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 Post subject: Re: planing the G.T.R.
PostPosted: Tue Mar 13, 2012 3:16 pm 
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Got here a bit tardy...

I am confident you could hit your goals with a Miata single donor build and a circa-'60 Le Mans racer body. The only things keeping Miatas from hitting 40mpg are streamlining (on the highway) and weight (in town). Seriously, it'll be cheaper and easier than you think BUT NOTHING that looks like a Se7en will get 40mpg unless you go to ridiculous extremes (and yes, a 32 horsepower Kubota tractor engine is a ridiculous extreme).

I think it's possible to produce a streamlined body for a Locost for two grand more than the standard Locost body. You can do it for less if you're prepared to do 200 hours of bodywork

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 Post subject: Re: planing the G.T.R.
PostPosted: Tue Mar 13, 2012 6:18 pm 
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Location: Edmonton, Alberta
krepus wrote:
I think your power to mileage ratio/ goal is a bit skewed... There isn't a 160 hp motor on the market that get 40 mpg's, especially if paired with either of those rears. That hp number is derived from the heavy end of the typical Locost scale... For that kind of mileage, you might want to check out Jack Mcormic's build....*I know I just butchered your last name, sorry Jack...* aero will be key in hitting high mpg numbers... But it won't be quick, comparitively speaking...



When the new Mustang V6 can get 300hp and 30mpg, in a car that weighs more than double a locost, I don't see why 160hp and 40mpg in a 1300lb car is unreasonable. Obviously if he's hooning around it won't get 40mpg, but with a small, efficient, turbo engine driven conservatively it should be attainable. Turbo G10 or G13 (Metro/Swift motor) seems like a natural choice. Not sure if you can squeeze 160hp from the 1.0, but I know you can get over 200 from the 1.3.


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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 12:51 am 
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As speed increases, aerodynamic forces become much more significant in the amount of energy required to maintain that speed. Keeping this in mind, consider the following:

For argument sake, we'll use the aero numbers I came across for the the Boss 302 Mustang, with a frontal area of 24ft^2, and around a .36 drag coefficient. From best data I have been able to find for a Caterham we'll call the Locost a frontal area of 16ft^2, and around a .65 drag coefficient. Thus the drag area (CdA) is 8.64 for the Mustang and 10.40 for the Locost. Based on a rough calculation from some random top speed horsepower formula I've picked up over the years, that shows the Mustang needing ~20.3hp just to overcome aero drag at 70mph, and the Locost showing ~24.4hp to do the same...So it would seem the Locost might require somewhere in the neighborhood or 20% more energy than the Mustang to punch a hole in the air. Yes a smaller engine will generally use less fuel at the same power output, due to lesser internal losses. And yes there is still an energy cost associated with all the extra weight the Mustang is carrying around. But a surprising amount of that will still be offset by the aerodynamic loading at highway speeds such that you might not get nearly as much of an improvement in fuel economy as it might seem at first glance.

If anybody has more accurate numbers or formulas, please feel free to correct me.

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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 9:20 am 
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The numbers I have found for the Locost agree very closely. I found this calculator: http://www.paladinmicro.com/pmicro.php?frm=HPvsSpeedCalc.htm If I punch in your .64Cd and the 16 sq ft. I get 29+HP to push a book-sized Locost at 70MPH.: Add about 10% more in frontal area for a +4 chassis and it takes about 31.4 HP Considering that Jack's original Max had a maximum of 32 HP and a max speed of about 72MPH-ish (governed of course), this all seems to support your CdA numbers for the Locost.

That calculator also has an estimated MPG which shows the effect of speed vs fuel consumption. He does state that his formula assumes a BSFC of 0.50 Lbs/HP and premium fuel at 6.35 lbs per gallon. He doesn't show the formula but it is fun to play with the inputs and see the different outcomes. According to that calculator, a 1600 lb Ron Champion Locost (I'm including a driver + some other weight) with that same CdA rolling down the road at 70MPH would require about 30 HP and would get about 30MPG. Any realworld signifacant deviation from those numbers would possibly indicate different tires or operating in a different area of the engine BSFC curve. If you had the chart for your engine, maybe you could scale the results? IF you are planning cross country trips, don't forget to include the weight of the driver and passenger and any luggage in your calculations. Although the graph clearly shows the aero as the ~90% contributor.

