mk3.5 bbr stage 1 fuel economy

HI folks,

Getting my pennies together and thinking about a turbo upgrade on the 5  (I’ve been thinking for a while

I’ve just got a new job where I’m travelling 60 motorway miles a day and i don’t want to change the car. 

I know an mx5 turbo’d or other wise isn’t really a motorway cruiser but any ideas from the turbo owners what sort of mpg they get on the motorway and do they have 6 speed box’s instead of 5’s? I wont be thrashing it in the morning traffic.

As it sits i get between 26 and 31 mpg and cant really afford to do that sort of millage with less mpg than i get now. 


Car is a 2.0 mk3.5 with the 5 speed.


Am i being stupid wanting a turbo kit and using it as a commuter?





Wait until your finaces are in a better condition as they seem well too tight if that fuel consumption is goig to be an issue for your finances.

Well I’ve had a Mk1 1.6, a Mk1 1.8 and a Mk3 2.0 They have all done around 35 MPG however they have been driven.

I stick (loosely) to speed limits  but do like to give it a blast when appropriate . I may be wrong but to get 25 MPG on the road I would think anybody would be risking at least their license. Either that or something isn’t quite right with the car.

Has anybody else had anything less than 30 MPG on the road?

No idea on MPG - you either drive the car, or stick it at home and use public transport - what there is these days! With that kind of usage, I would bang my head against the wall before I ever added a turbo.
Bear in mind that a turbo usually requires bigger injectors, though what use it would be on motorways is debatable IMO, speed limits are being re-enforced daily, and you either do 69 mph, or dead slow (on approaches to London and on the M25.)
As for your question - to put it bluntly –

Am i being stupid wanting a turbo kit and using it as a commuter? (Sorry - YES.)

Thanks all, it seems i just need bringing down a peg or two. aside from just doing it because it makes me happy i do take the points that it’s a bit stupid to do it.

The new job pays extremely well affording the fuel wouldn’t really be an issue but it would take up a large chunk of the increase in salary which defeats part of the reason for the change. 

That decided i’m starting to worry re fuel eco now. If i drive nice and stick to the speed limits around town and a few bypasses i can get 31 but if i drive like i stole it i will get 26 -28. i thought it was because of the 5 speed but i’m thinking otherwise, these readings are a tank to tank going off the on board computer.

will try a motorway run on cruise control at 70mpg and see what i get, if it’s not mid 35’s then should i be taking it to the dealer to be investigated as it’s under warranty. 





I bought our MX5 to drive, have fun and live a little. I have NO idea what MPG I get, why would I - fill it up - drive it - fill it up- drive it…


I can’t answer for a stage 1 but last time I measured it my stage 2 was doing about 29 mpg - compared with 32 mpg before I turbo’d it.  I converted mine when I was only doing a 15 mile commute on minor and A roads - where it was perfect.  However I then changed jobs and now do a 105 mile round trip, two thirds of which is on motorways (M25 and M3).  I quickly swapped the super sport rear box for the quieter GT one, but it’s still far too noisy to make a good motorway car (very hard to hear the stereo at 70mph) and the clutch is quite a bit heavier.

Bad enough that I’ve not bought a Golf GTI for the commute and use the MX5 for fun - though the Golf’s currently off the road so been using the MX5 for the last couple of weeks.

The stage 1 uses the standard exhaust and clutch so will be much easier to live with, but I still wouldn’t buy an MX5 for a mostly motorway commute…



Hi Brad, mine’s a 2.0 NC2 with the 6 speed gearbox & regularly returns around 43 MPG to 45 MPG on the motorway. sticking between 70 & 75 MPH.  I find it a very capable motorway car - I always have the power hardtop up on the motorway, although that does come down at every opportunity on the “A” & “B” roads etc.


Thanks Dave and Andy,


So really stage 1 won’t be as bad clutch wise but my mpg will drop a tad. I was hoping to get better mpg with a turbo due to not have it work the car as hard. But the logic doesn’t seen right haha.

