na & turbo diffs.pdf

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/ TECH / N/A & TURBO DIFFERENCES /

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FEEL THE

DIFFERENCE

This month Stu talks us through

the differences between

turbocharged and N/A engines.

I t’s more complicated than you

might think...

T his month I want to look at

one doesn’t, but I assure you

that nothing could be further

from the truth.

Let’s look at the majority of

major differences in the two

engines, using something like a

130bhp Mondeo or Fiesta Zetec

as our theoretical example.

the differences between a

normally aspirated engine

and a turbocharged one. I know

from bitter experience that

many of you think that the only

difference between the two is the

fact one has a turbocharger and

Let’s look at the majority of

N/A manifolds are quite

different to turbo applications

EXHAUST MANIFOLD AND TURBO

The first thing you need to

deal with is obvious, and

that’s the fact that you need

to add an exhaust manifold

and turbocharger to your

engine to turbocharge it.

The manifold on a turbo-

charged car is different to

that of a normally aspirated

engine and works on a

different principle too as

far as the primaries and

collector are concerned,

so take great care with this

aspect and ideally entrust

the work to people who

are recognised experts in

this field.

Words: Stewart Sanderson

Having worked as a tuner

for 17 years, Stewart ‘Stu’

Sanderson is one of the

most-respected names

in the business.

A Level 5-trained fuel-

injection technician, in the

past Stu has worked for a

Ford Rallye Sport dealer, a

well-known fuel-injection

specialist and various

tuning companies.

Then seven years ago he

joined forces with Kenny

Walker and opened up

Motorsport Developments

near Blackpool (01253

508400, www.remapping.

co.uk ), specialising in

engine management live

remapping, as well as

developing a range of

Evolution chips which

are now sold all over

the world.

He’s also jointly

responsible with

Webmaster, Petrucci for

www.passionford.com .

Started in 2003, it’s grown

rapidly from a few friends

contributing, to one of the

biggest Ford communities

on the web. His new forum,

www.fordrsforums.co.uk ,

is also up and running.

Stu’s enviable

knowledge of the

workings of modern-day

Ford performance engines

means that every month

he’s just the man to

explain how and why

things work, and most

importantly how they can

be improved.

Having worked as a tuner

The diameter is essential for the

exhaust of your blown motor

COMPRESSION

RATIO

EXHAUST

This is one of the most

complex parts of the turbo

conversion as it’s one of the

hardest to alter correctly and

requires the head and

sometimes the whole engine

to be removed and disman-

tled. It also has a great effect

on other aspects of the

engine so needs to be ﬁ nal-

ised early in the conversion.

Compression ratio is such

a complex subject that we

cannot go into it fully here,

but sufﬁ ce to say you will

probably need to change it

for your turbo conversion to

work properly as we tend to

run lower compression on

a turbocharged high-power

engine. If you are looking

for big power and reliability

I would advise you to lower it.

There are numerous

ways to do this such as

decompression plates that ﬁ t

between the head and block,

you can skim the pistons

making them shorter, bowl

out the combustion chamber

making it larger or use a

combination of all these

methods. However, the best

way is to use a combina-

tion of chamber re-proﬁ ling

and lower compression,

better quality pistons.

Once your new turbocharger has pride of place on your shiny

new exhaust manifold, your old exhaust is useless, or at least

the part that connects it up to the engine or manifold is.

You now need one designed to mount onto a turbocharger,

which will be in a totally different place. You also need to con-

sider that your exhaust now has to get rid of more than just

130bhp. It has to allow the extraction to atmosphere of 250bhp

worth of gas, so the standard 1.5in bore is no longer an option,

you could really do with 2.5in or more.

sider that your exhaust now has to get rid of more than just

130bhp. It has to allow the extraction to atmosphere of 250bhp

worth of gas, so the standard 1.5in bore is no longer an option,

you could really do with 2.5in or more.

and lower compression,

better quality pistons.

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MARCH 2008 FAST FORD

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/ TECH / N/A & TURBO DIFFERENCES

one doesn’t, but I assure you

that nothing could be further

The manifold on a turbo-

charged car is different to

that of a normally aspirated

worth of gas, so the standard 1.5in bore is no longer an option,

you could really do with 2.5in or more.

