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Sean
Firing on two.
Joined: April 22nd, 2009, 11:06 pm
Posts: 3684
Location: Ecosse
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 Re: Exhaust back pressure important?? balance pipe at L or multiple of L is where the 2 pipes join , however a smaller balance pipe near the head, there is no mention of it in the manual it assumes a 2 in to 1 as for the tail pipe ideally it again should be a multiple of L the start of any silencer/expansion chamber should also be at L as for the diameter of the 2nd pipe the original 2cv had a smaller bore tail pipe but it is relativley long i wonder if there is some relation sihip that if you half the bore you double the length....? and yes its peak power rather than peak torque and looking at yor pictures.......looks good and thats half the battle  Sean
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Kissing the Lash
"Any advice of a technical nature is given on the understanding that I've actually done this shit, not just read about it in D*lly club mag some time ago.
Last edited by Sean on November 3rd, 2010, 10:55 am, edited 1 time in total.
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| November 3rd, 2010, 8:41 am |
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2CViking
viking bastard
Joined: April 18th, 2009, 11:43 am
Posts: 2424
Location: Meneac, Bretagne France
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Re: Exhaust back pressure important?? Maurice is something eh. Love this  Not minded at any one in particular, just interesting comments What other wannabee mechanics say: „What about exhaust systems? Well, my favorite quote is, "That system doesn't provide enough back pressure for good low end power. You need back pressure for good low end and mid range on the street.“ Simply put the above is bullshit and reveals more about the speaker's lack of knowledge in exhaust tuning than anything else. He probably gives out lots of advice like this because he likes the sound of his voice or loves to see his name in print on forum boards. Back pressure (I assume our friend means restriction/resistance to flow) does not "help" mid range power. See the dyno chart examples of muffled 2CV6 engine:
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| November 3rd, 2010, 10:04 am |
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Sean
Firing on two.
Joined: April 22nd, 2009, 11:06 pm
Posts: 3684
Location: Ecosse
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Re: Exhaust back pressure important??
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Kissing the Lash
"Any advice of a technical nature is given on the understanding that I've actually done this shit, not just read about it in D*lly club mag some time ago.
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| November 3rd, 2010, 10:53 am |
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Harley
Firing on two.
Joined: May 3rd, 2009, 11:40 am
Posts: 816
Location: Melbourne, Australia.
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Re: Exhaust back pressure important?? 2CViking wrote: Maurice is something eh.
Anyone still in contact with Maurice, last i emailed him he was in hospital having a major surgery, heart i think, i have not heard from him in a while...? Harley
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samfieldhouse wrote: It is M9 for the shocks yes, the rest I'll check when next i'm underneath her. Ironically, this will be valentines day.
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| November 3rd, 2010, 11:21 am |
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2CViking
viking bastard
Joined: April 18th, 2009, 11:43 am
Posts: 2424
Location: Meneac, Bretagne France
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Re: Exhaust back pressure important?? Harley wrote: 2CViking wrote: Maurice is something eh.
Anyone still in contact with Maurice, last i emailed him he was in hospital having a major surgery, heart i think, i have not heard from him in a while...? Harley And you don't want to
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| November 3rd, 2010, 11:35 am |
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2CViking
viking bastard
Joined: April 18th, 2009, 11:43 am
Posts: 2424
Location: Meneac, Bretagne France
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Re: Exhaust back pressure important?? Forgot to add this Quote: A very interesting article found by PUMA Race engines about experience with clients and customers.
I fully agree with Mr. Baker:
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| November 3rd, 2010, 11:56 am |
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Sean
Firing on two.
Joined: April 22nd, 2009, 11:06 pm
Posts: 3684
Location: Ecosse
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Re: Exhaust back pressure important?? none of which really helps Joolz get his BM engined spesh going does it? 
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Kissing the Lash
"Any advice of a technical nature is given on the understanding that I've actually done this shit, not just read about it in D*lly club mag some time ago.
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| November 3rd, 2010, 12:07 pm |
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Devils Advocate
Firing on two.
Joined: July 26th, 2009, 3:36 pm
Posts: 1019
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Re: Exhaust back pressure important?? Sean wrote: joolz
you will need some info on the bike engine and the cam duration
from the 2cv tuning manual :-
length of primary pipe(s) in inches( american formulae?) from the back of the exhaust valve=L
duration of the exhaust valve from opening to TDC in degrees=ET
anticipated revs at which max power is anticipated-(less)500rpm
so L=(5100 X ET) / (RPM X 6)
that gives a theoretical length of the primary pipe the actual exhaust pipe will need to be L less the length of the exhaust port in the head.
primary pipes can be multiples of L
diameter of pipe formula again in imperial
Cylinder cc X2
divide by 16.4 to get cubic in
divide by L from above
divide by 3.14
Sq root
multiply by 2 add 0.120
from that you add 10% or 15% due to the fact that its a contorted pipe not a sraight one.
for a standard 2cv thats:
301cc X 2=602cc 602/16.4= 36.7 cu in 36.7/L(34.8in)=1.05in 1.05/3.14=0.33 0.33 sq root= 0.57 57 x 2 + 0.12= 1.27 finally add 10% and you get 1.4in
right thats the 2 main pipes length and diameter to the point they both join together
so the primarys on a standard 2cv producing(ideally) peak power at 5750rpm would be 11/2 inch pipe 30.18 inches long or 64.8 (or keep adding 34.8)
seconary or tailpipe
is the above formula but its cylinder cc X 4(1204cc) at the start
does that help?
Sean
(and jameswallace you are banned from chipping in to this thread if your maths is anything like your grasp of English) I have to confess a teeny bit of wee nearly escaped when I read that one... 
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| November 3rd, 2010, 12:14 pm |
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J-dub
Aircooled Idiot
Joined: April 24th, 2010, 10:01 am
Posts: 5733
Location: Location Location
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Re: Exhaust back pressure important?? i paassed maths with flying colours !!
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1988 2cv 652cc
1993 Toyota Hilux Surf 3000cc runs on Bio Diesel
2004 Toyota Landcruiser Amazon 4200cc runs on Bio Diesel
1998 Daihatsu Hijet 1300cc
2005 Susuki Bandit 650cc
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| November 3rd, 2010, 6:45 pm |
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Sean
Firing on two.
Joined: April 22nd, 2009, 11:06 pm
Posts: 3684
Location: Ecosse
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Re: Exhaust back pressure important?? and went out and checked the exhaust figures on the car on the drive tie in with the figures in the formula
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Kissing the Lash
"Any advice of a technical nature is given on the understanding that I've actually done this shit, not just read about it in D*lly club mag some time ago.
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| November 3rd, 2010, 7:57 pm |
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