Tuning tips from a master.

Frequently Asked Questions about the Cappuccino.

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Tuning tips from a master.

Postby Steve Lewis » Wed Apr 09, 2003 02:08

I have recently received a few emails from members asking about tuning modifications.
When I first had my Cappuccino I had the same questions which I posed to Dave Benson. Dave took a lot of time to answer my queries and point out problems that I had not thought of. I think the right place for all the help he provided me is here on the SCORE message board for the benifit of others rather than to leave it sitting on my harddrive (which could crash at any moment!).
The emails are reproduced in their entirity - I have included my question to Dave only if I think it is required to follow the gist of Daves reply.



Steve.

*****************************************************************************

9th July 2002

No problems... glad to help a fellow tuner..

Yep you will get stung on the VAT but your biggest
bill will be the transport..

You could seriously be looking at 200-300quid for the
shipping bill (mainly because of the weight rather
than size.. clutches are quite heavy and the lightened
flywheel is still heavy!)

IRS go to http://www.irs.co.jp/oversea/

SuzukiSport use a very expensive courier.. they also
expect a funds transfer which is a pain and costly
(another 20quid or so for transaction) whereas you can
fax or email your details to IRS.. they are extremely
good, ship quickly, knowledable about products and can
get other bits as well from other companies such as
ARC (Abbey Road Company) Crux Motorsport etc..

I did once use SuzukiSport (some stickers and some
engine mounts) and regretted it when the shipping
costs were more than the goods! (they used DHL)

Yes N2 comes with Injectors 330ml(if I remember
correctly)

yes N2 fits fine with original turbo.. wick up the
boost and the performance starts.. Done by a friend in
Australia (Justin Pickering) and also I did the same
on mine before I had the turbo fitted..

Yep its a pain to get parts.. the trick is to think of
bits that might fit.. i.e. the front discs are the
same dimensions as the Swift 1.0 & 1.3 (but not GTi)
and therefore I sourced a set of Black Diamond Disks
from Demon Tweeks.. again the same place can supply a
universal strut brace that will fit..

I will expand on a few things..

I have driven a Capp with the sports clutch, it is a
pig.. real race car stuff.. every pull away is a
launch.. so if you drive in traffic I would seriously
back off from it now..
The clutch and flywheel are an item, you cannot have
one without the other..
Taking those out of the equation leaves some spare
cash and your going to need it... why??

The turbo and N2 conversion is great but you run into
two big problems.. intercooler heat and compression..

AT MINIMUM you should fit a larger intercooler (ARC
one is dead cool.. and works well - think 400quid)
otherwise things get hot, detonation starts and things
go pop.. I'm talking from expensive experience here!

The other is compression.. similar deal.. if you run
the turbo at its designed boost (around 1.25 for the
Capp) you should be producing 127bhp with other
standard parts BUT there is a tendency again for
things to go pop, like pistons (done that one to!)
(look around 100quid for gasket)

Therefore for you setup I would suggest the following:

IHI RHB31FW
N2 ECU and Injectors
ARC Race Intercooler
2.2mm head gasket
No.9 Heat spark plugs

This should give you a stonkingly fast car.. get it on
some rollers to check and confirm fueling... you can
adjust slightly by way of the resistors in the engine
bay.. (opposite side to battery at front their is a
holder on the loom.. sometimes there is a resistor in
their and changing the value of that changes the
fueling richness throughout the range..

Fitting the turbo.. seriously think about getting
garage to do it.. there is a BIG possibility that the
bolts from the manifold to the turbo will break.. Its
because of the heat changes.. the turbo is alloy and
can be helicoiled if needed but Levois in Colchester
have no fear of mods and if your close(ish) to them
its worth the travel to get them to do it..

I presume that you've already got a Sports Exhaust
system and some sort of induction kit fitted..

If the worst does happen, your looking at around 450
quid for a set of pistons (race ones.. 657, 688, 698
or 708 - I'm up to 708cc) plus you will need to get
the block honed if your lucky and don't score the bore
too much.. otherwise its a bore out job..

Then your looking at 2k for that alone.. (engine out,
head off, new gaskets etc..)

My last thought is that if you wish to try and do it a
bit cheaper (i.e. not taking off the head) then once
the other bits are fitted (turbo, ECU and intercooler)
then get yourself to a rolling road to make sure that
your running nice and rich (the extra fuelling acts to
absorb heat during the combustion process and is used
on turbo cars to help stop detonation) that way you
can be more confident with what your running...