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tech / TECH / N/A & TURBO DIFFERENCES /

/ TECH / N/A & TURBO DIFFERENCES /

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CAMSHAFTS

COOLING SYSTEM

This is one of the most over-

looked things for some reason.

The amount of cars I get in

with turbo conversions and

overlooked cooling systems is

shocking. Adding bhp alone will

add heat energy due to the inef-

ﬁ ciencies of the internal com-

bustion engine so we have to

be able to lose this heat some-

where, ideally to atmosphere.

Don’t overlook the fact that

modern turbochargers almost

universally must run water

through their cores so you will

need to design the plumbing

for this so that it doesn’t affect

the ﬂ ow around the engine too

much. The water coming out of

the turbochargers core is often

superheated and will add con-

siderable heat energy into our

cooling system that we need

to get rid of.

Sadly, I even see cars come

in with the radiator cooling

fans totally removed as the

conversion company or person

couldn’t ﬁ t the fans and the

turbo in the space available,

so they just dumped the

fans. Thankfully, nobody

reading this would do anything

so stupid as I’m sure you are

all enthusiasts eager to do

things right, and realise that

radiators are air/air heat

exchangers and need to

have air ﬂ owing through the

core to enable them to cool

engines. That’s why we ﬁ t fans,

to keep the air moving when

the car is not.

Depending on the state of tune you

want, standard cams are usually ﬁ ne

You need to keep the fans,

especially when sat in trafﬁ c

Contrary to popular belief the

camshafts on a normally aspi-

rated engine are normally quite

good for a turbocharged appli-

cation under most conditions.

If you are running really wild

ones, or have variable cam tim-

ing then you’ll run into problems

but generally speaking the cams

aren’t a big issue for an average

turbo conversion and can be

dealt with later on if you want

to tailor your boost and power

curves to better suit your

intended application.

to tailor your boost and power

curves to better suit your

intended application.

ENGINE MANAGEMENT

PISTONS

OK, we’ve added lots of

lovely boost to our engine

and are expecting it to make

some nice extra bhp, and

we know the engine will

keep cool making it due

to our cooling upgrades.

However, to make that extra

power we have to get our air

fuel ratio nice and safe,

and in most cases that job

will be the sole responsibility

of our engine’s management

system. It has to be aware of

the boost and be programmed

to deal with it. So, what will

you have to upgrade just to

allow extra fuel for the on

boost conditions?

The pistons are generally made of a

different material or at a bare minimum

they will be cast in a different way on a

turbocharged engine, as they have to deal

with vastly different pressures than their

normally aspirated counterparts. Regardless of

material or construction though, you will

ﬁ nd you need to modify the pistons in order to

correctly change the compression ratio.

The pistons are generally made of a

different material or at a bare minimum

they will be cast in a different way on a

turbocharged engine, as they have to deal

with vastly different pressures than their

normally aspirated counterparts. Regardless of

material or construction though, you will

ﬁ nd you need to modify the pistons in order to

correctly change the compression ratio.

FUEL INJECTORS

PRESSURE

SENSING

Pistons will play a vital part in how

much power your engine can take

Pistons will play a vital part in how

much power your engine can take

We’ve sorted the management

and told the ECU to add more

fuel on boost via a chip, some

reprogramming or a totally dif-

ferent management system.

How do we know more

fuel is actually

available? You need some

information about your original

injectors and find out what

they will flow for power. If

they are not big enough

you will need to change

them to some that are

larger, then you need to

program the ECU again

to ensure that the fuel

is retained at the same

level it was before the

change until that extra

fuel is actually required.

Throwing in big injectors

without reprogramming

will just end up with either

a non-running or at best a

very badly running engine.

On systems without an air-

ﬂ ow meter (speed density

systems) and presuming

your management can

accept input from a sensor

that can see pressures over

and above atmospheric, the

ﬁ rst thing we must do is

actually ﬁ t one, because you

can be pretty certain the one

you have will only be a 1bar

sensor that can read up to

atmospheric pressure.

If you try to use boost with

the original one you’ll discover

to your pistons’ peril that

your ECU cannot see any

boost and continues to fuel

as though the engine was

normally aspirated, thus only

supplying the fuel for around

130bhp. Soon your engine

internals will resemble a

Mars bar in a furnace.

