16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

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ninjarrr
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16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by ninjarrr » Sat Sep 22, 2018 11:10 am

So the last 2 tanks have got 16mpg on the RX-8. Y'all prepared me for 18-20mpg, but 16 come on! This is for 95% city driving on 30/40mph roads.

On a serious note, should I be investigating anything that could be causing this fuel consumption or is not unheard of to consistently get figures so low?

The car has been street ported, by which I understand that the intake port has been enlarged slightly. Am I correct in then saying that this means more fuel is taken in in each cycle, producing a bigger bang and generating more power over standard. However given that slightly more fuel is consumed per cycle, MPG will drop slightly?

The highest I have got so far is 21.1mpg for motorway driving with cruise control on.

So questions for thsoe who know more than I do:
i) Is this normal / is there anything I should be checking?
ii) Have I understood street porting and its effects on fuel consumption correctly?

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by boosted » Sat Sep 22, 2018 11:26 am

I never really worked out mpg...but i was happy if i got 200 miles from full tank of super duper...about the same as my scooby and spirited driving...i found with all the 8s marginal difference between economy driving and spirited driving...how some of these guys break 300 miles if beyond me.

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by qwakers » Sat Sep 22, 2018 11:41 am

oh i dont know, lead footedness does affects economy.

see below for my (recorded, i dont bother for most fillups) history.

the ones marked in red are on track, the lower of the white ones are normal drivimg and the highest are motorway.
1908ABE5-605C-4DC2-B8E2-B9E99BBB625C.png

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by Culdranth » Sat Sep 22, 2018 12:20 pm

16, doing well. I get about 13mpg out of mine :/ standard original engine though. See about 180 miles a tank
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by New Duke » Sat Sep 22, 2018 12:23 pm

I wouldn't worry about it ninjarrr, provided your ignition components, steering and brakes are in good shape.

16mpg around town is normal for short drives. The RX8 drinks fuel when cold and town driving involves more throttle work. 'Motorway driving' isn't all equal (traffic, hills, speed, weather etc). It took me 2 years to finally reach 25mpg on a rare 300 mile drive.

Last week I managed 5 mpg on track. The variation is hilarious.

You can do things to help mpg if it concerns you:
Drive in a higher gear than you otherwise would once the car is warmed up. The RX8 can take it. It'll give you some headroom without forcing the engine to strain in lower gear (and suck on fuel). In general, if it drones when you accelerate, the gear is too low.
Don't push your foot all the way to the floor when accelerating.
Keep your tyres pumped up.
Avoid carrying around any junk that you don't need.
Use engine braking more and the foot brake less.
Turn off your engine if you're stationary for more than a couple of minutes. Once warm of course.

Driving like that gets me 18-20mpg out of a 'city' tank.

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by nightfire10 » Sat Sep 22, 2018 12:33 pm

With an8 you just fill it and drive till it needs filling again mind you I've got 1300 miles to do from next Friday and SPA LOL

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by Bullet5 » Sat Sep 22, 2018 3:11 pm

As people have mentioned above aound town/short drives will result in circa 16MPG. This is what I average with a 40k mile 192 on my way to work. As long as you're going stead on the motorway 25-30 is easy to achieve on a long run. I managed 29.9MPG on a tank which included a trip down to Cornwall, and also about 40 miles of short runs/town driving a few days prior to the motorway trip.

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by bigpete8 » Sat Sep 22, 2018 8:39 pm

My usual is 17 to 18 though this dropped slightly with trailing plug issue.
As said above ensure coils plugs and leads are a1
But also air filter and maf are clean.
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by Shagrington » Sat Sep 22, 2018 10:56 pm

New Duke wrote:
Sat Sep 22, 2018 12:23 pm
You can do things to help mpg if it concerns you:
Drive in a higher gear than you otherwise would once the car is warmed up. The RX8 can take it. It'll give you some headroom without forcing the engine to strain in lower gear (and suck on fuel). In general, if it drones when you accelerate, the gear is too low.
Don't push your foot all the way to the floor when accelerating.
Keep your tyres pumped up.
Avoid carrying around any junk that you don't need.
Use engine braking more and the foot brake less.
Turn off your engine if you're stationary for more than a couple of minutes. Once warm of course.

