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The monza seems to be a bit lower in bottom end torque than I remember, but it has quite a bit more top end power. Difficult to say for certain as it hasnt been driven hard since last June Now I am pretty sure it is all down to the rear exhaust section I am using. Standard monza has two pipes (3 cylinders each) with a centre box each these two pipes then run into a single back box with a single outlet. Now I thought the standard back box was quite restrictive and as it was past its best I wanted to change it. The one I have now is below. Now it sounds very nice on idle and when being revved, but more race car nice rather than road car nice (if that makes sense) Problem is the car seems flat mid range, now I think its down to two things. Firstly the lack of baffles and therefore back pressure means it is reducing the torque. The other is I now have 2 sets of three cylinders through each exhaust and I think it would help the car run smoother if I joined the pipes together (cant remember the correct terminology for this) with one horizontal pipe. Any exhaust boffins got any recommendations
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paul4be
Part of things
'86 Capri Laser, Frontera 4x4
Posts: 395
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Have read pros and cons to having a link pipe in a system for a V. For what its worth, when looking into a system for the XR (2.8 V6) almost all of the decent power systems were a 2 into 1 rather than 2 seperate pipes right through
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Exhaust questionDeleted
@Deleted
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(H or X balance pipe ) helps with low down torque and smooths out the exhaust note. they work very well on v8's and v6's don't see why one wouldn't work well on a straight 6 cylinder engine
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(H or X balance pipe ) helps with low down torque and smooths out the exhaust note. they work very well on v8's and v6's don't see why one wouldn't work well on a straight 6 cylinder engine They work because they balance out the pulses from each bank, the left assisting the right and vice versa... ...Getting the same effect from an I6 would be a bit tricky, I would imagine...? *n
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Top grammar tips! Bought = purchased. Brought = relocated Lose = misplace/opposite of win. Loose = your mum
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(H or X balance pipe ) helps with low down torque and smooths out the exhaust note. they work very well on v8's and v6's don't see why one wouldn't work well on a straight 6 cylinder engine They work because they balance out the pulses from each bank, the left assisting the right and vice versa... ...Getting the same effect from an I6 would be a bit tricky, I would imagine...? *n don't see how it would be so much different still 6 cylinders from a single crank. Normally I 6`s share the same back box or have a 6 into 1 manifold.. Next thing is if I am to do this where would be the best place. Normally balance pipes are fitted to downpipes I believe. Have to do a bit of research and try to work out whats gonna be best. Think I will trial a few baffles and see what I get from there. Could do with a rolling road at home would make things much easier
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Exhaust questionDeleted
@Deleted
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the effect would be the same as the exhaust manifold is split i belive meaning that each manifold covers 3 ports and 1 pipe each giving an off balance exhaust pulse by joining the two you give it a scavinge effect which will ade torque the pipes on a v engine are normaly best joined just past the bell housing but on your engine i would first try it where they would have been joined on the standard system
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Last Edit: May 6, 2006 22:20:36 GMT by Deleted
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Looking at 6 cylinder bmw`s they also run two seperate pipes from the manifold into a single back box. So might be worth while changing what I have back to a single box.
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bstardchild
Club Retro Rides Member
Posts: 14,948
Club RR Member Number: 71
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Exhaust questionbstardchild
@bstardchild
Club Retro Rides Member 71
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I reckon the problem doesn't lie in the back box but the middle ones - they are far more restrictive in terms of back pressure than the back box...... And they also break up internally and the wadding moves about cocking up the air flow
(In my limited exxperience back box changes on Monza's and Senators just change the noise thats all)
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bstardchild
Club Retro Rides Member
Posts: 14,948
Club RR Member Number: 71
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Exhaust questionbstardchild
@bstardchild
Club Retro Rides Member 71
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I've had a bit of a think about this and later 12V's (the ones with mapable Motronic 1.5's) have a different exhaust arrangement due to a lambda sensor requirement
2 x 3 - 1 siamesed into one where the lambda is and then splitting into 2 again for the mids and then back into one again inside the rear box
On the Monza the primary lengths are bloody huge - manifolds all the way to the mids and they are way way back under the car
I'd put a balance pipe right at the front just before the down pipes join the mids
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I reckon the problem doesn't lie in the back box but the middle ones - they are far more restrictive in terms of back pressure than the back box...... And they also break up internally and the wadding moves about cocking up the air flow (In my limited exxperience back box changes on Monza's and Senators just change the noise thats all) I know what you mean but the only exhaust change has been the backbox and bottom end does seem to have suffered. I am having a look about and doing bit of research might have a try with a few different things to see what I can come up with.