Oh and of course.. you must ALWAYS RUN SUPER UNLEADED

Hows that?

Dave

*****************************************************************************

10th July 2002

Glad to be of help.. even longer email....!

Another reason not to go clutch...
Clutches are around 80-90 quid, gearboxes are just a
tad more expensive.. mega powerful engine and a highly
dumped clutch on regular basis somethings gotta give..
I'd rather have a slipping clutch to replace than
trying to find a Cappuccino gearbox! :)
Also unless you seriously get on boost with the clutch
still slipping its pretty solid, I've never had it let
go from just accelerating hard..


Water Injection..

Yep got the kit.. :)

Check out Aquamist

If you went down that route you would need to be VERY
nice to them as the standard kit is a little overkill
for the small engine and therefore you need a smaller
jet (0.3mm i think) and also they can rate the pump
down (thats what they did to mine) so it flows less..
Yes Methanol will stop the water from freezing (which
wrecks your pump) but no more than 50/50, again its a
bit of an art as too much water can mean bore wash
which basically is when the side walls of the piston
get cleaned and washed by the excess water.. this may
sound good but the very thin layer of combustion
materials and oil actually help to keep temperatures
low and therefore in this case you would end up
INCREASING temperatures.. so yes the intercooler is a
lot easier to use, install, maintain and does look
damn cool (pardon the pun)

Strut brace.. not loads of difference as the main use
would be on a front wheel drive car (they tend to rip
the top mounts out) so you probably won't FEEL lots of
difference BUT my brothers car has suffered some
fatigue in the top strut areas so it should help
longevity PLUS it makes fiddling on the engine a lots
easier as you always tend to lean on it as you do
stuff underbonnet.. so yes money well spent as all
those bumps are going to leave their mark eventually.

Gasket.. yep reduces CR, difficult one re safe boost
with no gasket.. theoretically I would say 1 bar max
but what you have to remember is that because the
newer turbo is physically larger it actually pushes
more air in at 1 bar than the old one.. can explain
more if you wish.. but the benefits is that
compression (of air by the turbo) causes heat and
therefore the newer turbo helps to keep things cooler.
The only way to really know would be to install turbo
with lowest boost and to rolling road the car.

N2 (not sure if you know) will remove boost cut-off
limiter, raise rev limiter (to 9800) and remove speed
limiter.. it will not actually raise the boost level
BUT the turbo comes with an adjustable actuator arm so
it threads out to give the different levels of boost..
thought you should know.. the other thing the N2 does
is to advance the ignition spark.. this is another
reason to be careful and of course use super
unleaded.. the further the advance the more likelyhood
of knock and moving on, detonation.. the normal F6A
engine does not have a knock sensor so its up to you
to tune it within specs.. I believe the K6A (which has
an ally block) does have a sensor which is possibly
why they managed to increase the torque (just advance
the ignition to gain and let the sensor pull the
timing back when needed) oh and it also changes the
boost light.. it will only come on at 1bar of boost
when installed...

Spark plugs.. NGK IRIMAC #9 unfortunately I couldn't
find them in the UK tried nearly everywhere.. 6,900
yen was what I paid for 3 which is around 12quid a
plug.. :)

Air filter.. have fun.. not a lot of kit around to
help (unless again you buy an ARC kit from Japan or a
HKS filter from TDI)

Wheels and tyres..

Yep 7J too wide.. 15" 6.5J - they will fit though you
will need spacers on the rear to clear the suspension
on full extension.. they will likely to touch the
arches and you will never be able to lower the car..
you may even have MOT problems if they are a bit anal.
195/45 is the correct size but 195/50 do sort of just
manage to squeeze in.. again touching down a problem..
also I had some negative camber dialled into the rear
(its adjustable but you do need to laser it as the
adjuster ALSO controls toe-in so done by eye you'll
wreck the handling) to bring the tops in to help
clearance.. Plus pulled the lip of the arches in
slightly. You may very well be much better off by
filling the arches with a set of 14 x 6's with 185/60
tyres.. with something sticky like the Yoko A032's.
16 x 6.5J are available as they fit the Scoobies
(Impreza's) as standard BUT its nigh on impossible to
find someone that can supply blank to drill the PCD
needed.. Really fancied the OZ F1 Cup's but to no
avail...
I do have a set of original non kerbed and corroded
Capp wheels which you could relieve me off for a
bargain price :)

Best of luck and have fun....

db

*****************************************************************************

11th July 2002

Expensive to modify in a big way... and yes couple of
things VERY expensive.. mainly the roof, then bonnet
is suprisingly cheap but not so the front lights at
400 quid each...

