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#Post#: 97111--------------------------------------------------
Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: spitfiremk1uk
Date: April 16, 2015, 4:52 am
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On another thread a typical boy racer modification was mentioned
and as a younger landy driver I remember doing exactly the same.
These days knowledge, testing and proper evaluation means many
of the things I often heard from "experienced" people in days
gone past turned out to be totally misguided bordering on
outright lies. So here is a thread to discuss tips and tricks we
might have heard or think we know. Dont be shy with the ideas. I
used to have many that I was convinced of but now know better.
Unless people can openly talk and then analyze why they can or
dont work we will just be recycling old myths and ideas we hear
at the bar on a club night.
I will start the ball rolling with.
"boy-racer myths was the one about Big Bore exhausts giving
POWARRRH"
I remember taking the straight through back box from a 90 and
grafting it onto my old series replacing the standard silencer
with this new, louder straight through exhaust. You sure heard
me coming down the road!
Did it go any better? I thought so at the time but it only
lasted a couple of weeks when after several long journey's I
decided the noise was unbearable and I would prefer a brand new
paddocks cheapo exhaust over my boy racer alternative.
Is it worth buying a fancy exhaust silencer?
So does a straight through exhaust silencer help power?
Does a big bore exhaust help power?
Does an engine need back pressure to work properly?
Are expencive (ACR/Ashley) exhaust manifolds worth the money?
Lets try and keep this conversation to exhausts and see where it
goes. Maybe we can do other ones later.
#Post#: 97117--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: Hissing Sid
Date: April 16, 2015, 7:25 am
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In general terms I would expect a professionally designed and
made performance exhaust to improve things, a homemade lash-up
probably not.
#Post#: 97126--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: DarrenH
Date: April 16, 2015, 2:24 pm
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i think the main issue is that when you say "back pressure" to
90% of people into cars, they translate it as "restriction".
so the obvious answer to that would be no, we dont want to be
restricting waste gases exiting the cylinders.
but when you delve into it, its really more about gas momentum,
sizing the pipes and designing the silencers in such a way that
helps maintain gas momentum, reduce heat loss, and thus have
beneficial syphoning effect scavenging the cylinders of waste.
if the exhaust gas is completely unhindered it cools, it
expands, it slows down and youll get more of it left over in the
cylinders and (engine) efficiency will drop. so then the answer
becomes yes, we do need some back pressure.
i've only ever done back to back dyno tests with cylinder heads
on 2.25 landy engines so no real practical experience with
exhausts. other engines/cars yes, a moderate pipe size increase
(like 1/4 inch) and change from gated/baffled silencers to
straight through absorption type did see a measurable increase
in engine effort over the entire rev range.
#Post#: 97134--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: NoelC
Date: April 16, 2015, 5:15 pm
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--- Quote from: spitfiremk1uk link ---
>
> Are expencive (ACR/Ashley) exhaust manifolds worth the money?
>
--- End Quote ---
Absolutely not. I scored about £2k worth of ACR bits and bobs
second hand for £500 a few years back and have them on the 88.
That now runs a 2.5 petrol ex-boingy, stage 2 head, ACR intake
with SU carb (+BLOS LPG carb), ACR tubular manifold and exhaust
system with stainless steel high flow silencer.
It's generally accepted the main place for improvement on a
series 4 banger is the head, and I'm not one to disagree. As for
the rest, I wouldn't bother. The ACR exhaust manifold is of piss
poor quality, has rusted like mad and took a very large, angry
Polish bus fitter with oxy-acetylene to modify it so it didn't
foul either a spring bolt or the chassis. I'm not convinced the
SU carb conversion gives anything over a Weber 32/34DMTL off a
boingy either to be honest, plus the custom manifold has water
connections to keep it heated and the pipe is mild steel that
has rusted badly too. All in all not very good quality gear.
#Post#: 97140--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: DarrenH
Date: April 17, 2015, 6:42 am
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wondering if it was a ninety acr exhaust manifold or vice versa
(regards non fitting). its true tubular steel wont last long
compared to pig iron cast manifold.
wont comment on the rest because it was expressly forbidden at
the start of this thread :D
#Post#: 97141--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: towhitch
Date: April 17, 2015, 7:14 am
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If you have a gas flowed head (preferable a work of art from
Turners) a properly designed straight through silencer will show
an improvement. A BIG BORE straight through will destroy the
improvement. :lightblb:
#Post#: 97142--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: spitfiremk1uk
Date: April 17, 2015, 9:56 am
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I need to ask. Whilst I concede it might be loud. Why would a
big bore straight through silencer destroy performance enhancing
cylinder head work?
I will throw in both the theory and my experiences.
The exhaust system starts at the exhaust valve in the cylinder
head all the way through to the tailpipe exit.
Cylinder head enhancements starting with valve seats, pocket
porting and other improvements that come under the "gas flowing"
bannor are techinically part of the exhaust system but I would
think a discussion focussing on cylinder heads would cover this
better.
Any and I do mean ANY exhaust back pressure is hurting power
production. If your exhaust pipe has more than 1psi of internal
pressure then you can get more power simply by designing an
exhaust system to remove the pressure. Just remember this is one
of those diminishing returns situations!
