REPAIRS PAGE 29
THE POWER GAME - AN INTRODUCTION TO TUNING THE N/A
Writing an article like this is about as attractive as jumping into a
pool of ill-fed Piranha's - but I can't describe members like that - can I?
However I do get some enquiries in this area - so I guess it goes to
fall-guys like me to open the debate.
Well - first and foremost - in this article I'll deal with the N/A - the
Normally Aspirated MR2 only - simply as the majority of members have these.
That said I won't ignore S/C Supercharger owners - but most of them instinctively tune anyway (and better
then me - Lauren to help on future article - please!)
So - for the N/A - coded the 4-AGE - it has a damned good engine -
especially when it was designed 20-odd years ago. So it should be - as people
often claim it is a copy of the legendary Cosworth BDA race engine. This is
probably true - at least in part - the bore and stroke are the same, and the
cylinder heads are similar - but whereas Cosworth could only make the head as a
2 piece 'sandwich', Toyota managed to cast it as one.
This is not necessarily a good thing - the waterways are a bit suspect -
they tend to corrode through the head gasket between the very heavily 'siamised'
1/2 and 3/4 cylinders. In this area Toyota got it wrong - in their attempt to make a more compact engine.
Head gasket failure is quite a common occurrence at around 120,000 miles - if only they had adopted
the (better) Cossie cylinder spacing! For a start it could have been over-bored
to nearly 2 litres - and what an engine that would have been!
Still - there is no point in bleating on about weaknesses - we all have
them. - some more than others - and I count myself among them - why else would I
be sat here writing this article when I could be working on one of my MR2's!!
Back to the plot though - how to extract more power from the N/A?
Well it’s not that easy - as it is a pretty highly tuned engine anyway - but there are ways -
Please bear in mind that list is not exhaustive - and tuning is so
subjective that many members might have differing views to me - which is why I
encourage 'feedback' - especially with those differing views - after all - it is
your Club – as well as mine! Please feel free to add to any debate - or dispute views - just call me!
Having thus condemned myself to slow strangulation over the phone - I
must return to the technicalities of tuning the N/A.
Well - it is not that easy - as I have emphasised before - it is pretty
highly tuned as it left the factory. That factory was not a regular Toyota plant
- in fact it was part owned by Mazda - set up to hand-build specialist cars - as the MK1 certainly was. And to
add to the point - the engines were designed and partially built by Yamaha -
acknowledged masters of high revving motorcycles. As such it revs comfortably to
7500 - and 9000 - but only in short bursts!!
So - the 'nitty-gritty hard bit' - how to extract more power from the N/A?
Well - it can be done - but it costs - as anything to develop an already
highly tuned engine is bound to - it's simply the law of diminishing returns.
Well there are various options - and mine are by no means exhaustive -
please feel free to explore the market before you buy!
1) Change the air intake system to as near as possible to the throttle body. For
early MK1A owners (up to about mid-'86) - this is already the case - you have the best intake system!
For later N/A owners - bad luck -Toyota changed the whole engine bay to
accommodate the upcoming supercharger engine! This meant that the air intake had to come all the way round from the
grille at the back of the drivers door - adequate - but hardly ideal.
There are 3 main options here -
a) Replicate the MK1A - ie a filter on the throttle body intake. This is perfectly
feasible using a K&N 57i or a Ramair filter (both available from Fensport).
This set up certainly has the lowest pressure drop - but there is a downside -
the air drawn into the filter will be quite warm due to the engine heat - and
this definitely reduces power output. As a rough rule of thumb - the air intake
temperature can increase by up to 30 degrees C - which absolutely guarantees a
10% power loss. The MK1A's had a cool air intake duct disappearing downwards
past the battery to combat this - worth a try but a bit fiddly to make. Don't
take the intake too low however - dirt and water pickup will result.
Noise is also a consideration here - you will certainly hear the intake
roar! Nice if you like this sort of thing!
Digression - just for curiosities sake - the airflow through the engine
bay is upwards - the engine bay top is a low pressure area - albeit a bit
turbulent. The underside is at slightly higher pressure - this can't be helped without an even
lower air dam - impractical for those damned speed humps. As a further aside -
those side skirts are there to minimise 'air-bleed' ahead of the rear wheels -
which would lead to vortex formation - creating both lift and drag. So -
contrary to popular opinion - they are not just 'hairdressers' style accessories
- they have a real purpose in life. The undertrays also play a role in smoothing
this underbody airflow out - they are not just dirt shields.