There is also a slightly lower alternative and that is
the Superchip mod..

They de-restrict, raise the boost to 1bar and use a
piggy back chip to raise the fuelling.. basically goes
from 63 to around 80-85bhp.. though its a bit of a
wasted route if you really want to go the other route
later.. you'd be better off waiting..

I'll be totally totally honest.. the plugs is a bit
belt and braces approach.. it was that after one of my
bigger blow ups one of the casualties was a spark
plug.. with this in mind I asked IRS if they
recommended anything else to add to my car plus I have
a couple of imported Japanese K-Car tuning magazines..
all in Japanese but plenty of pictures and the odd
english word... :) basically the other thing to have
was the spark plugs so I went for them...
Never had any problems with them not starting or
running like normal.. only just recently put a new set
in and thats been about 3 years..

If you think about the fact that your paying carriage
and probably some commission on the credit card, you
need to think of all the little things that can fit in
with the order..

Spark Plugs
Anti-Roll bar uprated bushes (they call them
stabilizer bars)
Braided Brake hoses

Though some of these (like the brake hoses) aren't
really cheap (100quid) but still cheaper than the UK
OEM part. Though some parts you should stick with..
the pads for the front discs.. OEM are soft the
'Halfords' purchased ones are really the swift ones
and as it weighs nearly twice as much they are a lot
harder.. ok if you've got grooved discs as they bite
but with the standard dics not so good. The softer
pads are pretty good (unless your going the whole hog
of fitting say a set of Swift GTi discs and
calipers..)

Yeah Demon Tweeks are a bit pants with knowing the
Capp... for the front discs I got the dimensions, then
Levois found out that they were the same as the Swift
spoke (in poor) Italian to Tarox.. they gave me some
more details which I gave to Demon Tweeks and they
sourced me some Black Diamond discs.. mine are getting
very worn now (4 years later or so) so might have to
revisit the same all over again! :)

The universal strut brace still looks good.. try
asking TDi how much they would charge for a unit.. I'm
sure theirs is just a universal one but it will fit
could save some grieve... don't expect them to be mega
friendly or helpful.. they are if you're spending 10k
on mods but apart from that...

Demon Tweeks also sell intercoolers, or try looking
for maybe a smashed EVO (someone in Oz did this swap
but they have a lot of imports to scrap) or even bring
your cheque book with ya and you could fit TWO
standard Cappuccino ones.. (I would suggest turn the
original one 90 degrees the other one opposite so you
get a good flow (less bends the better) should look
pretty trick..

Wheels, yeah the problem is the width full stop.. 6.5"
means that a little more goes inside and some comes
out.. therefore when you really large it, or launch it
or load to high heaven the edge of the tyre _just_
touches the rear arches, obviously to clear you'd
change the offset to get more wheel on the inside but
because the Capp has a rather funky multilink
suspension as the wheel moves down it does so in a
straight line and moves straight in.. if you can
imagine this then the wheel eventually hits the top
strut/shock.. the best size is really to go for a 14"
wheel with a 6J width (don't 15x6 is available, though
anything is if you have enough money!) the Japanese
actually go to 13" as you can get some pretty funky
rubber in this size, it also helps to lower the centre
of gravity etc.. If your going to make a journey
down.. across or whatever then you can give my car a
good going over to see what I mean..

The other reason to get the slightly smaller wheel
combo is that you can then fit lower springs/uprated
shocks at a later date.. something I don't think I
could get away with at all.. also you mention the
bumps.. one thing you do notice is that when I went to
the 195/45-15's the ride becomes a lot firmer (no tyre
wall deflection) which is another reason why I tried
for 195/50's the next time around (no difference btw)
along with the fact that 195/50 are tuppence ha'penny
compared to other sizes..