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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 9:36 pm 
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had a chance to talk to jack and read the reasent posts. thats a ton of info. it looking like 30ish is a more realistic thing. but it may be improved slightly if i can find bsfc charts for my engine options. creating a new problem.

i dont know why im fighting the miata so much but bear with me. engine options honda f20, mazda miata, kubota desiel? and the options are endless and im a little more open after seeing max mashing threw some corners. so now im looking for BSFC charts for what ever you might have or know of. i keep thinking that what ever the engine is i would be able to get it in the car with wiring harness, rwd already or with parts for RWD readily avilable. please feel free to toss your two cents in.

just a thought here but had a chance to look at a R160 irs rear end out of a subaru legacy. very cool looking little rear end. i could have this rear end for free. i already have a early toyota carola rear end. but was just wondering if any one knew or had a thought about the R160? 510 guys are saying it good to right around 200 hp. drag, rotating mass and weight bring up these thoughts. compared to the toyota?


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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 9:57 pm 
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f20c BSFC ( g / k Wh)
at 4. 4 kW, 1500 r pm

i have no idea what this maens!!!!!!!!!!!!!!!! :BH:
can some one help


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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 9:59 pm 
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378 is in the colum next to my last post.
for some reason i didnt copy that part.


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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 10:24 pm 
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Location: san francisco bay area
Personally I think the R160 is a nice little rear end. ... :mrgreen:
Kinda limited on ratio choices, iirc the diff choices are; open, clutch type posi, viscous lsd. .. I don't remember a torsen version.
My opinion is, it's shock load that breaks them more often than anything else and that's more a matter of driving style.

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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 10:31 pm 
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BSFC = Brake Specific Fuel Consumption. "Brake" means measured on a dyno. The rest means the amount of fuel to produce a horsepower for a period of time. For us it is usaully measured in Lbs. / HP Hour. It's a basic design number, if you know this then you can figure out how much fuel you will burn to do a certain job.

That number is in metric, grams / KW Hr. 378 grams is .83 pounds. There are about 750 Watts in a Horsepower. A metric hour is just like ours! ( you'd think there would only be 10 of them, but I guess that caused problems... )

I don't think you're going to find big differences in BSFC in modern engines for your locost. If that is really what you want, you would need tall gears and run the engine with the throttle wide open at low rpm. The throttle in a gas engine is a big source of inefficiency, diesels don't have them and that is why they use so little fuel to idle and can get good city mileage. If you have a throttle and it is not wide open, it causes vacuum during the intake cycle. That must be subtracted from the pressure the motor makes, so there goes your mileage.

How you drive, skinny tires, attention to aero ( no windshield, cloth cover for passenger compartment, small rear fenders or MAX style bodywork etc. ) will make more difference. Unless you go so far as to use the engine Jack used, which was a cool choice.

You said you were interested in 200 HP/ton. That means 120 HP motors, not an F20 or even Miata... Having a high HP motor will kill your mileage because you will not have the throttle open. I think that is the big win that most small motors have. You need to shift them to get power so you are normally using larger throttle openings when cruising. Hard to do with a V8.

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 Post subject: Re: planing the G.T.R.
PostPosted: Wed Mar 14, 2012 11:01 pm 
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Quote:
i have no idea what this maens!!!!!!!!!!!!!!!!


Oh are you going to have fun! :BH: I know about enough to spell it differently every time. There are work measurement conversions (HP to KwHr), weight measurements (g/kwhr to lbs/hp) fuel mass calculations (regular, premium, E-10) and a whole lot more. Rather than reading somewhere else and then regurgitating that here, I suggest you do a search and plan on sittling down for a few hours to get familiar with the terms and how they convert. Start on Wiki[pedia and look up BSFC (Brake Specific Fuel Consumption) To work out the best engine, I think you will have to know the weight and gearing of your car, some nubers for aero and rolling resistance etc. The previously mentioned calculator and Driven's numbers are good starting points. Beware of " paralysis by analysis".

