MK2.5 (NBFL) 1.8 Sport Rolling Road Results in 2020 - are my results unusual?

Hi guys

I was curious what my entirely stock 2005 NBFL 1.8 Sport (which allegedly left the factory with 146bhp at the crank) was currently producing before I put on a few small engine mods (to see if the difference could be picked up on a rolling road).

The results, however, were pretty disappointing! The rolling road recorded around 100bhp at the wheels and estimated 125bhp +/- 5bhp at the crank (the machine apparently deducted around 5bhp as it was a cold day to make all readings comparable at different temperatures). I know crank readings are an estimate, but I find it hard to believe that you would lose a third of the power through the running gear alone on a car like the MX-5!

The car is on about 87k miles, but it’s lived a pretty easy life (the overwhelming number of engine miles have been at a steady, sensible, cruise on the motorway; no track day work at all) and it recently had a full service with new plugs and leads, etc. I’ve had it since around 46k miles and hadn’t noticed a drop off in power over that time… assuming it left the factory with the claimed bhp and 146bhp wasn’t just the reading of an optimised press demonstrator with a blueprinted engine and some cylinder head work, that’s a drop of around 20bhp!

I’ll find a way to convert the pdfs of the power charts to jpg to post them up here.

I just wondered if anyone else had tested theirs and whether this was normal or not (or whether I might be having a problem with my SVT mechanism, for example - I noticed that in recent weeks my car can now take a over 5 seconds on the starter to start from cold whereas it was always a quick starter before, the starter turns the engine over well though, so I don’t suspect battery - is this a sign of anything untoward?)…

If this is a genuine loss and not just what is to be expected, has anyone got any tips for reclaiming some bhp?

Any comments welcome!

Many thanks all!

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Youch! Consider me told!!! :stuck_out_tongue_winking_eye:

Apologies - I’m obviously using the wrong search terms, as I did check here, google, Nutz and PH. I found people had got around 115bhp on a 1.6, around 120-130bhp on pre-SVT 1.8 mk2s (thus my question really as I was concerned that my results were indicative of an engine not getting any benefit from the SVT mechanism), but couldn’t find anything for the Mk2.5 svt 1.8.

If that’s what I should expect too then do consider me reassured - thank you for your time!

I wouldn’t take the number from any one rolling road as gospel, merely ball park. I doubt the calibration is that good. They’re good for a before and after modification comparison though, using the same rolling road in similar conditions.

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I suspect its more to do with variability between rolling roads, and unless you think there is something wrong with the engine, treat it as a baseline.

Manufacturer quoted numbers are based on tests under laboratory conditions, according to some set of standards (SAE for North America, DIN for ROW). When the NB models were launched, there was great controversy on quoted power figures, with Mazda using in US literature, Japan market figures. This lead to compensation being paid out to owners for the apparent loss of of power.

My understanding is that manufacturers measure directly off the crank, but on a rolling road, its measured at the wheels, with some fudge factor to estimate the crank power.

I did one of these rolling road sessions once, as a bit of fun. Apparently my old 140k miler 1.6 was putting out as much as (at the time) a fairly fresh late 1.8, and not too far off the late GerryN’s then new SVT. I only had intake and exhaust mods. It was good for the ego, but no one took it too seriously.

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That was exactly my thought process (and why I took my stock car down there in the first place): I wanted to see what my induction kit, timing advance, etc actually brought to the party, so decided to take a reading whilst stock.

I suspect you may be right: but I am still a bit surprised it was that far off!

Whilst the handling, balance, feel of the car is superior in every way I always thought the MX-5 engine was pretty gutless compared with the MG K-seriies 1.8 VVT 160… (and always felt that MG levels of power and torque in the MX-5 would be all you need to feel fast instead of just that little bit disappointed when you hit the throttle). I’m starting to see why if in fact the real-world comparison between the two cars would always have given an even greater difference than the figures suggest…

If, however, I have lost some ponies over the miles/years does anyone have any suggestions for things to service / replace to bring the engine back up to stock spec before I start messing around?

I delighted to hear that it doesn’t sound like my SVT is playing up anyway!

hi all I’ve always found that you deduct 20% off the reading because of the gearbox and the diff im going to start playing with my 1.6 mk 2.5 because that is weedy on power all the best

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Before you do anything to an engine, always worth checking it over. With your increased reluctance to start, a compression test would be point 1. Them making sure everything else is right. Is the VVi mechanism working properly? A proper good engine flush to clear any restrictions in oil control valves. Air filter good? And all the other obvious things. Going and troubling the rev limiter for half an hour won’t hurt either.

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Thanks Nick

Is there any good way for checking whether the SVT is working properly?

I agree with Nick.
Also try a couple of tankfuls of V Power to clean out all the plumbing and help the breathing. The higher octane will also put a few more ponies under the bonnet.

