roadrunner
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| posted on 12/4/09 at 08:16 PM |
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I have a soft boot cover and to be honest its the last damn thing i look at when i am driving, but as far as the diffuser , i think it looks great and
should work by smoothing the air flow out the back, and as said before any little thing helps, i would'nt mind one.
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coozer
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| posted on 12/4/09 at 08:22 PM |
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Right then, thats enough, I'm going out to make one. Two reasons now, looks cool and keeps the diff and shafts out of the air and
clean
Ta,Steve
1972 V8 Jago
1980 Z750
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Hellfire
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| posted on 12/4/09 at 08:40 PM |
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Can you do some back to back testing in a wind tunnel Steve and let us know the drag co-efficients before and after fitting the diffuser?
Phil
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locoR1
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| posted on 12/4/09 at 08:42 PM |
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Made mine purely for the same reasons a Alan 1, i think it looks nice 2, i had a sheet of carbon look abs left over from trimming the car 3, gave me
something to do on a wet weekend last winter. really don't give a monkeys if it dose anything apart from look nice
More importantly Moto Gp on soon
 
Rear diffuser
 
Description
Check out my CB500T Cafe Racer build diary
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coozer
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| posted on 12/4/09 at 08:44 PM |
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Get in the garage, MotoGP cancelled...
Wind tunnel testing?? Your kidding, 8K along the local B roads is my kinda testing
1972 V8 Jago
1980 Z750
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:{THC}:YosamiteSam
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| posted on 12/4/09 at 08:45 PM |
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as been said - when i decided to make my diffuser there were a few benefits for very little downsides
for -
air travelling under the car in a narrow space speeds up (venturi effect - narrowing of a space the same air mass moves through at the same speed
makes the air speed up - hence jet engines - carburettor venturi's) - so if the air is travelling faster it creates lower pressure under the car
as it is moving faster than the air above the car - the air pressure above the car then pushes more down on the top of the car..
it also helps stop the rear boot box area being a 'parachute' effect - air under the car gets snagged on the rear end
the air on a car without a diffuser creates votices which create drag on the vertical boot box area - by forcing the air further away from the back of
the boot box area (diffuser sticks out from the back on mine by about 8" or so) it helps to stop the vortice drag
it also has the benefit of stopping the crud build up on the suspension etc
the diffuser has to be level with the bottom of the car really to work - so its keeping the narrow floor / road gap but just extending it.
when you look at a seven type car there really isnt that much difference between a single seater car - the biggest being the open cockpit acting like
a parachute - the front wings cause a lot of drag - headlights.. roll bars are not good either..
lol the whole car then...
the only real downside is the ground clearance - it needs to be low to work right - but going low can compromise speed bump clearance.. depends on
your individual car suspension travel
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coozer
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| posted on 12/4/09 at 08:50 PM |
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Terry, yours looks very purposeful indeed, however I will make mine a bit more discrete.
Just one more question.. do you need to cover the WHOLE of the rear boot place? including the area where the wishbones are??
Steve
1972 V8 Jago
1980 Z750
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:{THC}:YosamiteSam
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| posted on 12/4/09 at 08:59 PM |
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you cant cover it all really - with the bones going droop on 'errrr airborne' sections they may catch.. i just put some small bends in the
ally to miss. the diffuser goes the width of the floor
better pics
[Edited on 12/4/09 by :{THC}:YosamiteSam]
[Edited on 12/4/09 by :{THC}:YosamiteSam]
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matt.c
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| posted on 13/4/09 at 04:58 AM |
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Mmmm they look good.
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mr henderson
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| posted on 13/4/09 at 07:05 AM |
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There are various ways of conducting the air around a car, and some of them are better than others, and produce different results.
Never-the-less, if a car is pushed downwards that push has to come from somewhere, and there can only be one source of that push, the engine Unless,
of course, the wind happens to be blowing from a convenient direction 
John
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skippad
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| posted on 13/4/09 at 11:27 AM |
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made one for mine... decided not to fit after reading other threads.
Main thing bothering me is, what about the air that goes thru radiator circulates around engine then squeezed down tunnel?
If you practically cover boot floor with diffuser how doe s this "dirty air" escape?
Might look nice, but i want to go faster not slower!
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:{THC}:YosamiteSam
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| posted on 13/4/09 at 01:06 PM |
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quote:
Originally posted by skippad
made one for mine... decided not to fit after reading other threads.
Main thing bothering me is, what about the air that goes thru radiator circulates around engine then squeezed down tunnel?
If you practically cover boot floor with diffuser how doe s this "dirty air" escape?
Might look nice, but i want to go faster not slower!
because the boot floor isnt covered over completely - there are gaping holes where the suspension arms attach
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bassett
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| posted on 13/4/09 at 03:04 PM |
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Anyone got some pics of the part before fitting? Saw this today at Detling and thought it looked very smart
Damn i should really worry about finishing the car and getting it tested before i start with mods
[Edited on 13/4/09 by bassett]
My MNR Blog Updated Jan 2010 - Track Day Prep Begins!
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skippad
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| posted on 13/4/09 at 04:09 PM |
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quote:
Originally posted by :{THC}:YosamiteSam
quote:
Originally posted by skippad
made one for mine... decided not to fit after reading other threads.
Main thing bothering me is, what about the air that goes thru radiator circulates around engine then squeezed down tunnel?
If you practically cover boot floor with diffuser how doe s this "dirty air" escape?
Might look nice, but i want to go faster not slower!
because the boot floor isnt covered over completely - there are gaping holes where the suspension arms attach
Yes very clever, but there's still a lot space between diff and petrol tank to act as a parachute.
if your interested there's a Cleveland Kit Car Club meeting at Pathfinders, Maltby tonite starts about 8.00pm...Westfield, MK, MNR, Caterham
club members usually attend.
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:{THC}:YosamiteSam
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| posted on 13/4/09 at 07:52 PM |
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thanks for the invite - didnt see the thread till now! just come out of garden - workshop all day and goosed.. cars broken too.. need a gear selector
spring.. will sort one out tomorrow
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procomp
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| posted on 14/4/09 at 07:21 AM |
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Hi
Just a quick word of warning. By covering up the diff etc. You do run the risk of getting the oil rather hot. On the Kit race cars we can run the
diffusers for the short 15-30 minute races. But when testing in 1hr sessions the diff oil gets way to hot. Just be wary when on those long road trips
or when blatting for a length of time.
Cheers Matt
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PAUL FISHER
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| posted on 14/4/09 at 12:04 PM |
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A vent in the rear panel would be a good way of releasing traped air,when using a diffuser,as Caterham did with there RST V8
 