Make sure your injectors can

ﬂ ow enough fuel, else it’ll melt

SPARK RETARD ON BOOST

As well as more fuel on boost,

we need to program the ECU

to retard the boost as the

cylinder pressures get higher

and higher. Generally speak-

ing, the more boost you add,

the less spark advance will be

required. Get this wrong and

you could say goodbye to the

pistons in less time than it

takes to get to fourth gear on

your first-ever full power run.

It’s not that simple at all,

and there are a lot of other

spark map changes to be

done, but for the purposes

of this article we are just

simplifying. For more in-depth

info, see my three-part

management feature from

previous issues.

MAP sensors are needed to let

the ECU see positive air pressure

HEAD GASKET

Engine mapping is best

left to the professionals

Head gaskets on some normally aspirated vehicles are not very

good at all, simply because they don’t have to be. Very often

you will ﬁ nd a different material is used on the higher powered

turbocharged models, so be aware that this issue may need

addressing, although you will never know how tough the stand-

ard one is until you try it. My advice is if there is an uprated

one on an existing turbocharged model then ﬁ t it, as the OE

manufacturer didn’t uprate it for a laugh and something to do,

it was done as a necessity.

A custom mappable ECU

is the best route to go for

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CAMSHAFTS

Contrary to popular belief the

camshafts on a normally aspi-

rated engine are normally quite

good for a turbocharged appli-

cation under most conditions.

If you are running really wild

ones, or have variable cam tim-

ing then you’ll run into problems

but generally speaking the cams

aren’t a big issue for an average

turbo conversion and can be

dealt with later on if you want

to tailor your boost and power

PISTONS

fast tech

FUEL PRESSURE

FUEL PUMP

NEEDS TO

BE UP TO IT

Have you ever considered

how fuel, or for that matter,

any liquid or gas ﬂ ows from

one place to another? Any gas

or liquid will ﬂ ow away from

the highest pressure towards

the lowest pressure.

Let’s say we are running our

injectors at 3bar of pressure in

the fuel rail and that they inject

nicely into our inlet runners...

What happens to the ﬂ ow then

as the boost pressure in those

runners increases to 3bar?

At 3bar we would have equal

pressure on either side of

the injector and nothing

would ﬂ ow.

As the boost goes up our

injectors ﬂ ow less and less. So,

how do we ﬁ x that? We swap

our fuel regulator to one that

increases pressure in a linear

or greater fashion the more

inlet pressure it sees. Usually

we run 1:1 meaning for every

psi above atmospheric pres-

sure we apply to the regulator,

it will increase the fuel pres-

sure by 1psi.

As an example, a rail that

runs 3bar at atmospheric pres-

sure, will run 5bar if it is used

with 2bar of boost, this keeps

the differential pressure across

the nozzle the same from

As the boost goes up our

injectors ﬂ ow less and less. So,

how do we ﬁ x that? We swap

our fuel regulator to one that

increases pressure in a linear

or greater fashion the more

inlet pressure it sees. Usually

we run 1:1 meaning for every

psi above atmospheric pres-

sure we apply to the regulator,

it will increase the fuel pres-

Things are looking good

now. We have big injec-

tors and management to

cope, and we have sorted

the fuel regulator so that

it increases the pressure

as we run more boost, so

what next? Well, we have

to head back down the

line to the fuel pump. The

fuel pump on your car may

not be able to supply that

amount of fuel for the bhp

you are running, and it

most certainly may not be

able to do so at a couple of

bars extra pressure. Time

for yet another upgrade...

atmosphere right up to as much

boost pressure as the regulator

can deal with, normally about

2.5bar in my experience.

FUEL LINES

We have our fuel pump supply-

ing the volume of fuel, and the

injectors are ready and waiting

to supply that fuel to the ple-

num at the correct fuel pres-

sure to ensure atomization in

our highly pressurized inlet.

Great news, we are all done

now then? No, how does the

fuel get from the pump to the

new injectors? The lines are

far too small on many normally

aspirated cars so we need to

uprate the lines too. How big

we go depends on the

power we want, so take

specialist advice or risk

doing it twice, and don’t

forget the return to the

tank line. If that is too

small our fuel pressure

will be stuck too high

as the regulator can’t

bypass sufﬁ cient volume

of fuel to maintain the

required pressure, not

good news at all on our

huge new injectors.