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Richard, I agree with this completely (it’s not always the case that you’ll see a benefit, but I have found the high CR on the SVT engine does seem to give you a little more punch and a few extra miles between fillups with 98-100 RON fuel), but in my case I always run it on Super unleaded anyway (usually Esso as it’s ethanol free) to keep everything as clean as possible so that won’t be my magic bullet…

I have found a more Spritely drive is achieved with Tesco Momentum 99 petrol and believe the engine managment can tweek a little more after it has learned to accommodate the higher octane. This might be the engine pushing the timing against the knock sensor?

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Silkolene Proboost I find has a more dramatic effect , likely because how it cleans injectors etc.

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Hi Enjoyabull, it might be but I think it may just be down to the higher quality fuel having more energy per unit and lower activation energy, which means more complete combustion for a given cycle (which also means more power and better efficiency of the system as a whole). This does mean you can get away with advancing the timing, to get the advantages without as much drawback as you might have with a lower octane fuel, but I have no idea whether the engine management system on the NB is sophisticated enough to detect and do that on it’s own?

It’s funny as I’ve driven plenty of cars where putting in even 100 RON fuel made absolutely no difference at all to performance or economy: you were getting the maximum the engine was prepared to give with 95RON so super unleaded brought nothing further to the party and was only to be treated as a once-in-a-while luxury to help clean out the fuel system with the higher grade detergents that super unleaded usually contain.

On the other hand, I have read that higher strung, high compression engines can show considerable improvements with higher octane fuel and certainly my SVT with it’s 10:1 CR seems to run better on it (more punch and miles per tank).

As I say I run mine on super unleaded all the time as a result (I dont use Tesco as much, despite the higher octane they offer as I read their super contains 5% ethanol, like regular unleaded, which can, technically, corrode things - whether that’s true or current I have no idea (??), but it makes me lean towards Esso and BP who actively boast that their high o range offerings are ethanol-free in my area of the country) so that’s not the fix for me, but it seems like a great suggestion for those that use regular unleaded most the time and want to give their system a bit of a clean out…

Brilliant Saz, thank you - I’ll go get some and stick it in my tank on the next fillup.

Also, Nick suggested engine flush: I previously ruined an MG 1.8 K series VVT 160 VVT mechanism with engine flush made by a well known, reputable brand (it left the bearings on the cam shafts with a constant whine, which I later read is a common problem after using engine flush as it de-greases high velocity parts, damaging them)…but that was an MG K series engine! Is the (much more reliable) Mazda SVT alright with flush or is this still a bad idea? Has anyone tried it?

Here are the readouts by the way in case anyone is interested:

Estimated flywheel power and torque:

Power at the wheels and high speed AFR (whatever that is?)

Hi Dave

NickD is right regarding checking the physical condition of the engine. A compression test would reveal any serious problem and genuine sapping of horsepower. These engines actually have quite a high tolerance for compression drops but always reassuring to find that your engine is healthy. A leakdown test is another guide to engine health but less likely to indicate BHP loss if compression test good.
Any failure in the VVT should produce error codes, so worth doing an OBDII error code read off the port with a reader if you haven’t already done so.
In my opinion and hope you will find nothing wrong. These cars have pathetic BHP figures and the real judgement is the way they drive. In that respect you could always compare yours with a drive in another SVT sport in similar condition.

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I wouldn’t read too much into those figures as a first run as there are so many variables with the dynamometer and environmental factors that can affect the numbers on the day.

I’m not familiar with the vvti engines but vvti engines generally can have solenoids or actuator motors which fail to actuate but you would probably notice that it’s gutless as your revs increase or it would run rough if they had. If you put it on a diagnostic machine it might throw up a code if these had failed.

If it’s running well but feeling low on power check for leaks on your intake, spark plug and air filter condition. If you have an induction kit check it’s not sucking in hot air.

A compression check would probably also put your mind at rest regarding ring wear etc.

With those numbers though I wouldn’t be worrying. As others have said get your basis right I.e servicing items and these motors are pretty bullet proof if not the last word in rip snorting power :slight_smile:

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I would have thought that the loss of 20 bhp at over 80,000 mile was acceptable. The problem with all modern engines is that the manufacturers love the extended service periods. I have always for 30 years changed the filter and oil at 6,000 miles whatever the manufacturer says. Not only have I never had any engine problem even with 115,000 miles on a BMC A series driven really hard I have never had to top up between changes. Rings and valve seats get worn with old oil and as has been suggested a compression test will confirm how fit the engine is relative to the new readings.
I am not very impressed with the Skyactiv engine in my 30th Anniversary MX5. It is very limp at low revs and even at 50 mph in 6th is very reluctant to pull hard you have to drop down 3 gears and rev it to over 7000 to get it to go.
The 2 litre engine in the lastest Mazda 3GT has 180 ps and 103gm/km, my Mazda MX5 has 4 more hp at 184 ps BUT 156gm/km very expensive to tax.( and its lighter ) My BMW 2 litre has 190ps and 114gms/km ÂŁ30 Road tax and hauls 1,700 kilos at up to 60 mpg if you are careful. So I just understand what is wonderful about the Skyactiv engines.

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don’t before understand omitted in last sentence in last sentence. sorry!