, but most aerodynamic devices found on cars are only cosmetic.
 

·
Registered
Joined
·
1,558 Posts
I'm pretty sure downforce and drag go hand in hand for the most part, isn't that the trade-off? Does that mean the ducktail style spoiler doesn't make down force? I don't have a lot of experience with street car aero so I might be wrong but on more purpose build racecar applications anything that makes downforce also makes drag according to CFD sims.

Also, I appreciate the consensus that an MR2 spyder at 65mph is only robbed of 15 or so hp but how is everyone coming up with that number?
Well a brick (or a minivan) have a lot of drag and pretty much no downforce. The Spyder has a short tail with detached flow so a spoiler that extends the tail will increase both, since you're reducing pressure drag, not induced drag. The factory spoiler that sticks up into the air is more of a question mark, it probably reduces both to some extent but I would guess not as much as the Duraflex Type-W which sticks out the rear by several inches. Race cars usually have nearly fully streamlined bodies while street cars don't.

As far as the 15hp number goes, there's this easy calculator: Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
The Cd is a big question mark, but we know weight (I put 2350 for my lightened car with me in it), performance tires are usually in the 0.008-0.012 range for rolling resistance, the frontal area is something like 18sqft. Miatas and S2000s have an even shorter tail and steeper windshield than the MR-S and they have Cd around 0.37, so 0.32-0.34 is not unrealistic for the Spyder.
 
21 - 36 of 36 Posts
Top