To complete this digression - the rear airfoil - this has a real job - as opposed to being a styling
gizmo. As I recollect - the lift coefficient drops from 0.14 to 0.01 thanks to
this wing - all of which helps keeping the tyres attached to the ground at high
speed - very desirable for preventing sudden heart attacks (amongst us older
members) - and high speed impacts for the young track day turks!!
As for the perspex spoiler - well for me the jury is out. I've heard it
smoothes the airflow over the engine bay - but again racing driver Granville
Williams doesn't like it. I'd need to see wind tunnel or track day results on
this - but the fact that it has 'TOYOTA' splashed all over it inclines me to styling suspicions.
Well – that’s the end of this digression - they can't go on much longer without
being a new article!
So – back to improvement options-
b) Fit a low pressure drop filter in the boot - where the OEM cartridge
filter sits. Junk the ducting that feeds the cartridge - but leave the ducting
from the driver’s side to the boot to provide a reasonable airflow into the boot chamber
A K&N 57i or Ramair or Blitz filter can be used here (the latter
being the best - in my opinion).
Obviously the airflow into the filter will depend on what gets into the
boot - hence the suggestion to leave the driver side ducting intact to the boot
area. The boot then acts as a plenum chamber - but (as always – and was it ever thus!) - there are downsides
to cope with.
The first is - well luggage - as that what’s the boot is there for. Fill
it up like I do for long trips like Le Mans and the airflow is - well let's say
a bit restricted. Add to that a hot engine and an even hotter exhaust in close
proximity underneath means its a pretty poor plenum chamber for cool air.
All in all a pretty poor situation - so what to do? Well, a few ideas-
a) Overall - I prefer to fit the filter as close as possible to the throttle body -
to reduce pressure loss - which is crucial on a normally aspirated engine - it
has to suck every ounce of air in to give it power. But - in doing this - ensure
some cold air supply from the lower engine bay - if you don't do this you will
negate all the pressure drop gains - and have to endure more noise for your troubles!
b) If you can keep a fairly clear boot - then you are damned lucky! A good air
filter in here is a good option - the intake air is (moderately) clean and cool.
c) The best option for me is a boot mounted filter with a cool air supply from the
n/s engine bay. This avoids the noise problem whilst delivering good cool air to
the engine. The downside - a little surgery is needed - not a problem for me.
As for what can be gained by such air intake induction improvements -
well I have to say not a huge amount - probably about 6 - 8 bhp.
Not exactly the 'jewel in the crown' is it - but at least I've got the boring bit out of the way.
There are much better gains to be made on this engine - but that's for
the next magazine - cams and things - but I've run out of copy space for this issue! Read me next time!
ALAN JONES
TUNING THE NA ENGINE – PART 2
Now – if I
remember rightly (which admittedly is rarely these days - privilege of old age
etc. - and don’t argue with your elders - yet!) – I think in my last article
I covered the air intake system.
Moving
marginally downstream - gas flowing the head does have benefits – but to get
the best results Weber 45 DCOE carburettors are really needed – but don’t
expect to reach the next petrol station without a tanker following you (or pass
the MOT) – this is an almost race spec!
Cams – this is
not my ‘native’ country – so I can only recount other members experiences.
The cams as fitted as standard are predictably fairly sporty – don’t ask me
what the valve overlap angle is –I’d have to consult the BGB.
However despite
my technical frailty here – I can recount a story – whether you like it or
not – but at least its sort of meaningful.
Once upon a time
- and not so long ago - one of our ‘trackie’ minded members bought a set of
Piper ‘fast road’ cams. These work by having slightly higher valve
‘lift’ – to assist gas flow - and increased valve ‘overlap’ – to be
sucking intake fuel:air in whilst the exhaust valve is still open –inefficient
but power productive.
Unfortunately
they didn’t work too well – as they were fitted into a supercharger –
where the increased valve overlap is counter productive – the blower merely
blasts unburnt fuel straight into the exhaust.
These increased
overlap cams are really for N/A’s where ‘suck’ rules supreme and every
ounce of gas flow matters crucially - as opposed to the S/C ‘blow’ where
(virtually) anything is possible to be easily changed at will.
Back to the
story line, these cams were removed by one disgruntled owner after only 2 weeks
use - and bought by one sympathetic (or is it just pathetic?) Technical Advisor
to take the pain off his wallet. (I just can’t resist buying MK1 ‘goodies’
– must see the doctor – yet again!)
