Forced Induction Systems - anyone pay attention to fuel economy?

[KfabR8]

In the next few months I'll have put 50K miles on my car and intend on looking into a forced air induction system - I was pretty set on the VF setup, but the Heffner TT setup now has my attention too (especially since Heffner now owns an R8 - the personal interest he has in the system and car is a bonus in my eyes).

One thing that I've not seen addressed is: What do these systems do to fuel economy?

I realize that if you're on the fun pedal that economy's going to suffer. It always does when I decide to get rambunctious, but I am also quite conscious of trying to get the best economy out of the car when I'm just driving it. Lots of 5th and 6th gear use in slow traffic, short shifting, easy throttle application and such. I can see a big difference from tank to tank depending on my driving "mood", if you will.

I average around 22-24 mpg on road trips and around town I can get 16-17 mpg when I'm "good". Thus far, I've averaged 16.836 mpg over the life of the car. (I keep a running ledger of fuel use, price per gallon, milage per tank and such of all my vehicles).

So, what do these systems do to the expected mpg? If I'm "good", will I see a drop overall economy or will I see similar numbers to what I am currently getting? (and no, I don't expect the economy to go up.) Will I still get 400 miles out of a tank of fuel when I'm driving across the country like I enjoy doing on occasion? Will I still average about 300 miles per tank in general?

Yea, I know, some idiot (me) that owns an R8 is actually worried about fuel economy and that may seem a bit odd, but I use the car as my every day driver.

While I'd really enjoy the additional HP that either the VF or the Heffner TT setup would give me, the question of "Am I going to end up with a total fuel pig?" sits in the back of my pea brain - It was one of the (very many) things that got under my skin about that pile of crap Cayenne Turbo I had. 10 mpg was not acceptable and it would not be for my R8 either. God I hated that Porsche...

So, how 'bout it guys? Those of you that have done forced air induction systems: Have you seen a change in mpg? And if so, what sort of change?

Thanks in advance.

[AnOutsider]

Unfortunately, I haven't bothered to check (nor did I before the VFSC), but I haven't noticed a difference in my fill up routines.

I drive back and forth to my office daily (about 10 miles round trip) and once per week I do about a 100 mile round trip. I usually have to fill up the day before my weekly trip.

Nothing has changed in that routine. Should also be noted though, that the SC's power is higher up in the RPM range -- a range I rarely hit in normal driving, so take that for what it's worth (whatever that might be).

[Bodhii]

I'm afraid my habits in noticing actual MPG are almost nonexistent.
I do have the VF/SC on my R8 and a TPC turbo powered Porsche Cayman.
Outsider is correct about getting the more thirsty power boost at higher RPM's or when on full throttle. If you drive with an idea to max out MPG, you can get almost identical MPG as with normal aspirated cars. The more one plays with the full engine power, the higher the fuel consumption.

On the track, I am empty in a little less than 2 hours of full hard driving. Keep in mind that the supercharger engine is much more smooth and therefore, more difficult to feel when it is powered up than with turbos. There is nothing very subtle about turbos, no matter what the builders will tell you.

Both systems drink very heavily when used. But keep in mind that in normal street use,.. the total minutes spent at big power on any normal drive, are usually very very few indeed. On the streets, high power is usually measured only in a VERY few seconds at a time; usually only 2-3 seconds. Anything more than that and you are going way too fast!

Enjoy!

[smoothy]

I can't speak for the R8 with FI, but from experience with my Saleen. When I drive with a light foot and keep the car out of boost, my mileage is very close to the numbers reported by normally-aspirated Mustang GT owners. When I go heavy and into boost a lot, then mileage is somewhere between atrocious and horrendous.

[KfabR8]

Thanks guys - great info. It more or less parallels what I was thinking too.

Two comments stick out:
A) All three of you mentioning that it really doesn't drink until you get on it - perfect replies and makes total sense.

2) Bodhii - the turbo comment is what scares me about the idea of going w/the Heffner setup. I like the idea of more hp than what the VF produces, but that unleashing of the Genie, boy do I hear that.