By the sounds of it I should be getting considerably more mpg on a run than I’m getting so I will get that checked out.

 I may as well just keep the kendo in the garage for fun and mileage down and buy a golf or a 3series. 


Thanks again all for the advice, much appreciated ???

I went down to Cornwall in the mx5 and was getting 43 miles to the gallon 3.5 2.0 sport tec well impressed with that.

I don’t know how some of you are getting those mpg’s!  Pre turbo mine was consistently averaging about 32 mpg.  I’ve just brimmed the tank so have calculated the mpg - 30.6.  That’s over 207 miles which is a mix of “sticky” M25 and M3 in the morning and freer running in the evening plus some A road.  Mostly going with the flow and a few squirts of acceleration.

Car is a 2.0 Sport Tech with 6 speed box btw.


When cruising on the motorway at the same speed as the rest of the traffic, then one can only use the same tiny amount of power as everyone else.  In this instance turbo is not needed.

If sudden urge is needed, 2l NC has a near instant 20mph in hand in top starting from 70-75, and when dropped down a cog or two it is very quick (rev limiter at about 90 in third).

I remember many years ago watching Stirling Moss talking about fuel economy.  In essence he said something along the lines of; use the engine around its most efficient revs while accelerating and stay in low gear for as little time as possible even if it means full throttle, be in the highest comfortable gear while cruising but always keep aware of the efficient revs range, and most importantly use anticipation instead of brakes whenever possible.

Possible reasons for poor fuel economy might be nothing to do with driving style, but could simply be from under-inflated tyres, or brakes not freeing completely, or poor wheel alignment.  Symptoms of these can be seen with relevant excessive wear on tyres and/or pads.


When I drive our cars, over the last forty years I’ve tended to get about 20% better mpg than SWMBO, even though I usually take less time on the same journey.  She drives as instructed all those years ago when learning, I drive bearing in mind what Stirling said.  Heaven help me if I suggest she change her driving habits!

NC 2l 5speed, V-Power, I get between 33 to 45mpg depending on road conditions and traffic, 14,000 mile average is 38.7mpg. (Climate control always on, set to 19C.)

Mazda3 2l 6spd, V-Power, I average about 45mpg (eg 46.5mpg for 420miles on the most recent tankful with four up to Shropshire and back and around the lanes there for a few days as a long weekend), SWMBO averages about 36-38mpg (mostly suburban light traffic).  I’m the one who always brims it regardless of who has driven the last tankful.


Why not look at getting an exhaust manifold upgrade and remap?

From what I gather this will increase MPG when the car is driven economically and you can have another “sporty” map setting with all the bells and whistles on for when you’re out on a weekend blast.

Just my suggestion.

Purpose-designed turbo engines run a compression ratio of about 8:1.  An add-on kit has to run quite rich on boost to avoid detonation at the standard compression ratio (this also applies to most of the new turbo cars on the market, which are running 10:1 or higher).  Therefore, whenever the turbo is working, it will drink fuel.  This doesn’t show up in the NEDC fuel economy test with its minimal acceleration but owners of Ford Ecoboosts and the like only get about 70% of claimed mpg.  If the compression ratio were lowered, the car could run stoichiometric on boost but would be inefficient off-boost.  So it’s all about gaming the system.

The short answer to the OP is that the BBR kit won’t affect fuel economy much, as long as you never use the added power!

Thanks everyone for the advice. As much as there seem a big difference in opinion it has opened my eyes to other possibilities. Manifold and remap potential for came too are being considered. 


Getting the wheels refurbished as a pot hole as ruined one, after that alignment and springs from wim tyres change and then I will see what mpg I’m getting and decide from there. 


Really appreciate the advice folk cheers



Interesting thread.


I was wondering if you can swap maps with a BBR stage 1? One for economical and one for power or different types of fuel? Or is it just remapped and that is what you run on?



Also as far as servicing the Turbo- Do you change the oil/different oil more frequently and what sort of life span do you expect on the turbo itself?


Thanks in advance