Driving like that gets me 18-20mpg out of a 'city' tank.
I agree with the rest, but did you get the higher and lower gears bit (in blue) the wrong way round? In my experience driving in a lower gear (keeping revs between 3k and 4k) is better for mpg and the engine will strain more and drink more if you accelerate or need press the throttle harder to maintain speed to, for example, go up hill if you are driving at low revs in a higher gear and don't change down.

Most of my driving is in town and short journeys but I still expect to get 200 miles and more by the time I'm thinking of refilling (with about 1/4 tank left).
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by New Duke » Sat Sep 22, 2018 11:37 pm

Yep I got in a muddle, thanks Shaggy. I'm glad someone is on the ball!
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by SeeJay » Sun Sep 23, 2018 6:35 pm

Basically,if you're concerned about fuel consumption then you've bought the wrong car :-k

The words 'economy' and 'RX8' don't belong in the same sentence ;)
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by bigpete » Sun Sep 23, 2018 7:49 pm

well I get around 3mpg on track 😂😂
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by geofftl1000r » Sun Sep 23, 2018 7:55 pm

bigpete wrote:
Sun Sep 23, 2018 7:49 pm
well I get around 3mpg on track 😂😂
Did you replace the rotors with water wheels? :D
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by ninjarrr » Sun Sep 23, 2018 8:05 pm

Ha thanks all, seems like it's not that far off "average" then.

You all misled me with dreams of 18-20mpg at all times - not that I'm complaining after driving the '8 all weekend :)

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by xamtex » Sun Sep 23, 2018 8:41 pm

to work and back,13 miles each way the first bit through town then the last on lanes where the urge to play cannot be resisted results in around 17 mpg.
at a recent trackday at mallory i started the day with 3/4 tank,added 20l at dinner time,another 25 in the afternoon and had to abort the day 10 mins before the end due to fuel starvation exiting gerrards because it was almost empty.god knows what mpg that equates to?
not the most economical car ive had,but i knew what i was getting into when i bought it...68k miles on std engine.

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by tyler82 » Sun Sep 23, 2018 8:43 pm

16 isn't much worse than 18!

And yes, very normal :lol: :lol:
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by njkmr » Mon Sep 24, 2018 1:24 am

It’s all about smiles per mile with an rx8...!

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by Englander » Mon Sep 24, 2018 7:47 am

Everyone takes the P*** out of me at work for my cars MPG, I just respond with "better to have 18mpg of fun and happiness than 50mpg of boredom" 8)

It's a sports car, not a economical car, if I wanted that, I'd buy a Prius.
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by bigpete8 » Mon Sep 24, 2018 8:46 am

Tend to find the people at work who get good fuel economy do lots of miles anyway.
My commute is 8 miles e/w so fill up less often than most of the guys who have longer commutes but get 50 to 60 to the gallon.
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by AndyBrad » Mon Sep 24, 2018 9:11 am

i dream of days of 16mpg!

11 around town here :)

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by PeteH » Mon Sep 24, 2018 11:01 am

I surprised by how many people are running in the teens. I know the car will do this when driven hard, or around town, or with lots of cold starts, but is that really how most people use the car all the time? When mine was a road car I used it as a "Grand Tourer", with lots of motorway, A-roads, and the occasional blast along interesting roads. I used to aim for 27mpg generally, and expect it to drop to 23 / 24mpg if I was driving it hard.

(It now does 6mpg on track, but you'd expect that, and it's better on track than most piston engine competition cars)
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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by AndyBrad » Mon Sep 24, 2018 11:45 am

i drive a LOT of short cold runs and as soon as its warm its driven off the limiter.

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by Ian9 » Tue Sep 25, 2018 9:42 am

Englander wrote:
Mon Sep 24, 2018 7:47 am
Everyone takes the P*** out of me at work for my cars MPG, I just respond with "better to have 18mpg of fun and happiness than 50mpg of boredom" 8)

It's a sports car, not a economical car, if I wanted that, I'd buy a Prius.
Just because something gets up to 50 to a gal doesn't mean it has to be boring, christ look at most diesels the power and torque are anything but that. Then a remap..

Granted some might not be sporty but definitely not boring no way. Anything can be boring or sedate when driven slow even an 8.

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Re: 16MPG!!!! :@ ;) Normal? And pls help me understand street porting :)

Post by warpc0il » Tue Sep 25, 2018 10:13 am

An 8, only ever driven below 4krpm, is not only boring but uses more fuel than one driven with the available rev range.
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