There will be many that have heard down the pub that an engine
needs back pressure to run properly. This is simply not true.
This is a myth that has come about when lads have removed the
exhaust pipe from a 2 stroke motorbike and found it doesnt run
or only runs at full throttle and high revs. But its not the
back pressure thats the issue.
As has been mentioned previously in an ideal world an exhaust
can use the mass of its exhaust gas and the energy it carries to
create a vaccum to help "suck out" left over exhaust still
inside the combustion chamber. For this to work however you need
individual exhaust runners/pipes of specific lengths to make it
work at any given rpm. This is why performance exhaust systems
will replace the standard landy exhaust manifold because in this
regard standard is total crap! 2 of the runners are not bad but
sized for very high rpm, yet the 2 inner runners are even
shorter and all terminate into a large holding area where heat
is passed into the inlet manifold and then hopefully the exhaust
gas finds the pea shooter outlet hole and passes into the down
pipe. I wonder how much pressure would actually be in the
exhaust manifold?
Has anyone ever checked the back pressure in the exhaust on a
standard landy 2.25? I have only indulged on V8 conversions so
its not really a fair comparison.
In its simplest thinking any exhaust back pressure means that
the piston has to push the exhaust out of the exhaust valve and
you wont get any negatative pressure waves helping with
scavenging of the combustion chamber. All of this means you are
using and losing power/fuel just to pump exhaust fumes out the
exhaust pipe.
I have not checked out the ACR 4 into1 tube exhaust manifold so
I can only comment on the ashley 421 version. The 421 layout is
supposed to be better for bottom and mid range torque. Take that
from the general performance world into old landies and even at
max rpm of 4250 it seems a 421 system could make a lot more
torque/power over a 4 into 1 set up and a hell of a lot more
than the standard exhaust manifold.
The ashley exhaust is made OK but my biggest grip is the huge
size of pipe they have used. To get maximum effect and tuning of
the system the exhaust header diameter needs to be sized to the
engine capacity and rpms it will be used at least as a base
measure. In the case of a standard landy a header pipe would
ideally need to be smaller than the exhaust port in the cylinder
head! So the best that is practical would be to make the header
pipe the same size as the hole/port in the cylinder head. ( I
will leave out the anti reversion properties of a bigger pipe
for another day) The ashley exhaust pipe looks great but seems
to be made from too large pipe to be ideal. Anyone ever tested
the ashley exhaust on a dyno? Or measured the ACR one?
A big bore exhaust is almost never a bad thing. Too big to cause
problems is rarely an issue.
A good effective silencer that is free flowing can only be a
good thing. I should just say that "restriction" is a very good
noise suppressor! So a good silencer needs to reduce noise
without restriction of flow! Also many "free flowing" silencers
are crap at reducing the noise! and simply allow sound waves to
pass straight through!
Less back pressure is always good for performance and fuel
economy. If the diameter of the exhaust pipe is small and
causing high pressure/restriction, then a big bore exhaust would
help. If its the silencer causing the backpressure then a free
flowing silencer will help. Of course there is still the exhaust
manifold to deal with!
I once thought about converting a 6 cylinder exhaust system into
an 88 system because it was a larger diameter. But when it
arrived I found it to be so far removed from fitting a 2.25 88 I
didnt take that project any further. I guess until an exhaust
system is measured properly and compared to standard and
modified options the "best" exhaust system will remain a
mystery.
I am damn sure a standard exhaust manifold and pea shooter cheap
exhaust are not optimum but they are cheap!
Any suggestions for reasonably priced off the shelf "large bore"
exhaust systems?
#Post#: 97144--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: DarrenH
Date: April 17, 2015, 11:27 am
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--- Quote from: spitfiremk1uk link ---
>
> I need to ask. Whilst I concede it might be loud. Why would a
big bore straight through silencer destroy performance enhancing
cylinder head work?
--- End Quote ---
depends on the definition of "big bore straight through"
if it meant just the the tail pipe silencer as in your original
reply, it wouldn't destroy performance.
if it meant an entire exhaust system made from 4 inch outside
diameter tubing, and all the silencers were doubled in size, it
probably would destroy performance in most of the usable rev
range.
i know you didn't specifically say these words, just saying it
out loud, exhaust gases aren't syringed out of the cylinders by
kinetic energy from the piston rising, majority of the energy is
thermal the hot waste gas trying to expand to atmosphere. if
you allow it to expand or radiate before it gets to atmosphere,
temp drops, gas speed plummets. the best ways to ruin gas
speed are increase (to the extreme) the exhaust tube size,
increase the volume of the silencers, make it go round corners
(the last is two is why baffled silencers are bad news). this
theoretical stupid exhaust would probably make more power at max
effort, but be detrimental everywhere else.
if pushed for an opinion, rather than just theory, i would agree
the standard exhaust manifold is terrible design purely for
having unequal volume primaries. although i've not measured the
hot spot area so the volume might equal that of the longer
primaries on 1+4 anyway, but its still abruptly altering flow.