Wheels.. yep sitting here.. still have centre caps if
that also helps (some people seem to have lost
theirs!?!) plus they have some tyres on them but
they're not fab.. reminds me of a couple of things in
my ramblings.. tyre sizes.. you can go one up on the
standard rims.. i.e. 175/60 don't go for 185 even if
the tyre bloke says they're fine.. they just balloon
over the rim and cause shite handling..
Oh and dump valves.. standard one (which is the brown
plastic thingie at the top near the exhaust manifold)
the diaphram on this is a little weak so if you get a
situation where you hit the gas then back off and get
on really quick it sometimes ends up open when the
boost is on.. i.e. no power and lots of wheezes.. if
its doing this then 1. its old and 2. its past its
performance envelope.. you'll have to think of
something like a blitz unit or you can look at the HKS
SQV unit I've got fitted..

I think that brain dump worked OK..

Wheels - give em away.. say 275quid (yes for all 4!)
:)
Tyres should get you straight through MOT.. the tyres
are just a little boring being 'standard' car
Yokohama's rather than anything super sticky..
Intercooler say a ton..
Other bits floating around.. (got a couple of turbo
timers if your any good at electrical - they're boxed
with instructions but they look a little fiddly)

Have a good day.. (or is that night!?)

Dave

*****************************************************************************

15th July 2002

> I had previously considered a Superchip, also
> considered fitting a fuel cut
> defencer and a speed limit defencer both available
> from TDI at £90+ each.
> However as you say they would have to be 'junked' if
> I wanted more power so
> I decided to start from the top so to speak.

Good idea!

> I am going to turn you down on the wheels for the
> present until I have
> researched it a bit more. I have found a couple of
> places which do 15x6 and
> one that will go all the way up to 18x6 but their
> pretty expensive as you
> say. I have also found a place that will refurbish
> the Cap wheels for
> £125+vat (I may get them done in white:))

No probs..

>
> May be interested in the intercooler though. I'll
> have to get my hands
> dirty soon and see what will fit - I have a spare
> one from a Rover Vitesse
> which I think is a fair bit larger than the
> Cappuccinos. I like the idea of
> twin intercoolers though, so if the Rover one will
> not fit I may well take
> you up on you offer.

Either way you'll need to make up brackets and or
piping to get this done.. The trick is to get maximum
flow rate.. that means an efficient Intercooler as
possible.. therefore if trying to replace then try
look at a more modern vehicle.. I know that the
Renault 5 is one to avoid as it kicks back and has bad
flow.. maybe an importer for Japanese cars is worth a
visit to see if a FTO, GTO3000, Skyline or similar
vehicles are lying around damaged..

> Do you still have the original ECU that you replaced
> with the N2? - If you
> would you consider selling it? IRS have given me a
> quote for an N2 of
> 80,000 yen but this is on an exchange basis and I
> don't really fancy sending
> my only working one to Japan!!!

Yeah, car off the road for a week or two plus shipping
costs to Japan... nah.. sorry did a silly and sold
mine to a guy in New Zealand that blew his standard
one up.. Think theres a market for old ECU's in Japan
heard a similar story of people being given prices for
exchange.. sounds like trouble.. what if the N2 is
damaged in transit!
>
> Turbo timers - do these alter the boost depending on
> what gear your in and
> the revs your running?

Think your thinking of an FCON or electronic actuator
control.. the turbo timer just measures the boost
levels and running times so when you stop and switch
off the car, the car stays running for a time to allow
the oil temperature to drop around the turbo
bearings..
Its pretty funky, can't remember if it shows boost
level or not though..

I'm also on the look out for
> a decent boost guage but
> if the turbo timers indicate the boost pressure they
> may be a better
> alternative - can you give me more details and the
> number of beer tokens
> that would be involved.

SPA gauge is a fantastic unit.. LED and double gauges
can be bought so you can have boost pressure and say
intercooler temperature on the same dial..
Expensive though.. so maybe you just want to stick a
normal analogue boost gauge in.. quite easy to fit..

I currently measure.. Oil pressure, Oil Temperature,
Boost Level and Intercooler outlet temperature.


> I'd love to see your Capp someday - sounds awsome!

Sure, anytime..


*****************************************************************************

16th July 2002

Ouch,

I heard before that there were problems with ECU's and
someone else said they were asked for their old ones..
strange...

Uprated turbo.. try a Turbo Technics dealer.. the
uprated turbo is a slightly larger (impellor wise)
version of the original so bolts straight on the
original manifold and inlets..

The original is an IHI RHB31 whereas the larger one is
the IH RHB31FW

They should be able to get hold of one if they try
hard enough.. worth a shot if your going to go down
that road...

