TopGear.com America high mpg project (regeared, aeromodded diesel Rabbit)

[Deezler]

Dang, data for the 1981 VW Rabbit is hard to find. I at least got this much hard data:

Weight: 1755 lbs. (Est. with driver & fuel = 2000lbs)
Height: 55.5 in
Width: 63.4 in
Frontal Area (x 0.84) = 20.52 ft^2

So here was my input data for the calculator Metro linked to:

Weight: 2000lbs
Crr: 0.01
Cd: 0.35 (guesstimated)
A: 20.52 ft^2
Air Density = 1.22 kg/m^3

Then I repeated for a Cd estimate of 0.25 (achievable?)

I remember someone said they were going to get about 1800rpms at 61 mph. using this effective gear ratio, we can plot the estimated road load for the two aerodynamic drag coefficients. Because the online calculator spits out data every 5 mph, I used 60 mph for my own calculations of the HP, to torque (to BMEP) required for this speed given each Cd.



Now, interpolating BSFC values from the chart, we get the following (lets see iif I've figured out the table formatting yet...)

.	mph	rpm	load(kW)	BSFC est.	gal/h	mpg
Cd = 0.35	60	1770.5	10.23	255	0.811	73.98
Cd = 0.25	60	1770.5	7.99	279	0.693	86.60

So, there you have it. 74 mpg even without any aero mods (provided my various assumptions all somehow perfectly correct).

100mpg could be possible..... don't settle for 70!

[eyesoreracing]

Originally Posted by Deezler

Dave! Didn't realize this was your project. Always enjoyed your nerd-columns in SCC back in the day. You should be pleased to note that the above BSFC chart is from your engine, the VW TDI ALH.

Mostly Jared Holstein's project, actually. I'm helping as as much as I can, but he's the one losing the most sleep. It is quite fun getting the band back together after a few years off.

I am, indeed, quite pleased that chart came from our engine. Any idea what the original source was? Looks like an SAE paper perhaps? Got a paper number?

-Dave

[Deezler]

Originally Posted by eyesoreracing

I am, indeed, quite pleased that chart came from our engine. Any idea what the original source was? Looks like an SAE paper perhaps? Got a paper number?

-Dave

It's listed right on the figure dude. SAE972686

Realizing Future Trends in Diesel Engine Development

[eyesoreracing]

Originally Posted by Deezler

It's listed right on the figure dude. SAE972686

Realizing Future Trends in Diesel Engine Development

Aaaah. Excellent observational skills, sir!

-Dave

[MetroMPG]

Originally Posted by Deezler

Then I repeated for a Cd estimate of 0.25 (achievable?)

Achievable? Yes.

With "consumer acceptance?", or something most TG readers won't laugh at? Probably not.

[roflwaffle]

Originally Posted by MetroMPG

Sounds to me like they're saying 70 mpg @ 61 mph = success.

Somehow I don't think that's too much of a stretch for a TDI with tall gearing. They probably aren't going to have to Aerocivic the crap out of the thing to meet that goal.

A stock rabbit at 61mph requires about 18-20hp, so with a 90hp@4000rpm ALH, that's ~40hp peak at 1800rpm, and half of that is around 220-230g/kWh, so ~225g/kWh. That's ~3350g/hour of diesel fuel per 61 miles, and at 7.3lbs per gallon of diesel or 3300 grams if we're using not crazy units, they should hit at least 60mpg@60mph with just the TDI swap/taller gearing. Going with LRR tires should add a few mpg, so they wouldn't need to do much in terms of aero to see 70mpg@60mph.

If they had researched CA emissions laws instead of just assumed they had to have emissions tested they could've used a Scirocco and probably hit 70mpg@61mph right off the bat. CA doesn't require emissions test for diesels, they could've followed the letter of the law and spent a couple hours at the state ref in order to update it from a 1980 something emissions spec gasser to a 1990s or 2000s spec diesel, w/ no emissions testing required. I suppose knowing what they're doing instead of winging it would've gone against the spirit of the project.

[eyesoreracing]

Originally Posted by roflwaffle

If they had researched CA emissions laws instead of just assumed they had to have emissions tested they could've used a Scirocco and probably hit 70mpg@61mph right off the bat. CA doesn't require emissions test for diesels, they could've followed the letter of the law and spent a couple hours at the state ref in order to update it from a 1980 something emissions spec gasser to a 1990s or 2000s spec diesel, w/ no emissions testing required.

In my experience engine swapping in CA, the ref won't let you do any swap that changes the emissions category. No truck engines in cars, for example. That means you can't legally put a B20 engine in an Integra originally powered by the nearly-identical B18, because the B20 is from a CR-V which is laughably classified as a truck.

I haven't specifically asked about a Diesel swap, but I would be shocked if that was allowed under these same rules. Are you speculating, or speaking from experience?

Originally Posted by roflwaffle

I suppose knowing what they're doing instead of winging it would've gone against the spirit of the project.

I would be offended by this comment if it wasn't true...

-Dave

[MetroMPG]

Originally Posted by roflwaffle

A stock rabbit at 61mph requires about 18-20hp

Really?

Those fancy aero drag & rolling resistance formulas disagree by a pretty wide margin.

[dremd]

In my limited experience (1 Vehicle) just saying that your vehicle has a Diesel in it is enough to avoid California Emissions testing.

We told Cali. that a Mustang had a Powerstroke in it and it never again had to be emissions tested (I haven't followed the car in the last 2 years, but for the first 5 it worked).
That car was actually highly modified Gasoline.

I have *Heard* of Diesel Swaped VW's being called in to verify that it is actually Diesel in the last year. (I have NO experience here and have ONLY HEARD).

[dremd]

Quote:
Originally Posted by roflwaffle
A stock rabbit at 61mph requires about 18-20hp
Really?

The fancy drag & rolling resistance formulas disagree by a pretty wide margin.
__________________

Originally Posted by MetroMPG

Really?

The fancy drag & rolling resistance formulas disagree by a pretty wide margin.

My But-O-Meter on a Non Turbo Diesel MKI Rabbit/ golf would guess 40HP to do 60. I truly have not calculated it, just guessing by load, and engine max power on this guess. (That being said if the formula is ~40 I'd say it is at least close).