its a good design for cost and durability which i imagine were
at the top of the list in 1958, i've never had carb engine that
has run better on cool ambient air rather than be preheated. so
i guess the hot spot setup was pretty high tech back then, using
waste energy to improve engine efficiency. something to do with
petrol homogenizing better in warm air.
in an ideal world you'd want the exhaust ports at the back of
the engine bay, the manifold have bolt straight primaries
merging somewhere inside the dashboard and the exhaust be bolt
straight through the cabin and out the back window, no bends, no
silencers, a slight taper outwards along its entire length like
a comedy alpine horn, and be made of something which doesn't
conduct heat.
production exhausts are so far removed from ideal purely for
packaging and cost reasons, it does make you wonder why bother
at all if you are only fine tuning that last 3%. but i
completely agree something specifically designed for the engine
and its intended use would make a big difference. but i dont
agree it should just big as your ears can stand
#Post#: 97148--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: spitfiremk1uk
Date: April 17, 2015, 4:57 pm
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I would come back and say that gas speed and inertia are only
going to make a difference at our engine speeds in the primaries
on a 4/1 exhaust manifold right at the top end of the rev range
if at all and 4/2/1 in the primaries and secondaries throughout
the rev range if a suitably long enough manifold was used. So
these pipes need to be kept at the ideal diameters around 27mm
diameter (cylinder head ports dictate the need for a larger 32mm
be used anyway) for the primaries but once at the collector pipe
our engine speeds are never going to show much of an improvement
in power in trying to "tune" its length or volume.
Using a standard manifold and "tuned" exhaust seems such a waste
and contradiction to me. The manifold is plain crappy except for
the longevity aspect. With exhaust gases directed against each
other and the 2 centre cylinders just being dumped into a large
plenum before making it try and find the exit hole! The large
plenum that is shared by all cylinders means the "primaries" are
of totally unequal length and volume.
There are a few things that can be done and still keep the
engine looking standard though.
Before assembly take the time to port match the exhaust manifold
and remove any mismatch in port alignment. Then check the outlet
hole against a new down pipe and open it up as much as possible
to match the down pipe hole. Also check for and remove any
casting flashes insde the runners and remove with a small
grinder.
This wont make it a great exhaust manifold but it will make it
pretty much as good as it get whilst keeping it "standard"
enough to pass scrutiny.
Once the exhaust gas has done its work in the manifold/header
there seems little point in worrying about gas speeds and
keeping up energy levels. Let the gas cool down asap, lose some
of its volume and pipe it to exit in a low pressure area at the
rear of the car. So long as it is quiet enough I really think
any pipe diameter not causing back pressure would be fine. Of
course anything more than 2 1/2" diameter would have a hard job
following the standard routing. I think the best silencers use
reflection, expansion and absorbtion to keep noise levels
reasonable. Expansion is a hard one though because it literally
takes up lots of space. I agree some baffled silencers can be
bad especially when they restrict flow. I just dont think at our
engine speeds pressure wave termination or alteration makes even
the slightest difference making system pipe diameter and volume
purely a practical size issue whilst trying to keep back
pressure to a minimum.
Why bother? Well that last 3% you mentioned might only be 2hp on
a standard engine but I have learnt over the years that you do
seek out those 3% and 5% points and when you add them all
together they make a huge difference to the driving experience
as well as the fuel economy. And when you add them onto other
mods that 2hp can easily double. I look at it this way. Rather I
added 2hp instead of taking 2hp away!
COOLING FANS
Is it worth the effort and expence to remove the steel fixed
cooling fan and fit an electric fan instead?
#Post#: 97149--------------------------------------------------
Re: Landy Boy Racer tips and tricks or Myths and bull...t.
DIR By: NoelC
Date: April 17, 2015, 5:55 pm
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--- Quote from: spitfiremk1uk link ---
>
> Any suggestions for reasonably priced off the shelf "large
bore" exhaust systems?
>
--- End Quote ---
Steve Parker makes (or at least he did the last time I looked)
systems that mate to the 11H/17H manifold on a series. They are
a larger bore than standard, coupled to the Weber 34/34DMTL it's
hard to believe you wouldn't experience a noticeable
improvement.
--- Quote from: spitfiremk1uk link ---
>
> COOLING FANS
>
> Is it worth the effort and expence to remove the steel fixed
cooling fan and fit an electric fan instead?
>
--- End Quote ---
Back in the mid-90s I had a conversation with Richard Turner
(Turner Engineering) about several things, one of which were
electric cooling fans. He told me he liked them, as they
generated him so much business. I've never gone near one based
on that testimony. Opinions vary on this about as much as
braking systems, some people swear by them, some quite the
opposite. If you're in the zone of scrutinising MPG and
performance personally I'd consider waiting for a spell of cool
weather and simply remove the fan, making sure of course the
temperature gauge works! Run for a tank of fuel like that and
again with it attached. I'm sure it makes some difference but
how much I wouldn't want to estimate. You do have to delve into
the optional equipment catalogue to see it but in there
somewhere is a viscous fan system for the 2.25. Can't say I've
ever seen one in the flesh and whilst the viscous fan became
standard on the six there must have been a reason it didn't on
the four.
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