Saying that.. TDi did manage to get a friends car
running pretty quick with the original turbo running
1.5bar of boost and the original unit does spin up
quicker than the larger one which comes with a little
lag.. they went for HKS FCON to control boost as well
as a lot of other gadgets.. they wouldn't admit it
fully but I know that they turned up the fuel rail
pressure to give more fuelling capabilities whereas
Personally I would fit some Baleno injectors as these
would flow more but with the standard pressure
settings.. bit like the larger N2 injectors.

Did you ask about the N1 ECU??

Reason I ask is that with that box you could fit a
boost controller, whip it up to around 1.25 bar of
boost (18psi) and have 100bhp quite easily..
This gives you about 150bhp/tonne which is pretty fast
in itself.. you still have to run super unleaded but
its an easy upgrade that should work very well..

There are quite a few superchip dealers around (their
website lists them) its not a hard setup to do
consisting of a black box to remove speed limiter.. a
box to increase the boost fuel cut-off limiter a
daughterboard on the ECU with richens the mixture.
Then a bleed valve is added to make the waste gate to
open later and voila..

Dave



*****************************************************************************

18th July 2002

Yeah my Pistons's, and small end bearings are all Crux
Motorsport, but I dealt with them through IRS..

If you go through all the links and find the Kaikemon
site, then the girl that has that car (orange one with
loads of gadgets) has some fantastic links on her page
to lots of Japanese tuning houses such as Heart and
Abbey Road..

Oh and I emailed Blitz in the UK for you..
unfortunatley they don't list anything for the Capp.

db

*****************************************************************************

18th July 2002

Get through to this part:

http://c-press.zone.ne.jp/links/cappu_shop.html

This has all the shops..

Check out the Bill Works..

Go to second link up.. got manifolds.. see the Capp
one?? Curly manifold in stainless??

Got that fitted.. :)

db


*****************************************************************************

19th July 2002

Yeah they can take their time..

I always use pigeon language..

Dear Sir,

Can you supply parts for Suzuki Cappuccino EA11R,
engine F6A

Regards,

I think that way they see a least a couple of bits
that makes them think its worth working out..
Again.. IRS seem to be a good Portal to getting info
out of the other companies..

I once faxed Bill Works to try and order that
manifold.

I faxed the picture across circled with "How much -
deliver to England" written on it.. I never got an
answer! :)

I'm also lucky enough to have a K-car magazine so I
knew the parts I wanted were available, I just had to
try and find out how to get understood!

Maybe with the World Cup they might know a few more
words of English. :)

--- Steve Lewis <> wrote:
>Thats a very very nice curly bit:)
>
> Do you have a trick for dealing with the Japanese as
> I do not seem to get
> replies from them (at least not from SuzukiSport or
> Crux).

*****************************************************************************

13th September 2002

Nice one!

Stereo access is as follows:

Empty compartment next to handbrake inc rubber lining.

Undo Couple of screws
Undo Screws at back near roof panel lever
undo screws at front

Remove Gearknob (screws off)

Lift panel, handbrake gaiter has velcro and popper
Unclip window switches you'll have to lift the rear
window release handle to get it past.

I think at this point this console can be moved to a
save place.

If I remember correctly the stereo has a boomerang
shaped ally bracket on each side.. you should have
again two bolts to remove and get the stereo out.

Everything pretty much accessible from that point..

A lot of stereo installers struggle as they don't know
that the middle bit has to come out first.

Boost gauge places

Demon Tweeks 01978 664466
Ripspeed (in Halfords)
Burton Power Products 020 8554 2281

Paul will show you a place to fit.. you might need to
visit homebase to get the T-Piece..

Have Fun..

db

--- Steve Lewis <> wrote:
>
> I've surpassed myself and managed to fit the
> intercooler - talk about tight fit!

*****************************************************************************

20th September 2002

Sounds like the sort of fun the day I had when I
picked mine up..

The new turbo is larger, therefore the AMOUNT of air
it flows is greater... whereas boost is the amount
that it is Squashed before it goes into the engine..

So what we have achieve is a greater flow of air with
less squashing... the squashing causes greater heat
therefore to get the same flow of air with the smaller
turbo you would need to run a lot higher boost and
therefore you would get the flow but with a lot hotter
air, which as you know has less oxygen to burn, causes
detonation etc.. etc.. the intercooler then does its
job to cool the air even more to give a better
charge... all in all more power...