My '03 RS6 is brutal in delivery compared to the R8. It takes a deep breath and then just unleashes when you romp on the fun pedal. The R8 is smooth as silk and, while it has a hit, it's not a kick in the kidneys.

I quit riding two stroke motocross bikes 10 years ago because the two stroke Genie was one scary S.O.B.. I love the delivery of the modern four stroke. It's sort of the same between my two cars. The R8's a modern four stroke mx bike and the RS6 is an old Honda CR500. I'm not sure I want my R8 to be like a two stroke.

[rmicroys]

Fuel economy is all in how you drive the car... again, a completely different car, but shows how radically one can alter one's economy.

My 04.5 Volkswagen Jetta GLI, with a chipped 1.8T engine around town and to and from work can get anywhere from 6.0l/100km when driving very much like a grandma, to a dreadful 13l/100km when I drive like a total arse. When the car spikes at over 21psi, it drinks a whole heck of a lot of fuel, even for a little 1.8 liter engine. Though, in some sense, if you have to ask about fuel mileage in a V10 or a V8 supercar, hhmmm, maybe one has to rethink the question? And didn't TopGear already answer that question, in that the Audi R8 V8 was the supercar for those who wanted one if one were to consider its economy as a purchasing criteria over all the other supercars? lolz.

[KfabR8]

Though, in some sense, if you have to ask about fuel mileage in a V10 or a V8 supercar, hhmmm, maybe one has to rethink the question? lolz.

LOL!! I hear what you're saying.

There was just something about getting 10 mpg in that P.O.S. Cayenne that got under my skin and it's stuck with me. I don't want to go there with the most fun car I've ever owned.

[AnOutsider]

My '03 RS6 is brutal in delivery compared to the R8. It takes a deep breath and then just unleashes when you romp on the fun pedal. The R8 is smooth as silk and, while it has a hit, it's not a kick in the kidneys.

To be fair, I let the engine rev higher today on my way into work, and when I shifted I was already in the 5k RPM range and let it ride. Man, the power came on so strong (but linearly) that I was blown away. Here I am flying down the road, plastered to my seat and with this HUGE grin on my face.

Ah the simple things

[Maverick]

Hi
It seems we have very similar taste in cars. I also own an '03 RS6 which has a Milltek exhaust and an MTM chip so its kicking out some 525hp +. And the turbo kick in is very smooth in that car and as you say, it just pulls and pulls. A very fast sedan.
I put the VF supercharger on my R8 in the UK about a month ago. Driving up to the tuners that were to do the work, north of London at 80 - 85 mph I think I registered about 22 mpg (british gallon). On the way back I checked it at a steady 85 and I think I got about 21.3mpg. So, it seems when I drive it in relaxed mode it is not dramatically different than the stock setup. When I drive it hard it is lower but I haven't had a full track day with it yet.

As to power delivery, it is dramatically faster than the stock R8 and I'd say it feels more in your face than the RS6 as well. I also am lucky in having an '03 996 Twin Turbo 911 to compare with and I'd say the R8 with the VF supercharger is every bit as fast as that car. The fact that it revs to 8,000 rather than the just over 6,000 of the 911 also gives it an edge. When I push the R8 now it really performs and all round as the chassis really feels up to it in the corners as do the brakes. I was disappointed last weekend when I was planning to drive at Spa Francorchamp but the racetrack suffered a freak tunnel collapse damaging the surface so all track events were cancelled.

Anyway, I chose the VF because I felt its margins for safety were better and it doesn't have the possible heat challenges of the twin turbo. In addition, it is reversible if I want to sell the car at a later date. But for now, I believe I have a car faster than the V10's for far less than the upgrade cost and I'm very happy with it.
Back to your original question, my experience when driving relaxed has been that it is not dramatically down on stock MPG. IMHO this is the best solution for V8 owners that want more urge and performance.
Regards
Mike

[Wheelb]

Honestly i great fuel economy ! no question about it feels like OEM but when your on the boost it does take it down fast lol .. but every day driving i notice not much difference.