You need bigger fuel lines

if you’re turboing your car

Make sure the wiring

is up to the job, too

LUBRICATION FOR TURBO

Turbochargers do require a

good supply of oil under very

high pressure to ensure lubrica-

tion of the journal bearings at

high turbine speeds and core

temperatures. Have you consid-

ered where you will get this oil

supply from?

Nine times out of 10 we

use the oil pressure switch

drilling and ﬁ t an adaptor here

to allow us to supply both the

switch and our oil feed, but I

can think of a couple of exam-

ples where this isn’t possible,

so think ahead.

You also need to bear in mind

that not only do we need to get

oil into the turbo we need to get

it back out too, and down to the

sump again. This requires a tap

into the sump of suitable bore

and angle so as not to restrict

the oil return path, as doing

so will cause oil to be forced

past our turbine seal, leading

to smoke. Even the big boys

get this wrong at times as Ford

proved when it got this design

wrong on the early Fiesta

Turbos and had to uprate the oil

return pipe to ensure reliability.

You need a high-pressure oil feed to

keep your expensive turbo going strong

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FUEL PUMP

atmosphere right up to as much

boost pressure as the regulator

can deal with, normally about

You need bigger fuel lines

if you’re turboing your car

fast tech / TECH / N/A & TURBO DIFFERENCES /

BREATHER SYSTEMS

OIL COOLING

When you increase the power

of an engine, you invariably

also increase the piston ring

blow by, which means we

have a certain amount of air to

process and remove from the

crankcase if we don’t want all

our oil seals to fail. Normally,

an engine’s breather system

will simply link the top and

bottom of the engine with a

series of pipes and route the

resultant oily air mixture into

the inlet plenum for re-diges-

tion into the combustion

process, as that’s the greenest

way of doing so.

The problems you will face

with this method are

numerous, but the main

problem is that your nor-

mally aspirated breather

system pipework isn’t

normally of sufﬁ cient

bore to move all the gas

required on a high power

engine, also the normal

system is easily over-

come by excess oil on a

high-performance engine that

throws its oil around in the

sump a lot. So, you will often

need to add another port to

the opposite side of the block

to deal with oil surge under

hard cornering.

An oil separator is advised

to allow the mixture to enter a

canister as a heavy oil and air

mix. The canister then sepa-

rates this oil/air mix and sends

the air to the atmosphere or

back to the inlet of the engine.

The spare oil that was sepa-

rated is then returned into the

sump, thus lowering oil loss

quite dramatically.

How many of you are aware of,

or have ever considered, the

fact that oil is the engine’s pri-

mary coolant? All the surfaces

of your engine that generate

any heat such as bearings and

bore walls etc are lubricated

and cooled directly by the oil.

The oil transfers this heat

to the block and sump etc.

The water jacket then absorbs

some of this heat and transfers

it away to the radiator to be

radiated back to atmosphere.

Get yourself an oil tempera-

ture gauge and monitor it to

ensure you aren’t running the

oil too hot because of your

turbo and extra power genera-

tion. If you are, time to look at

one of the various oil cooling

options available.

Oil coolers are a good idea to

help keep the engine cool

INTERCOOLER

FUEL

OCTANE

It looks like the management

and fuel system are sorted

now and we are safe to turn

the boost up a little and see

what our new powerplant can

do. Well, maybe...

The amount of boost you

intend to run will govern

what we have to do about

intercooling. If you’re looking

for just 3 or 4psi you will

be fine.

However, if you want more

than that, you should look

very seriously into ways to

cool down the air coming out

of the turbo, you won’t be

making much power with air

temperatures upwards

of 100 degrees Celsius, so

you will need to fit either an

intercooler or a chargecooler.

See FF issue 262 for more

in-depth information on the

differences between charge-

cooling and intercooling and

details of how it all works.

This sadly is one of the

biggest killers for a DIY

turbo conversion. People

seem to forget that per-

formance engines require

performance fuels, and

they continue to run

their new high-power

boosted engines on low

octane shopping fuel and

detonate it. High power

engines without complex

management incorporat-

ing active knock detec-

tion require the best fuel

octane you can buy at the

pump. Ignore that advice

at your peril.

With intercoolers,

bigger really is better

So there you have it,

hopefully that will have

given you some idea of

the complexities involved in

converting a normally aspirated

engine to a turbocharged one. See

you next month.

NEXT MONTH

We will look at exhaust gas

temperature, how it’s measured

and why it’s important.

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