Or you can just build something and see where it goes.... Unless you get something like my gas guzzling rotary, you will probably get between 25 and 35 MPG at 70 MPH. I only get 20 MPG with my rotary.

Oh I just saw what horizonjob wrote. As he said, to maximize MPG assuming the same vehicle, smaller engines working harder is better than bigger engines working less hard. But he and I disagree on the math for your HP. His 120HP assumes a 1200 lb car. very few of us get that. I'm in at 1400# not counting driver/ passenger/ load. And that makes matters worse for fuel efficiency

So we basically killed your 40MPG goal, now we're rapidly killing your 200HP/ton goal. What are friends for? :cheers:

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“Any suspension will work if you don’t let it.” - Colin Chapman

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 Post subject: Re: planing the G.T.R.
PostPosted: Thu Mar 15, 2012 6:15 am 
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Location: Park Hills, KY
Build it with what you have or can reasonably acquire and enjoy the thing. Don't over think it... You can always improve it later on.


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 Post subject: Re: planing the G.T.R.
PostPosted: Thu Mar 15, 2012 10:12 am 
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The voice of reason
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Quote:
But he and I disagree on the math for your HP. His 120HP assumes a 1200 lb car.


Agreed, no real thought involved there. :) I was just trying to nudge towards a smaller motor if gas mileage was a goal. Most engines these days have more then enough power for 200 HP/ton...

And krepus is right, build it and you will have a delightful sports car. A good body for mileage can always be phase II. Then you can drive something while you deal with all the body work. Maybe Jack will have a body for sale by then, maybe something from Curtis who knows...

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.


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 Post subject: Re: planing the G.T.R.
PostPosted: Thu Mar 15, 2012 1:01 pm 
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Not a real issue. I was just trying to put a realistic spin on it.

I have been doing some BOE calculating based on what we have learned here. By using the paladinmicro website and making some adjustments for real-world experience of RX-7 drivers and EPA estimated mileage etc. (not including the 5%-10% hit for E10 fuel) I can state with 100% confidence that estimated mileage for my rotary powered Locost should be around 20.1. Like I said, I'm getting around 20 at 70MPH. That estimate changes by -/+5 MPG for 60 and 80 MPH respectively so I guess I'm not all that bad, considering.....My 2 biggest problems are my 5 gallon fuel tank, and wiping that grin off may face every time i go for a ride. :)

BTW I just found this site where a Caterham got 131 MPG with a gas engine. Not bad if you only want to drive 15MPH!

http://www.gizmag.com/go/5921/

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“Any suspension will work if you don’t let it.” - Colin Chapman

Check out my rotary build log: click here


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 Post subject: Re: planing the G.T.R.
PostPosted: Thu Mar 15, 2012 10:37 pm 
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the car is being stalled becouse i have to finish the bike in the shop first. so this is just planning at this point for the next project. which is why im in the theory section.

so hp and mpg. just a thought. if gas is a strech why not diesel. 1.9 td vw. can be hooked to a samuri or toyota trans. could be done for about 2k. 120ish hp? 74hp stock and i have no idea about mpg. its a thought and i could be fairly cost effective.


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 Post subject: Re: planing the G.T.R.
PostPosted: Thu Mar 15, 2012 10:52 pm 
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fastmonkey wrote:
the car is being stalled becouse i have to finish the bike in the shop first. so this is just planning at this point for the next project. which is why im in the theory section.

so hp and mpg. just a thought. if gas is a strech why not diesel. 1.9 td vw. can be hooked to a samuri or toyota trans. could be done for about 2k. 120ish hp? 74hp stock and i have no idea about mpg. its a thought and i could be fairly cost effective.


And not a bad idea in my opinion. I think I even still have the CAD drawings somewhere. ..
If I can find them, I'll post them.

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