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Mr K
Posted a lot
Posts: 2,993
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don't forget that for best performance an x pipe would idealy be positioned around 1 pulse away from the previous collector. i have a few pages i did for my college exhaust project on how the pulses work and what needs to be taken into account - i can post this up if anyone wants.
while we are one the subject - does anyone have a pipe bender that they cant make exhaust pipes with? i need a few bits doing for my side exit. (1.75" tube)
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Aha, this is a subject I have an unhealthy interest in and a slight degree of ignorance still. No moving parts involved so its tricky to visualise whats going on sometimes. It also makes me laugh with the money the Max Poo types spend on back boxes on stock systems and the "gains" they claim from them etc. Ho ho ho. Anyway... I share the concern that its probably not the back box causing your problem unless you fitted one which was very restrictive which would blunt top end power. Unless the rest of your system offers like zero resistance to flow and is perfectly tuned... Which is unlikely over such a length, from my understanding. Again, from what I understand the first boxe(s) in the system is (are) the critical ones. If the flow path to the first box is right it shouldn't really matter too much what happens after this so long as there is no additional restriction. Backpressure in the system is usually only needed for warmup cycle, although depending on the system and what sensors and hookups are used to control stuff its possible that the vacuum signal for the timing can be messed up by excessively low (close to zero) backpressure in the system, although my tortured mind on a monday morning says this is only on the over run... But I could be talking BS by this point. As for X & H pipes - I don't understand how your system is set up if you think you can use or fit one? Surely all the pulse tuning is done in the exhaust manifold? The purpose of ballance pipes is simply to cross link the two banks of a Vee-engine to allow pulse tuning effects where the firing cycle occurs between banks. Vizard put is thus: You are effectively running two 4 cylinder engines with a pulse tuned V8. If the maniold is not tuned length/pulse tuned you cannot do anything to improve this further back in the system. The manifold has to be right first. I'm assuming that the manifolding on the Senator world like a pair of V6 manifolds on the same side of the engine from what's been said. From what I understand of pulse length & frequency all the balance activity would need to be done pretty close to the front of the system. I've only really seen single 6-3-1 style headers on the cars I've looked at (all pulse events confined to the header). Perhaps theres not enough room in the engine bay to pull off the lengths of tube needed to achieve this in a Senator / BMW? Everything I've read suggests significance of effect depends on proximity to the head. Before blaiming the backbox I'd be tempted to check you don't have a coincidental fault in the ignition or some other system causing your flatness. Worth looking at anyway. Vizard also makes the point that 6 cylinder engines are far harder to pulse tune effectively as you do not get full cycles spread over the number of cylinders (4 stroke, 4 cycles, 4 cylinders or multiples thereof are easier, and V8s are easier than V4s or inline 4s) Ratlookreliant - even if nobody else is interested, I am...
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1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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it doesn't matter if it's a Morris Marina or a Toyota Celica - it's what you do with it that counts
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bstardchild
Club Retro Rides Member
Posts: 14,948
Club RR Member Number: 71
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Exhaust questionbstardchild
@bstardchild
Club Retro Rides Member 71
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but am facing building a DIY system. V8 8-2(decent cast job manifold)-1(Y) with just 1 box at the back. the pipe bit seems quite simple straight as poss @ 2.5-3", Its the choce of backbox that puzzles me. I could go standard cossie but that seems boing and expensive at £90, i've been looking at those flowmaster jobs, but don't know how much, how noisy (legal?), and how worthwhile they are, or what other alternatives are. the boyracer market seems to have loads! I think on a 6 or an 8 you can get away with one box due to the pulses being much closer so you get a mellow sound rather than loud - I've got two small straight thro boxes on the Monza both Powerflow supplied and it's not that loud - well unless you really gas it then it's well how can I say it - nice ;D Some of the back boxes on boyracer cars sound absolutely horrible IMHO in fact I had a Janspeed system years ago on a four pot car and that was a disaster sound wise
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Cool, yeah some boyracer systems you seem to getthe feeling its all about noise. I'm trying to make sense of the flowmaster range. I had a powerflow system put on my old xr2 for £150 and although it replaced a student-budget-temporary fiesta 1.1 pea shooter, it felt ace after the new exhaust, totally different, a joy to drive even though it was knackered in every other dept! LOL
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it doesn't matter if it's a Morris Marina or a Toyota Celica - it's what you do with it that counts
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