The idea of this
was to eventually fit them to my N/A – which is currently undergoing a DIY
restoration project – which at the current rate will be completed about 2
weeks before my final demise – the shock of finishing will surely kill me –
but at least I’ll go out with a smile on my face!
Given that I was
unlikely to derive any benefit from these cams – except for the afore
mentioned two weeks – I was persuaded – under the usual Billing ‘haze’ -
to pass these on to a very keen (and valued) member. These were duly fitted to
his car - and at first it was a disaster – the outfit (despite having a dyno)
– just could not time the car. The next outfit were much more clued up –(and
I reckon fitted vernier timing belt pulleys - which really are needed to
optimise such cams) – end result, a dyn’oed 20 BHP gain with little bottom
end loss. All in all not a bad result – but it does cost ca £500.
Exhaust –
Mongoose and Magnex both do good stainless exhausts - but GDS do both stainless
and mild steel - and the latter is better if tuning changes are contemplated. A
decent exhaust such as any of these will give ca 5 BHP power boost – albeit
slightly more noisy.
Exhaust manifold
– cast iron and only moderately good - and they crack near the head – but
much better fabricated jobs are unfortunately just not available (to my
knowledge) without paying a fortune. I reckon a good manifold could yield about
6-8 BHP – pity no one seems to make one.
Ignition – its pretty strong as it is – but a new distributor cap and decent leads don’t go
amiss – if the existing ones are more than 20k miles old – they do
deteriorate in that time. Magnecor are (to me) the best – obtainable via
Fensport – see back pages of the mag or the Club web site.
Fuel – adjustable fuel pressure regulators are available – which increase the
pressure in the fuel rail to the injectors. More pressure equals more fuel flow
during each injector pulse. This is the sort of modification to do having done a
few others – to do it on a standard car is not very productive – it will
richen the mixture to little avail. However if a couple of modifications have
been done – then it makes sense – the standard regulator is a pretty weedy
thing. I’m not sure what power boost this would give – but would guess its
in the order of 5 BHP – anyone dyn’oed one?
Water pump – this is driven by the fan belt - and being centrifugal, the power consumed goes
up with something like the cube of the engine rpm – or something vaguely like
that – after all I am only an old delinquent engineer! The bottom line is that
the pump is sized for the worst conditions – traffic jams. This means it gives
enough flow at low revs - and massive flow at high revs – but at the expense
of high power consumption – which I reckon is about 8-10 BHP. This power loss
can be mitigated greatly (indeed almost totally at high road speed - where only
a small flow is required through the radiator – as the ram-air flow increases
the radiator heat transfer capacity by a factor of at least 10.) In other words
– at high engine speeds the mechanical water pump is over working needlessly -
and draining power accordingly.
The answer – an electric water pump – preferably with an electronic controller. This is
again a centrifugal pump – but the key difference is that it is not driven
‘blindly’ by the fan belt – but by what the engine actually needs. The
next question is where to fit one. The ideal location for this new pump is at
the bottom of the gearbox – ie well under where the battery resides. This
gives the best suction head for the pump to work at best efficiency. The harder
problem is how to disengage the mechanical water pump. The best option by far is
to remove it and fit a blanking plate in its place. Trouble is this is quite a
complex shape and not really a simple DIY job. I have contemplated making one
– but as usual never found the time. There is another way – remove the
impeller from the pump – this is not quite as energy efficient – but at
least it looks normal.
Water injection - not really of much value for an N/A – much more suited to S/C’s
Nitrous Oxide – great for massive power – but forget it unless you have a good supply of
replacement engines!
Chipping – well it does work – but on an already highly tuned engine it can’t make the
spectacular miracles (as claimed for lesser cars) –it gives ca 8 BHP and
better torque pickup. Having said that – if power is the game - then OK –
but remember engine life will be reduced a bit and regular maintenance needs to
be really thorough – nothing comes for free and without some baggage!
Really though I can’t claim to be any great expert in this area – my N/A experience has been
mainly in body restoration – tuning will follow that – eventually. What I
can say though – is that if you are seriously interested in any of these
tuning items – you can’t go wrong in talking to Fensport (07000 336776) –
what they don’t know on Toyota tuning just isn’t worth talking about – if
I’m stuck they advise me – and very well!
That’s all I can think of for now – anyone got more ideas – just contact me and I’ll
put them in the next issue!
That’s engine tuning – but that leaves the suspension. I have covered this before – but
mainly in the context of my S/C. I’ll try to write one more N/A specific for
the next issue – so if anyone has got any experiences (good or bad) – just
let me know and I can build them into the article !!
ALAN JONES