ca993twin

I can get about 22 mpg in my TT in sustained hiway driving. This seems pretty low, considering the size and weight of the Porsche, especially compared to.. say my old Expedition which would get about 20 mpg under the same circumstances (we actually drove both cars to Lake Tahoe once, and that was my observed mileage). On the other hand, the Porsche has fairly fat, sticky tires, which must contribute to the rolling resistance.

I bring this up because it seems the the Ruf turbos (both TT and single turbo varieties) are reporting much higher mileage... up around 28 mpg. I would suspect from this that the Ruf cars are running leaner, but my amazing clean tailpipes indicate that I'm not running a very rich mixture.

I'm baffled by this. I'd like to hear other TT owners, especially Ruf owners, pitch in with your observed fuel mileage, and thoughts on why mine seems so low.

Details: my TT has 63,000 miles, uses almost no oil, and seems to run plenty strong. It is all stock, except for the Gemballa ECU and Fabspeed muffler bypasses. It has had all its proper services, including the recent 60,000 mile with new plugs, etc. BTW, fuel mileage is pretty much unchanged before and after the ECU swap.

robroy72

I have a 1997 993TT, 13.5K miles and it gets 22MPG highway, and about 16MPG backroads. Car is bone stock.

I'm not sure on the A/F ratio that the car uses, but I'm guessing it's helluva rich!

ScottMellor

14.

Hey it's better than my old 450SL (12.5)

ca993twin

I'm thinking that "around-town" mileage is highly variable based on how hard you rocket out of intersections, but steady-state cruising at say 75mph eliminates much of this variablilty. I'm more interested in your steady-state hiway mileage.

Scott... I've seen you drive "FrankenCar"... I'm surprised that you can get the mileage up to 14 around town. How does she do on the hiway?

ScottMellor

14.5

flatair

Some possible differences:

1) If the RUF's you're talking about are BTR2's, you have the extra weight and drag of AWD vs. their 2WD. BTR4's would have the same parasitic drag.

2) Primary difference is probably in the gearing, I'm pretty sure the 993 TT is geared lower than the RUF cars. Porsche & RUF standard specs are as follows:

REAR: both 3.44
RUF,TT
1 3.15, 3.82
2 1.79, 2.15
3 1.27, 1.56
4 .97, 1.21
5 .76, .97
6 .60, .75

3) Compression ratio is 8.4 on the RUF vs. 8.0 on the 993 TT (stock).

4) Not sure on the heads of the RUF, if they're twin plugged that might help a little too...


Brad

Jeff 993TT

About 14 around town.. At the track it's probably like 3 mph...

edrewitz

Jeff, 3mph at the track is HWFR at it's finest

Hey Steve, I averaged about 20 - 23 cross country w/ avg speed somewhere around 80. With my daily driving I'm lucky to see 12.

OldGuy

Edre's right Jeff 3mph is pretty dang slow! Maybe evn by turtle standards!

Mines the same 14 around town 21-22 on hwy's and bwys

ca993twin

OK... my gas mileage is right in line with most of the others... where are the Ruf guys to tell us what they observe?

I had a thought about why our mileage is so low compared to cars like the Lexus... hiway mileage is really concerned with two factors... total drag (aero + rolling) and engine efficiency. weight is not really a factor, once a car is up to speed. Our engines, with low compression, are pretty inefficient when not under boost. Is it as simple as that?

flatair

Yup. Additionaly, newer cars run high compression, variable cam timing/valve lift, better aerodynamics, higher gearing (for non sports cars), etc. If you're still looking for differences between your car and a RUF, see my post above.

ca993twin

flatair,

Yes thanks for the data. I believe that a couple of Ruf guys, one with a BTR4 the other a BTR2, both claimed around 28 mpg on the road... quite a remarkable difference. In fact, with that mileage difference, a Ruf can actually pay for itself in, ummm, 214 years.

ScottMellor

Steve: Slow news day?

ca993twin

Scott,

Yes, kind of you to point that out! I don't want to uncork any new projects on a late Friday afternoon. I suppose I could clean up my overflowing mailbox? Nah.

I'm an engineer, and its always bugged me that the stupid Expedition could get nearly the same mileage on the road. I need root-cause analysis.

Bill (NC)

Steve, my car varies a lot, depending on the drive. From 26 on the highway to 21 normal combined city/hyway to 5 on the track. So I think the biggest factor to mileage is the right foot.