REPAIRS PAGE 67
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