Other mods... If you haven't done anything to the
exhaust then go for a 2.25 bore pipe with say a 2.5"
end (the end is up to you..) this is generally the
size people end up with as its big but not silly for
the Capp. I would advise better stiffer rubbers for
the exhaust (I ordered some racing ones from Japan) as
if its Stainless then the extra weight tends to move
it around a lot.. (and it has a bracket to the gearbox
so that gets tugged around)

If you can get there I recommend Haywood and Scott on
the Burnt Mills estate in Basildon, Essex.
Their kit just always sounds SO much better than the
rest.. they supply all the Scooby Sport exhausts but
are better known for their classic car parts such as
V12 Jag manifold systems etc.. only prob is you have
to leave car for around 3 days... or try the London
Stainless Steel company as they have blueprint of the
original exhaust and can build a performance unit to
your spec. The other way is the HKS exhaust.. TDI can
supply you with one of those... they are not totally
Stainless but are pretty nice all the same..

try:

tdi
racecar
Haywood and Scott don't seem to have a site but there
are a suprising number of hits with people having all
sorts of cars fitted with their manifolds/exhausts and
pipe work..


You COULD get it de-catted but not sure on the year of
your car.. the M regs and lower easily get away
without a cat test by Mr MOT man so if you know thats
all ok then you could BUT it doesn't tend to do
anything as the design is very good..

Also designed well is the manifold.. the shortness
sort of squirts the exhaust pressure at the turbo fins
and I find that this allows for a lot better bottom
end. Whereas my lovely looking manifold helps to
possibly allow the car to rev out more but ends up a
little more laggy because of it..

I would maybe think about braided hoses to help it
stop.

But really unless you want to go VERY silly (and
expensive) what you now have is a very rapid
Cappuccino.. add the exhaust for the soundtrack, oh
and you might want a new dump valve such as the HKS
SQV unit, if you're finding problems partially dumping
or if you release the throttle and pin it quickly and
the original one stays open for a moment or two then
you need a better one..

Have fun!

Dave
Steve Lewis
 

Postby Ian Linden » Wed Apr 09, 2003 09:02

Great idea, Steve :idea: Well Done :D

Reviewing Dave's sage advice, I recall I always had a doubt about the advantage he claimed for the larger turbo, but I never queried it with him. If I understand correctly, he said that the larger turbine shifted more air without compressing it as much, so it was cooler when it arrived at the manifold - that bit's fine.

The next bit is where I have the doubt, because the mass of air entering the engine is fixed (at a given engine rpm) by the displacement and the pressure. So, although the larger turbine has the capability of moving more mass at a given turbine speed, it won't get any more into the engine at any particular boost level and engine rpm. It seems to me that the advantage of the larger turbine is to allow the boost to be maintained at higher rpm than would be possible with the standard. If that's right, Dave's other advice, to use the N1 ECU with the standard turbo, seems more appropriate, unless you are going to uprate the bearings and whatever else would be needed to sustain higher rpm.
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Postby Murray Betts » Wed Apr 09, 2003 19:29

A lot of really useful stuff there; thanks Steve (and Dave).
Yes Ian, you're right. The engine determines the pressure/flow rate demand characteristic. This can be changed by altering
1- swept volume,
2-exhaust backpressure,
3-valve events,
4-second order things like compression ratio, port geometry etc.

You then select a turbo/compressor trim to suit the demand curve of the engine over the range you want to use it. The choice of compressor is a compromise, and it depends what compromise you choose to go for. Usually on a road engine you would select something to suit mid range, since in reality this is where you use the engine most of the time. As long as you don't exceed the compressor capability at max power all is fine. If you run a too big compressor for the engine, you run into compressor blade "stall" at low speed (exactly like an aircraft wing), where it can't deliver the required pressure rise at low flow rates; it then goes into a cyclic surge, which can be quite severe. The compressor efficiency map looks like a "hill", (with a "sweet spot" if you like), and going away from this best efficiency flow/pressure ratio point means that the air heats-up more. You usually try to get the demand curve of the engine through the middle of this "sweet spot", and choose the trim to give the sweet spot at a higher or lower flow value, according to compromise. That's the essence of the "trim" selection for a basic compressor size; a bit like the difference between different swept wings on aircraft. Hope that helps a bit :?
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