Poor supercharger fuel mileage

[BIGBOBO]

What is the average fuel mileage for a supercharged mr2? I suspect mine is getting pretty poor results.

Mine used around 10l/100km (28mpg) during the last two tanks. I drove it very gently at 100-110kmh (60-70 mph) on the highway (almost no city miles) without activating the supercharger. On my old NA engine I would get more than 40mpg with this kind of driving. I struggle to reach 300km out of a tanknow , while my NA would hit 400 every time.

I replaced the spark plugs, distributor cap, rotor arm, plug leads, O2 sensor and thermostat while swapping this engine in my car. I recently rebuild the brakes and they are fine to (no dragging). What else could affect the fuel mileage or is this normal for a SC?

[aussieGT]

What is the average fuel mileage for a supercharged mr2? I suspect mine is getting pretty poor results.

... without activating the supercharger…. On my old NA engine I would get more than 40mpg with this kind of driving. I struggle to reach 300km out of a tanknow , while my NA would hit 400 every time.

Now I could be mistaken (it has happened once or twice before) but as the supercharger is belt driven the only way to 'not activate it' is by not turning the car on. Sure if you hammer it and wind it out its going to gulp a lot more but either way its always making a difference.

I think the 100km difference in total out of each tank is the price you pay, i have a turbo and a a non turbo mr2 - they are consistent in their use, but the turbo consistently uses more than the n/a.

[Ben]

The supercharger is operaed by an electro-magnetic clutch in the pulley, so when it's not activated the belt is effectively just spinning the outside of a pulley, rather than the whole SC.

Having said that, I rarely get more than about 220 miles from a full tank of Super in mine, although I don't remember my old NA being much better. I've never really been for an economy drive in it though...

[BIGBOBO]

I know the SC will use more fuel than an NA which isn't a problem, I just suspect something is wrong with mine since it uses quite a bit more than I expected and more than what I read elsewhere online.

As Ben mentions he rarely gets more than 220 miles from a tank in his SC while driving normally. I barely reach 185 miles (300km) with very economical highway driving. Hence I suspect something is wrong...

[synXero]

I think you're just being optimistic!

The electromagnetic operation of the charger is fascinating. Off I go to read.

[kaiowas]

The supercharger is operated by an electro-magnetic clutch in the pulley, so when it's not activated the belt is effectively just spinning the outside of a pulley, rather than the whole SC.

It is operated by a clutch pulley however once you're above idle speed the clutch is engaged pretty much all of the time. I seem to recall that the "Supercharger" light on the dash isn't connected to the pulley and lights up based on manifold pressure or something meaning that it's a bit deceptive in it's operation and doesn't truly indicate whether the SC is running or not. As mine is a conversion I don't have the light so I've never really bothered finding out the full details.

I won't comment on fuel usage as my car isn't really representative however on the times I have done a long road run in it I've found that it does drink a hell of a lot more than my n/a's used to.

[Ben]

Is it getting up to temperature OK? When I first had mine it was running a bit cool, replacing the thermostat cured that and also improved the fuel efficiency a noticeable amount.

[andyj]

Well I find my SC (standard pulley) gives 32 mpg town/bit of dual carriageway compared to 34 mpg I was getting on same roads with two previous NA's. I'll probably activate the Supercharger a few times a day, overtaking and uphill. For those not familiar the supercharger engages when you put your foot down say an inch but most of the time in traffic, you can't use it. Those mpg figures are brim to brim comparisons on similar routes.

I had similar thermostat issue to Ben when I got the car so see it reaches just below half on temp gauge.

Has it always been like this? In Japan they sometimes bend the AFM to get more fuel in. Imagine that would show up on a rolling road.

[kaiowas]

This documents pretty comprehensively when the SC is running and when it's not:

http://web.archive.org/web/200506150726 ... ration.pdf

[Lauren]

Worth checking your oxygen sensor. It's the most common reason for high fuel consumption.

[aw11rally]

I'd think 28mpg was about right. I don't remember getting much more than 30mpg out of a standard N/A.

Have you checked your tyre pressures, from experience they are one of the biggest factors affecting fuel consumption (other than driving style).

Also check that the rear calipers arn't binding, Mk1s are a b1tch for it.

[Lauren]

Yes 28mpg is about right.

[BIGBOBO]

Thanks for all the replies. The rear brakes were rebuilt and aren't dragging. Tires are inflated to factory requirements (1.8 and 2.0 bar).

Both the thermostat and O2 sensor were replaced but I'll check them out. I already know the thermostat might be wrong, the old one was marked 87 degrees while the new one is 82. So it might be opening to soon.

[BIGBOBO]

Replaced the thermostat with a genuine toyota one and this solved the problem.

Fuel mileage increased to 9l/100km (31 UK mpg) while driving it normally and I'm sure I can get even more when driving economically.

[oukie]

Well I routinely get 40+ mpg in fact I got well over that on a long run ie to JAE
I did around 340+ miles out of one tank although I used 39.5 litres out of the 40 litre tank

Should mention it's a n/a and I only ever use shell v power

[andyj]

Replaced the thermostat with a genuine toyota one and this solved the problem.

Fuel mileage increased to 9l/100km (31 UK mpg) while driving it normally and I'm sure I can get even more when driving economically.

Sounds good. That 31 mpg is almost exactly what I get in general mixed motoring in the SC.

The NA was actually rated at 34.9 mpg in the Government Urban Cycle in it's day with 47.1mpg at steady 56 mph. So potentially a well set up NA driven carefully, should be quite economical. Road Tests often got about 28 mpg overall though, so it's very much how you drive it. Imagine that view is even more applicable with the on/off blower under your right foot.

[ulysess1966]

I have a cut-out switch on my car which knocks the SC off completely. Main reason is because it has a big pulley fitted and I'd be lucky to get 28 mpg if I'm driving lively. With the cut-out activated, the car drops to about 90 BHP, is fine for town driving and fuel economy improves to about 35 mpg.

The SC light is definitely not connected to the SC relay. It's fairly easy to fit an LED to the relay so you can see exactly when the SC is engaged.

I've been tempted to put another switch in to 'lock' the SC on and see what happens, but I've never had the nerve yet.