Rescued attachment 94E76095E5AC217AC253645F27E2B.jpg
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Snap-off
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| posted on 14/4/09 at 08:45 PM |
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Another pic of the Caterham:
 
Description
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nstrug
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| posted on 15/4/09 at 03:44 PM |
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quote:
Originally posted by iiyama
Actually diffusers add down force without producing much drag. Wings create drag for obvious reasons, this being that there is basically a big plate
at an angle to the airflow. Because it is a wing it has a high pressure area above it and a low pressure area below it creating the downforce. Also
because of this the high pressure trys to get into the low pressure area and creates a vortice, (seen in Malaysia due to the high humidity). This is
also drag as its dirty air. (why all passenger aircraft have the vertical winglets on the end of the wings, reduces the drag so they use less
fuel).
A diffuser is used by making the entire bottom of the car flat, (making the air move faster under this area due to being compressed), when it reaches
the diffuser which turns upward the air decelerates creating low pressure which is the downforce. All the vertical winglets stop the air from
seperating and all this creates very little in the way of drag. Cant get something for nothing!!!
^^^^^
All spot on...
Diffusers (and ground effects in general) increase downforce without significant drag.
Nick
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mr henderson
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| posted on 15/4/09 at 06:24 PM |
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quote:
Originally posted by nstrug
quote:
Originally posted by iiyama
Actually diffusers add down force without producing much drag. Wings create drag for obvious reasons, this being that there is basically a big plate
at an angle to the airflow. Because it is a wing it has a high pressure area above it and a low pressure area below it creating the downforce. Also
because of this the high pressure trys to get into the low pressure area and creates a vortice, (seen in Malaysia due to the high humidity). This is
also drag as its dirty air. (why all passenger aircraft have the vertical winglets on the end of the wings, reduces the drag so they use less
fuel).
A diffuser is used by making the entire bottom of the car flat, (making the air move faster under this area due to being compressed), when it reaches
the diffuser which turns upward the air decelerates creating low pressure which is the downforce. All the vertical winglets stop the air from
seperating and all this creates very little in the way of drag. Cant get something for nothing!!!
^^^^^
All spot on...
Diffusers (and ground effects in general) increase downforce without significant drag.
Nick
All depends on what you mean by significant. IMHO, any drag is significant on a se7en.
John
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grusks2
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| posted on 15/4/09 at 07:41 PM |
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quote:
Originally posted by locoR1
Made mine purely for the same reasons a Alan 1, i think it looks nice 2, i had a sheet of carbon look abs left over from trimming the car 3, gave me
something to do on a wet weekend last winter. really don't give a monkeys if it dose anything apart from look nice
More importantly Moto Gp on soon
Rear diffuser
How did you bend the ABS sheet at the edges to a perfect form
spence
http://mac1worxbuild.wordpress.com/
forgot my old password so another username doh
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locoR1
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| posted on 15/4/09 at 08:19 PM |
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To bend it use a heat gun to warm it up sounds easy but like most things its not
The most important thing is start of practising on small off cuts i did a lot of 90deg bends when trimming the car radius's are harder you only
want to heat the bend not the surrounding abs otherwise it ripples.
To do the diffuser i made a former out of wood to bend it over clamping wood ether side to protect the sheet and just warmed and folded the bend.
Description
Check out my CB500T Cafe Racer build diary
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grusks2
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| posted on 15/4/09 at 08:39 PM |
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quote:
Originally posted by locoR1
To bend it use a heat gun to warm it up sounds easy but like most things its not
The most important thing is start of practising on small off cuts i did a lot of 90deg bends when trimming the car radius's are harder you only
want to heat the bend not the surrounding abs otherwise it ripples.
To do the diffuser i made a former out of wood to bend it over clamping wood ether side to protect the sheet and just warmed and folded the bend.
Nice one cheers for that, what size thickness sheet is out of.
http://mac1worxbuild.wordpress.com/
forgot my old password so another username doh
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locoR1
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| posted on 15/4/09 at 08:48 PM |
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Its the thinner of the two sizes usually available its about 3mm if i remember right!
Description
Check out my CB500T Cafe Racer build diary
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grusks2
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| posted on 20/4/09 at 12:33 PM |
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can you recomend anywhere to get some on line, gooled ABS sheets and for a sheet 1800mm wide 1000mm long, enough for the side drops and centre flaps
etc £80 for 3mm in carbon 
http://mac1worxbuild.wordpress.com/
forgot my old password so another username doh
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